Irem M97 Video Interference

[alexqts]

Hi,

I have an Irem M97 Bomberman board that came to me with faulty sound. It was very scratchy with pops and video interference when turning up the pot.

First changed the 470uf main cap and this helped the sound but not the video interferance.

All other electrolytic caps tested good but changed every one for good measure. Great sound now but still no change to video. Tested volume pot and seems to be OK on multimeter.

If the sound is very low I have no problems, but as soon as you turn up the sound the screen goes very fuzzy. It actually looses sync if you turn it up enough!

I have a meanwell RT125A (with no -5v) but the -5v rail on this board looks to be obsolete. Is this correct?

I am running on a Unico 26” LCD via CGA.

Anyone know what the fault might be? Thanks

 

[Ape Cosplay]

Hi,

How is sound wired in your cab? Could be one of the audio pins from the JAMMA is grounded instead of going to the speaker(s).

 

[alexqts]

Jamma + - terminals go to a line level converter and then off to a logitech 2.1 system that has been built into the cab. Works well with other jamma boards but I did totally disconnect the speaker wires to test and it is still the same screen problems.

I am also running through a RiddledTV switcher, perhaps I should try bypassing that. I just assumed if other boards work this should too - but I suppose they are all different… !

Thanks

 

[Ape Cosplay]

You disconnected the speakers or the terminals going to the line level converter? I'd completely disconnect the JAMMA sound +/- pins.

 

[alexqts]

Yes I disconnected completely and still the same. I need to go over the board again and check all ground connections.

The board also has 3 large red poly caps in the audio circuit. I am sure I read something about them being problematic but not sire.