T&L Publications

I am working on a MA Audio high power amp, model #HK401SX
I can't get a service manual for this unit.

The protection circuit is triggered, checking through SMPS , the PWM is a TL494CN all of the pins including the oscillator output read normal VDC accept pins 9 & 10 which should be 5VDC & bias the mosfets. There is 0VDC on these two pins thus no mosfet operation.

With all of the other pins reading normal I replaced the PWM but I have the same results, checked all of the power mosfets and they are all good.

Any input or advise would be appreciated

We don't have a schematic, but you can check the datasheet for the TL494:
http://focus.ti.com/lit/ds/symlink/tl494.pdf

Do you have voltage on pins 8 and 11 ?

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In accordance as to what drive configuration they were using, check to see that there are not pull up resistors used and that your drive is then outputted on pins on pins 8 and 11
instead of 9 and 10. That is, unless you have circuit path traced the drive lines to the PS SW FETS.

73's de Edd

[email protected] ...........(Interstellar~~~~Warp~~~Speed)
[email protected].........(Firewalled*Spam*Cookies*Crumbs)

Hmmmmm. . .?. . .Do witches run spell checkers?

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hi Edd ! nice to see you here again, i especially miss your quips at the end,they are always good for a chuckle {:>D

Sorry!!
Was busy with in-laws for a bit. Thank you for your input.

Yes pins 8 & 11 are at 14VDC. I am checking on the drive configuration as you suggested and will let you know.

Again thank you.

is Luke5555 the same spammer as Luke4444?

amelecsol2000 wrote: ↑Fri Aug 15, 2008 6:27 pm Sorry!!
Was busy with in-laws for a bit. Thank you for your input.

Yes pins 8 & 11 are at 14VDC. I am checking on the drive configuration as you suggested and will let you know.

Again thank you.

I think pins 8 & 11 work well.