One of the amps in this model was damaged; I repaired the PS bjts 2n6488, and ALL caps in this amp. Now one channel has 2.5vDC on it, and the other has -0.6vDC on it. With a speaker load, the amp draws just a few amps of current as it sucks in the speaker just slightly. The channel with 2.5vDC on it has a lot of noise through a test speaker. I replaced the 5532 opamp, and pulled the 5533 opamp to clean under it's pads. I dont have a replacement for the 5533, except I may try swapping the 5533 from the good half of this amp which is actually working just fine.
Good rail, +-18vDC. Good regulated +-14.5vDC.
Nothing seems open, shorted, or anything. Any clues where there might be so much DC on those channels?
The other amp's half, which I also replaced ALL electrolytic caps is working just fine.
Good rail, +-18vDC. Good regulated +-14.5vDC.
Nothing seems open, shorted, or anything. Any clues where there might be so much DC on those channels?
The other amp's half, which I also replaced ALL electrolytic caps is working just fine.
Last edited:
Will the bad channel (pins 1, 2, 3 on the 5532?) produce audio up to clipping?
Post a photo of the noisy waveform/output.
Post a photo of the noisy waveform/output.
Actually the other side 5/6/7 pins are leading to the channel with more DC.
This morning I awoke and to my surprise the amp is acting a little better than yesterday. Both channels only have less than 1vDC on them. Both channels will play; I hooked up a 4-ohm test load and get clean audio at speaker terminals. I did not run loaded up to clipping however as the amp is out of the sync awaiting more parts. Unloaded signal looks alright to clipping bit the bottom half reaches clipping first on account of the DC offset.
I went and re-soldered all the new caps thinking there might have been a corroded via somewhere but that didn't improve anything.
Today the amp is almost passable. Yesterday the DC offset on the bad channel was causing too much amperage draw.
I'm going to try swapping the 5533 and the networks from the other amp's half thats working fine. Im suspecting the 5533 mainly because one of the 10uf caps unloaded electrolyte right near pins 5/6/7 at some point.
This morning I awoke and to my surprise the amp is acting a little better than yesterday. Both channels only have less than 1vDC on them. Both channels will play; I hooked up a 4-ohm test load and get clean audio at speaker terminals. I did not run loaded up to clipping however as the amp is out of the sync awaiting more parts. Unloaded signal looks alright to clipping bit the bottom half reaches clipping first on account of the DC offset.
I went and re-soldered all the new caps thinking there might have been a corroded via somewhere but that didn't improve anything.
Today the amp is almost passable. Yesterday the DC offset on the bad channel was causing too much amperage draw.
I'm going to try swapping the 5533 and the networks from the other amp's half thats working fine. Im suspecting the 5533 mainly because one of the 10uf caps unloaded electrolyte right near pins 5/6/7 at some point.
Last edited:
5533
1 0.060
2 0.021
3 13.62
4 -14.5
5 12.45
6 0.024
7 0.023
8 12.72
9 -0.703
10 -0.052
11 14.5
12 0.072
13 -0.572
14 13.61
1 0.060
2 0.021
3 13.62
4 -14.5
5 12.45
6 0.024
7 0.023
8 12.72
9 -0.703
10 -0.052
11 14.5
12 0.072
13 -0.572
14 13.61
Isn't there AC coupling that breaks the DC path between the two op-amps?
Is either pin 5 or 6 of the 5532 connected to the RCA shields?
Is either pin 5 or 6 of the 5532 connected to the RCA shields?
Pin 5 of the 5532 is connected to the muting transistors which have 40 ohms to RCA shields. Last night I did try pulling both muting transistors but that didn't help anything.
Im not totally sure about the path from 5533 to 5532 but I would presume that one of the caps I changed out has to do with that signal path.
Im not totally sure about the path from 5533 to 5532 but I would presume that one of the caps I changed out has to do with that signal path.
Do you consider the amp to be repaired as of now?
If not...
The 40 ohms is likely the muting jfet that you're reading. What's the resistance between the center leg of the jfet and pin 5?
If not...
The 40 ohms is likely the muting jfet that you're reading. What's the resistance between the center leg of the jfet and pin 5?