Alpine MRV-1507 Protection Circuit Fix

Therum · 9th April 2011, 02:12 AM

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 · 9th April 2011, 03:44 AM

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 · 9th April 2011, 12:36 PM

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 · 11th April 2011, 02:20 AM

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 · 11th April 2011, 03:43 AM

Try it at ±35v.

Therum · 13th April 2011, 08:26 PM

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 · 13th April 2011, 08:31 PM

Repost the voltage on IC702.

Therum · 13th April 2011, 08:40 PM

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 · 13th April 2011, 08:46 PM

Hold on I found something. The values above are incorrect

Therum · 13th April 2011, 09:28 PM

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.

9th April 2011, 02:12 AM	#1
Therum diyAudio Member Join Date: Oct 2009 Location: Douglasville Ga	Alpine MRV-1507 Protection Circuit Fix 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!

9th April 2011, 03:44 AM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	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. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

11th April 2011, 03:43 AM	#5
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Try it at ±35v. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

13th April 2011, 08:31 PM	#7
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Repost the voltage on IC702. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

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9th April 2011, 12:36 PM	#3
Therum diyAudio Member Join Date: Oct 2009 Location: Douglasville Ga	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!

11th April 2011, 02:20 AM	#4
Therum diyAudio Member Join Date: Oct 2009 Location: Douglasville Ga	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!

13th April 2011, 08:26 PM	#6
Therum diyAudio Member Join Date: Oct 2009 Location: Douglasville Ga	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.

13th April 2011, 08:40 PM	#8
Therum diyAudio Member Join Date: Oct 2009 Location: Douglasville Ga	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!

13th April 2011, 08:46 PM	#9
Therum diyAudio Member Join Date: Oct 2009 Location: Douglasville Ga	Hold on I found something. The values above are incorrect

13th April 2011, 09:28 PM	#10
Therum diyAudio Member Join Date: Oct 2009 Location: Douglasville Ga	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.

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