Alpine MRX-V60

[scampo77]

Hello everyone!

I have an Alpine MRX-V60 that seems to power up but there is something wrong in the audio part. I cannot get any voltage to the speaker terminals.

I have gotten pretty good at figuring out power supply and output failures but this one seems to have micro controlled circuits and a multitude of dual channel op amps. I don't know if these are even serviceable or if anyone has a schematic for this amp. I have had the worst luck trying to fix digital stuff but I am still have lots of questions as to how the function and how to diagnose faulty digital stuff.

Anyone who could possibly point me in the correct direction would be appreciated. I can post pictures for anyone willing to help me.

 

[Perry Babin]

Post at least one good quality photo of the main board.

 

[scampo77]

Even from my fancy new close up camera!

 

[Perry Babin]

What sort of voltage were you looking for on the speaker terminals? Audio?

Do you ever see any rail-rail oscillation on any of the terminals of any of the output transistors?

 

[scampo77]

At the speaker terminals i was looking for anything >0v AC, right now that is all that i have and my RCA inputs are jumping around .4-.7v AC

Would I sound like an idiot if i said "I cant find any output transistors?

I have 4x IRF3205s bolted to the heat sink. and some rectification TO-220 cases next to them, but on the other side there is nothing. I have not pulled the mainboard out of the aluminum case yet and I suspect they could be under there?

 

[Perry Babin]

They could be under the board. If you don't see anything that looks like a normal transistor, they could look like the ones in the attached image (gray squares).

 

[Perry Babin]

The large trace that connects to the output filter inductors is very likely to be the output from the output transistors (you would see oscillation there).

 

[scampo77]

I have never seen anything like this before.

I found all of these on the underside of the board. covered in the gray rubber blankets.

 

[Perry Babin]

The gray pads are thermal gap pads. They transfer heat from the transistors to the sink. Do not lose or damage them.

Did you check for oscillation?

 

[scampo77]

I'm not too sure where to find either of the "output filter" or "rail voltage". I am rapidly thumbing through my notes and found that on previous repairs I found rail voltage at the largest capacitors on the board. I checked these ones and with my test lead on the ground terminal of the power coming into the amp and my red probe on the legs of all of the capacitors, I cant find any voltage greater than 0v DC

 

[Perry Babin]

The inductor should be the component indicated by the yellow arrow. The trace indicated by the orange arrow appears to go to the inductor.

 

[scampo77]

I do not have any voltage <15v DC any where on the board. I have checked almost all of the capacitors, the 2 linear transformers, all legs of the outputs, rectifers and power supply.

This is with my black lead on the main ground terminal and me stabbing away with the red.

 

[Perry Babin]

Did you mean greater than 15v?

 

[scampo77]

Sorry, yes that is what I meant.

 

[Perry Babin]

With the black probe on the amp ground and the red on the positive terminal of the rectifier, power up the amp while watching the meter. Does the voltage change when you power up the amp? Watch the meter from just before you apply remote voltage to about 10 seconds after applying remote voltage.

 

[scampo77]

Yes, it spikes then drops off on pin "A" and "L" it jumps instantly to ~23v DC and after a second it drops to 0v

 

[Perry Babin]

For all of the bridging speaker terminals, check for a pulse of DC as the amp attempts to power up (when the voltage on the rectifier goes towards 23v).

 

[scampo77]

yes, It moves to about +3v then down to -3v DC, then 0

 

[Perry Babin]

All of them or only one channel?

 

[scampo77]

The 2 bridged channels and the sub woofer channel are oscillating DC at start up

I enjoy following your steps but I am always left wondering what you are thinking, its rewarding chasing this down and watching my meter jump around, but what are you thinking is a possible cause of this symptom? or what is leading you to tell me to check this or that?