I haven't replaced the gate resistors so I assume they are original. The output FETs were the 31N20D before, replaced them with the 38N20D
They aren't heating evenly. on the high side 3 out of 5 FETs are heating up more, 1 specifically seems a little hotter than the other 3. on the low side all of them are cool.
They aren't heating evenly. on the high side 3 out of 5 FETs are heating up more, 1 specifically seems a little hotter than the other 3. on the low side all of them are cool.
Are all of the high-side from the same batch?
Did you use exact replacement parts on the driver board?
Are all of the gate-source signals the same on the high-side?
Did you confirm that all of the gate resistors were within tolerance?
Did you use exact replacement parts on the driver board?
Are all of the gate-source signals the same on the high-side?
Did you confirm that all of the gate resistors were within tolerance?
All of fets are 431P date code, same assembly lot code.
On the driver board I replaced everything with their MPS equivalents (KSP42 replaced with MPSA42 and such)
All of the gate-source signals on the high side look exactly the same.
All gate resistors are close to 47ohm
On the driver board I replaced everything with their MPS equivalents (KSP42 replaced with MPSA42 and such)
All of the gate-source signals on the high side look exactly the same.
All gate resistors are close to 47ohm
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Close to 47 ohms? I don't know their tolerance. Are they within tolerance?
No need to post them but are all of the waveforms for the high-side essentially identical (shape, amplitude...)?
Do you have any spare 38N20s?
No need to post them but are all of the waveforms for the high-side essentially identical (shape, amplitude...)?
Do you have any spare 38N20s?
They are rated 47ohm, all are within tolerance.
They are identical, shape and amplitude is the same.
No spare 38N20Ds
They are identical, shape and amplitude is the same.
No spare 38N20Ds
Swap 2 of the high-side FETs, one hot with one cold. Does the heating follow the FET or does the heating remain with the hot FET's original location?
Have you clamped the FETs and tried driving a load to see if the amp would produce clean audio?
For the heating FETs, how hot and how quickly?
Have you clamped the FETs and tried driving a load to see if the amp would produce clean audio?
For the heating FETs, how hot and how quickly?
Today I won't be able to work on the amp anymore and tomorrow is Christmas, so most of the day I'll be doing other things, so I will swap the FETs tomorrow morning, also will try driving a load.
In about 2 minutes the hottest FET got to about 45c on the drain tab. Other 2 warm ones were about 35c. Cool ones were about 25c, ambient air being 22c.
In about 2 minutes the hottest FET got to about 45c on the drain tab. Other 2 warm ones were about 35c. Cool ones were about 25c, ambient air being 22c.
Switched 2 FETs, the heat followed the FET.
With a speaker it SOMETIMES pops it like it sends DC to it, but then powers on and works. It sent 14v RMS into a 4ohm rated speaker just fine with a perfect sine wave on the output.
With a speaker it SOMETIMES pops it like it sends DC to it, but then powers on and works. It sent 14v RMS into a 4ohm rated speaker just fine with a perfect sine wave on the output.
The FETs may not be good matches. This can happen and why you should never order exactly the number you need.
2 minutes for that difference in temperature isn't a huge problem. Do you have a FLIR imager?
Does your test speaker have a direct connection or does it have a series capacitor?
2 minutes for that difference in temperature isn't a huge problem. Do you have a FLIR imager?
Does your test speaker have a direct connection or does it have a series capacitor?
How often does it pop (every time, 1/10 times, other)?
Loud pop or something not audible with the subwoofer in the trunk (boot?) of the vehicle?
Loud pop or something not audible with the subwoofer in the trunk (boot?) of the vehicle?
50%
Experimenting, it probably is related to my power supply this time, as it seems to pop when it powers on, but then PSU doesn't have enough power and cuts power for a short moment.
Experimenting, it probably is related to my power supply this time, as it seems to pop when it powers on, but then PSU doesn't have enough power and cuts power for a short moment.
Since it powers on fine, I will hook up my better power supply, should be fine with a 12v 25a capable supply
Do I just install the other pair of rectifiers and see if it still goes into protect with the bigger supply?
Power up and drive about 25 or 50w into a load (preferably a dummy load) and check the temperature of all of the output FETs at regular intervals. Do they all heat up evenly or do the same ones heat up more quickly as they did at idle?
Yes. Install everything.
Yes. Install everything.
Reinstalled everything, it fires up.
Hooked up a sub and did 30VA (21v, 1.5A) clamped for about 4 minutes.
Hottest FETs were on the high side, the 2 side ones (Q130 and Q134), but it was only 28c, rest were about 24c.
Hooked up a sub and did 30VA (21v, 1.5A) clamped for about 4 minutes.
Hottest FETs were on the high side, the 2 side ones (Q130 and Q134), but it was only 28c, rest were about 24c.
4 degrees hotter when all were clamped could be a problem. I'd order a new batch of FETs with extras to see if you could find a better matched set.