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You're quite welcome George. Thanks for sticking with it as well. It's quite satisfying to see someone's effort pay off.
I hope you can finally get some good use out of this amp. :)
120mV at ch.B output is too much, and I think indicates a problem.
I can understand if you just want to move on with ch.A, but in that case, you should remove the ch.B darlingtons and keep them for spares. It would be terrible if you got it all fixed and it blew up again because someone...
Yes, on bulb, I would check DC volts at E,B, and C of Darlingtons for both channel amps, and check for DC at both channel output jacks.
If both channels seem in agreement, you can proceed to attach load.
40mV DC at the output does not seem like anything to worry about.
But it will be helpful to you to continually compare to Ch.B, then if anything sticks out on either channel you will be able to deal with it before it does any damage.
If your voltages at the output transistors and output jack for...
Probably. You can de-solder C or E of each and re-check without having to remove them. If they then read ok, it will be something else like the bridge rectifier.
Not sure what will have caused them to blow, check TR2,5, and 10 as well.
You may want to consider building a 'dim bulb tester' to...
Did you check for DC at the outputs before connecting the loads? There may have been some there after you repaired the traces. That might account for the hum. If you connect loads with any DC at outputs, things will burn eventually.
Sounds like TR1 will be gone now, you can desolder the...
This is actually good news, as it explains the odd readings for TR18 in circuit.
Probably the trace that goes from TR18 base to R48/D8 is cracked. If you remove the solder at TR18 base and look at the trace with a magnifier, you will probably be able to see it.
You can just install a jumper...
Sorry, my mistake. With these particular darlington's, there is an added internal resistor which makes them measure the same as normal transistors.
These readings look pretty good but you have the 'type' listings reversed I think. No problem, I will assume the 'location' names are correct...
It sounds like that 3270 is equivalent of 'OL' (over-limit or open) reading on most meters.
For your meter: "if the diode is reverse biased or there is an open circuit the reading displayed will be between 3150mV and 3450mV"
Here is a good write up on the transistor test...
Yes, diode checks or resistance readings need to be done with power off.
The pinout for all the TIP type transistors in this amp is BCE, from left to right.
What do you mean by 'no contact/signal' ?
Usually a beep or zero reading on diode check function indicates a short.
Can you check if the probes are reversed at the meter?
Pin8 should be +, pin4 should be - (when black probe to chassis).
For now, I'll assume those readings are just opposite polarity but otherwise correct.
Pin5 voltage indicates there must be DC at the output of Amp B, can you check it?
I think you must mean the 142's ?
I see on your order sheet TIP142T. Sorry I did not notice that earlier, the T suffix is for a smaller, lower power part.
You will want the 142 with no suffix, mouser # 511-TIP142.
As it is working, I don't think that is causing the sound problem all though it...
Correct.
When you power up with no speakers/load connected, make sure there is no DC voltage at the outputs.
If there is any more than 50mV or so DC (0.05VDC) do not proceed, there is still something wrong.