| swordfish689 |
Hi, been reading the posts on the forum for a while and learned plenty. But i seem
to have a problem with 2 of my amps, they are p-miller rsa-75hc, very nice sounding amps.they run 1 ohm stereo. Anyway here is my problem, i can't seem to run the amp when both left and right power supply mosfets(irf46n)are installed 3 on each side. When i take the left side out the amp runs fine, even produces sound. Now when i install the power supply mosfets on the left side back, it will turn on for a second and then shut down,I measured with a scope and get nice square waves on each power supply resistors, the tl494 is running fine, no shorts, on any of resistors, caps, or diodes, i searched over and over. I know the outputs are ok because i can get it running with 3 mosfets, if some one has a suggestion i would be grateful. And i replace the dual diodes on both sides and that's not the problem. |
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| gearheaddruid |
| Hi, I would check to see if you have a shorted drive transistor on one bank of mosfets. Another cause could be a shorted diode in the bridge rectifier. Half the mosfets would only create one half of a square wave. If that half does not have the shorted diode then it may allow the supply to run. I'd check the drive transistors first. Regards, Steve |
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| sss |
what if u take the right side out and check the left side when the amp is running ?
if the result is the same then something wrong with the duty cycle- duty cycle is too high , or maybe something wrong with the snubber filters |
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| gearheaddruid |
| That almost sounds like a shorted primary winding. I would check the duty cycle with a scope and be sure the sides are inverted with voltage swing from supply to ground. Possibly there is a ground trace burnt open on the under side of the board. Regards, Steve |
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| swordfish689 |
Thanks for the replys, well, i tried all your ideas, i still have the same results, when
i remove the right side mosfets and install the left side the mosfets will get really
hot, and eventually will burn the mosfets, so there is something wrong with that side, i narrowed it
down to there. I checked all the drive transistors and the bridge rectifiers and there all ok.Now, for the
shorted primary what am i looking for on the scope. And i really doubt the burnt ground trace,underneath the amp is heavy solder on all the traces. |
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