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Old 25th October 2013, 09:21 AM   #1
NIJosi is offline NIJosi  United Kingdom
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Location: Belfast
Default Alpine MRV-1507 Fault

Hello all,

As is normal for the internet I'm asking for help with something!

I have one of these amps from a friend, according to him he accidentally touched the +12VDC from a power cap to the chassis of the amp. The protection light came on (don't know what colour) and it hasn't made a sound since.

It's been sitting around for a couple of years, only really getting round to looking at it. I suspect its a power supply fault at the moment but could use
some guidance.

PSU - Thurlby Thandar Instruments PL320QMD
Multimeter - HP E2373A
Have an ancient oscilloscope if needed.

With amp connected to bench supply (14.4V current limited)
Power Light - flashes red (low batt voltage)
Music Light - flashes green (music input)
Protection Light - flashes red (RCA ground float)

Grounding RCA gives:
Power Light - flashes red (low batt voltage)
Music Light - green - (no music input)
Protection Light - green (Normal)

Test points TP5 to TP7 gives +49.5V and TP5 to TP6 is -49.5V which are correct.

TP1/TP2 and TP3/TP4 give 0mV, I didn't adjust VR401/402 at this time.

Current draw on the PSU is about 1500mA

I'm thinking next should be the IC601/602 voltage checks?

Thanks.

Last edited by NIJosi; 25th October 2013 at 02:39 PM.
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Old 25th October 2013, 03:31 PM   #2
NIJosi is offline NIJosi  United Kingdom
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Current draw from supply - 200mA
With PSU board disconnected from Amp Board:

IC601

Voltages ok except on pins 3, 9, 10

Pin 3 - should be 2.36V, reading 3.81V
Pin 9 - should be 3.36V, reading 0.5V
Pin 10 - should be 3.36V, reading 0.5V

IC602

Voltages ok except 3, 6, 9, 10

Pin 3 - should be 2.36V, reading 3.84V
Pin 6 - should be 4.2V, reading 3.75V
Pin 9 - should be 3.24V, reading 0.5V
Pin 10 - should be 3.27V, reading 0.5V


Voltages out on CB603:

Pin 1 - -46.8V
Pin 2 - +3V
Pin 3 - -69.3V
Pin 4 - +73V
Pin 5 - +3V
Pin 6 - +52V


Looking at the datasheet for UPC494GS pins 9 and 10 are the outputs?
No emitter output = gate not active = issue with inputs or ICs dead? Or something further back dead?

If there is no output from this to the power transistors how is there voltage on the supply cable to the amp?

What next?

Last edited by NIJosi; 25th October 2013 at 03:42 PM.
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Old 25th October 2013, 09:07 PM   #3
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The 494s can't be dead if you have positive and negative rail voltage.

The voltage on the pins you list vary greatly. Reduce the 12v power supply voltage to about 11.5v and you'll see they all change significantly. If you load the amp's power supply, they will also change.
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Old 25th October 2013, 09:30 PM   #4
NIJosi is offline NIJosi  United Kingdom
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Hi Perry,

Reading through your excellent material as we speak! Been several years since I looked at electronics, I never grasped switchmode and PWM circuits the 1st time round! Head is spinning...

What's confusing me (well most of it is to be honest!) - if pins 1 and 2 are both 0.9V then why is pin 3 at 3.85V?
From your Switching PSU page it would infer that this should be close to 0V for 50% duty cycle, why do Alpine give a reference of 2.36V?

With pins 9 and 10 at 0.5V I presume that this is the meter interpretation of the square wave output? So I still have a functioning PWM just at reduced output/duty cycle from pin 3 being at 3.85V?

I'm sure this is babble, sorry!

I'll dial the PSU down tomorrow and remeasure the voltages. I'll see about digging the scope out too, maybe that'll help me see what's happening.
Any suggestions of what else I should be looking at?

Thanks
Peter

Last edited by NIJosi; 25th October 2013 at 09:37 PM.
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Old 25th October 2013, 09:38 PM   #5
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This is a regulated power supply circuit. When there is low demand or relatively high voltage, the pulse width (duty cycle) is reduced as the supply reaches its target voltage.

Pin 3 is higher when the duty cycle is low.
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Old 28th October 2013, 02:48 PM   #6
NIJosi is offline NIJosi  United Kingdom
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Hi Perry,

Should have picked up on that, duh..

I've remeasured at 11.5V source and I'm seeing exactly as you said.

Pins 1 and 2: 0.85V
Pin 3: 90mV
Pin 4: 226mV

Pin 9 and 10: 4V

Voltage outputs on the PSU CB603 are about the same as before, little lower as expected:

Pin1: -44V
Pin2: +3V
Pin3: -60V
Pin4: +62V
Pin5: +3V
Pin6: +50V

Little skewed to the +ve rail but still no load on it.

So is the PSU is actually ok and the LowBatt light is a red herring?

Guess I'll have to start deciphering the amp schematic now!
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Old 28th October 2013, 05:49 PM   #7
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Confirm that the voltage across ZD701 is 5.1v 10%.
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Old 28th October 2013, 07:00 PM   #8
NIJosi is offline NIJosi  United Kingdom
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4.66V across ZD701
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Old 28th October 2013, 07:06 PM   #9
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It should be replaced but it's not causing the problem.

Post the DC voltage on all pins of U702.
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Old 29th October 2013, 10:02 AM   #10
NIJosi is offline NIJosi  United Kingdom
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IC702
Pin1: 2.17V
Pin2: 4.66V
Pin3: 5.20V
Pin4: 1.56V
Pin5: 0V
Pin6: 1.62V
Pin7: 1.62V
Pin8: 1.95V

There's something up there!

Front P.W. Board still disconnected.
Thanks
Peter
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