Hey,
Im working on a blown sd 12k. One channel was shorted, other looks fine. I fitted new driver irs20957, 2x zxgd3005 and new zeners. I still have yellow led lit. When im feeding amp with just 12v with no remote i have 12v on high side gate/drain and 8v on source. Low side has 8v on drain and 0v on gate/source. But on the blown channel i have 12v on high side drain and only 1.6v on gate/source. Thus im only getting 1.6v on low side drain and 0v gate/source. I cant for the life on me figure out what im missing. And obviously i have 8v on one output terminal and 1.6v on blown channel terminal.
When measuring i have drivers etc removed from the board.
Im working on a blown sd 12k. One channel was shorted, other looks fine. I fitted new driver irs20957, 2x zxgd3005 and new zeners. I still have yellow led lit. When im feeding amp with just 12v with no remote i have 12v on high side gate/drain and 8v on source. Low side has 8v on drain and 0v on gate/source. But on the blown channel i have 12v on high side drain and only 1.6v on gate/source. Thus im only getting 1.6v on low side drain and 0v gate/source. I cant for the life on me figure out what im missing. And obviously i have 8v on one output terminal and 1.6v on blown channel terminal.
When measuring i have drivers etc removed from the board.
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If you touch a load from each speaker output terminal to ground (driver ICs out of the amp), does that pull the DCV to 0v without causing an increase in current draw?
I managed to remove all the fets meanwhile so i cant test it right now. Also discovered one fet was blown open on the so known healthy channel and one mur120 diode shorted. Stupid thing i did was i forget to deplete the rail caps when removing fets. There was only 12v on the rail but still i could have killed those myself while removing. So i need to order new parts and wait again.
Do you have enough parts to get it together enough to continue testing?
Soundigital and Stetsom use push-pull secondaries that boost from the 12v B+ so you have 12v rail, even if you don't switch the supply on. They are like the flyback type supplies, in that regard.
Soundigital and Stetsom use push-pull secondaries that boost from the 12v B+ so you have 12v rail, even if you don't switch the supply on. They are like the flyback type supplies, in that regard.
Yes i'm familiar with that. I also repair it in so known "service mode" where no rail voltage is built at all. Only the 12v thats fed into the power terminals is on the rail. But no, i have to order some mur120 diodes and can continue next weekend.
If you still have the DC on the output without the driver ICs. Install a resistor (virtually any value will work, I'd use a 100k) to pulldown the high-side out to Vs and the low-side out to the Com. This should prevent any DC from being present on the output terminals of the amp.
Okey, 2 weekends later i finally got some life out of the amp. I asked around local bassheads if anyone has an sd12k laying around that i can borrow and compare measurements. And i made sure that the "healthy" channel was actually faulty too from the beginning and my whole voltage difference on the speaker terminals came from that "healthy" channel. I looked for hours and hours til i finally noticed a strange looking trace under the damn filtering cap and under the yellowish glue. Took the cap off and removed all the glue and voilla there was no trace. Blown right under the cap. I fixed that and put the cap back in and finally both channel have indentical numbers on output. I installed all the "new" parts and still silence. Then i dropped in the original driver that came off the board a poof one channel is up and running. I tried all the 3005's that came from china and all work well but both irs20957 are dead. Have they ever worked i dont know but now i only need one more legit driver and it should be fixed.
Was the damage due to leaked electrolyte or possibly from the fixative turning corrosive (the amp probably isn't old enough for this, yet)?
No it was just burned. It was a really thin trace coming from low side drain to somewhere before the buffers. Probably when the amp popped there was voltage drifferences on the terminals and current was drawned from that trace i guess.
One thing i really love about brazilians is that you can power it up with only 12V on rail and force the pic to turn the output on so you can make only one channel working at a time like i did.
One thing i really love about brazilians is that you can power it up with only 12V on rail and force the pic to turn the output on so you can make only one channel working at a time like i did.