Alpine MRV1507 repair

[Arron210]

Assuming the base of q801 is the middle leg, there is 1981ohms between there and the collector of q802.


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[Perry Babin]

The base is the one with the B below it.

 

[Arron210]

Ok. Before I detach the ps board again I made a discovery (accidentally) if I short the two legs furthest from the battery terminals on q801 the amp comes to life, no warning lights, all green, connect speakers and we have audio! Would you still like the resistance from q801 and q802?


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[Perry Babin]

Yes. When Q802 is switched on by the remote signal, it pulls leg 3 of Q801 down about 1/2 voltage which makes Q801 conduct from leg 1 to leg 2.

As a side note, accidentally shorting random terminals can result in very significant damage to the amplifier.

 

[Arron210]

Neither the board nor the component has a B on it. One leg has a white square and the others a white outline.


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[Perry Babin]

Look on the bottom of the board. It should be marked.

 

[Arron210]

Right you are! 16.2M ohm.


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[Perry Babin]

It would appear that R805 is open or that there is a bad solder connection on it. It connects the collector of Q802 to the base of Q801 and should read approximately 2.7k ohms.

 

[Arron210]

I'm getting 16.2M ohms directly across R805


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[Perry Babin]

Before you can do anything else, you'll need to replace that resistor. Temporarily, you can use a standard resistor with wire leads if that's available locally and the SMD resistor is not. a 1/8 watt resistor is large enough and the small leads should prevent damage to the pads.

 

[Arron210]

Great. Thanks very much for your help Perry Babin! I'll see what I can get hold of tomorrow.


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[Arron210]

Ok so I had to use a 1/4w 27k resistor. Measured 26.8k prior to install. Post install I get 13m and 2.3m across aforementioned legs of q801 and q802. And quite often get no reading (open loop) even if the probes are directly either side of the resistor.

Amp powers up with no remote and displays low voltage error. Fan only spins around half speed.


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[Perry Babin]

Post the voltage on the two transistors again with and without remote.

Did you check the 27k resistor that you removed after removing it?

 

[Arron210]

Unfortunately it dropped the old resistor and cannot find it.

Q801 no remote.
E. 12.52
C. 5.00
B. 11.78
Q801 with remote applied do not change.

Q802 all 3 legs have 0v until remote is applied then top right in photo goes to 2.208v



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[Perry Babin]

Confirm that you read 0 ohms between the collector of Q802 and one end of R805.

Do the same between the base of Q801 and the other end of the resistor.

 

[Arron210]

Confirmed!


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[Perry Babin]

I think Q801 may be defective.

If you read ~9v across R805 with remote applied and 0v with no remote applied, replace Q801.

 

[Arron210]

I get 10.30v across r805 with remote applied or not.
Ps. Have have checked remote voltage numerous times to make sure it's on because it seem to have no effect on the test you require me to perform.

Thanks once again for your time.


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[Perry Babin]

Did you check Q802 to see if it was shorted between collector and emitter? If not, do so now. Use the attached photo to identify the terminals.

 

[Arron210]

Q802 collector to emitter = 1990ohms


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