PowerBass ASA 2000.10

Dr Zeus

Member
2010-10-17 5:12 am
I got this amp in for repair from a collector who was hesitant in letting me work on it. I've never worked on a Class-D amp before but it really doesnt look all that much different thatn what I've learned thus far. This amp is big, one of the largest I've worked on. On the cover it says 4000w which makes it potentially the most powerfull and/or most dangerous.

The amp powers up with a 10a fuse and plays, but its got an absorbant ammount of distortion. Theres not much the built in corssovers do for tuning the signal. If I adjust the qBass control it almost looks like the amp is about to correct but by the time I stop turning the qBass knob the signal is well distorted again.

I checked the JRC5034G opamps and all have +/- 13.5vdc. The large coild in the center measure up about 110v, and the rail voltage is +- 70v.

When I remove power from the amp, the test speaker POPs. I think it might be a Class-D thing, as if I simply remove REM the amp powers off and the speaker wont pop.


Here is what the signal always looks like on the scope while the test speaker is distorting badly.

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Dr Zeus

Member
2010-10-17 5:12 am
Heres the pics. In these, youll notice I removed and moved some of the rail caps. The ones I pulled off tops were puffed out, and now that they are off the board I can hear sometime moving inside when I shake them. They measure OK with the meter though. To balance the caps, I left 2 on the 'bottom' row and moved two to the top row. I'll likely need to buy probably all 8 for this area after the faults are solved. The amp still powers up and makes the distortion.

I shuld have mentioned because I just love this forum. A previous repair shop quoted $120 to fix this amp

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Dr Zeus

Member
2010-10-17 5:12 am
Just pulled Q124 and Q125 off. I forget which one came out of where, but one of these boys isnt measuring anyting at all on the meter. its completely OL across all leg combinations. Looks like both are going to be replaced!

BTW, Has anyone ever told you how much AWSOME you are?