Michael J. Mahon wrote:
Alex Freed wrote:
So the line-side supply is fine and stable, but the low voltages
are out or regulation? Or in regulation but at too low a set point?
(Do they drop much when a load is applied?)
Sounds like you have an unusual failure mode. ;-)
Well, yes. The line-side supply is close to perfection.
Looks like the problem was a tiny 1 uF 35V cap. The pads under it
were corroded which could mean that the electrolite left the cap a while
ago.
Remember that all electronic components run on smoke? When the smoke
gets out they stop functioning. And electrolitics need liquid in
addition to smoke to operate.
So I took it out and measured approximately 0 uF. Replaced by a fresh
1 uF and the device is much happier.
Probably blindly replacing the electrolitics is a good strategy unless
something is clearly wrong on the board. I just didn't have 100 uF by
200V caps in my junk box and Jameco is closed :)
As a side remark this particular supply uses a 7905 and 7912 for the
negative voltage low current linear regulation. Which confirms what was
written in a recent thread.