amp repair - not PG - Blaupunkt BMA5350B

Thumper88 · Post by **Thumper88** » Thu Apr 05, 2007 10:50 pm

Just got this amp off of eBay, seller said it was working when pulled....but I bench tested it and the power light comes on, but quickly turns off. It's flashes on and off about every 10 seconds. Hooking the multimeter up to one of the speaker outputs shows like it's trying to start up, but it shuts off immediately after reaching about 0.9 VAC.

Any ideas? It was remanufactered a few years back according to the listing, have to contact the seller about that. Not too sure about the work that was done on it...

One of the diodes (they are in a row - BYW80's) has obviously been replaced looking at the solder job, with a BYW29...could this be causing it to not turn on? Looking at the parts on digikey, the BYW29 is only rated for 8A while the BYW80 is rated for 20A.

Other than that...I don't see anything popping out. The main transformer looks like some of the leads have been resoldered. Nothing appears to be burned up, just that it turns on for a short while, and shuts off....repeating the process every 10 seconds.

Here's a scan of the circuit board...

click to enlarge the image, I also labeled the BYW29

flipped · Post by **flipped** » Fri Apr 06, 2007 1:44 am

well, there's your problem........ no flux capacitor

sorry i'm no help

Post by **Eric D** » Fri Apr 06, 2007 7:16 am

Remove the BYW29 and run a diode check on it with a DMM. That would be a good start I would think.

Thumper88 · Post by **Thumper88** » Fri Apr 06, 2007 7:28 pm

Thanks, I will have to do that.

On another note, below the signal card, it says "Designed by RZ/GW/BW"...

R.Z. = Robert Zeff

Thumper88 · Post by **Thumper88** » Thu Apr 12, 2007 12:13 pm

I checked the diode, it checks out to be ok....

Could it still be going into protect because of it being different?

Thumper88 · Post by **Thumper88** » Wed Apr 18, 2007 1:46 pm

alright,
I have new capacitors on the way, they will be here tomorrow...all nichicon.

A side note, the originals are nichicon and panasonic.

But as you could imagine, a board made in 1989, the caps are leaking....and this is what is causing it to go into protect as far as I can see.

I've seen Doc's tutorial already, already replaced some capacitors before on some computer boards...

My question is, should I use hot glue to keep them in place? Or will bending the leads over and of course the solder hold them in place okay? There's some sort of black epoxy that they used....I'm not sure how to get it off the board without ruining the board, any tips?

Thumper88 · Post by **Thumper88** » Mon May 14, 2007 5:55 pm

Ok, so I replaced all the capacitors a while ago, and it is still flashing the protect light, at which point I kind of just gave up for a while.

I am now back at it after receiving the owners manual from the seller (I tried buying a service manual for it, but they said that they couldn't find a copy of it after I bought it).

The amplifier has protection for Speaker Shorts, Reverse Battery, Overvoltage, DC Offset, and Thermal.

On the troubleshooting page...

(1) Improper speaker impedances (including shorts)
(2) DC offset (including + 12 vdc on speaker terminals)

If problems 1 or 2 occur, the POWER indicator shuts off and the amplifier will shut down for approximately 30 seconds. After this time delay, the amplifier automatically turns back on and tries to operate properly. If the problems has not been corrected, this sequence will cycle indefinitely.

This is exactly what is happening, the power light flashes on, turns off, then comes back on after a while...as described. The other problems, thermal overload would be it shuts down until it cools off...it's not getting hot at all. Overvoltage from the charging system...no, that would cause it to completely shut down. And reversed polarity on the terminals would cause the fuse to blow.

So I check out DC offset, searched a little and found this:
http://www.stereomanuals.com/articles/g ... offset.htm

So I hooked the my DMM up to the outputs of the amplifier.....when I turned it up it gets to about 400mv DC on the subwoofer section, and maybe 250mv on each multichannel stereo output (forget exactly what it was, but it's outputting DC voltage)...

So what causes the amp to do this? What do I check and how?

I'm trying to learn, I could just send it to someone to repair it...but what is the fun in that and what do I learn?