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-   -   Alpine MRV-1507 - RCA Ground Floated - Need help (http://www.diyaudio.com/forums/car-audio/123915-alpine-mrv-1507-rca-ground-floated-need-help.html)

silversweden 28th May 2008 07:29 PM

Alpine MRV-1507 - RCA Ground Floated - Need help
 
Hello!
Recently bought a Alpine MRV-1507.

Protection light blinks Red indicating "RCA Ground Floated"
according to Owners manual.

Doesnt matter if i have an input signal or not.
(have an solid state cd player connected to the RCA)

I have checked the ground, and its connected to the
+-15V regulator circuits ground. OK

And now the funny thing, THE AMP PLAYS MUSIC! ;)

No DC at the outputs...

Someone please help me, what should i look for?

http://www.itxpress.se/MRV-1507.pdf <-- schematic here

Perry Babin 28th May 2008 08:00 PM

If you're using a home cd player, the RCA shields are floating. If you connect them to the chassis ground, the indicator should go back to green.

silversweden 28th May 2008 08:17 PM

I allready tried to ground the RCA shields to chassi.
No difference... what is the next step?

Im not sure if there is any fault or not.

I noticed that if i measure from Battery ground to RCA shield
i have almost 2 Volts.

But this is just normal since its not the same ground reference?

The RCA shields should be connected to 2nd Ground directly
according to schematic.

In the 15 volt regulator ground i have a direct connection.

But then i measured from the centertap of the secondary
winding of the transformer to RCA shield, looks like a
cap is charing as i measure Ohm.

Perry Babin 28th May 2008 09:56 PM

You'll need to have the shields grounded to the chassis ground. Confirm that the shields are at 0v DC.

If the amp still indicates that there's a fault, go to Q703 (on page 21 of the PDF file). Is the base-emitter voltage 0v?

If it is, is the voltage on its collector near 8v?

What is the voltage on pin 13 of IC703.

The secondary ground is not tied to the secondary center taps of the power transformers in this amp.

silversweden 29th May 2008 04:39 AM

Those Alpines are tricky..But i love them =)

When you mean chassi ground...where is the best
place for this? It should be the same as Battery Ground
or am I at the wrong side of the road? ;)

So after I connect them to ground i should have
0VDC refering to (chassi/battery)Ground?

Before i had nearly 2VDC when measuring from
battery ground to RCA.

I will check the voltages on the transistor when i come home
from work :)

Where is the "real" measuring reference for the secondary
ground.

And where is the "real" reference point for the chassi ground.

Cant find any star ground point its just symbols on schematic.

Thanks perry!

Perry Babin 29th May 2008 06:12 AM

chassis ground = battery ground

After connecting the shield ground to the chassis ground, the difference should be 0.0v.

Ideally, all of the points on the secondary ground are the same. The shields of the RCA connectors are the most accessible.

Use the ground terminal on the amp as the reference point for the chassis/battery ground.

silversweden 31st May 2008 11:17 AM

yes if i ground the RCA shields to chassi ground i have
a 0V reading on them.

Q703
The base-emitter voltage is 0,13V

IC703
Pin 13 has a reading of 8 volts with
a small pulsing difference about 7,8 volts to 8 volts.

Strange thing is that Pin 1 has 10 volts pulsing on it.
Exactly the same frequency as the LEDs are flashing.


I am starting to think that some Elyts are leaky in the
protection/led driver circuits?

Perry Babin 31st May 2008 02:23 PM

The pulses on pin 1 are the clock pulses and are normal.

If Vbe for Q703 is 0.13v, Q703 should not be on so Vbe for Q721 should be ~0v. If that's the case in your amp, Q721 should not be conducting and the voltage on pin 13 of IC703 should be ~0v.

Since you're seeing pulsing in pin 13, the IC may have failed and is leaking internally. Confirm that the supply voltage feeding IC703 is steady (not pulsing). If it is, I'd suspect the IC.

If possible, lift 2 legs of Q721 to remove it from the circuit. If there are pulses remaining on pin 13 and the supply voltage is steady, the IC is almost certainly defective.

silversweden 31st May 2008 11:17 PM

Ok I will try that tomorrow!
But isnt it very odd if the IC have failed without reason?

One more thing I noticed is that the Power LED is blinking
Red indicating that the Battery Voltage is below 10Volts.

Thought that it just was my battery that was weak.
But after charing it for several hours i measured
the voltage above 11Volts with the amp powered.
Should be enough i think...

So maybe the IC is defective and causing this LED
to blink as well?

One more question, what component is making the Pulses?
And what is the FLIP-FLOW thing?
Looks almost like a current mirror with two elyts.

Why are they doing it this complicated :P
A whole circuit for three small leds....

Perry Babin 1st June 2008 01:29 AM

A defective IC could possibly make the other LED blink also.

I don't think there was a reason for the failure (if it has failed). Sometimes semiconductors fail.

The flip flop is a free running oscillator. They used to use them to drive switching power supplies but the caps were smaller so the oscillator ran at a much higher frequency.


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