8903A Error 14, power supply circuit diagram - diyAudio
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Old 15th July 2014, 04:20 PM   #1
usul27 is offline usul27  Switzerland
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Default 8903A Error 14, power supply circuit diagram

Hi,

I have a HP8903B here that does not work. It always outputs "Error 14" which is an input signal above the measurement range. However there is no input signal. I couldn't identify the problem yet, but it seems to come from the front end board. When I remove this board, the analyzer starts and displays 0Hz, 0.003% THD+N. This seems reasonable. Now I have to find the problem.
One thing I noticed is the voltage on the +15V rail. It is only 13V. This doesn't seem normal to me. However I could not find the circuit diagram for the power supply. Does someone have a scan of it?

Any known issues that led to Error 14?

Thank you
Daniel
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Old 15th July 2014, 05:09 PM   #2
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I think HP has the schematic on their site, iirc.

Sounds like a possible DC offset in the card you removed?

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Old 16th July 2014, 01:40 AM   #3
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First thing to check is all electrolytic and tantalum capacitors. These are often the first thing to go in devices this old. After that, I would look for bad op-amps.
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Old 16th July 2014, 01:44 AM   #4
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I have the SM, but the site refused to upload it.

If you for some reason fail to get it off the HP/Agilent site, PM me with ur email and I can attach it - it's two parts pdf, and about 20meg each part.
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Old 16th July 2014, 01:53 AM   #5
WSJ is offline WSJ  United States
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Old 16th July 2014, 07:30 AM   #6
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Thank you, I've got it. The 13V on the +15V rail are clearly out-of-spec. I will start here.
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Old 17th July 2014, 02:58 AM   #7
1audio is offline 1audio  United States
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You may have a shorted cap in a supply or a bad input opamp or protection diode. Either would give the error message your mentioning.
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Old 18th July 2014, 11:35 AM   #8
usul27 is offline usul27  Switzerland
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Yes, at least one capacitor in the power supply failed. I'll start by replacing this one.
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Old 18th July 2014, 01:49 PM   #9
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Quote:
Originally Posted by usul27 View Post
Yes, at least one capacitor in the power supply failed. I'll start by replacing this one.
Replace as many electrolytic capacitors as you can because in old equipment they are often ticking time bombs.
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Old 18th July 2014, 02:04 PM   #10
usul27 is offline usul27  Switzerland
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Yes, I think this makes sense. There are 3 huge screw-in caps in the power supply. Is there any reason to use these huge screw-in models? Modern electrolytic capacitors with same capacity/power rating would be much smaller.
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