Just for testing purposes can I clip the legs of all the gates on the fets and remove the gate resistors and test my wave forms that way? At the point I do that can I remove the treble pot from the LM6171 and re-install R31 and R35 for my tests?
If you're going to clip the legs, you may as well cut all of the legs.
You can make a quick check with the pot then remove it.
You can make a quick check with the pot then remove it.
Ok Perry back to this beast. I replaced all the fets that blew, and replaced their gate drivers as well. I built a new test pot and soldered it to the the pins on the U17.
Please refresh my memory on the +/- switching I am looking for on the output fets, was it the drain leg I was checking?
Please refresh my memory on the +/- switching I am looking for on the output fets, was it the drain leg I was checking?
Reading back in old posts you want black probe on source and red probe on gate looking for +10 vdc switching to -10 vdc and you only want me to check Q107 and Q104?
If the amp passes this check then I can remove the pot?
If the amp passes this check then I can remove the pot?
Yes. When rotating through the point on the pot where the voltage switches, do so quickly. I've never had a problem blowing FETs doing this but it 'may' be possible of you go through the switching point slowly. I'll have to try this again to see if I can duplicate the problem.
As soon as I powered up the amp the emitter for Q105 went up in smoke. I am sure the fets blowing in this section of the amp took out the MIC4420CT driver. Can I still power up the amp safely with that driver failed?
Why would the gate for Q105 smoke upon powering up? Could Q105 being shorted cause this?
Why would the gate for Q105 smoke upon powering up? Could Q105 being shorted cause this?
I didnt replace Q105 before it looked fine but upon clipping the legs it fell apart. I must have missed it. I will replace Q105 and emitter and re power amp and do the test. I only replaced the fets that blew. Eventually I will replace them all in that section but want to get the testing done first and figure out the problem with the amp shorting with the 4 IRF3415's from the other section installed. I still have R35 and R31 removed, other wise the amp wont power up.
I replaced Q105 and the emitter and powered up the amp. Seems to be fine other than a tad of current draw not much. Dont know what this amp is suppose to draw at idle??
Checked Q104 and Q107 black probe on source, red probe on gate and both fets switch from +9.84 to -9.84 upon rotating the pot.
Does this mean I can now remove the pot?
Checked Q104 and Q107 black probe on source, red probe on gate and both fets switch from +9.84 to -9.84 upon rotating the pot.
Does this mean I can now remove the pot?
Ok pot has been removed, what am I looking at next. Did this determine it is not a drive problem?
Previously the amp would not power on with these resistors installed, UNLESS I removed Q101, Q102, Q103, and Q12. Then it would power up fine. Q105 and the others that blew were a result of the pot malfunction.
You want me to re install the resistors anyway and try to power up the amp?
You want me to re install the resistors anyway and try to power up the amp?
Amp powers up with resistors installed but is drawing about 5 amps current. Do you want me to try and test audio anyway? I dont want to damage anything.
Wait............the 1k resistor for R31 is not making contact looking at it under the magnifying glass let me replace it and try again. It does power however with R35 installed, just drawing a little current.
Does the amp draw 5 amps before the protect LED goes off or does the current draw increase (from about 1A to 5A) when the protect LED goes out?
Ok R31 is installed and the amp still powers up. The current draw is a little less with R31 installed. When I first power the amp it draws about 2 amps when the protect led is lit, then when the protect led goes out it slowly creeps up to about 4 amps.
Providing I am reading my guage right, between 0 and 20 amps there are no numbers just marks. 0 being mark 1 and 20 being mark 6. There are 4 marks in between 0 and 20 so counting backwards 5 amp increments and the last mark being 2 1/2 amps?
If you have other working 1500s, put one or two on the bench to see how much they draw.
If you let the amp idle for a few minutes, do any of the FETs get hot (constantly monitoring the temperature of the transistors)?
If you let the amp idle for a few minutes, do any of the FETs get hot (constantly monitoring the temperature of the transistors)?
I will put another on the bench real quick and see. I will then put this one back on and monitor fet temps.
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