On Mon, Dec 13, 2021 at 02:39 AM, James55 wrote:
Hi all,
please excuse the lack of input, however I became deflated and just put a cover over the scope and walked away.
Thing is, I really do need a working scope, so today decided to give it another go.
The mains input is now running first through a dimbulb, which dutifully illuminates when the unit is switched on. All of the low voltages rails are close to zero. For example the 65v rail is up at a whopping 10.4v. The minus 15 rail is 0.5v. The minus 8 is 0.4v and the 140v rail is 5.3v with the 5v being shorted to ground at zero volts.
I removed the A5 Trigger, and A7 Timing, boards in the hope of narrowing down the search area.
Things got off to a good start with the discovery of the shorted R1377 resistor, although that made no difference to any of the readings. There is a pure short circuit on the 5v rail however for the life of me I cannot seem to find it.
I have tested and tested all over the A6 and A10 boards, testing voltages and also bell-testing for shorts with the power off. It really is at the point where I can only see trees, without a glimpse of any wood...
I have also covered the board in IPA which all just sat there wet for ages. There are no warm components, or even areas... I wish something would just explode or at least go up in smoke, as I have no real idea as to where else to look.
It did cross my mind that it might be the 5v rail 5500?f filter cap yet although I only have a DMM it still reads 7000?f, so I am assuming it is not shorted.
If anyone has any suggestions at all as to where I might check next please feel free to chip in.
Perhaps I'll just leave it plugged in, as surely a direct short has to start smoking at some point?
James
James55