Hi, I'm new on the forum and I'm hoping you can help me out, I have a punch 40ix with only one channel working so what I did was to check the Output Mosfet and it was bad (Q215)BUZZ11 so I replaced it with a new one and it worked for a minute and then no sound again, so I disconnected the power and check the FET and it was grounded so now the question is what do I need to check before I put a new one and burn it again? thank you guys for all your help.
Grounded> Did you mean shorted?
Confirm that all of the audio gate resistors are within tolerance.
Confirm that all of the audio gate resistors are within tolerance.
The gate resistors connect directly to the gates of the FETs. It won't do any harm to check the others.
What's the PC# on your amp? 0912?
Did you monitor the temperature of the output FETs the entire time that it was powered up to confirm that none were heating up?
What's the PC# on your amp? 0912?
Did you monitor the temperature of the output FETs the entire time that it was powered up to confirm that none were heating up?
Got it so just these 2 in red.....yes the pc board is 0912 and yes the Q215 got super hot very quick and then fail, compared to the other channel didn't get hot just a bit warm. anything else I should check?
What about the bias adjustment potentiometer below , do you think this can cause the Mosfet to fail if it adjusted wrong?
Sure, the bias could be the issue. After replacing output transistors, you have to set the bias to the minimum position before applying power. When adjusting the bias, you must have all transistors tightly clamped to the heatsink.
How did you set the bias?
How did you set the bias?
I didn't, I was just thinking out loud what else could be the issue..... anything else you could think I need to check?
Heat the terminals on several of the 10uf/16v capacitors. Do you smell electrolyte burning?
Do you have an amp meter on your power supply?
Do you have an amp meter on your power supply?
Here is the update from last night..... checking the gate resistors no issues there they were 10 ohms both, then I replaced the output Fet's, put everything back together and adjusted the bias all the way down and power up the amp..... the same side start to heat up a lot and draw about 24amps, so I turn the power down again and turn the bias all the way down to the other side and turn the power up again and no issues..... it got stable but the sound was not great, so I start moving (highs, lows and the inputs) potentiometers and the inputs they were questionable and replace both LH and RH...... and it sounds decent, here is the question How do I set the bias to the right value?
Thanks Perry just adjusted them......one more questions thu, I was checking all the voltages and on the LM337 I got a lower negative voltage (-13.25v) vs the LM317 at (14.8v), I did the math using this formula just to corroborate Vo=-1.25v(1+R2/R1) and it should be like around 14.8 just like LM317 so I check the resistors R26 and R28, and R26 is reading 2.4ohms and is should be reading 2.6ohms, Do you think this difference is affecting anything?
What's the DCV measured between the output terminal and the adjust terminal? They should both read 1.25v or something close.
In this amp, the difference won't do any harm. It's up to you whether you change them. If you're considering it, I'd pull the original resistors and measure them out of the circuit. If you did that, install new resistors (can be leaded and can be multiple series parallel to get to the right value) to confirm that that gets the voltage where it should be.