Category: LAB equipment

Getting an Rohde Schwarz AMIQ up and running

Introduction

The Rohden Schwarz AMIQ is an IQ modulation generator. According to the documentation of Rohden Schwarz this device has:

 

 

    • 100 MHz sample rate
    • 16 M Samples memory depth
    • IF generation up to 25 MHz
    • Multiple carrier simulation

And the best part is.. these devices can be picked up for little money.  Even if one is not into IQ modulation and such, the device is able to put out some very nice looking sine waves. There is a catch however. (There is always a catch): The AMIQ can only be controlled remotely.

What to look for when buying an AMIQ

When buying an AMIQ, look at the options the unit has. The user manual which can be found online, list all the available hard-, and software options.

Secondly, the AMIQ has a built in hard disk. If this drive is damaged, you could be out of luck. I searched online, but could not find any firmware images. If you bought an AMIQ, then make a image of the internal hard disk.  The AMIQ boots OpenDos.

There is an easy way to determine if the AMIQ is in a working condition. And that is to listen to the beeps at startup. The device will give one beep when turned on, and a few moments later, a second beep is produced. It’s the AMIQ’s way of letting you know it’s past it’s error checking thing. This second beep,should be followed by a steady green LED on the front panel.

If none of the above is happening, the AMIQ is having a fault, or the AMIQ didn’t start in a sane state. There seems to be a service manual for the AMIQ, where you can troubleshoot. Unfortunately I could not find the service manual online.

So when buying an AMIQ, let the seller boot up the AMIQ, and let the seller describe to you the boot process.

Once you got physical access to the AMIQ, you could run the the command:

*TST?

This should return a 0 when no errors are found, or a 1 if a error is found. The user manual describes in detail how to hardware test the AMIQ. Also note that the above command doesn’t test the RAM memory.

The third thing you may be aware of, are the different models:

    • AMIQ02
    • AMIQ03
    • AMIQ04

I never encounter the AMIQ01, however the AMIQ03 and 04 are the newer models, with more memory, sample rates etc. The main difference between the AMIQ03 and 04 is greater memory: The 04 has up to 16 000 000 IQ values, compared to the 03: 4 000 000 I/Q values)

Only the models 03 and 04 can have the option “AMIQ-B3” fitted. So if you see an AMIQ listed with the option “AMIQ-B3” you know it has to be a 03 or 04 model.

Controlling the AMIQ

To let the AMIQ do something useful, like spitting out signals, the AMIQ needs remote control. And for this remote controlling there are several options:

    • Through serial connection
    • Through IEEE-488 (GP-IB or also called HP-IB)
    • Use an Rohde Schwarz SMIQ
    • Use software like WinIQSim (version 1.x)

Luckily I got all the options…

Talking to the AMIQ

The easiest way of getting the AMIQ up and running is to connect a null modem cable to the RS232 port. If someone has changed the default serial parameters (9600,8n1) an formatted floppy disk (MSDOS) is needed with the file: AUTOEXEC.IEC with the following line:

:SYST:COMM:SER:BAUD 9600

Insert the floppy disk into the AMIQ, turn the AMIQ off, and on again. Once the AMIQ is fully booted, the serial console should be accessible.

When you have the luxury of having IEEE-488 or you could reset the the default address 6 with similar procedure, the line in the AUTOEXEC.IEC must be:

:SYST:COMM:GPIB:ADDR 6

Once a working connection is established to the AMIQ, the following command should give you the directories on the hard drive C:

:MMEM:DIR?

To load an waveform, and put out the signals on the I and Q outputs, give the following commands:

*RST;*CLS;*WAI
:MMEM:CD 'C:\'
:MMEM:LOAD RAM, 'GSM_TSC1.WV,TRAC'
:TRIG:MODE CONT
:OUTPUT:I FIX
:OUTPUT:Q FIX

The commands on the first line resets the device. Next the directory is changed to the C: drive. On the third line a waveform called: “GSM_TSC1.WV” is loaded into RAM memory. By setting the trigger to continuous on the next line, the waveform is send to the outputs, which are enabled on the last two lines.

This produces the following signal:

In the next article I’m going to hook up the AMIQ to the Rohde and Schwarz SMIQ04 and generate some signals.

Having fun with a R&S SMT03 and HP8591A Spectrum Analyzer

Playing around with the R&S SMT03 and an HP8591A Spectrum Analyzer

Now that I fixed the R&S SMT03 I find finally time to play around with the SMT03. The idea is to learn more about modulation, and how to display this on a Spectrum Analyzer. In a previous article I used the Siglent SSA 3021X Spectrum Analyzer in this article I’m going to use a HP 8591A Spectrum Analyzer.

Preparing the R&S SMT03

First off I need to setup the R&S SMT03

I’m going to use a carrier signal of 100Khz, and AM dept of 27%. And since the SMT03 have a second LF Generator I use that one to generate a sinus wave of 1.000 Khz. To protect the input of the HP SA I set the amplitude to 0 dBm.

Setting up the HP8591A Spectrum Analyzer

After setting up the R&S SMT03 it’s time to configure the HP8591A

After setting the center frequency the SPAN is set to 20 Mhz. To see the AM modulation, a smaller SPAN is needed. After the SPAN is set to 1.5Mhz the AM modulation becomes visible:

This shows the AM modulation. I really like the HP 8591A SA, it has a easy to use interface. And having a R&S SMT03 and the HP8591A in my lab is really awesome.

Use a spectrum analyzer to find interfering signals

Understanding the difference between Oscilloscope and Spectrum Analyzer

Before diving into the use of a Spectrum Analyzer (SA), a short explanation between an Oscilloscope and a SA might be handy. If you used a SA before, this article might not be to any interest to you, since this article covers a basic understanding.

For those who a curious to what a SA is, hang around, since this article is about to demonstrate the difference between a  Oscilloscope ans a SA.

When starting with electronics, sooner or later you might find yourself wanting an Oscilloscope to look at (fast) changing electronic signals. In other words: An scope is a multi functional tool in a electronics lab, and every good electronics labs should have one. With a scope it’s possible to look at electronic signal, being it digital signal or analogue signal which changes over time. But a scope can also be used to measure voltages, and all other characteristics of a signal. For example, the fall and rise time of edges, period of a signal, the max and min voltages, and perform math functions on signals.

Using a Oscilloscope to look at a signal

Most often a scope is used to look at a signal, and see how it looks like. For example a sinus signal:

Looking at the signal we can tell that the signal is 50mV (Peek to Peek), and that the frequency of the signal is 100Khz. Looking at the signal closer, it’s not a sharp clean sinus signal. So what’s wrong ?

If we zoom into the signal to have a closer look, the signal looks like:

This is doesn’t look like a clean signal. At this point several things may be the cause:

      1. Is there something which interferes with the signal?
      2. Is the measurement done properly (aka signal integrity)

This is the point, where it’s very difficult, to use a scope to investigate this further. Just let’s assume that this is no measurement fault. Short ground leads are used, and the probes are calibrated.

That leaves us with a interfering signal of some kind.

      • How to determine what kind of signal this is?
      • What is the frequency of this interfering signal ?

At this point some want’s to use a feature which is called “FFT” which some  scope might have.  FFT stands for: Fast Fourier Transform spectrum analyser  When using this feature the scope is behaving like a SA.

Having a FFT feature on a scope might be handy, in my case the FFT feature on my Rigol Ds1054Z is not very helpful:

It shows that there seems to be an extra signal, but it’s not possible to get any detail on this signal. To get more detail, a real Spectrum Analyzer is needed.

What is a Spectrum Analyzer (SA)

A Spectrum Analyzer might at first glance be some kind of a scope. It has a display to show signals, and has a lot of buttons, like a scope.

However the main difference between a scope and SA is that:

      • A scope shows signals in the time domain
      • A SA shows signals in the frequency domain

This means that a SA show on the horizontal the frequency, and on the vertical the power of the signal, which is shown in  a Logarithmic scale. This can be for example in dB or dBm. The reason for displaying the power (on a scope you would say the amplitude) of the signal in a Logarithmic scale  is that low power signal can be displayed next to high power signals.

And since a SA displays signals in the frequency domain, it’s possible to see how “pure” or “clean” a signal is, since we can actually look at the “spectrum” of the signal. Hence why it’s called a “Spectrum Analyzer”.

Using a Spectrum Analyzer to look at a signal

Let us look at the same signal which we looked at on the scope, but now feed into a Spectrum Analyzer:

Here is the same signal, but it looks quite different from the signal which is shown on the scope. However it’s frequency is 100Khz, and the power of the signal is -46.00 dBbm. Which is about 3.169 mVpp (There is some loss in the cables, and adapters used).

Looking at the signal it’s seems “not clean”, But it’s hard to see. So like on a scope, it’s possible to zoom into the signal, and get more detail. To this we need to set a smaller SPAN. The SPAN on a SA is the bandwidth were we are looking at it. It’s like the zoom-lens on a camera, by zooming in, more details are visible. Currently the SPAN width is 20.000Khz.

If we change the SPAN width to let’s say 1.000Khz, we see the following:

And suddenly a second signal appeared. To get more details about this signal, the SA provides a easy way, and that’s by placing a marker. In this case a delta marker is used. A delta marker can show the difference (delta) between signals.

And then we see that the interfering signal is a 100Hz away from our original signal of 1oo.ooo Khz signal.  So the interfering signal is 100.1 Khz.

Conclusion

And this shows the difference between a scope and a SA. An SA is a very handy tool when looking at the spectrum of a signal. It’s how every a more complex, and sometimes more confusing tool to use. On the other hand, a scope is also a complex tool to use. But in general, a scope is much more used for looking at signal then a SA. A SA is mostly used when dealing with RF, radio’s transmitters and alike.

Repairing a Tektronix PB200 Bert tester – part one

Repairing a Tektronix PB200 Bert tester

The Tektronix PB200 BERT

Before diving into repairing the Tektronix PB200 BERT tester, let me explain briefly what a BERT Tester is. BERT stands for ” bit error rate test ” In the most simple form, a BERT tester sends out a random bit patron, and an analyzer receives the bit pattern and compares this bit pattern to see if there is any bit error.

Obviously this is more complicated, how does the analyzer now what the original bit stream was ? The theory behind it this is quite complex, and beyond the scope of this article. For a more in depth explanation see [this] Wikipedia article.

A device like the Tektronix PB200 is used to test different data transmission devices, like optical interfaces, or a like.

The Tektronix PB200 has a data generator and an analyzer built into one device. The specs for this device:

GENERATOR
     Clock Frequency: DC to 200 MHz.
      Amplitude: 0.5 to 5.0 V p-p.
      Termination select: 50 Ohm to -2 V, +3 V, AC or GND.
     Input range: ECL, TTL, PECL compatible.
     Threshold resolution: 10 mV step.
    Internal synthesized clock source: Frequency: 1 Hz to 200 MHz.
    Resolution: 1 Hz.
    Accuracy: 10 ppm.
    BURST clock:
    Programmable gap: 16 Kbits
    maximum, 8-Bit resolution.
Pattern Generator
    PRBS: 2 N- 1, N = 31, 23, 15, 11, 10, 9, 7.
    Programmable word: 256 Kbits maximum, 8-Bit resolution.
    Mark density: PRBS 2 10 1 (1/8, 1/4, 1/2, 3/4, 7/8).
    Mixed mode frame: 256 Kbits maximum, 8-Bit resolution.
    Error injection: Error: Single, Rate, External (TTL).
    Field select: Overhead, payload or both.
    Error rates: Error rate of 10-n, n = 3, 4, 5, 6, 7.
    Outputs: Data and clock outputs:
    Format: NRZ.
    Configurations: Differential (True/Complement).
    Source impedance: 50 Ohm.
    Amplitude: 0.5 V to 2.0 V, 10 mV step.

A Tektronix PB200 which is dead

Before I can play around with this PB200, the device needs a  repair. I bought this device as a “none working, for parts”. And well.. it sure is in a “none working” condition, since the device doesn’t power on, at all.

That is one of the reasons I bought this device. When a device is not able to power on, this normally means the Power Supply (PSU) has a problem. The downside of this is of course that their is no easy way to test the rest of the functionality of the device.

Assessment of the problem

Once the devices arrived at my doorstep, I could inspect it further. And I noticed a sharp bent in the front panel once I removed the covers.  Not a good sign to start with. The second thing I ran into is that this device is a complete nightmare to take apart. The construction is just horrible. Screws on places which are heard to reach. I suspect this is just a branded by Tektronix. I got my hands on some Tektronix equipment, and repaired some, and the construction is always good engineered. In this case, it’s definitely not.

So it took a lot of effort to get the PSU out of the chassis. Once the PSU was out I noticed a burned up diode, and a burned spot on the PCB. A quick check of the fuse confirmed: This PSU had a very bad moment. This means that on the primary side of the PSU a lot of other components could be damaged. So the first thing I did was to hunt for a Service Manual, and well these cannot be found.

So I started to de-solder the diode, so I could get a marking of the component. The diode was next to some transistors, or MOSFETs so I decided to desolder them as well, since they are most likely also damaged , or are the cause of the damage.

While taking the diode out carefully, I could not prevent it from falling apart.

 

The diode literally exploded and split into halve. With a lot of trouble I managed to get some marking, but I wanted to make sure that I got it right. Primary side of a PSU always makes me nervous. So I started a [thread] on the EEVblog forum.

Another member also suggested to get a PSU replacement, which is almost the same. The only difference is the output voltage.

So I decided to buy this PSU, so I have a reference, and if I’m unable to repair the primary side of the PSU I could perhaps convert the secondary side so it gives the right voltages.

In part [two] I’m trying to fix the PSU

Repairing a Tektronix BP200 BERT tester – part two

An attempt to fix the primary side of the PSU

I started  to measure and test several components, and found some diodes which where shorted. Replaced them. However I could not measure any voltages after the full bridge rectifier. Some components are mounted on large heat-sinks. Removing them to get access to the components and be able to read the markings or to test them out of circuit, would be a pain.

Fighting with this power supply for a couple of evenings, I decided to take another route. In the meantime the alternative PSU was delivered. After comparing both the PSU’s together I noticed that only one voltage rails was different.

Modifying an PSU

Since fixing the primary side of the PSU would be very difficult to do, I started to look at the secondary side. Both the PSU’s are from the same series. So I figured the manufacturer probably used a couple of zener diodes, and resistors to control the output voltage. So I started to swap out diodes and resistors which where different and which I could relate to the voltage rail I wanted to adjust.

The moment of truth

I powered to PSU up, and measured all the good voltages (they where a little higher, but that’s okey since no load is attached.). I decided to go for it, and placed the PSU on top of the chassis, so I could test the PSU without going through the rather complex method of installing the PSU.

And after connecting the main power, and flipping the power switch, the PB200 came back to live.

 

 

A few quick tests showed me that the generator and analyzer are working without any problems. And I refitted the PSU back into the PB200.

 

Repairing Rohde & Schwarz SMT03 RF Signal Generator – part one

The R&S SMT03

The R&S SMT03 is a RF signal generator which can generate signals from 5Khz up to 3Ghz, while the signal level can be from -144dBm to +13dBm with 0.1dBm resolution.

A datasheet of the R&S SMT03 can be found [here]

Signal generators like the SMT03, and other (for example the HP ESG series like the E4421B) are mainly used to test communication devices and a like. Signal generators like this, are not arbitrary signal generators (however they may have an option to generate LF (Low Frequency) signals like square, sine, sawtooth wave-forms.

RF Signal generators generate sinus signal, and can generate different modulations (FM,PM,AM etc). These signal generators are a specialized piece of equipment.

An R&S SMT03 with problems

The SMT03 I’ve got in the LAB has some problems:

    • A few lines are visible on the LCD screen
    • When the unit is on for some tine, above 1.8Ghz the error: 110 Output Unleveled ALC failure is displayed .

The lines on the LCD screen are somewhat annoying, they don’t influence the working of the unit. The ALC Unleveled error does. When I try to measure the signal, the level is all over the place, and has a low level.  I noticed that in the short time this error is not present I can loose up to 4dBm when I generate signal above 1.8Ghz.

The challenges

When trying to fix an error like this, it’s important to understand the error. At the time this error presented itself, I didn’t had access to a Service Manual. And from the User manual I didn’t got any wiser. So after some thinking I concluded that ALC must stand for: Attenuation Level Control

This leads me to the conclusion that a possible cause could be a PLL circuit which is unable to establish a successful lock.  The bad news is: this may be due to a lot of other problems:

    • The input frequency may be of, or the signal is to low
    • Power problem (low / not working power rail
    • Mixer problem
    • And a lot of other related problems

Trying to diagnose the problem futher

So to diagnose such a problem, a block diagram and a schematic would be very helpful. But I got neither of them.

Another challenge is that the unit consists of modules, which plug into a back-plane. Operating the modules outside of the  unit seems only possible with a “service kit” which I don’t have access to, and cannot find any information about.

Despite the fact I don’t have the above items, I can observe the error, and take a look at how the physical signal path. So I opened the unit by removing the covers. Which is a simple and straightforward process: By unscrewing the bumpers on the back of the unit the top and bottom covers come off.

R&S SMT03 on the inside

Tracing from the output connector the signal path back I noticed that:

  • From the output connector, the signal is going through an attenuator, and then straight into a 3Ghz module (W154).
  • From the 3Ghz module the signal is entering an 1.5Ghz module (W104).
  • From this module the signal is going to a synth module, and a signal generator module.

And this tells me that the 3Ghz module has some kind of “pass-through”, so that signals up to 1.5Ghz are passed through the 3Ghz module (not sure at this point if some additional filtering is done). When signals are above 1.5Ghz the 3Ghz module generates the frequencies from 1.5 till 3Ghz.

This could mean that the ALC Unleveld error is somewhere in the 3Ghz module. Which means I could leave all the other modules alone.

For a moment I was thinking about a possible power rail problem, however this is most unlikely, since I aspect that for every frequency the ALC Unleveled error should be displayed, or that other errors would pop-up.

To summarize

    • Working on these units is not easy
    • A Service manual would be a great help

In [part 2] I’m going to try to repair this R&S SMT-03

 

Repairing Rohde & Schwarz SMT03 RF Signal Generator – part two

Trying to find a service manual

In part one I looked at the problems, and could conclude that the ALC error I’m seeing is most likely generated in the 3Ghz module.

So I started searching for the Service manual, and the ones I could find have description on the working of the modules, but the schematic and part lists these descriptions refer to, are not included. Without schematics this is already complicated, but without part numbers, most likely impossible.

Most of the components are SMD, and their markings are not always very descriptive. For example: A09 is this a A with the number zero, or the capital letter “O” ? or a component with just H2 on it won’t help either.

While I was searching for a service manual I investigated the error even more, since the error manifest itself when the unit gets warmer.

So I let the unit run for quite some time, and quickly removed the 3Ghz module, so I could feel where most of the heat is generated. Since these spots are the most likely candidates.

Taking a look inside the 3Ghz module

At that point I was at the end of the troubleshooting I could do. So I started to disassemble the 3Ghz module. Which got a lot of screws. And this is also the first time I opened a RF module. And at first glimpse, these kind of PCB look intimidating. Some RF parts and arrangement looks like RF black magic. But at the end of the day, it’s just a bunch of SMD components, and some specific RF stuff. Which I hopefully don’t have to mess around with. I also noticed a scratch on the PCB, where the scratch is coming from I don’t know, but it looks like someone worked on this module before.

the R&S SMT03 3Ghz module

While I was studying the layout of the 3Ghz module I made a list of possible components which could be the problem. The ALC error tells me that the problems must be before the signal leaves the module. Once the signal leaves the module, there is no way of detecting the level of the signal.

So may first plan of attack was to replace every opamp in the signal path, closest to the connector where the signal would leave the module.

Finally I found the Service Manual for the R&S SMT03

While making the list, a kept on searching to find the service manual. And to my surprise I found [here] the service manual with schematics, and most importantly a list with components.

Once I had the service manual I also could read the the 3Ghz uses the top cover as a heat shield. And from my experience I already notices how hot the module could get. So Without any proper cooling I don’t want to run this module without any covers. Which complicates troubleshooting even more.

But I figured: Since I’m already on the path of “guessing”  let’s continue with it. After studying the schematics, I picked a few places where the ALC error could come from.

Got it fixed

Long story short: I replaced all the opamps (which are 3 or 4) in the RF detection section, replaced 3 opamps in the 1.8Ghz filter range. And swap out some ceramic capacitors in the hot spots.

R&S SMT03 3GHZ sections where parts are replaced.

Of course, did didn’t solve the ALC error. After studying the schematics more, the only place could be the amplifier or pre-amplifier section.

While going ever the PCB I noticed someone replaced a component, since there was a lot of residue left. And this confirms that someone had worked on this module before. Was this also the person cause the scratch on the PCB ?

Could this be the cause of the 110 output ALC error ?

The component “A09” is on the other side of the module: This component turns out the be a “Hewlett Packard MSA-0986 Silicon Bipolar MMIC Amplifier”

This part is not easy to get, but I did mange to find it on Ebay. And as soon as it arrived, I replaced this part. And I could clean up most of all the residue.

The result after replacing the component and cleaning up the residue

As it And as it turns out, this part was the cause of the ALC error. I let the unit run for a couple of hours (fully assembled, so with all the covers on) and the error was gone.

The 110 ALC output error is gone

While this is not my preferred way of fixing It payed of in the end. Mainly because I could pin point the problem to a specific module, and I notices the work of someone else.

This brings me to another point: Lately I noticed on Ebay that prices has gone up for second hand , broken equipment. A R&S SMT03 with a lot of problems still cost over $500 or even $700 dollars. Fixing these units without a proper service kit is very hard to do. Especially if like me, lacking RF skills. For a trained electronics engineer, it’s more easy.  I think I just got luckily. But beware of units like this, and their (hidden) problems.

 

 

 

How to setup an Electronics lab

So how do you setup a electronics lab?

I did read a lot of articles, forums, and watched a fair amount of YouTube movies about how to set up a electronics lab. However in all those articles, and movies I missed a few things, which in my opinion,are essential even before you set up a lab in the first place. And so I think a better question is: What kind of electronics lab to setup ?

Before getting to setup a lab

Once you get involved into electronics, there comes a point you need equipment, to do your electronics stuff. And if your going to read up on this subject, you will discover that in most cases, people will tell you get quite an amount of stuff. For example:

    • Get multi meter
    • Get even one more multi meter
    • Get a soldering iron
    • Get a decent scope (analog or digital, or both)
    • Get a lab power supply (PSU)
    • Get all kinds of pliers
    • Get screwdrivers an such
    • Get a function generator
    • Get a frequency counter
    • Get a shitload of components

You get the point. The list is endless, and it will cost you at least a 1000 euro’s to get a basic lab like this together.

So let’s stop here. And think about it for a moment. Once you get involved or want to get involved into electronics, there is a learning curve. In other words: What kind of electronics are you interested in ?

And when talking about electronics, I’m not talking about putting some Arduino modules together, and writing code. To me, that’s not electronics. That’s programming electronics. Once you get to the point in troubleshooting the modules itself, I call it electronics.

So when starting electronics, one of the basic things to get are: stuff to learn. Now you can go to any (online) bookstore, and buy a few kilograms of book’s about the subject, and starting out your own personal library. But you also can get a book, a few parts, and start building the projects which are described in the book.  A good example of this is the series: Make Electronics. The best part is: There are kits you can buy, which contains all the components.

Another approach may be to get an Arduino, or Raspberry PI, and some resistors, and LED’s and play around with these, and create small projects.
You may also need  one or two (small) breadboards.

In the example of the Make Electronics, the beauty of it is: you get a small stock of components, which you can play around with. Of course you need some tools, and the bare minimum is a multi-meter, and a soldering iron, and some cutting tools, to clip off some wires. One or two small pliers is a must.

However at this point, you’re not sure if your going to stick to this hobby, or that it’s fun, but not for you. If you start with the list a few lines back, you invested a lot into something you never going to use again. Of course you can sell it on, but there will be a loss of money.

Another important thing to think about is: get a dedicated place where you can practice or build your stuff. I reasonable workspace, to work at, is a must. This is most likely the place where you start building your electronics lab.

And once you learned some stuff, you may find a certain part of electronics interesting. That can be repairing like  audio, or analog stuff (old radio’s, receivers)  Maybe you like RF or HF stuff,  Or you really like to design stuff. Or you want to dive into digital stuff. In other words: Electronics is a broad area.

I started with a make electronics book, and once I played around with the 7400 series logic IC’s I was hooked, and wanted to learn more about digital stuff. Logically (pun intended) I started to put together a electronics lab, which is suited for troubleshooting digital stuff.

Once you get into a certain field of electronics, and you’re more sure that you keep involved into electronics, you may start to look around for equipment. Once at that point, getting a decent lab power supply, a scope and a function generator is a good way to go.

And once you know and understand these devices, and getting better in electronics in general, more specific equipment can be bought. If your into RF stuff, a Spectrum  Analyzer, when dealing with different protocols, and buses like I2C for example you may want to have a USB protocol / logic analyzer or a logic analyzer build into your oscilloscope. And sooner or later, you’re going to discover that buying equipment which is sold as “for parts or repair” is much cheaper, and that it can be fun to repair equipment. And doing so, you learn at the same time 🙂 However when you going to walk the path of ” I can like to fix stuff” The more likely it is that you’re getting more and more equipment, and a pile of electronic components.  And eventually run out of available space..

At the point you know what your interest is, it’s much easier to get a stock of components. You also know which equipment you need to get. This way setting up a electronics lab, you can keep the initial costs down. So to summarize:

To get a minimal electronics lab together, start with the basic stuff:

    • Learn Electronics, buy book, and a small kit of components
    • Multi meter
    • Create your own dedicated workspace
    • One or two breadboards
    • A couple of screwdrivers
    • One or two pliers

Once your convinced that electronics is something you really like to do, go out and buy a soldering iron. When building small projects on breadboards, you don’t need a soldering iron. However if you want to make the circuits permanent, you do need a soldering iron.

And when buying a multi meter, don’t buy a meter which is in below or in the 15 euro range. Just don’t. For 50 euro’s you can get a decent meter. Even if you don’t know if electronics is something for you, don’t buy the cheapest multi meter you can get. Because you really going to regret it.

Getting equipment like Multi-meters,Soldering iron, Scope etc.  is a topic on it’s own.

 

 

 

 

 

 

 

Refurbish a HP8175A

Refurbish a HP8175A

Both of the HP8175A’s have some issues. And that is to be expected when getting equipment which is from the 80’s.The first HP8175A I bought has the following issues which needs to be addressed:

    • Replace the blown filter RIFA cap
    • I noticed some heat-sinks on the processor board are loose
    • The capacitors on the Power Supply board must be replaced
    • General clean-up of the front panel and casing.The second HP8175A has the following issues:
    • The keyboard panel is loose
    • The capacitors on the Power Supply board needs replacing

On both of the machines I have to:

    • Replace the blown filter RIFA cap
    • Replace a leaking Nicad battety
    • General clean-up of the front panel and casing

So to get these devices in a good running condition takes some effort. But without a Service Manual, this can be complex tasks. I searched online for the service manual for days but could not find any. Looking on Ebay the manual is also hard to find, and when a listing for a Service manual pops-up, the prices are in my opinion way to high.

Replacing the capacitors

The power board. This board is really heavy. It’s a beautiful design board, with golden traces on back.

To be honest, replacing the capacitors can be done without a service manual. This however requires some thinking ahead. The silk screen on the board doesn’t list the polarity of the caps. So a good practise is to take detail photographs of the Power board. Some of the caps are hidden under heat-sinks, so it’s difficult to take a good picture.

What I ended up doing is to replace the caps one by one. So de-soldering one cap, put it aside, making sure I write down the polarity, and place the capacitor besides the PCB in the same orientation it came from the board.

Also before ordering the capacitors, make sure to get the right sizes, so they actually fit on the board. Here is the list of the capacitors I replaced (per device):

    • 4x 270uF 40VDC  lead spacing 5mm
      5x 470Uf 25VDC   lead spacing 5mm
    • 1x 330Uf 35V          lead spacing 5mm
    • 2x 1000Uf 200VDC  lead spacing 10mm (snap-in)
    • 2x 5600Uf 6.3VDC   lead spacing 10mm (snap-in) Note: these capacitors aren’t replaced.

I also soldered in the replacement for the RIFa cap: which is a 250V 0.022uF Y2 cap.

When replacing capacitors, or working on Power supplies: Know what you are doing. If you don’t feel comfortable working on PSU’s which can have high voltages in them, then don’t mess around with them. Always make sure to discharge any capacitor. Some capacitors may hold a lethal charge!


Testing after the capacitors are replaced

Once all the capacitors are changed, time to test if everything works. Before replacing the power board I double check the polarity of the capacitors. And I  Also recheck the voltages and capacitance. Just to make sure every capacitors is replaced by the correct one.

And Again things go boom!

Once every thing is checked I applied the power.. and a loud hissing noise, a bang.. and another capacitor exploded. After a quick inspection I find out that a capacitor on a board for the FANS had exploded. Luckily this is a 270uF 40VFC cap, which I got in stock, so I replaced the capacitor.

Next I had to figure out why the capacitor has blown. As it turns out I misaligned the connector for the fans, causing a short. After I placed  the connector correctly  I powered the HP8175A on again. The devices works! However I noticed the fans are now spinning at a high speed. Telling me there is some damage on the fan PCB.

And that is bad news. HP (but others like Tektronix ) like to use their own part numbers. So it’s really hard to tell which IC or component your dealing with. Having a Service Manual, with a part number reference table, and / or the schematic of the board would be very helpful. Unfortunately for this device the manual is hard to get.. or is it ?

Getting the Service Manual

Looking around the Keysight website I noticed I could send a support request. And so I did. I aksed for the Service Manual, and a few hours later I got a reply e-mail, with the requested service manual attached. So after all it was quite easy to get the service manual, and of course a big thank you to Keysight!

Getting the fans working again

The chip in the middle is the LM324 I had to replace

The service manual has no reference to a fan PCB board. Which doesn’t surprise me. The other HP 8175A doesn’t have this board installed, and the power board is a slightly different. Both of the fans are directly connected to this power board. But I was able to get the part numbers and as I suspected one of the IC’s is an opamp a LM324. And after replacing the opamp the fans working again, that is: they run at a much lower speed, being temperature controlled again.

Re-seating the heat-sinks

A lot of heat-sink came loose, so I had to glue them with a thermal compound back on to the IC’s.

The first time I took the first HP8175A apart after a filter cap had blown, I noticed a small black metal piece fall out of the machine. At that time I didn’t had a clue where this little heat-sink was coming from. I didn’t had take all the board out yet. But once I did, I find that the processor board was missing two heat-sinks. I started to feel if the other heat-sinks where still glued, and just touching the heat-sink made them come loose from the IC’s.

So I used some thermal compound to glue them back on again, and since one was missing I ordered a heatsink for a DIP-16 package online, and put that one in place as well.

Replacing the NiCad batteries

The leaky battery, this is nasty stuff.

The HP8175 have a 2.4V Nicad rechargeable battery which holds the configuration. This battery doesn’t hold any calibration, so it’s easy to replace them. However finding a exact replacement is not possible. (There is some New Old Stock (NOS), but since these batteries are very old, I don’t recommend buying and using them.

 

The new batteries installed, and it fits perfectly. The batteries are in series, and hot-glued together.

So I ended up buying four 1.2V batteries, and put two batteries together in series. (so I created 2 sets of 2 batteries)  I cleaned up the board carefully making sure to remove any acid from the leaked batteries. This stuff will eventually eat it’s way through the PCB, causing a lot of damage. The best way to clean this is with vinegar.  After that I cleaned the board with alcohol.

Cleaning up the front and case of the machines

I used some rubbing alcohol and other soft chemicals to clean up the front and the cases, and after that the machines looked a lot better. I also used some double-sided tape to stick the keyboard cover back on. And at this points both of the HP8175A are ready to be used again.

All in all it took some fair amount of time to get these machine usable again, but it was worth the effort. Especially taking into account  that these machines are fun to use and to play around with 🙂

Closer look at the HP 8175A

The specifications of the HP 8175A

In the first part of the article about the HP8175A I talked briefly about what this device does. In this part 2 I’m taking a look at what the HP8175A is capable of doing. Before jumping right in, a short look back at part 1. In part 1 the HP 8175A released a lot of smoke, and the fix was easy.

However I realized that fixing these complex devices is almost impossible without spare parts. So I bought a second unit. As it turns out, the seller from which I bought the first HP8175A, had a second HP8175A to sell.

Since I let the seller know the magic smoke escaped , I could pickup the second unit really cheap. By arrival the device powers up, but nothing appeared on the screen. After reseating the boards, the device seems to work. I didn’t test all the outputs, but at least it starts up without problems. Of course I took out the RIFA cap, before it could explode 🙂

So now on to the specifications of the HP 8175A:

The HP8175A can be used in “parallel or serial” mode. In parallel mode the speed is 50Mhz. In serial mode, the channels runs at a speed of 100Mhz.

The “Operating and programming” describes the HP8175A as:

The 8175A is a digital generator which can deliver parallel and serial data with programmable patterns pattern durations. It can interact with a device under test and so provide simulation of a wide range of data paths in digital systems.

Per channel:

Parallel data patterns: 24 channels / 1 kbit / 50 Mbit.                                        Serial  data patterns:    2 channels   / 8Kbit 100Mbit

The HP8175A uses virtual memory Expansion: 255 memory segments, can sequence between 2 to 1024 patterns ea.

The patterns durations which can be programmed: 20ns to 9.99 seconds range / 10ns resolution. individually programmable.

Interface with the Device Under Test (DUT) 8 bit trigger / 8 flags.

Two HP8175a  device can be connected together in a master/slave operation.

Most of the logic families are supported: TTL/CMOS variable, ECL fixed.

The options available are:

001: Fine Timing (100ps resolution on four channels)

002: Arbitrary waveform generator.

D04: Deletes stands POD set

908: Racl Flange kit

910: Additional Operating/Programming/Service Manual

So this is quite a list. When designing digital circuits this devices is very useful. Since I have a couple of Logic Analysers in my lab, the HP8175A is nice instrument to have.

The HP device in action

Since this is a complex device which is very versatile, demonstrating the device is difficult. Even if I made a video demonstrating the device it will be long. So what follows are a few screenshots showing the device in action.

Here you see how to setup a pattern. Each bit can be set for a channel. And it’s also possible to set the duration.

 

 

It’s also possible to use a more graphical view to enter the digital waveform.

 

 

Since one of my HP8175A has option 002 installed, arbitrary waveforms can be created. This can be done in a kind of a program language, where mathematical functions are easily selected, and for loops can be used. In this case the “sin” function is used to create a sinus waveform.

Here the HP8175A in action to find a fault on a C64 PCB board. The HP8175A is used to inject digital signals onto the databus and address bus, and a HP 1670G Logic Analyser is used to read the bits.

 

In the upcoming part 3 I’m going to repair some of the issues the devices have, and refurbish the devices. And I also let you know how to get the service manual for the HP8175A. The service manual is hard or impossible to find online, and if you want to buy the Service manual the prices are going through the roof. I’ve seen hardcopies sold for $100…