Need Some Advanced help - Lanzar Vibe248 oscillating

[EWorkshop1708]

I'm really getting frustrated trying to fix this amp.

The Power Supply is Good (4 pairs of IRFZ44 Mosfets with TL494, nothing special)
The Amp is good (two pairs per channel 10A 100W Toshiba BJT)

I had problems with "hum" the first time, and I changed out one of the inline-8 4558 opamps with a DIP-8 4558 opamp, and repaired two burned ground lines on the PCB and it worked fine.

I get the amp back, same hum again. I later on got music by wiggling the PCB, but the music had a weird quality - I hooked it up BTL, but it played cancelled stereo (just the differences between the L and R channels) and this amp has no BTL switch.

So I took it apart and resoldered all the solder joints in the amp on the input side, and now it hums still, now with no music.

I changed out all the opamps to 4560s and it still hummed, just louder, LOL

There's also another chip JRC 13600D that I can't find, and I don't know if this chip is good or not (I usually just change the chip when in doubt if I have one)

I'm totally at the end with this amp, I look at it, the PCB looks simple, and yet I'm stumped on how to fix this thing.

Any tips or ideas are greatly appreciated.

Thanks,
EWorkshop1708

[Perry Babin]

With no RCAs connected to the amp, what's the resistance between the RCA shields and the non-bridging speaker terminals?

[EWorkshop1708]

Originally Posted by Perry Babin

With no RCAs connected to the amp, what's the resistance between the RCA shields and the non-bridging speaker terminals?

Thanks for your tip!!!!

I check, I get OPEN between those. Should it be short, or low ohms?

It has two RCA in and outs. The ground (shield) is common on left and right in. Also common with L & R out, but it's open resistance from RCA shield from in and out, either L or R.

[Perry Babin]

In most of these amps, that should read 0 ohms. Look for an open ground trace between the RCA jacks and the secondary center-tap of the transformer. Sometimes it's a long thin trace in the center of the board that burns open.

[EWorkshop1708]

Originally Posted by Perry Babin

In most of these amps, that should read 0 ohms. Look for an open ground trace between the RCA jacks and the secondary center-tap of the transformer. Sometimes it's a long thin trace in the center of the board that burns open.

Thanks. The ground terminals on the rca jacks themselves were broken. You are the MAN Perry Babin.