well i replaced the irf540s and the amp worked great....... for about an hour.It was playing at moderate volume and didn't seem to be overly hot or anything when some of the power supply fets gave out along with the small resitors near them.The newly replaced irf540ns survived. I feel bad because i was repairing this for a buddy at work and it was working great and then nothing.Is it possible that when the outputs gave out originally that it caused some harm to the power supply fets that I obviously missed?
Anything is possible depending on the load and volume he was driving.
Its more likely that the bias circuitry for the damaged channel might have made the channel pull excessive current, or the input was damaged and now that damage is causing excessive current draw on the supply while operating.
I hate to say this but I generally replace all the transistors and the zeners in a bad channel. I realize this is shot-gunning the amp but I have much higher success with this method of repair on these amps.
These are designed rather unusual with a unique zener regulated bias circuitry. I find when they go, they are GONE, and for the extra 2 each 6 volt and 2 each 15 volt zeners, and a few MPSA-06 and 56 SST's I just get better repair and lower rework rate on these exact amps.
I would replace the power supply and test the amp by watching its idle current and output bias levels and DC offset numbers with no signal applied to the amp, and no load. If the amp is stable it will just set there after normal warm up and idle soak < about 30 minutes > and there will be no unexpected rise in any of the readings. If it past that idle test i would run the amp at 30% power level and recheck the amps setups to see that they temp tracked properly.
My first lessons on these amps were painful as yours is becoming, but after a few reworks I found that I had overlook several different issues in the channel that caused it to run way out of spec very quickly after warm up.
Hope this helps...
Its more likely that the bias circuitry for the damaged channel might have made the channel pull excessive current, or the input was damaged and now that damage is causing excessive current draw on the supply while operating.
I hate to say this but I generally replace all the transistors and the zeners in a bad channel. I realize this is shot-gunning the amp but I have much higher success with this method of repair on these amps.
These are designed rather unusual with a unique zener regulated bias circuitry. I find when they go, they are GONE, and for the extra 2 each 6 volt and 2 each 15 volt zeners, and a few MPSA-06 and 56 SST's I just get better repair and lower rework rate on these exact amps.
I would replace the power supply and test the amp by watching its idle current and output bias levels and DC offset numbers with no signal applied to the amp, and no load. If the amp is stable it will just set there after normal warm up and idle soak < about 30 minutes > and there will be no unexpected rise in any of the readings. If it past that idle test i would run the amp at 30% power level and recheck the amps setups to see that they temp tracked properly.
My first lessons on these amps were painful as yours is becoming, but after a few reworks I found that I had overlook several different issues in the channel that caused it to run way out of spec very quickly after warm up.
Hope this helps...
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.