LM324 Quad Op Amp on MVS

I'm trying to tap the audio from one of the LM324's on the board to use for a line-level audio output.

I have it connected to the headphone connector and have removed the headphone connector from its original circuit. No sound is outputted through the connector and through the JAMMA a strange sort of buzzing sound is outputted.

Board sounds fine when nothing is connected to headphone connector.

What board? Some of the boards use the 1/8" jacks for audio INput and not output. The 4 slots are this way.

Yes its an MV4, but according to the schematic I have the LM324 I have connected to outputs to the 2099D which then outputs to the headphone connector.

I should point out when I say headphone connector I mean the header, not the jacks.

The 4 pin connector should not have any bearing on the audio output on the JAMMA connector. It's isolated by a separate amplifier circuit.

If you follow the headphone slider pot connections on the board, there's a spot that should give you a good line output.

One side of the pot is grounded, the middle goes to the amp chip, and the other connection is what the audio signal comes into the pot through. Follow that connection backwards across a resistor and a cap. On the other side of that cap you should be able to get a good line level signal.

There are two of those lines coming off the slider pot. One is for left and the other is for right.

RJ

Thanks channelmaniac, I'll try that.

Do you have any idea why tapping the audio from the op amp didnt work? According to the schematic I have the sound outputs from the LM324, and goes through a cap and resistor to the pot. Surely a 4.7uF cap and a 2.7k resistor can't be the difference between the sound working and not working?

The other side of the caps you mentioned connect to the op amp I was originally trying to tap the audio from so obviously the result is the same.

I tried to get the audio from the headphone pot and I'm not getting anything at all.

This is really doing my head in so any help would be greatly appreciated.

Still struggling with this, can someone give me some assistance please.