On 22/01/2012 02:34, jtjewell83 wrote:
?
David and Magnus,
I'm thinking Q872 and the other 2 transistors are OK.
There's just not quite enough base current to turn on
Q872, and the others. The collector of Q860 is only 2
volts. It should be about 52V when things are normal (+50V
supply + drops of 3 transistors' B-E junctions).
R860 (680K ohms) may be open. David, can you measure the
volts ACROSS that resistor.
-67.6V
Based on your previous measurements of the +130V supply,
you should measure about 70V. Or you should get about
71.5V on side of that resistor, referenced to ground.
71.8V ( no sign of cracked solder pads.)
Inspect for cracked solder joints around that area.
Also, wiht the scope OFF, measure R860 ohms.
R860 = 12KOhms ( with R860 in place on pcb )
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 must thank you for your persistent help so far Jimmy, very
explicit instructions that are very easy to follow!
re cap ripple testing, do I put scope probes only on the cap pins of
each individual cap to test each cap?
Thanks.
David.
ps. I have found what looks like a mistake in the service manual A11
low voltage regulator board,I think that R860 and R866 are mixed up.
I have ignored the print out and concentrated on looking at the
colour codes to find the correct resistor.
I'm thinking Q860 is OK.
We've getting close!!!
Jimmy
