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Gesendet:?Dienstag, 24. Oktober 2023 um 19:10 Uhr
Von:?ThirtykayDEV@...
An:[email protected]
Betreff:?[HP-Agilent-Keysight-equipment] HP 8568A Spectrum Analyzer failure, BOTH INSTR CHECK LEDs off, Test Pattern OK and keyboard not responding once Self-Test passed.

Hello everyone,

I recently got my hands on a HP 8568A Spectrum Analyzer and his IF/Display Section HP 85662A.

I got the 8568A for 40 euros, sold As-Is mentionning "Keyboard not responding".
I got the 85662A for free, hanging around in the trash, waiting for someone to save it.

It goes without saying, with such a price, it has to be very very faulty and of course it is.

HP 8568A Serial Number is : 2216A02211 Option 001.
HP 85662A Serial Number is : 2318A05097 No option.

The symptoms are:

I apply power to the analyzers, The INSTR CHECK leds shutdown after self-test, so i assume there's no big fatal failure and yet no display activity 2 minutes after start up, moreover the keyboard does not respond to any input.

What i did so far, in order:

? ?Checked both RF/IF Section supplies - OK, all within tolerances.
? ?Checked 50-wire inteconnect cable - OK

? ?Performed the preliminary check provided by the service manual, which are:
? ?Checked keyboard while self-test - OK, INSTR CHECK right led stays on as expected?
? ?Ran HP-IB Test - OK
? ?Ran LONG-POP Test - OK
? ?Ran Digital storage Test - NOK, No test pattern displayed but INSTR CHECK left led on, as expected.

? ?Then i moved to IF/Display section 85662A:
? ?Hooked up an external XY monitor - OK but i do only have symbology element, like the grid, the HP logo and some text. Check attachment.
? ?Checked CRT Filament resistance - 19 Ohms, OK
? ?Checked CRT Filament voltage on A1A3 TP1A-B, NOK, 0V
? ?Checked HV +18V on A1A6 TP100-5 - OK, +18.12V
? ?Checked DRIVE signal for the HV Transformer on A1A6 TP100-4 - NOK, No oscillation.
? ?Checked CRT DSBL signal at 0V on A1A6 - NOK , 4.5V, CRT is disabled.
? ?Performed a visual check of the A4A9 Board and U6 in charge of CRT DSBL signal - OK.

? ?After a night of meditation i came back to the 85662A:
? ?Shunted CRT DSBL line in order to clear any doubt on HV part of the CRT - OK, Display working, some progress !
? ?Ran Digital storage Test AGAIN -?OK, Test pattern displayed and INSTR CHECK left led on, as expected.
? ?Reseated all the A3 board and sprayed some contact cleaner - NO CHANGE.

? ?Reseated A15, A14, A13 and A12 in the 8568A - NO CHANGE.

Since then, no more progress, i'm having trouble narrowing it down to either the 8568A or the 85662A, but my inside tells me to go for the 8568A, RAM/ROM or Processor.
And there's is still my keyboard not working after self-test that worries me the most, it seems the processor fail to execute some code and his stuck forever. just an assumption.?
Just in case, if someone have the ROM/Firmware for the 8568A, it could help me quite a lot in the case of a ROM chip failure.

Hoping that i've been clear enought. As i wait for your kind answers, i go back to the service manual :)?


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