Zenith 25" System 3 console - vertical problems

[Adam]

There is no vertical hold control, its all automatic.

I found the problem, remember I said in the last post it looked like there was a .68mfd capacitor where the schematic said there should be a 680. There's a picture where it divides the main board into a grid and then tells you which square each component is in. It said the 680 was in sections F-9 (where the 0.68 is), but it's really in section F-19. I replaced the real 680 and that fixed it.

[zeno]

Well done !

As for the 9-181 look for a little paper tag on the PCB. Dont remember the difference but plain 181's had plug in IC's & R-G-B outputs. A real PIA.
Anyhows the jug looks near mint, nice catch !


Zeno

[old_tv_nut]

Originally Posted by Adam

There is no vertical hold control, its all automatic.

I found the problem, remember I said in the last post it looked like there was a .68mfd capacitor where the schematic said there should be a 680. There's a picture where it divides the main board into a grid and then tells you which square each component is in. It said the 680 was in sections F-9 (where the 0.68 is), but it's really in section F-19. I replaced the real 680 and that fixed it.

Great! A tidbit about the Zenith sync IC: it worked by looking for the whole vertical interval pulse pattern, and was so noiseproof it could sync on a signal so weak that you couldn't recognize the picture in the snow. The first models, though, expected only FCC standard sync and had trouble with video games until a redesign was done.