# Alpine 3539 faulty? (DC between RCA shield and supply ground)



## michelino (Jun 6, 2016)

Hello everybody,
I'm an italian guy with passion for HIFI.
I don't know where to get support so I decided to subscribe to DIYMA forum. Maybe some good people will help me! 
Let's talk about my alpine 3539 car amplifier, just bought used some days ago.

The problem is that I measure a DC voltage (more or less 12Vdc - no AC present checking with the oscilloscope) between the ground of the main supply and the ground of the audio stage (RCA input shields). I've studied the schematic of the amplifier and the two gruond should be separate (floating ground on the audio stage, so no DC between the two grounds). There are only some capacitors between the two grounds.
The voltage is more or less 12Vdc - no AC present checking with the oscilloscope. Obviously when I install it in my car, I hear loud bump and other noise.

Have you got any idea? What should I check?
the amp is working properly connecting any battery source like mp3 player.
I've already checked some main I.C. but are ok.

Let me know if I can post here the service manual or some abstract.

Many thanks to everybody who can help me.

Michele


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## michelino (Jun 6, 2016)

I've got some news.
A service center suggested me to check if the secondary winding of the DC-DC transformer is shorted to the primary. The transformer is ok: there are some hundred of kohm between the two windings and I do not have any DC between the RCA shield and the negative supply of the amp when it is connected to the supply but switched off (remote disconnected).
I've re-checked all the main ICs. I've found a defect on the IC801 that is the PWM ic. This is an alpine branded IC with 20 pins. The pins 19 and 20 are the feedback from the output rectifier stage of the secondary of the DC-DC transformer that supplyies the audio section of the amp. On this pins I should find something like 0,6 and 1,7V (I don't remember the exact values). I measure about 18V.
I think that I should find a replacement of this IC but this is a serious problem.


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## --Kei-- (Sep 8, 2011)

From previous experience repairing my own old alpine amps, you definitely need to make sure both primary and secondary grounds are linked together whilst you test run it on the bench else all sorts of peculiar behaviour occurs. If you think about it, the RCA shields on the headunit are tied to the common ground anyway.

I'd also replace all of the electrolytic capacitors in the unit with new parts. Both my 3566 and first gen V12's needed new capacitors as the old ones were just starting to leak underneath where you cannot see. Strangely my 3553 was fine but I still replaced them anyway.

There's a guy by the name of Perry Babin on diyaudio who is both very knowledgeable and very helpful who should be able to point you in the right direction.


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