Macintosh SE flicker and interference

[Mirokai]

I recently got 2 Macintosh SE (lets call them A and B). A is a Macintosh SE 1/20 from 1987 and B is a SE FDHD. Macintosh B had a broken CRT where air got inside. So I replaced the CRT today but there is some flickering going on (moving thin horizontal lines.)

Even worse when I placed both SE side by side and turned both on I could see some huge horizontal lines on Macintosh A (perfect condition, works like a charm). I don't know if I just imagine it but I think I got a tingling sensation in my hands when I placed them near the case. When I ran the logic test on Snooper 2.0 the screen glitches although I tested the logic board in A before and all tests passed.

Other than the flickering the picture looks very good.

How do I troubleshoot this?

 

[LaPorta]

Were the cases open when you did that? Could be EM interference.

 

[Mirokai]

Both cases were closed.

 

[Mirokai]

It seems like it is getting better the longer it is powered on. Should I resolder the flyback?

 

[LaPorta]

I would suspect capacitors first thing (I assume they have not been replaced). Start there, then see what happens.

 

[jessenator]

Second on the capacitors. 68kmla member JDW has an excellent video on replacing the SE analog board caps, and it's not too bad to do, just mind the hot glue portions.

I had a situation just like yours on my SE/30: wavy screen drawing that would get better the longer it was powered on. Just recapping the analog board made it all go away. Doing the power supply also wouldn't be a bad idea while you have it all disassembled. Would save on parts shipping  

 

[LaPorta]

Absolutely on the shipping. It isn't crazy, but you save like mad if you order a huge bag of stuff at once. As for the glue, I always personally re-glue what was done at the factory for appearances and for longevity.

 

[jessenator]

Definitely. In clarity to my glue comment, follow JDW's advice on getting to those specific components and don't go wild with a set of pliers :/  

I did this to my Astec-branded PSU when I recapped it but just reaching for a mass of glue and pulling…

Thankfully I had another capacitor of that value on hand.

 

[Mirokai]

Maybe I will recap it. But how do bad capacitors explain the interference on the other CRT?

 

[jessenator]

If your RF shielding paint is still good on the case, and there's nothing terribly powerful nearby, I suspect it's more due to bad caps than it is interference. But I'm out of my wheelhouse there.

Granted there's probably a minimum distance for older CRT-driven equipment that's understood, maybe that's the right word? Purely supposition, but something like a broadcast monitor has a heckuva lot more shielding on it. These old compact macs have relatively little. Maybe they weren't meant to be butted up to one another? ¯\_(ツ)_/¯ I don't know how close you're putting them. Again, supposition on this particular aspect. Just anecdotal, personal experience has told me getting CRTs too close to each other, without proper shielding, can lead to interference.

 

[Mirokai]

Strange. After turning it on and off a couple times yesterday and letting it run for some time it seems to be fixed today. No more horizontal lines and the screen looks perfect. Maybe I will still recap it but this is very nice.  I remember reading about self-healing of capacitors.

 

[Compgeke]

 I remember reading about self-healing of capacitors.

Don't trust it. Capacitors are cheap and can fail short and/or go pop when they fail, spewing corrosive goo all over the board. In general capacitors tend to work a little better once warmed up a bit which is probably why it's seemingly working now. Let it sit a few days and it'll be back to before.