Alpine MRV-1000 repair

[Perry Babin]

Using the primary ground, do you have approximately 5v on the gates, 12v on the drains and 0v on the sources?

 

[Kei]

All I had was 5V at the gates. Both drains & sources were at 0V.

 

[Perry Babin]

Blown fuses?

 

[Kei]

Here is where I now admit to the daft mistake I made right at the start, that I've only just noticed. I took both 30A fuses out and only put a single 10A fuse in. Having looked at the schematic, it explains why the left side doesn't work. This is why working on this stuff late into the night after a day at work isn't the best idea.

Since I run an adjustable 10A current limited supply anyway, I assume that changing the fuse value isn't really necessary.

 

[Kei]

Two fuses in place and I now have correct rail voltage on both channels. Idle current is still very low at 0.6A but both power supplies are behaving identically. Current draw at switch on briefly starts at 0.1A then spikes to the 7A limit I've left set and then drops back to 0.6A where it stays with no input.

Left channel which I just replaced all the FETs and the 494 is now working ok. Will fetch the other speaker and test the right channel now and leave it playing. Maximum current draw I've seen so far with it very loud is 1.7A using a single 8 ohm load. Think I might need to deafen myself in order to see it draw more.

 

[Kei]

Right channel is working well too. Both channels happily playing away. Push the volume as far as I dare and got a peak draw of 9.1A. I'll leave it play for now just to be sure it's all good.

Thank you for your help Perry, brilliant as always. Now onto the MRV-F400 and back to the 3566.

 

[Kei]

Found one issue when shutting down for the night. Mute doesn't seem to work. Disconnect the remote and it keeps playing for 10 seconds or so until the caps discharge. I reckon it's probably the mute driver circuit as both channels are affected and I doubt the muting transistors in both amps would have died together.

I still haven't replaced all of the electrolytic capacitors in this amp yet either.

 

[Perry Babin]

Does the mute delay work when powering the amp up?

 

[Kei]

Don't think so as there is some initial turn on thump, though not as loud as I'd expect. I've tested the transistors in the mute driver circuit but I think the pre-biased 104M parts are giving odd readings due to their design. I've tested the ones from the F400 and they measure the same on diode check.

Q601 - KTA1266
Base to Emitter - OL
Base to Collector - OL
Emitter to Base - 0.7V
Collector to Base - 0.7V
Collector to Emitter - OL

Q602 - KRA104M
Base to Emitter - OL
Base to Collector - OL
Emitter to Base - OL
Collector to Base - OL
Collector to Emitter - 2.5V

Q603 - KRC104M
Base to Emitter - OL
Base to Collector - OL
Emitter to Base - OL
Collector to Base - OL
Collector to Emitter - OL

Q604 - KTC3198
Base to Emitter - 0.7V
Base to Collector - 0.7V
Emitter to Base - OL
Collector to Base - OL
Collector to Emitter - OL

 

[Perry Babin]

Measure the muting voltage from before remote is applied until about 10 seconds after it's applied. Black probe on Q607 collector, red probe on D608 anode. Do you get a voltage swing? If so, what's the highest and lowest DC voltage you read?

 

[Kei]

With the remote disconnected I get -0.04V. Once I connect the remote it momentarily changes to roughly -1.2V for a moment then jumps to -6.6V and stays there.

There isn't any turn on thump as I previously thought. It's just switch off muting that doesn't work.

 

[Kei]

One other thing I noticed, there is some distortion/white noise momentarily as it unmutes at switch on. The same noise is heard just as the caps drain and output stops roughly 6 seconds after pulling the remote. The voltage between Q607 & D608 starts to drop slowly when the remote is removed but only when the noise above is heard does it drop below approximately -4V. I can double check the exact voltage where output stops if need be.

 

[Perry Babin]

The collector of Q602 should go high during muting (turn-on and off). If it's not going high initially, confirm that its base is going low when the amp should be in mute.

Also check E602. It appears to be responsible for the delay time.

 

[Kei]

Ok now the F400 is out of the way, I'm back to finishing the 1000.

The collector of Q602 does indeed go high momentarily at switch on and high again when remote voltage is removed. (still doesn't mute) E602 is a new 10uF 50V part so should be ok. (UCC KY series)

 

[Kei]

Based on the measurements taken so far, the mute driver seems to work exactly as it should. I will double check the measurements at the muting transistors but I'm confident that they were correct.

Switch on mute based on my measurements is correct and it is just switch off muting that doesn't work, like something is holding the base of the transistor at -6.6V even though the mute driver is putting +14.4V to them correctly.

 

[Perry Babin]

Be more precise, the voltage is being held at -6.6 on which terminal of which transistor?

 

[Kei]

Sorry, the voltage was measured between the base of Q607 and the anode of D608.

 

[Kei]

I've redone all of the measurements for the running (remote on) state this evening. All voltages have been measured with the black probe on battery ground except for the voltages at Q606, Q607, D607, D608 and R613, R614 & R165 where I used secondary ground. I've highlighted the cells for the transistor measurements based on whether they marry up with the voltages in the service manual or not. (green match up ok, red are not right.)

An externally hosted image should be here but it was not working when we last tested it.

I also found E602 had blown it's rubber seal out, so I've replaced it with a new one. It was still measuring ok at 9.8uF though.

 

[Perry Babin]

If you short Q602 collector to emitter, does the amp remain in mute constantly and mute completely?

 

[Kei]

Nothing happens to the output, it remains un-muted.