Re: HP 8568A Spectrum Analyser not booting up. Both INSTR CHECK Leds on
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What happens if you disconnect the bus cable and then turn on the analyzer? LED 1 should stay on, while LED 2 should extinguish. I suspect both will stay on as they have so far, but if things change it may be a clue.
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As far as any other easy tests, I would also check all the front panel keys. They have leaf springs in them so that they return to their normally-off position. These springs can dislodge and leave a key in a state where it's always acting as if it's pressed. During preset, the processor checks for that condition. If a key is in such a position, you would get just one of the LEDs remaining on, but I would check anyway because of the age of this analyzer.
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The easiest way to check for errand springs is to press each key and note if there is a click. The key should firmly return to its resting position. Keys with missing or dislodged springs will feel ¡°mushy¡±.
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Other than that, check that the processor clock is working. Everything else becomes more difficult to troubleshoot because of the need for a signature analyzer. Even with one of those, chasing a problem can get circular until you have replaced almost every part on a board.
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Pragmatically speaking, if you can find a processor and memory board for sale, it would be easiest to just swap them. Most 8568A (and 8566A) have been updated to ¡°B¡±, which left many unwanted ¡°A¡± boards around. I am not sure if they still show up for sale, but the cost should be minimal due to lack of demand.
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Vladan
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