Alpine MRP-M1000 with rail voltage but no output

[Perry Babin]

You can't connect to the reference through a resistor.

 

[mild2wild]

Can you please explain post #11 for me, you said to connect through a 1k-10k resistor. I may have misunderstood.

Can you please give a detailed description of how to inject the audio into the amp using an aftermarket deck playing a music CD?

I don't have a signal generator, other than a square wave terminal on my USB scope designed for probe adjustment. I have test tones on my ipod also...

 

[Perry Babin]

The output of the signal would connect through a resistor, not the ground side.

What were you using before as a signal source?

 

[Perry Babin]

See also 23.

I was thinking that the clamping transistors were SMD since that's mainly what alpine uses (and they're epoxied down to the board). If they're through-hole, remove them. That should let the signal from the audio input pass.

 

[mild2wild]

Which are the clamping transistors? (Q9701/9702?) These are A1266 through-hole.

I am using a car deck playing an audio CD. I am still unsure of how to inject the rca jack signal to the amp. Please specify.

Do I remove Q9701 and Q9702? Then the RCA male center pin goes to the collector pad of Q9701 and Q9702 through a 1k resistor, and the rca ground connects directly to the secondary ground of the amp?

 

[Perry Babin]

If you remove 9701/2, the signal that you saw before the op-amp (when drivign signal into the RCA jacks of the amp) may pass through. It's also possible that the DC on the op-amp will hamper the signal passing. Try removing those transistors first to see if audio will pass.

 

[mild2wild]

Still testing using the voltmeter at the moment. I removed Q9701 and Q9702 and fed signal to the collector pads through a 1k resistor. I connected the rca shield to the secondary ground. I got audio on Pins12 and 14 of the IR2010S ICs. I had high side gate drive (Pin1) on both IC9801 and IC9802, but only low side gate drive (Pin8) on IC9802, no gate drive signal on IC9801. At some point the low side output of IC9802 also stopped working.

I removed both ICs but there was some damage to the pads on the board as these have been changed at least twice before. I am hoping that Pins4, 5, 9, 10, and 16 have no connection in this amp as some of those pads came off the board but appear to have no connection. Let me know if my assumption is incorrect.

I only have 2 new IR2010S ICs remaining, so I was hoping there were checks I could make to the pads, or elsewhere in the amp before installing the new ICs but the amp does not power up with IC9801 and IC9802 unpopulated. So, I replaced them, but when tested again afterwards, I still have no low side gate output, but I have high side output on both ICs.

 

[Perry Babin]

What is the DC voltage on the points where you're injecting the signal?

The diagram shows the pins with no connections (NC).

Are the output FETs in the circuit?

Is there any DC across the speaker terminals?

 

[mild2wild]

DC voltage is - 42v at the collector pad of Q9701 and Q9702.

Across the speaker terminal I am currently reading +38.2v. With the black probe on ground terminal I read -39v on the - speaker terminal, 0v on the + speaker terminal but there is a momentary 3v spike when the amp is turned on.

Output FETS are installed. None read shorted so I assumed they were OK. Do they need to be replaced? If so, did I damage my remaining pair of IR2010S ICs by installing them now?

 

[Perry Babin]

Measure the DC voltage on all of the outputs FETs with the black lead on the source leg and the red on the gate. Do any have any significant DC voltage?

 

[mild2wild]

No significant DC voltage on any output transistors when measured between gate and source.

 

[Perry Babin]

If you touch a dummy load from the negative terminal to ground, does that drain the voltage?

Which of the output FETs has approximately -40v on both the drain and source? Black probe on ground.

 

[mild2wild]

The dummy load reduces the - 38v to - 0.02v when touched to ground.

Q4001 and Q4002 have - 38v on drain, and - 42v on source.

 

[Perry Babin]

Does the amp draw additional current when you touch the load on the terminals?

Does the voltage return when the load is removed?

What's the resistance between the gates of those outputs and the output pin on the driver IC that drives them?

 

[mild2wild]

There is no significant increase in current draw when the dummy load is connected.

The DC voltage returns when the load is removed.

The gates of those two measure 10.3ohms to the IC output pin, as do all the other six outputs.

 

[Perry Babin]

Something is leaking voltage to that speaker terminal. It could be a contaminant on the board. One of those two outputs could be leaky.

 

[mild2wild]

So, do I remove them and recheck?

If the DC voltage goes away, can I remove those two that are parallel and take one of the other pair and install it in one of those locations just for testing purposes?

If it is not the outputs, what else can I check?

 

[Perry Babin]

If you don't see any voltage when rubbing your meter probe on the board (on non-metallic areas), you can pull those two outputs. Pull one and then re-check. If you get lucky and there is one that's leaky, you may get it on the first try.

 

[mild2wild]

I pulled all of the outputs (Q4001 - Q4004) one by one until all four on that side were removed but the - 38v was still there. I tested all four outputs out of the amp and they all appeared to be good. It wasn't until I disconnected the rca connection to Q9701 and Q9702, then the - 38v was gone.

What do I check next?

 

[Perry Babin]

Are you sure that you didn't do anything else besides remove the drive signal from the transistors to make the DC go away?

Is the 0.1uF cap that you're using a film or ceramic type capacitor (or other non-polarized)?