Onkyo M-504 VU meters not moving

[NEWbe-BeEasy]

I recently came across a few decent pieces of home audio that was for sell at a great price. One of those pieces is a Onkyo M-504 amplifier. Once I plugged it in I connected one speaker for a test run but no movement from either of the meters. I do receive sound though. I have replaced all known fuses. I have tried methods observed on other forums to lessen them but nothing has worked that I have tried? Anyone have a solution?

 

[WaynePflughaupt]

What speakers do you have? If they are extremely efficient, like many Klipsch models, and don’t need much power to play loud, the amp might not be putting out enough power to move the meters.

Regards,
Wayne A. Pflughaupt

 

[NEWbe-BeEasy]

I just had them hooked up to some old Bose low wattage speakers. I can certainly fix that problem though. I have some ESS AMT-1D's and HEF IQ9's I can try in about an hour. I know both of those love some juice.

 

[TLS Guy]

I recently came across a few decent pieces of home audio that was for sell at a great price. One of those pieces is a Onkyo M-504 amplifier. Once I plugged it in I connected one speaker for a test run but no movement from either of the meters. I do receive sound though. I have replaced all known fuses. I have tried methods observed on other forums to lessen them but nothing has worked that I have tried? Anyone have a solution?

The meter driver circuit has failed. It is driven right off the speaker output. It is quite a complex circuit and requires a signal generator and o-scope for service. there is a dual opamp IC (Q606) in the circuit with each half driving each meter. I suspect that IC has failed. On older gear IC chips are frequently NLA. So you will likely have to make do without the meters working.

 

[NEWbe-BeEasy]

The meter driver circuit has failed. It is driven right off the speaker output. It is quite a complex circuit and requires a signal generator and o-scope for service. there is a dual opamp IC (Q606) in the circuit with each half driving each meter. I suspect that IC has failed. On older gear IC chips are frequently NLA. So you will likely have to make do without the meters working.

What would it take to fix if that is the problem?

 

[TLS Guy]

What would it take to fix if that is the problem?

A tech who knows what he is doing. He needs a signal generator o-scope and high impedance amplified meter at the minimum.

He needs to have the skill to isolate the problem and the skill to solder in a new component without messing up the board.

Before you spend money you had better make sure the Q606 IC especially is still available and also the other IC. That is an 80s unit, more likely than not the part is NLA. If the part is NLA you will still have to pay the tech.

You next problem is finding a tech. There are not many left now.

 

[NEWbe-BeEasy]

Not exactly sure I am loving your responses, SMH, haha. How sure are you the problem I am experiencing is caused by the meter driver circuit?

By the way, thank you for your time.

 

[TLS Guy]

Not exactly sure I am loving your responses, SMH, haha. How sure are you the problem I am experiencing is caused by the meter driver circuit?

By the way, thank you for your time.

If the meters do not move when you drive the amp hard, then I'm 100% certain that the meter driver circuit is the problem unless both meters have failed which is very unlikely.

I had a good look at the circuit, and the only thing between the speaker output and the meters is the meter driver circuit.

 

[NEWbe-BeEasy]

Okay, so make this thing do some major labor 1st to see if they jump correct? I'm just going to hook it up to 1 of the KEF's since they are still boxed but I think that should be plenty. Let me know if I'm wrong and need to do both.

 

[TLS Guy]

Okay, so make this thing do some major labor 1st to see if they jump correct? I'm just going to hook it up to 1 of the KEF's since they are still boxed but I think that should be plenty. Let me know if I'm wrong and need to do both.

Not one, both! If one works and the other does not then their are other possibilities other then the IC I mentioned. The only commonality between the left and right meter drivers is the IC I referenced, as far as I can tell.

So both speakers, not one.

 

[NEWbe-BeEasy]

Okay, thanks. It'll take me a min to get it hooked up and test. If too late, please check back tomorrow.

 

[NEWbe-BeEasy]

So hooked everything up. then connected the VU meters up (one at a time...not sure if that would matter.) The needle jumped when 1st connected to left side. Did not move any further when connected to the right side.

 

[NEWbe-BeEasy]

Speakers sounded good though, hahaha

 

[NEWbe-BeEasy]

Anyone that says these IQ9's don't sound good need a better amp...

Sorry, had to throw that in there.

 

[TLS Guy]

So hooked everything up. then connected the VU meters up (one at a time...not sure if that would matter.) The needle jumped when 1st connected to left side. Did not move any further when connected to the right side.

The meter driver is shot.