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Silicone heat grease, heat sink grease, silicone thermal compound, heat sink compound.
Look in the chemicals section of most any electronics supplier for silicone and I bet it comes up.
If I thought U7B was funny, I'd disable it. Stick it in its socket with pin 7 bent away, or lift either R80 or C50. It is not in the DC path of U7A.
That quarter volt offset MIGHT just be the amps way of compensating for component variation in the stages.
When a amp puts out a nice sine wave that collapses under load, to me that means the output cannot provide the current the load demands. I would suspect a bad output device first. The three output devices on each side are in parallel. The amp will run on just one per side. It will drive the full output voltage but will now lack current capability. SO don't drive a load hard. Your output collapses with a small signal anyway. Without demounting them you could disable any xstr by lifting its emitter resistor I would think. ANd since they are in parallel, trouble on the base of one could affect the other two there. Just in the way that in a tube amp a grid short on a power tube can kill the bias to the one next to it.
If 12v of output is loaded down to 1 volt by 8 ohms, clearly the thing cannot source current. Look back at R120-123 there. I think we said they total 0.06 ohm. Pull the speaker cord out. Measure resistance from the sleeve contact of the main speaker jack to ground. Is it abuot 0.06 ohms? Yes, I know that is silly. Does it seem to have more or less zero ohms to ground from there? It should.
Look at inductor L1. R112 is in parallel with it and sits next to it on the board. Measure R112. If you get 10 ohms, then the inductor is open. Look for cracked solder or an actual broken lead on it. If R112 measures short, then things are normal.
I forget, voltages aside, did we ever verify all six of the ballast resistors? The 0.47 ohm R100 etc.? And you might try that trick of lifting D21, D22 to disable the limiters. A funny limiter could be reacting to the output current draw of the load.
Just for fun, make sure there is no signal on either C55 C56. Those in the Q10,11 string.
I don't know why, but C53 caught my eye there under U7A.
Look in the chemicals section of most any electronics supplier for silicone and I bet it comes up.
If I thought U7B was funny, I'd disable it. Stick it in its socket with pin 7 bent away, or lift either R80 or C50. It is not in the DC path of U7A.
That quarter volt offset MIGHT just be the amps way of compensating for component variation in the stages.
When a amp puts out a nice sine wave that collapses under load, to me that means the output cannot provide the current the load demands. I would suspect a bad output device first. The three output devices on each side are in parallel. The amp will run on just one per side. It will drive the full output voltage but will now lack current capability. SO don't drive a load hard. Your output collapses with a small signal anyway. Without demounting them you could disable any xstr by lifting its emitter resistor I would think. ANd since they are in parallel, trouble on the base of one could affect the other two there. Just in the way that in a tube amp a grid short on a power tube can kill the bias to the one next to it.
If 12v of output is loaded down to 1 volt by 8 ohms, clearly the thing cannot source current. Look back at R120-123 there. I think we said they total 0.06 ohm. Pull the speaker cord out. Measure resistance from the sleeve contact of the main speaker jack to ground. Is it abuot 0.06 ohms? Yes, I know that is silly. Does it seem to have more or less zero ohms to ground from there? It should.
Look at inductor L1. R112 is in parallel with it and sits next to it on the board. Measure R112. If you get 10 ohms, then the inductor is open. Look for cracked solder or an actual broken lead on it. If R112 measures short, then things are normal.
I forget, voltages aside, did we ever verify all six of the ballast resistors? The 0.47 ohm R100 etc.? And you might try that trick of lifting D21, D22 to disable the limiters. A funny limiter could be reacting to the output current draw of the load.
Just for fun, make sure there is no signal on either C55 C56. Those in the Q10,11 string.
I don't know why, but C53 caught my eye there under U7A.
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