Hello,
I turned on my 8655 yesterday and found out that I don¡¯t see the staircase noise floor. PL1,PL2 M/N, YTO, REF all shown as unlocked. Instrument responds to first key press, and then display freeze. It does always respond to the green instrument preset key thought. No good, last time I used it is 3 month ago and it was working.
First suspected the CPU and front panel boards but nothing seemed wrong there. After some troubleshooting, the culprit was found to be the negative regulator where -40 is dead. I pulled a neg regulator A18 from a spare unit and swapped, now it¡¯s great again ¡ª whew.
I¡¯m trying to figure out why the -40 is dead as the A18 is quite expensive on ebay. I don¡¯t see anything obvious wrong. The fuse is ok suggesting the -40 crowbar is probably ok. Did diode test on Q5, Q6 and the diodes around the -40 regulator circuit, seems ok to me. Have anyone seen this?
Thanks,
Calvin
