Without the mosfets, check with your scope to see if you are getting drive to the power supply mosfet gates. Post a screen shot.
In my experience replacing shorted outputs and power supply mosfets with same date codes usually fixes the amp. Checking the drive will determine if the driver transistors and or the timing capacitor needs replacing. I will check schematics and post the Locators and value/part numbers tommorow.
In my experience replacing shorted outputs and power supply mosfets with same date codes usually fixes the amp. Checking the drive will determine if the driver transistors and or the timing capacitor needs replacing. I will check schematics and post the Locators and value/part numbers tommorow.
ok will do, I have them all out of cuircuit with no outputs or power suppy mosfets and it just draws current, despite changing the shorted diode. I was told that B+ touched ground? Seems more likely it was run at avery low indepence load. The power supply is burnt badly. I worked on this amplifiers output section a few years ago.
The D25 and D26-1N5402 are across the power terminals-B+or Battery terminal to Ground terminal, which is there to protect against reverse polarity, but can be a casualty when there is an excessive load or improper fusing and under rated cable gauge. So, you may be right, shorting the B+ to ground should not have caused the diodes to short.
Using the edited pic check the sawtooth and drive waveforms and post screen shots of sawtooth, drives at Pins 9 & 10 of the TL494, one screenshot of each bank of the mosfet gate pads.
Also, Check the DC Voltages of the pins on the TL494, using power ground for the black probe of meter.
Check the rectifier diodes with an ohmmeter.
Also, Check the DC Voltages of the pins on the TL494, using power ground for the black probe of meter.
Check the rectifier diodes with an ohmmeter.
Attachments
There are a number of things that may be causing an 8 amp draw.
Q12,Q13 shorted, check these mosfets first.
Check to be sure you have no solder bridges on the power supply mosfet pads and check the 1N5402's to be sure you have them installed properly.
Shorted windings on one of the power transformers(Twisting and turning the transformers may bear this out).
Shorted or leaky input capacitors(C29-36) or L4.L5 may have damaged cores or shorted windings.(If you don't see any obvious shorts and twisting and turning transformer doesn't change current draw pull inductors out one at a time. Check across the capacitor bank(C29-36) if shorted you will have to remove each cap one at a time.
I may be missing something, I will continue to ponder this. If anyone has any input it would be most welcome. It's an unusual problem!!
Q12,Q13 shorted, check these mosfets first.
Check to be sure you have no solder bridges on the power supply mosfet pads and check the 1N5402's to be sure you have them installed properly.
Shorted windings on one of the power transformers(Twisting and turning the transformers may bear this out).
Shorted or leaky input capacitors(C29-36) or L4.L5 may have damaged cores or shorted windings.(If you don't see any obvious shorts and twisting and turning transformer doesn't change current draw pull inductors out one at a time. Check across the capacitor bank(C29-36) if shorted you will have to remove each cap one at a time.
I may be missing something, I will continue to ponder this. If anyone has any input it would be most welcome. It's an unusual problem!!
I kept reading a short across everything in that area. I removed all the capacitors first. Same result, short or very low resistance across the pads for the caps, and the b+, and negative terminals. So I removed them both one appears ok. Buy I have two very similar, from two Memphis trash boards that I believe will work.. once I find out the value I'll go from there.
That was not a crack an optical illusion I took the ferrite out of both and they are ok. So I removed all the capacitors and the power supply torrids. The board now Powers up and the relay engadged. So it was something short,,all the capacitors tested fine. I do know that if I place one of these toriods back on the board, it draws 8amp of current.
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I will try them out. I have two of them identical. I'll repost after. Or if I by new materials be to rewind 2, do you know where I can buy such parts? Either one of these I place in the board cause the same 8amps of current draw, and pulls down the voltage to 2vdc on the supply. Thinking it's somewhere else on the board.
ive pulled and checked all of the capacitors, i changed c28/25v, the gate drive is present with the inductors removed. Im leaning towards one of the transformers, i dont see any bad spots on them, i can pull one and check closer. ill attempt to use the inductor from the other amp and see what happens.
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