HP 8903E Distorshion Analyzer Help Needed - diyAudio
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Old 22nd July 2011, 01:48 AM   #1
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Default HP 8903E Distorshion Analyzer Help Needed

Is anyone familiar with the HP 8903E to help diagnose a problem? I have one thatís worked fine, no problems over the years. Today I needed to make some measurements on a serviced amp and all I get is all 8.8.8.8.8 .8.8.8.8 All 8,s across both displays. All the controls seem to be locked up. Microprocessor failure? I have the operation, calibration manual for the unit, not much help in leading me into the fault area, any ideas?
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Old 22nd July 2011, 01:51 AM   #2
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Ask on the Yahoo HP/Agilent group -- lot's of guru's there
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Old 22nd July 2011, 02:23 AM   #3
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Dose anyone have the Service manual for this unit/ The user/cal manual on line is missing that section and can't seem to find one. I know there's at least a few here that have one of these units.
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Old 22nd July 2011, 04:12 PM   #4
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Never mind, I found it. Not getting much help here anyway.
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Old 29th July 2011, 11:17 PM   #5
tomchr is offline tomchr  United States
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A garbled display is usually a sign of a microprocessor (or support circuitry) failure. I fixed one like that a while back. I happened to have two 8903's and could swap boards between the two. Once I identified that the CPU board was the issue, I swapped the CPU and some I/O, memory controller and found the issue to be the memory controller. I was able to find one on-line for $3 at a surplus store. Problem fixed.

I actually found the service manual to be quite helpful. I bought a paper manual on eBay -- much better quality print than the scanned PDF's on-line. But without the symbol analyzer required per the service manual, getting that CPU board debugged can be a shot in the dark.

Based on your description, my guess is that the CPU board in yours might be OK, but somehow, the CPU doesn't get out of its reset state.

~Tom
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Old 29th July 2011, 11:32 PM   #6
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I found what is wrong with the unit, U2 is open. The led for the 12v is off and there is 24vdc at the test point. Further testing of U2 shows open. The problem now is there are no number on U2 so unless I can find someone that has one and is willing to check it for me I'm out of luck. I have all the manuals 1 and 2 but there are no parts BOM in either one of the volumes. So, if anyone has one and can tell me what U2 is I would very happy.
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