Oh Sorry, I think I just confused the issue -- I ONLY get a vertical line
when I use the flyback transformer connected to the OTHER Mac (put them
back-to-back and used the other Mac's flyback to power the 128k's CRT,
both
Mac's powered on at the same time), i.e. I have disconnected the 128k's
flyback -- taken it out of circuit -- and if I understand your schematic,
without the flyback in-circuit, there's no HV as the flyback takes its
voltage from pin-1 via the Q3 transistor and routes it to the rest of
the HV
circuitry? Correct? (I did this when I originally tested the flyback
on the
128k to see if that was the problem -- I now know that the flyback is
perfectly fine after transplanting it to the other Mac, but on the
128k it
gets NO power, so the problem is before the flyback on the 128k -- there
might be a problem after too, but I tested everything you mention and
everything checks out, I even transplanted the nonpolar electrolytic
cap to
the other Mac and it worked fine. So FORGET that the I ever got a
horizontal
line, the flyback transformer is definitely NOT getting power from the Q3
transistor which also checks out on the other Mac, so it has to be before
the Q3 which isn't getting power either. Without any outside influence, I
get no picture whatsoever. Thanks!
Oh, ok -- I think I understand now. Here are some suggestions for
narrowing things down a bit.
1) Verify that you have horizontal drive at the base of Q6. That's a bit
challenging if you don't have an oscilloscope handy, but you can
sometimes make do with a multimeter set to "AC." If you measure zero (or
close to it), then you know that the problem lies upstream of that point
(assuming that you've already verified that the transistor is ok).
2) Verify that R7 is ok ( it's a beefy 5W resistor). You should see 12V
on one of its terminals, and not zero on the other. If C13 fails
shorted, it will kill the horizontal and HV ckts pretty effectively (and
will make R7 run very hot, causing discoloration over time).
3) Verify that T2 shows continuity across both primary and secondary,
but none between those windings.
4) Verify that Q3 is ok. You'll need to pull it out of the circuit to
make a valid determination. Verify that drive is getting to its
base-emitter circuit using the same multimeter check you used in step 1.
5) Check CR1. You should see 12V on the anode (unbanded) terminal.
6) Check C3 and CR5. You can check C3 out of circuit using a multimeter
set to a high resistance setting. Connect the leads to apply voltage of
the wrong polarity across the cap, and leave them there for a few
seconds. Reverse the leads quickly and see if the capacitor charges up.
These tests should allow you to pinpoint where things are going awry.
Good luck -- I hope that you're able to fix it in short order!
--Cheers,
Tom
--
Prof. Thomas H. Lee
Center for Integrated Systems, CIS-205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu
650-725-3709 voice, -3383 fax
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