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…

4 thoughts on “Closer look at the HP 8175A”

  1. Thanks for sharing your equipment experiences it is all very interesting.
    I too have a HP8175A with opt 002.
    It came with a dead PSU, I changed some caps and chips and Transistors then I decided the spark gap arresters were faulty and replace some from Israel – ebay. It no longer sparked continuously but it had 2 LED trips lit. It stayed like this for years on my shelf at work.
    Eventually I brought it home as I had no time in my lunch breaks. I found a Diode blown and replaced it with a modern diode with some improvisation.. The chips caps and transistors were all OK and I have put some of the original caps back.
    I do not have the service manual and it probably would not have helped. I did find a list of HP component codes which was helpful.
    My problem is the user manual on Keysight does not cover opt 002 like it says it does.
    I would like to use the Arb to test a circuit I am making to help a friend. I have guessed my way around the buttons once but got stuck in the programming, I could not exit. Can you send me a link to a manual for opt 002 please.

    1. Hello Graham,

      Nice to hear another HP8175A owner 🙂 That was quite a repair! And yes.. the manual doesn’t mention option 002. I found this document:

      From around page 17, you find some info about how to program. All in all it’s a nice read. I like the engineering put into the HP8175A.

      Another problem with the HP8175A is finding the “mini grabbers” for the TTL probes.

      1. I’m also a HP8175A owner. I got the 8175A specifically for option 002 and figuring out how to use it is a pain in the ass. I’m learning it by trial and error now.

        1. Hello Ernest, Nice to hear from another HP8175A owner 🙂 And yes the Arbitrary waveform generator is complex to use, mainly because the documentation on it is limited. However the engineering of this device, and the user interface is incredible.

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