I am trying to repair a Power Acoustiks power supply that was pretty badly burned up. I replaced all of the power supply mosfets (IRFP064N) and all of the gate resistors (33ohm).
When I power the amp up through a current limiting resistor to check the drive in the power supply the following pictures is what I see.
There are six total mosfets in the power supply and each pair is driving an individual transformer.
The first picture is taken at the gate and the second picture taken at the drain of the mosfets.
What could be causing this anomaly? Damaged via or trace maybe?
David
When I power the amp up through a current limiting resistor to check the drive in the power supply the following pictures is what I see.
There are six total mosfets in the power supply and each pair is driving an individual transformer.
The first picture is taken at the gate and the second picture taken at the drain of the mosfets.
What could be causing this anomaly? Damaged via or trace maybe?
David
Attachments
What does the signal look like at the output of the IC and board?
I've seen some strange PS issues on these amps when there was a shorted transformer. Did a resistor under the driver board burn?
I've seen some strange PS issues on these amps when there was a shorted transformer. Did a resistor under the driver board burn?
I checked the drive circuit pretty thoroughly and it looks pristine as well. I’ll check the drive at the IC in a minute. I had to repair some snubber networks in front of each of the power supply mosfet pairs. The one circled was burnt the worst. I just replaced the film caps, all of the resistors checked within tolerance out of circuit.
I’m thinking I have a shorted transformer as well. That was my first suspicion when I saw that anomaly in the drive.
Can you please advise me of a fairly simple way to check a transformer for a short in circuit before I start the repair so I’ll better know what I’m in for before I begin.
Thanks,
David
I’m thinking I have a shorted transformer as well. That was my first suspicion when I saw that anomaly in the drive.
Can you please advise me of a fairly simple way to check a transformer for a short in circuit before I start the repair so I’ll better know what I’m in for before I begin.
Thanks,
David
Attachments
Ok. I’ve got to cut through the glue they used so I can get some movement out of them. They are locked in place pretty tight. I tried twisting them earlier but I couldn’t get them to budge.
David
David
Thanks for your help Perry. It turns out that the problem with the power supply drive was the film caps that were burned up that I replaced were the wrong value. The circuit needed 4700pf caps and I think I may have used 470nf caps. Once I got the correct caps in there the drive looked normal.
Now I have to hunt for some output mosfets. The ones in here (IRFP264N) are obsolete and one of them is shorted. I have some IRFP250N in stock. Not sure if they’ll work. I also have IRFP064N, and IRFP360L. Not sure if those will work or if I need to order something entirely different.
Any suggestions?
Now I have to hunt for some output mosfets. The ones in here (IRFP264N) are obsolete and one of them is shorted. I have some IRFP250N in stock. Not sure if they’ll work. I also have IRFP064N, and IRFP360L. Not sure if those will work or if I need to order something entirely different.
Any suggestions?
When the 264 initially went obsolete, the IRFP4229 was suggested but they caused a problem in one amp (slight distortion). The IRFP4232 and the IRFP4332 were suggested when the 4229 went obsolete. I didn't have to use many replacements so there may be better suggestions.
I am wondering your thoughts on IRFP4868 as a replacement since the orion 5000.1dspl has a similar design to this amplifier. I believe the gate resistors are 4.7Ω