David,
More for you below. Hope it helps:
Could also be C866 is shorted, but that would be extemely rare.
To eliminate that, pull one side up temporalialy, and power up and
re-measure R860 volts.
+69V with ref to ground.
I think you measured the "high" side of R860(the 130V supply line). Maybe I should have said measure the collector of Q860; this is the same as the base of Q869 and the low side of R860; or should be if connections are OK. Again, this would be with one end of C866 lifted.
I must thank you for your persistent help so far Jimmy, very explicit
instructions that are very easy to follow!
Thanks.
re cap ripple testing, do I put scope probes only on the cap pins of
each individual cap to test each cap?
First, did you see my earlier posting about measuring ripple with an old analog meter that has an "OUTPUT" terminal? Anyway...
Here's how I would check for excessive ripple using another (test) scope. This will work for all of the big filter caps that have one terminal connected to chassis ground. DO NOT use this method for the filter cap (C806) in the 130V supply because neither one of its terminals is connected to chassis ground:
<<<<<<Be carefully around the AC input/mains power!!!>>>>
1. Ground a 10X probe hooked to the test scope to chassis of problem scope. Use a good-quality clip lead to extend the probe's ground lead if the length of the ground lead is not enough for easy measurements, AND INSULATE the 2 alligators' connection with some black electrical tape so this won't short something out if it accidentally touches anything.
2. Set test scope channel to 50V/div. (Use 5V/div if you've got a scope that does not auto-sense probe attenuation). Be sure to use a 10X probe.
3. Set test scope channel to AC coupling and vertically center the sweep. (You can initially use DC coupling if you want to see the DC component also.)
4. Set test scope for Line trigger, and about 10mS/div. Adjust trigger for a steady sweep (flat line when probe tip is not connected to anything).
5. Carefully probe the "hot" side of each big filter cap. For most, the "hot" side is the "+" terminal. However, for some like C808 (1800 uF) for the -50V supply, it would be the "-" terminal.
If the cap is good, you should see a sweep that's still nearly flat. I'm thinking no peak-to-peak waveform on a filter cap should be more than about 3V. If necessary, increase vertical sensitivity to 5V/div, or less, so V peak-to-peak can be more accurately measured. You DON'T won't to overdrive the test scope's channel amp by using too much sensitivity (As a general rule, don't let the waveform go vertically too much off the top/bottom of the screen.) It is good to return the test scope's channel to the 50V/div before going on to the next cap!!!!!
To check filter cap C806 in the 130V supply use two 10X probes, two scope channels of the test scope, set one channel for "Invert" and use the "Add" vertical function. Make sure both channels have equal V/div settings, and they are adjusted for equal gain. This is basically a differential measurement. To verify test scope's settings (equal gains, etc.), probe a common signal point with both probes and make sure there's no (or very little) signal/ripple.
It will be good to post your ripple measurements.
Regards,
Jimmy
