On Sun, Jun 23, 2013 at 2:27 PM, Christopher Brown <[email protected]> wrote:
> Do have have a shorting bar in place between guard and gnd? > No, but it didn't make any difference if I shorted guard and either terminal. > > One of the issues I tracked down on my worst unit was a leek from output > + to guard. Some of the tin had flaked off of the traces and formed a 6 > ohm connection from + PS out to guard. Besides guard being hot I saw > intermittent output. > > Simply probing with a scope would return voltage to normal. > > Simply placing a _dry_ fingertip across the traces/guard in front of the > guard would do the same. > > I asked about the shorting bar, because connecting guard to gnd in my > case would pull the ps output _way down_. > > Anyway, worth checking for voltage on guard. > > Yes, there is some leakage to guard and a couple of V is readable, but the leakage in the order of M ohms. I did some checks with the DMM on ohms, one lead on guard and ran the other probe around the power supply board and there are definitely areas with measurable resistance. I scrubbed some with alcohol and electronics 'q-tips' and got the meter to read overload. It looks like I'll have to take the bridge rectifier out to scrub under it. I was hoping I wouldn't have to do it, but I guess contamination from a previous battery leak wasn't cleaned up well enough and I'll have to take the board out. Oh well, I can fix the broken pins at the same time. The output voltage is behaving itself now though and holding steady at two counts above 10V on the 3456A with 6-digit display selected. Another thing I noticed is that the zener voltage has a lot of broadband noise on it. 0.1uF or so across the zener makes it invisible on my 'scope. Orin. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
