bally mcr tapper power question.. Audio noise on hacked in switcher..

mrbill2084

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bally mcr tapper power question.. Audio noise on hacked in switcher..

I am fixing a friends tapper. Someone hacked in a switching power supply. they tossed the original power supply, cut the wires off 1 connector and wired them directly to the switcher.

The game had no audio. The grey-black wire(j1 11) +12v to the dual audio amp and the white-green audio return(j1 6) wires were not connected but cut out.

Connecting them to +12v and ground gets audio. But it makes a loud noise for about 15 seconds when it boots up and again for about 15 seconds during and after setting high scores.

I think it might have something to do with battery. Anyone know a quick fix for this or should I fix the connector and drop in an arcadeshop power supply? I would also assume the coin door lights are not connected, but I have not gotten that far on it..
 
Also its not a pcb problem. board works great in my tapper cab witn no audio problems. I even swapped audio amps.

So its either running with a missing battery problem or an improperly hacked wiring problem...
 
It depends on the noise -- make a recording or video maybe? You should rule-out the battery. VBatt goes to one circuit, to two chips for saving scores, and should have nothing to do with audio. Instead check some things that might explain wiring issues:

- A.Gnd (comes into mainboard J1-20, Y-W) provides an isolated audio ground -- unconnected on the PCB, only connected back at the power supply. If this isn't hooked up properly the audio won't have a ground and won't quite right. With the game powered off check continuity from some point labeled audio ground on the schematic (side of C167?) to a point that would be logic ground (any non-audio IC).

- With the game powered up, test that you're getting +12vDC at the audio chips, for example feeding into LM3900 at D3. That's a second check that you have good audio ground.

- Inspect to make sure you have the transformer block on the bottom of the game nearly cut-out of the circuit (except for the monitor's isolation transformer). Everything should go back to the switcher, not pulling weird grounds or voltages from that block.

- If you really want to unf--k the game, consider crimping new 15 pin connectors as they would've been originally. You could always buy one of those arcadeshop MCR adapters (link) for use with the original connectors for a much cleaner installation.
 
I can't imagine any way that a diode (alone) would be useful or even a good idea on the A.Gnd. Yes you might have some ground loop issues by replacing the original design with this hacked wiring, but I don't see how that would do anything positive.

Whoever advised you should explain and defend that idea on the forum.
 
he said to try a diode on a audio return... I am a bit busy to look at it right now to see if its the same as a.gnd.

I spoke to my buddy and he wants me to make it back as close to original(restore battery function). So I am going to replace the cut out connector and drop in an arcadeshop power supply. Thanks for all the suggestions/help. I wanted to give him options when I called him.
 
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