Alpine MRV1507 fault

[vincegironda]

Hi all, wishing you all good health at these testing times.

I have an Alpine MRV1507 on the bench, it's pulling excessive current a few seconds after applying remote power.

I've tested the power supply and although it's had a previous repair it powers up and idles fine if I disconnect the 6 pin molex which connects to the output board.

All the output transistors also test good.
Q819 has been replaced with a 2SD600 which had a loose solder pad which I have resoldered.

Initially it would power up then trip my power supply after 8-10 seconds, now it trips within a few seconds.

Any help appreciated, thanks

 

[Perry Babin]

Did you try reducing the bias?

Did you check the TO-126 voltage regulator transistors?

 

[vincegironda]

Thanks Perry, I tried reducing the bias - no luck

I pulled these 2 transistors as the one on the left looks like it has been replaced previously - the 2SD600, incidentally it tested as failed off the board, the A1220A tested good.

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[vincegironda]

The 2sd600 looks like it was used to sub another transistor

 

[vincegironda]

2SD600 was in the Q619 location

 

[Perry Babin]

The 2SC2690A is the complement to the 2SA1220A

The KS prefix is common (KSA, KSC).

 

[Perry Babin]

Have a mod remove your duplicate post.

 

[vincegironda]

I checked the zener diode zd608 and it was dead short so pulled that too. Would the amp power up OK now?

 

[Perry Babin]

Don't power it up without the Zener.

If you don't have a TO-126 replacement transistor, you can drop any TO-220 transistor in that location (reversed pin configuration so installed reversed) to test.

 

[vincegironda]

I've ordered the parts so I'll wait to replace and update.
Thank you

 

[vincegironda]

So I installed the Zener and the two transistors, the amp still tripped my power supply.

I noticed the output transistors on channel 2 had also been replaced at some stage so I tested them against the opposite side and the readings were quite different so I pulled all eight and re tested the amp.

This time it powered up without tripping my power supply, the amp idle would fluctuate slightly every 5-6 seconds but it stayed on without tripping.


The output devices were IRF 540N + IRF 9540N
I noticed the gate resistors hadn't been changed, they're readings also fluctuated on the meter so I'll be replacing them too.

So are the IRF540N and IRF9540N the correct output devices for this amp?
and what spec are the gate resistors meant to be, going by channel one they read 19ohm?

 

[Perry Babin]

The N version was the original but I had at least one that the N would not work. I had to use the non-N. I have notes that this was for the 540. I don't know if I had to go with the non-N 9540.

 

[vincegironda]

Thanks Perry, ill try both non N 540 and 9540

 

[Perry Babin]

I don't know if the non-N will work better than the N in your amp. I'd order both versions of each part.

 

[vincegironda]

I already had non N versions of both which I just tried and it's still tripping my power supply,

I tested a few other transistors on the defective side and found C249 and C248 had a short between the collector and base, I pulled the pair and C429 still had a dead short, C4258 had no short.

I also tried powering up the amp with both removed and although it didn't trip my power supply the current draw was beginning to creep up suggesting I may have damaged another component although I cut the power quickly???

 

[vincegironda]

C2690A-Y is the shorted transistor I pulled from C249 and C248

 

[vincegironda]

I've now got the amp up and running, finally.
It's making nice clean audio but the red protection led is flashing even when the rca shield is earthed?

 

[Perry Babin]

The indicator circuit may be damaged.

 

[vincegironda]

Does anyone have a schematic for the MRV-1507

I inspected the low voltage indicator circuit and found Q703 is damaged and I can't read the part number.
Thank you

 

[Perry Babin]

See attached.