Please help me diagnose IBM 5151 Monitor Fault

[izools]

I'm in the process of restoring a 5160XT with Hercules graphics and all that lovely stuff...

I had a short on the -12V line so replaced all the tantalum caps.

I had only 320K RAM detected - swapped banks 2 and 6 of the AST SixPakPlus that is installed and now 576K detected so faulty chip is now in bank 6, I'll just replace all 9 chips.

Last fault is this 5151 monitor behaving as attached:

I've disassembled and can't see bulging capacitors, or dry solder joints. Didn't go much further as monitor internals give me the willies... If someone knows what might cause this I'd sure appreciate the advice:

https://youtu.be/jPryi-k_XXY

 

[Chuck(G)]

Discharge the anode connection--slip a probe whose other end is grounded underneath the anode cap on the CRT and contact the clip. If you want to be double-good-safe, short out any electrolytic capacitors on the PCB. If unpowered, your monitor is now safe for tinkering. You know--"Hello Kitty" decals, whatever.

 

[izools]

Yeah I've dismantled and discharged him last night and removed all 15 electrolytic capacitors.

I've ordered nichicon replacements for all of them along with an ESR meter to test out the old ones.

I found the SAMS online too, which is a wealth of information:

https://www.google.com/url?sa=t&sou...FjAAegQIBhAC&usg=AOvVaw0pk_nptG0S0Zt3gCSmgsJr

There's no dry solder joints, it's a really good job IBM did.

The caps don't look swollen and there's no skidmarks on the PCB but they are Teapo caps and Teapo don't have the best reputation.

So, let's see what happens later in the week when new caps arrive

 

[Chuck(G)]

Old caps go bad from internal heating also. Eventually, after the electrolyte has dried out, they test as almost-empty cans.
This is not uncommon in switch-mode power supplies, as the ripple currents can be quite high.

 

[NeXT]

Old caps go bad from internal heating also. Eventually, after the electrolyte has dried out, they test as almost-empty cans.

I know you partially meant that for effect but I can confirm that when you get some REALLY dried out caps you can hear the inside rattle around when you shake them LOL.