One channel of amp distorts when the volume is turned up. It's goes from clean to distorted around ½ power.
The voltages across r206, 207, and 208 are identical to the voltages across r306, 307 and 308.
Audio remains clean at c304 a and c201
The voltages across r206, 207, and 208 are identical to the voltages across r306, 307 and 308.
Audio remains clean at c304 a and c201
Attachments
It won't bias but it still acts the same otherwise?
I'm going to go through the pile of amps I have and see if I have one that I can experiment on and try to find some tests that we haven't tried here.
It may take a couple of days. Today, I'm concentrating on a JL 500.
I'm going to go through the pile of amps I have and see if I have one that I can experiment on and try to find some tests that we haven't tried here.
It may take a couple of days. Today, I'm concentrating on a JL 500.
No. There is no audio out of the affected channel. The other channel has very low output. The amp is only drawing .9a of current. Same as if the pots were full ccw.
Let's work on one at a time. My tiny little brain can't deal with multiple repairs for the same amp. Which one do you want to concentrate on?
This is the amp (green)that when turned up would start to distort before I made the bias stop working.
The other amp (tan) was distorting at anything outside of 15-30hz. Replacing a single .1 ohm resistor seems to have fixed it.
The other amp (tan) was distorting at anything outside of 15-30hz. Replacing a single .1 ohm resistor seems to have fixed it.
Attachments
I'd like to see if disabling the protection circuit will make a difference. It's somewhat risky but this is an odd problem and we need to eliminate some of the circuit. Removing D305 and D307 will disable it. Be careful, all semis tightly clamped to the heatsink, be ready to power down if there is a problem.
Ok so I have the bias working again. 1 of the 640n fets was shorted. I now am back to getting distortion on one of the channels 20v ac on the speaker terminals.
Do you like that scope? It's not too expensive and has some good features.
DCV on the collectors of Q306 and 307?
Do you see any strange spikes on any of the terminals of either of those transistors?
DCV on the collectors of Q306 and 307?
Do you see any strange spikes on any of the terminals of either of those transistors?
Its not too bad. I got the floating version so it makes it safer for dummies like myself.😁
I should be taking these measurements when the distortion is present correct?
I should be taking these measurements when the distortion is present correct?
Yes. When the distortion is present. Remember to measure the voltage on the collectors.
What you have to remember is that when the shield has voltage on it for one channel, that feeds the other shield so if the other probe is plugged in and laying on the bench, it won't be safe. Only plug in one channel when you're connecting the shield to something other than ground.
What you have to remember is that when the shield has voltage on it for one channel, that feeds the other shield so if the other probe is plugged in and laying on the bench, it won't be safe. Only plug in one channel when you're connecting the shield to something other than ground.
