And make sure Q13 is seated properly without trash or raised hole underneath. Common problem with heatsinks you drill and tap yourself. I use a file to level.
Ok I removed Q7 and Q8 replaced Q13 same result. I am only applying about 20v through my veriac at this point and with my finger on Q13 is still getting very warm very fast. Rt side LED is lit at this point Lft is not.
Yes according to the markings off my Pass diy power supply it worked fine for my Alph J build...different transformer. Even if it was wrong why would one side be fine and the other not?(just asking)
I'm afraid, ran out of my remote-healing properties.
Perhaps you could write down voltages on test points as J2M did, and post it.
Perhaps you could write down voltages on test points as J2M did, and post it.
Of course if Q13 gets so hot with even lower voltages, it would be a bad idea.
I think that I would compare to the good and the bad channels resistance values at different locations without power.
I think that I would compare to the good and the bad channels resistance values at different locations without power.
I assume Q14 does not feel hot? Perhaps you can check around R19 to see if it
has the correct value or is there might be a short around there.
has the correct value or is there might be a short around there.
Hi mk47,
Perhaps I can offer a few suggestions if you don't mind.
According to Nelson's schematic Q13 is a TL431 so if it is running hot then check the value of the associated resistors, R15, R17 and particularly R19 as this is the one supplying Q13 from the 28V rail. Also check the orientation of diode D1, making sure that it is reverse biassed from the 28V rail.
As to the LED close to Q13 remaining unlit then check also its orientation as this must be forward biassed to illuminate.
Finally when I have completed the soldering on any PCB I always apply Methylated spirits to the underside and then use a stiff bristle brush to remove any remaining flux and loose solder. After which I inspect the circuit with a magnifying glass; it can be surprising what is revealed.
If you have already done these things then please forgive the intrusion.
Regards, John
I would like to help to you, God sees my soul!
Check that LED with a DMM, to be sure it is good.
Check voltage on R32 (V- and T1) with DMM at DC 200mV setting, while you are raise PS voltage. without power VFETs, I measured about 5-6 mV.
Without LEDs in the circuit, however LEDs in circuit will not raise it too much.
If it goes much higher, there are something not so good.
You can trust in what J2M said, these are good suggestions.
Regards,
Gyuri
Check that LED with a DMM, to be sure it is good.
Check voltage on R32 (V- and T1) with DMM at DC 200mV setting, while you are raise PS voltage. without power VFETs, I measured about 5-6 mV.
Without LEDs in the circuit, however LEDs in circuit will not raise it too much.
If it goes much higher, there are something not so good.
You can trust in what J2M said, these are good suggestions.
Regards,
Gyuri
As the pictures says, D1 is in the right direction.
But it worth a check, is it a diode yet or not?
But it worth a check, is it a diode yet or not?