Mac Plus analog board - horizontal flickering lines

[tom_B]

Video:

Analog board has been recapped, no cracked solder joints or anything that I can see. I reflowed the joints for the flyback, and all of the connectors that go between the logic board/CRT.

Happens with multiple logic boards

If I have it on, and tap around the analog board with the rubber handle of a screwdriver, nothing seems to change at all, so I'd assume if it was a cracked solder joint or something it would have showed normal, even for a second.

Any ideas of specific spots to triple check? Any components that may go bad on the analog board that would cause this? I have an analog board I bought with a Parts Mac Plus, but the flyback transformer was cut off, so I was thinking worse case I could remove that flyback, and move the flyback from this one to the other one, but I'd like to avoid doing that if anyone has any ideas

 

[luminescentsimian]

hmm, doesn't look like sync is dropping, just the video signal. I suspect that there's a transistor or amplifier chip taking the TTL signal from the logic board and generating the power for the electron gun.

 

[tom_B]

Ok, so

Checked a couple of the ICs on analog board 1-they test fine(U1 and u2)

So I decide screw it, grab analog board 2, swap the flyback from 1 to 2(because the 1 on 2's wire is cut)
move all the new caps over from 1 to 2

Turn it on, same issue

Issue is across 2 logic boards too

So, it's either;
1- same exact component is dead on both analog boards(i feel thats unlikely)
2- something with either one of the cables from the AB to the Logicboard, CRT neck, or CRT yoke
3- capacitor issue. either a failed cap(they're brand new from console5) or a wrong value somewhere
4- issue with flyback transformer(don't think this would be it)
5- CRT issue?


So next step is I'm gonna open a 2nd plus, and start swapping cables and parts. see if I can at least verify its the analog board, and not another component, and start going from there

 

[jajan547]

Check the cable that connects to the logic board there is a small cap or resistor (forget which) in the cable this can fail quite commonly.

 

[tom_B]

Doesn't seem to be anything on the cable. Just wire and plugs(and a ferrite core). I checked the cable with the meter and it seems solid
checked the cable that connects to the neck of the CRT as well, and that seems fine

I noticed the pins on the CRT look a bit discolored, so I'm starting to lean towards a CRT problem

 

[tom_B]

With some help from Techknight on the TD discord, and some parts swapping, turns out it's the tube(not caused from the discoloration on the pins, but either gassy, or a short in the CRT)

Thanks for the advice too luminescentsimian and jajan547!