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Old 3rd April 2007, 07:05 AM   #1
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Join Date: Apr 2007
Default mtx 7801 power transformer

my old mtx 7801 went up in smoke (the one i can use for parts)
i replaced the power input transistors originally huf73559p? with irzf48's and applied power to the amp again only to hav it start smoking as soon as i applied power but this time it was from the power transformer. lokked at it and the enamel on like 4-5 of the wires was melted together and some bare wire showing. so i guess i need a new power transformer and ill check the transistors again to make sure theyre good. is there anything else i should check for? where can i get the transfomer? nay help will be much appreciated!
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Old 3rd April 2007, 08:37 PM   #2
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If you can get a replacement transformer (or if you rewind the one you have), you need to check the driver transistors (Q102-Q105) that drive the FET driver transformer (small toroidal transformer near the TL494 driver IC). Also check resistors R111, R112 and resistors R138-R141.

The original FETs were likely HUF75339P3s.
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Old 4th April 2007, 08:06 AM   #3
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thanks for the help and everything. i shecked all of the stuff you told me to on the board and its not worth my time and effort to fix it. called mtx they said that they charge a $98 flat rate to fix these things so i think im gonna ship it to them and just have them fix it so i know its good to go.
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Old 27th March 2008, 07:53 AM   #4
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Default mtx 7801 Newbi

New to this site and dunno how to post anything yet... But for starters, Mtx 7801 amp. Fans failed and so far it seems like the 8 voltage regulators blew... No black spots or anything on the mother board that I can see... Included are pics. Question is- Should I be looking for anything else with the naked eye to be burnt or blown up??? Had the Radio Playing while i was replacing the Throttle body that I bored, and all of a sudden the subs quit hitting... Turned everything off and smelt the amp burnt... Any help answers will be greatly appreciated thanks again...
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Old 27th March 2008, 08:15 AM   #5
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Location: Louisiana
The capacitors are missing. Are those the 'voltage regulators' you're talking about?

The inductor (near the caps) looks broken.

Have you read this thread?
MTX TA7801 repair

Have you checked any of the heatsink mounted transistors?
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