HP 8903B repair

I really like my HP8903B audio analyzer. While PC based systems can outperform it in some areas, I like the robustness and simplicity of this standalone device. However it failed with “Error 14”. The analyzer is almost 20 years old, this can happen.

The modular design makes debugging relatively easy. After removing the analog front-end card, the analyzer worked again. Ok, there is a problem with this card. Looking at the card there was no obvious problem. Further debugging showed the one rail of the analog power supply was out-of-spec 13V instead of 15V. Looking at this on the oscilloscope showed a huge amount of ripple. At this point it was obvious that at least a capacitor in the power supply had a problem. There are 3 huge capacitors in the power supply, 2 for the analog +/-15V and another one for the digital 12V and 5V. Checking these capacitors showed that one of them was defective. Have a look at these huge parts. I replaced them with more modern caps (the black ones in the picture):

capacitors

The replacement was done in a few minutes, as these are screw-in capacitors. There is no need to solder anything.

hp8903b-caps

Looking at the picture now I think, I should also clean the device ;-)

Was this the root cause of “Error 14”? Let’s power it on again:

hp8903-raspberry

Yes, it is working again – great. If you ever get this error with your HP8903, check the power supply first.

6 thoughts on “HP 8903B repair

  1. Ted T

    Hi,
    I am trying to repair my 8903B. The servic emanual does not have a power supply schematic (A13). Might you have one?
    Thanks
    TedT

    Reply
    1. Andre Beaudoin

      You can get the two service manuals on Keysight web site
      You will find the power supply schematics at section 8E
      Note that +12V supply is inexistent in later SN

      Reply
  2. ted Telesky

    My 8903B is dead. Do you know where there is a schematic of the power supply (A13) PCB?
    Thanks
    TedT, California

    Reply
    1. Ted Telesky

      I have a PDF copy of the service manual. Send me a personal email and I will send it to you.

      Reply

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