"unless Q52 is defective. Have you checked it carefully (leakage, opens/shorts)?"
Yes, Pulled it and tested it.
"What shorted the driver ICs? I missed it if you said that the outputs failed again."
No the outputs didn't short again. I tried them on one bank and got the noise. I pulled them and tested. They were good. I tried two more in a different bank and got the noise again. Pulled them and tested. They were good. Tested the drive again and didn't have it. then it went into protect. The two driver chips that I replaced were shorted again. Don't know why. I'm very careful running tests on these things and I'm getting really good at changing the driver chips. I take a fine cutting disc on my Dremel and cut the legs at the chip. Clean the cuts legs with my iron. I use a fine bead of solder paste across the pads. All I have to do is just touch it with the iron. Then clean them up to remove any paste that might still be on there. I check them very carefully with LED light and magnifiers. You have to respect these amps. They can get away from you quick. Originally only the power supply was burned up. I rebuilt it. Checked all the outputs. No shorted outputs. Powered it up and POW! My ears rang for a few hours. I think I'm going to wind a low voltage supply every time. Just make it standard procedure on these things.
"Remove the speaker/load and only monitor the output of the amp with the scope. Does it produce audio or do you only see the signal that was causing the squeal?"
Put two outputs in one bank and test without a load. Even with it pulling current?
Yes, Pulled it and tested it.
"What shorted the driver ICs? I missed it if you said that the outputs failed again."
No the outputs didn't short again. I tried them on one bank and got the noise. I pulled them and tested. They were good. I tried two more in a different bank and got the noise again. Pulled them and tested. They were good. Tested the drive again and didn't have it. then it went into protect. The two driver chips that I replaced were shorted again. Don't know why. I'm very careful running tests on these things and I'm getting really good at changing the driver chips. I take a fine cutting disc on my Dremel and cut the legs at the chip. Clean the cuts legs with my iron. I use a fine bead of solder paste across the pads. All I have to do is just touch it with the iron. Then clean them up to remove any paste that might still be on there. I check them very carefully with LED light and magnifiers. You have to respect these amps. They can get away from you quick. Originally only the power supply was burned up. I rebuilt it. Checked all the outputs. No shorted outputs. Powered it up and POW! My ears rang for a few hours. I think I'm going to wind a low voltage supply every time. Just make it standard procedure on these things.
"Remove the speaker/load and only monitor the output of the amp with the scope. Does it produce audio or do you only see the signal that was causing the squeal?"
Put two outputs in one bank and test without a load. Even with it pulling current?
Do you check the driver ICs every time (before applying power) to make sure that they survived the installation?
Does the rail voltage build fully (even low voltage) before the amp starts to oscillate?
Drive a signal into the amp to ensure that it starts oscillation precisely when enabled.
Does the rail voltage build fully (even low voltage) before the amp starts to oscillate?
Drive a signal into the amp to ensure that it starts oscillation precisely when enabled.
I do check the drivers each time before I apply power.
Tested it several times bleeding the rails before each test. The rails are +/- 22 volts. It starts oscillating at about 14 volts.
Tested it several times bleeding the rails before each test. The rails are +/- 22 volts. It starts oscillating at about 14 volts.
What if you repeatedly power up/down to let the rail voltage build then leave it on to see if it squeals if it begins to oscillate after the rail caps are fully charged.
Possibly. Some people are using the 2SC3326.
The VCEsat seems to be what's important to ensure that the shutdown pin on the 21844 is pulled down far enough.
The VCEsat seems to be what's important to ensure that the shutdown pin on the 21844 is pulled down far enough.
Answering post #44.
Doesn't make any difference. Still pulls current and squeals.
I have good input signal to all four driver chips. I'm getting feedback on the feedback pin. Good low side drive to all four output banks. No high side drive on any of the output banks. Using 9V battery on each. One at a time. Can't see what can kill the high side drive on all four driver chips. The drive goes direct to the output banks. No outputs in any banks.
Doesn't make any difference. Still pulls current and squeals.
I have good input signal to all four driver chips. I'm getting feedback on the feedback pin. Good low side drive to all four output banks. No high side drive on any of the output banks. Using 9V battery on each. One at a time. Can't see what can kill the high side drive on all four driver chips. The drive goes direct to the output banks. No outputs in any banks.
Yes, good low side drive on all driver ICs. Modulates with the input signal. Checking it at the output gate resistors.
Good morning Perry. I all ways check the ICs using your chart after install. Checked again and yes they all read approximately the same resistance on all ICs.
Pin 2 on all ICs referenced to negative rail, 5.2 Volts.
I had a 9V battery on one of the high side output caps. Decided to put the scope on it again and had high side drive. Moved the battery to the next chip. No high side drive. Moved to the next and had high side drive. Moved to the last no high side drive. Went back to the chips I had high side drive on and no high side drive. I'm very careful hooking up the battery making sure I don't short anything. Always kill power to the amp when changing. Tried flexing the drive board to see if it would come and go. No change.
Pin 2 on all ICs referenced to negative rail, 5.2 Volts.
I had a 9V battery on one of the high side output caps. Decided to put the scope on it again and had high side drive. Moved the battery to the next chip. No high side drive. Moved to the next and had high side drive. Moved to the last no high side drive. Went back to the chips I had high side drive on and no high side drive. I'm very careful hooking up the battery making sure I don't short anything. Always kill power to the amp when changing. Tried flexing the drive board to see if it would come and go. No change.
I rebuilt another driver board and I have the exact same problem. Good low side drive out of all the driver ICs. No high side drive out of all 4 ICs. 5.2 volts on pin two of all four driver ICs. Good signal on the feed back pin. Good drive on the input pin 1 of all four driver ICs.
Have you used ICs from this batch in other amps?
Why did you have, then lose the high-side signal?
Why did you have, then lose the high-side signal?
I haven't used any from this batch in other amps.
I don't know why. I put the scope probe on the gate to the high side bank. I had a 9V battery on the high side cap. I had high side drive. I moved the battery to the next driver IC and had no drive. Moved it back to the previous IC and had no drive. I tried it on all four ICs. No high side drive. It's a mystery.
I don't know why. I put the scope probe on the gate to the high side bank. I had a 9V battery on the high side cap. I had high side drive. I moved the battery to the next driver IC and had no drive. Moved it back to the previous IC and had no drive. I tried it on all four ICs. No high side drive. It's a mystery.
Check the high-side drive (after the relays close) with a load on the speaker terminals.
If you can use your scope in differential mode, check with the probes on the gate and source pads.
If you can use your scope in differential mode, check with the probes on the gate and source pads.