+61.36V from the pad of leg 1 (leg is cut) to the pad of leg 2
FYI FB5 is now reading 126vdc which is well over the cap voltage rating of C27 (100v)
FYI FB5 is now reading 126vdc which is well over the cap voltage rating of C27 (100v)
leg 1 to leg 2 of U9?
Leg 2 is the ground for U1. I'd expect leg 1 to be no more than 25v above leg 2.
Leg 2 is the ground for U1. I'd expect leg 1 to be no more than 25v above leg 2.
Roughly 14.2v between leg 1 and leg 2 of U9. The voltage was slowly going down after powering it up but I didn't want to leave it on too long to totally stabilize.
They measure the same - but something to be aware of, I can see evidence of cooked resistor below R110 We're back into the area where I suspect it's been worked on.
Are there possibly bad connections between D6, D27, R64 and FB5?
Designation of cooked resistor?
Are D6 and D27 OK/good?
Designation of cooked resistor?
Are D6 and D27 OK/good?
I wish there was a quote function;
Bad connections - Yeah definitely possible but they ohm out fine. There is a lifted trace here, but resistance is fine.
R110 looks fine, but I can see smoke damage on the board below it. Its not burnt, but I see some soot.
I did check all four of the diodes and they test good.
Bad connections - Yeah definitely possible but they ohm out fine. There is a lifted trace here, but resistance is fine.
R110 looks fine, but I can see smoke damage on the board below it. Its not burnt, but I see some soot.
I did check all four of the diodes and they test good.
Resistance from transformer end of R64 to transformer end of R110, resistance?
Resistance, same components but diode ends?
To quote, while making the new post, go to the text you want to quote, highlight it and select quote. It will drop into the new post.
Resistance, same components but diode ends?
To quote, while making the new post, go to the text you want to quote, highlight it and select quote. It will drop into the new post.
0.1ohms (could be my leads for the .1)
I need to grab my other meter, this one is dead again. Are you looking to test the sides of the diodes opposite of the resistor?
Awesome thanks!
I'm trying to determine why you have 14v for the negative supply but less than 2v for the positive supply.
You earlier stated that the voltage across c27 was 126v and above the 100v of C27. C27 should be a 160v cap according to the diagram.
You earlier stated that the voltage across c27 was 126v and above the 100v of C27. C27 should be a 160v cap according to the diagram.
You're right about the schematic, but the amp has 100V caps in it. I know the previous owner replaced some of the caps, these must have been a couple of them. I just looked again. C27, C11, C61, and C76 are 100V caps in this amp. Obviously that will need to be fixed. I got my other meter let me see how things look.
From transformer side of R64
D6; Banded - OL, unbanded 67.7ohms
D7; Banded - 67.7 ohms, unbanded 11Mohms and climbing
From transformer side of R110
D26 ; Banded - 67.8ohms, unbanded 12Mohms and climbing
D27; Banded - OL, Unbanded 67.8 ohms
Recheck the voltage on U1 pin 1-2. I don't see a reason that the voltage isn't the same (opposite polarity) that you have on U9.
All 4 of those diodes read ~0.6v when forward biased, correct?
All 4 of those diodes read ~0.6v when forward biased, correct?
Diodes - More like .48 on those but they are all the same.
Voltage from board (cut pin) of 1 and 2 is about 62v. U9 is about 14.5v
For a sanity check looking at the drawings of U9 and U1 I should be using pins 1-2 for both to check right?
You need to read G to VI for both.
If you still get a significantly different reading, replace the caps and recheck.
If you still get a significantly different reading, replace the caps and recheck.
I did snip the leg for VI on U1. Do i need to resolder that to compare voltages or can I use the stub on the board?
Noted on the caps, they need to be replaced anyway apparently.
U1 doesn't need to be connected to the circuit. You're essentially measuring the voltage across C27 but I didn't think it would be easy to get to those terminals.
Yeah same deal with the voltage. I am going to remove this from the heatsink and flip it over (who knows what I'll find under there). It'll be a day or so before I can get to it, but I understand what we were working at so I can do a little more investigation and report back.
Off to bed, thanks so much Perry.
Off to bed, thanks so much Perry.