help with soundstream amp

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I have a Soundstream Rubicon 550-5. Stopped working on the way home today and blew the fuses. Took it apart and found a resistor that looks to have been shorting out against the chassis of the amp and eventually completely burned up. The resistor is completely charred and color bands are unreadable. Location is R161. If anyone has access to schematics or has any other ideas it would be greatly appreciated!
 
Well, I got the schematic for the amp and I now know the value of the resistor. A little more looking into it and it looks like possibly one of the transistors in that circuit is burnt as well. Would these two issues be related? If so, should I replace all 6 transistors in the circuit as well as the resistor. I am going by the schematic and to me it looks like these 6 transistors and resistor are seperate from the rest of the others.
 
Okay, need some more help. I have somehow lost all the emails that people have sent me trying to help out. I got the parts in today and replaced the resistor and the six fets. The amp powers on and doesnt blow fuses anymore but it is reaching temps of close to 200 degrees shortly after being powered on. I removed power right away as I do not want to further damage anything else. Anyone else have any ideas of what else I need to check.

Thanks
 
You could have one or more of the following problems.

Shorted rectifiers.

Shorted transformer

Shorted output transistors

All of the above should have blown the power supply fuse.

Bad conections on the gate of one or more of the FETs. For each bank of FETs, place one meter lead on one gate and the other lead on the gate of either of the other FETs. They should all read the same value (meter set to ohms).

Open/out of tolerance gate resistors.

Defective gate drivers. Q43 and Q48 are the most likely culprits. Pull them to check them.

Double-check the FETs to make sure none are damaged. The easiest way is to check the resistance from the gate to the drain of each FET. They should read the same. If you get one that reads slightly less resistance, the FET is likely damaged.

Check all of these with no power applied to the amp.
 
Well, a little of that was over my head as I do not know a whole lot about this stuff. I did check the things you told me with my meter and everything seems okay. I did read that transistors, D4, D7, D12, D14, D16, and D17 seem to all be shorted. As far as gate drivers, how would I go about checking those.

By the way, thanks for all the help!
 
The 'diodes' (D4, D7, Dx..) are going to appear shorted between the two outside legs but should not have low resistance between the center leg and either outside leg.


To check the 2SA1562s...

Meter set to diode check
Black lead on leftmost leg (looking at face of transistor and legs down).

You should get a reading of ~0.6v when you touch the red lead to either of the other two legs. You should get no reading (same as when the leads are open) when you touch the red lead to the middle leg and the black lead to the rightmost leg. The transistors should be removed from the board for reliable testing.

If the transformer is shorted, you can sometimes twist the transformer and the short will temporarily open and allow the amp to operate.
 
If twisting the transformer didn't change the current draw, it's not likely the problem. Unless the windings got so hot that the enamel is flaking off, the short is usually between two very tiny points and is easy to break (by twisting).

Try pulling the rectifiers (D4, D7, Dx..) and powering it up. Mark them so you can be sure to reinstall them in the correct locations. If the high current draw still exists with the rectifiers removed, the problem is in the power supply.
 
i did try twisting the transformer and noticed that when I did this, a high pitched sound that i use to have coming from the amp would go away. I can let go of the transformer and the high pitch comes back and as soon as i twist it, the sound goes away again. As far as if this also changed the current draw i do not know as i was not able to test this.
 
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