Alpine MRV-1507 Protection Circuit Fix

[Therum]

Hello Everyone, I have a Alpine MRV-1507. I have repaired it a while ago but never got around to repairing the Protection Circuitry which is indicating that battery voltage is below 10v. The amp functions normally as if nothing is wrong but the red blinking lights are somewhat annoying. So here we are. My power supply is above 12v. I know Q702 , Q720 and IC702 are responsible for detecting the voltage. I found some odd voltages on IC702 and they are as follows

pin1 -13.54v
pin2 11.97v
pin3 6.17v
pin4 -14.83v
pin5 77mv
pin6 72mv
pin7 72mv
pin8 15.33v

Any help will be appreciated.

Thanks!

 

[Perry Babin]

First, check ZD701. It's a 5.1v Zener. The voltage on pin 2 should be about 5v, not 12v. Measure the DC voltage directly across its terminals.

 

[Therum]

You're the man Perry. I actually erroneously replaced that zener with a 12v zener. I will be ordering the correct one. I had 1 more question. Back in the day we ran these amps at 2ohms mono. I figured out the hard way that this cannot be done reliably. I know that you have to lower the rail voltage when you ATTEMPT to do these things. Current rail is 49v. What voltage would you suggest lowing the rail to and what should I be monitoring when bench testing this setup. Please note that this amp will not be leaving my possession in that configuration (for 2 ohms mono). I just have a need for an amp that can run 2 ohms mono and I really hate to sell this amp since its in such great shape.

Thanks!

 

[Therum]

Suggestions? Id even accept a solid "Dont do it or you'll be sorry" But I am interested in doing so. Even if it's gonna take some research.

Thanks!

 

[Perry Babin]

Try it at ±35v.

 

[Therum]

Well. I replaced the zener and it now reads 5v across it. But the amp is still indicating "poor battery voltage" I confirm the PS voltage is 14.8v.

 

[Perry Babin]

Repost the voltage on IC702.

 

[Therum]

1. -13.44
2. 4.99
3. 7.03
4. -14.73
5. .7mv
6. -5.4mv -- Shorted to pin 6
7. -5.4mv -- Shorted to pin 7
8. 15.30

Thanks!

 

[Therum]

Hold on I found something. The values above are incorrect

 

[Therum]

thought I had something but I didnt. Its supposed to be tied to ground. The above voltages are indeed correct. What could be causing pin 4 to go negative. its supposed to be positive.

 

[Perry Babin]

The IC is defective. With the non-inverting input (pin 3) above the inverting input (pin 2), the output from pin 1 should be a positive voltage.

 

[Therum]

Yes, I overlooked that detail in the beginning. Thanks for pointing that out. I replaced the IC with a NE5532. I was thinking since the 4560 wasn't doing anything special that it would be a suitable sub for this sort of duty.

Which brings me to another issue. The amp is indicating floating ground. Which I have tried grounding the rca shield which yields no difference. I found that Q703 , a DTC143TK , is shorted (Shows about .033v in diode check across any leg of your choice) but I cant find the exact part nor a datasheet to find a sub. Any thoughts on this one?


Also I can only get rail voltage down to 42.3v. I guess Im gonna have to test this voltage.

 

[Therum]

I found the DTC143tk.