Noob diamond audio d5600.4 no output on channel 1 and 2

Hi guys, I'm very happy to have stumbled across this forum. I've had fun with car audio for a little while now, and have decided I want to fix an amp that I recently acquired. It is a diamond audio d5 600.4. channels 3 and 4 play cleanly, but I get no output other than a very faint hiss from channels 1 and 2.

The power supply obviously works, as channels 3 and 4 produce output, and the rails show +30v and -30 volts, and the +15v and -15v sections also check out.

I do see what look like two blown resistors in the channel 2 section, and w resistors that look like they are blackening, but resistance still checks out in channel 1.

I have been testing the output transistors with a multimeter in diode mode, and don't think I have any failed ones.

Why would those resistors burst on channel 1 and 2?
I'm a bit of a noob, but I can follow directions pretty well. Hoping to fix this thing and see how it sounds...
 

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Thanks for the response. I have found the two offending resistors in the schematic. Should I be concerned about the two transistors leading up to the resistors? Why would only the two on the positive rail side burnt up?
Thanks. I'll be trying to pick up some resistors tomorrow. 220ohm and 100 ohm.
 

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I will picking up some resistors and transistors today at the store, they don't have the 221 ohm resistor, but they do have a 220 ohm resistor. If I replace both, it should work ok, I think... good thought process? Or severe misunderstanding of how the circuit works?

Also, they do have the correct blown transistor, the (q37 in the diagram) MPSA56 for the negative side of the wave, but for the top part, (q29 in the diagram) they do not have the MPSA06. They do have both of the items specified on the diagram though, the TIP41C and TIP42C. Those are the transitors specified for the d5 600.2, while the MPS items are what came in those locations for the d5 600.4. They seem to be just larger beefier transistors. Would they cause a problem in the 600.4? I could also replace Q8 at the end of the circuit.

Anyway, plan is replace resistors, replace one toasted transistor, see if it works, if it does, then try the bigger transistors and see what happens. :D

Thanks again.
 

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The larger drivers are probably used because the output stage has more transistors to drive. The TIP drivers may work but could also case problems if the circuit has any other differences. You'd need a scope to confirm that the drivers are working properly in the circuit.

The pin configuration is different so you'd have to twist or otherwise reconfigure the leads to make the TIP drivers fit.

I'd suggest ordering the right parts (not from ebay).
 
Well the above post didn't add much to the thread. I did get some sound to come out of channels 1 and 2, but it sounds very poor. Lots of scratching and popping, and certain output transistors heat up more than the rest. I got the replacement transistor installed. It was not a mpsa56 like the orignal, it was a nte159. The guy at the electronics store said it was a drop in replacement, a little Google action convinced me that it was.
I replaced several 100 ohm resistors that had appeared discolored, or popped, as well as a couple of 221 ohm resistors.
When I put an audio signal to channel 3 or 4, it comes out loud and clean. When I send an audio signal through channel 1 or 2, it sounds scratchy or popping. Badly. If you fiddle around with the gain knob, it will do a bit better as you turn it higher. It also is low volume. All output transistors check out, as do all of the smaller ones in the individual 1 and 2 channels. The output circuit is exactly the same as the 600.2 one posted, except, 600.2 has the extra output transistors per channel, and the larger driver transistors.
Why would get a lower volume,and lots of scratchiness? Sounds now come out of channel 1 and 2, so that is a little bit of progress.

Here is the weird part. The 2sc5200 output for channel 1 are hearing up, and the 2sa1943 for channel 2 are hearing up more than the other output transistors.
 
So I have success with channel 1. Bunch of mpsa06 and 56 transistors showed up today, and replacing the circled transistors brought channel 1 back to life. Nice and clean signal. Actual music out of the damn thing. I changed the same items for channel 2, and it did not resolve the issue. There may be other issues further up stream as there was a more catastrophic looking failure on that side. But I am very encouraged.
Resistors circled were replaced on channel 2 as they had burned up. I will be changing out more bits on channel 2 with the hope that it also comes back to life.
 

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So I got all 4 channels working on the rest bench. All 4 channels will play a 60hz test signal from phone. Gains for 1 and 2 behave as expected, increasing the voltage at the speaker outputs. The signal sounds clean on all 4, and the main output transistors seem to all warm up at the same rate based on my advanced finger probe. Before 3 and 4 behaved this way, but channel 2 did not. I didn't do any extended testing, but it will last at half gain setting through a whole song and the output transistors are all uniformly mildly warm, and the music sounds clean. Tomorrow I plan on sticking it back in the heat sink and testing louder in the garage. It is only hooked up to a 13v 30amp max power supply. If it passes it that test, I'll throw it in my car and giver a go.
Perry, thank you for your help. I enjoyed the process so far, and will likely look for another class ab amp to fix.