On Thu, Apr 21, 2022 at 06:23 PM, Mark Vincent wrote:
I checked one of my 453s that is above 20,000. The TP voltages in the
schematic are right. Check the transistors and diodes in that area. The 3,3mfd
condenser could be bad. I have had ones with high ESR I replaced with Nichicon
ULD type. R473, R674 and R483 I raised to 1 and 2W respectively. Yours could
be high in resistance. The originals are 1/2W carbons. The tunnel diode will
be good if you can get a signal to trigger.
The trace problems you describe sound like the astig and geometry(?) need
adjusting.
Mark
Thanks for doing that. I looked at that whole area and I didn't find any bad components. I have also suspected that maybe C485 (3.3uF) was bad. It tests as open with ESR meter and ha a very funny looking curve when looking at it with an "octopus" curve tracer. I replaced it but none of those voltages changed. Apparently, per a post after your, the voltages I measured are correct IF IT IS TRIGGERED. The schematics make it appear like you have to use the conditions on Page 1 of the schematics, but I guess I did not interpret that correctly.
Anyway, the astig and geometry are fine. When I'm using the scope in any other mode besides Mag (x10) and Ext. Horiz. the traces look pretty good except that in certain positions of the Time/Div switch you can see a little noise on the waveform, but it's still very usable. You can also see it with the beam finder too. Still have not found where it's coming from.
diyguitarist