Hey Matt, I'm going to try and do this to my kickman soon, and is there anyway you would have free time to guide me threw this abit?
What I gather is we want to separate the 12 volt off to its own using a 12 volt walwart.
So can I wire this in off the 110 legs of the switcher and run its 12 volt positive and ground to the audio amp?
Is that the 2 place lead that plugs into the adapter from arcade shop.
Thing is I get this thump noise every time the kick lights flash, and when you coin up you get that back ground hum like you say, and it's kinda annoying. If you can throw some pics or if I can take pics of my stuff and post them, I can make a new thread but I figure this is good as any..
I'd like to get this done, I kinda get what your saying I'm just curious how you tied everything in together and what was separated.
My harness is stock and I just used the arcade shop adapter, which works great but it's definitely flawed with this sound issue
I dont have any pics, well I might but have no idea where they are.
But yeah, the walwarts output would be wired to AGND and the +12 thats supplied to the CPU board. The idea is to isolate the circuits, at least thats what it looked like to me. More on this below and I was wrong BTW.
AGND comes from J4 pin 4 and shares a connection with two other pins but they dont look like they are used. +12 comes from J4 pin 12. AGND does seem to be tied to logic GND at the transformer though. That would dispute my earlier thoughts that the GNDs needed to be isolated from each other. Hmm...
Back to the subject at hand, I dont think doing this will get rid of the thump and noise you are hearing. I needed to do it on my bench to get the board to stop screaming at me.
in looking at the schematics Midway used the same +12 rectifier to supply the lamps and the audio amplifier, I think THATS where the pops and thumps are coming from. The lamps are supplied right off of the positive output of the rectifier while the amps supply is passed through a diode and then filtered across a 4700mf cap. All this is on the original power supply and is where that 2 wire 3 pin connector is connected (it supplies this circuit).
I'm going to assume that the adapter some what mimics the above described circuit in that it still uses the same +12 to provide the lamps and the audio amp from that 2 wire 3 pin connector. If you look at your adapter you will see 4 good sized diodes near a cap or two, thats the circuit being duplicated.
So maybe this might work. Either supply the amp (J5 pin 13) or the lamps (J5 pin 9) with the +12 from the walwart. Before you do though please check the two pins for +12. You will need to remove the pin from the connector or cut the wire. I'd try supplying the lamps with the walwart because if something is backwards nothing "should" blow up.
hmm.. Looking again at the schematics. AGND gets tied to logic GND on the power supply board via JW4. Even if its not there the GNDs get tied together when the cables are plugged into the audio amplifier.
Anyone else want to chime in, feel free. My thoughts on this are all messed up now.