Working on a Sundown 7500.1 amp. Power supply was shorted and one set of outputs shorted. Repaired the power supply. Trying to repair the output circuit. Removed all the outputs. Replaced the driver chip being careful not to over heat in the process. Removed the rail voltage diodes. Set up a low voltage +- 15 volts to the rail caps using a 12 halogen lamp for current limiting. Put one pair of outputs in each amp section one at a time. When I supply power the 12 volt lamp glows bright. I get the same results on all four output sections. Replaced all 4 driver chips. Same result. Current limiting lamp glows bright when I install a set of outputs. Any ideas? I did check the signal into the driver board before installing the driver chips. Had good signal on pad 1 of the driver chips with chips off the board. Hope this makes sense. 12 and 15 volt regulators are good.
Do you have only one lamp or do you have one on each rectifier?
Did the regulators fail when the one IC failed?
Are you getting low-side drive to the FETs with no FETs in the circuit?
Did the regulators fail when the one IC failed?
Are you getting low-side drive to the FETs with no FETs in the circuit?
I'm using 1 lamp going to secondary ground. A half wave rect for + and - 15volts. Is it necessary to use a full wave?
The regulators did not fail when the IC failed.
Yes I'm getting low side drive to the FETs. Square wave. -13.3 volts.
The regulators did not fail when the IC failed.
Yes I'm getting low side drive to the FETs. Square wave. -13.3 volts.
Half is OK but if you use a lamp on each output, you can tell if the drain is positive or negative.
If you don't see any high-side drive, use a 9v battery across the high-side cap of the 21844 and check all of the driver ICs high-drive.
If you don't see any high-side drive, use a 9v battery across the high-side cap of the 21844 and check all of the driver ICs high-drive.
Perry thanks for all your help. I've been doing a lot of reading trying to find the answer on my own. When you said use a lamp on each output, did you mean use a lamp on each the plus and minus rails?
Also, what do you mean by the high-side cap of the 21844?
Trying to understand.
Also, what do you mean by the high-side cap of the 21844?
Trying to understand.
Yes. In series before it connects to the board/caps.
The high-side has a power supply that's not generated unless the outputs are in the circuit. The 9v battery is connected across the filter cap for that supply. It's generally a ceramic cap and is across terminals 11 and 13 (13 is positive).
The high-side has a power supply that's not generated unless the outputs are in the circuit. The 9v battery is connected across the filter cap for that supply. It's generally a ceramic cap and is across terminals 11 and 13 (13 is positive).
Okay got the amp back on the bench. Realized I didn't check all four low-side drives. Rechecked and found one missing. Hooked up a 9V battery to the high-side drive. The signal looked really bad. Changed the driver chip again.The high and low drive signals look the same on three of the drive chips. The first two pics.
The next two picks are the drive signals on the fourth driver chip.
Trying to get pics to upload.
The next two picks are the drive signals on the fourth driver chip.
Trying to get pics to upload.
