Flicker problem with Coleco tabletops

[Jumpman1981]

Hey All, I know I have mentioned this on other topics, but I have this issue with all my Coleco tabletops that I really need repair info on.

 

The issue is that whenever a sound is played, part of the display flickers, but, the odd thing is, if it's the little jingle that plays when you start the game, the screen flicker will get higher and higher, like someone is using the screen as piano keys.

​Each game has a different amount of flicker, I've listed them below as severe or mild.

 

Donkey Kong: Severe, even ​jumping ​(a really quiet sound)​ causes it to flicker.

Ms. Pac-Man: Severe, though not as bad as DK

Galaxian: Mild and barely noticeable at times, I would leave it.

Pac-Man: a roll of the dice, sometimes it's mild, sometimes it's barely noticeable, sometimes it's severe, it's odd, because, whatever type it is, that's how it stays for most of the day

 

I really would appreciate help, as I can't find info about this anywhere and no other games I've seen do this.

Edited June 6, 2017 by Jumpman1981

[SignGuy81]

Sounds like something in the audio circuit pulling the supply down from the batteries. Can you hook up a volt meter to the power from the batteries and see if it stays consistent when the sound plays?

 

EDIT:

 

Also can you post pictures of everything, board and all.

Edited June 6, 2017 by SignGuy81

[Tanooki]

It is the audio circuit from my experience. I've gone through a few over the years and still have a few of them now (now more than ever than before at one time) and like when you move Mario around in Donkey Kong and it makes those banging beep sounds the screen illumination does change a bit. I wouldn't call it a flicker or a drop out of lines so something more is going on there, but they've always kind of dimmed a bit from audio.

[Jumpman1981]

Just opened by Donkey Kong to see what the issue is, but can't find anything. any suggestions?

 

It's a Revision C board, if that helps

[R.Cade]

You're sure you have good, strong, fresh batteries? When I was a kid, I used to recharge regular batteries with a little radio shack charger. It did work, but the batteries got weak and lasted less and less each time. I recall this was one side effect (the screen flicker when audio plays).

[Osgeld]

there's a few electrolytic caps in those that could be getting weak, but yea ... audio amp eats power, giant ass florescent tube display eats power, combination of both, there's a lot of power demand at almost random.

 

from memory, cause people around me had these things for years they would dip and dim a little depending on whats going on ... outside pac-man with that ear rape noise it constantly makes

 

might be able to put a large cap across the power input to help, like a 1000uf + on +, - on - to make a buffer, but in theory good batteries should be able to vomit out infinite current until they discharge (battery life being a function of current draw, current capacity and time ... in a perfect world, in the real world its on a curve)

 

edit, It also could be the VFD getting weaker which impedance usually increases on those things as they get used making a minor effect into a more noticeable one

Edited November 15, 2017 by Osgeld