In article <n7r9pg$1at$
3...@dont-email.me>,
Cursitor Doom <
cu...@notformail.com> wrote:
>Interesting. What component was failing? There's a 1.5kV transformer on
>this board which is encased in opaque grey plastic so if it's something
>arcing inside that it won't show up in the dark.
Try the Grand-Dad's Ear Horn approach. Get a length of 1"-diameter
plastic pipe, hold one end against your ear, and move the other end
around the board. This will let you "listen" to the individual
components, while still maintaining a safe distance from any high
voltage.
Seems to me that you could be hearing either:
- Actual venting. I'd be a bit surprised, though, if this were
happening and you couldn't spot the culprit. Maybe fire it up in a
really cold location, and look for a cloud of vapor?
- Switching noise from a failing cap. I've heard SMPS capacitors
begin to hiss like this when they began failing due to the infamous
"'lytic capacitor electolyte plague" a few years ago. They'd go
high-ESR well before they'd start to leak and vent.
Checking all of the caps on that board with an ESR meter (with the
power off and fully discharged, of course) might locate the
culprits.
- High-voltage leakage. I had a Tek 7904 scope which was suffering
from corona discharge and hiss (and an occasional "snap") due to
some contamination/deterioration on the high-voltage lead from the
power supply to the CRT. Cleaning didn't help. Coating the lead
(from the PSU, through the cage) with a bit of high-voltage
silicone putty made the problem go away.