I have a Ct sounds 2k amplifier. I am trying to sort out issues in the power supply. The ps mosfets are shorted, a few gate resistors are out of spec and it appears that half of these small transistors are burned. I am having an issue identifying the transistors, I can see L6 stamped on a few of them, I think they are 2sc1623L6TP. Can anyone confirm? Also I can’t confirm the part #’s on the burned ones, any thoughts on how to figure those out?
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Ok I have the small transistors replaced, I also replaced a few gate resistors in the power supply that were out of spec. I am concerned about the TL494 ic. I currently have the power supply fets removed and the output transistors removed. I powered it up and probed the power supply gate, I have a very cheap oscilloscope for now. I attached a photo of the square wave, does this look correct? Is there a test I can do for the TL494?
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Do you have any small capacitors in the range of 0.01uf to 0.1uf?
What about the waveform has you concerned?
What about the waveform has you concerned?
I don’t have any small capacitors on hand, I’m lucky enough to have a family owned electronic supply store close by, I could check there. I thought the waveform looked ok with my untrained eye but I was not sure. I was concerned about the ic because of the burnt components in the power supply. I was not sure if there were additional tests that need run before I installed the fets.
The test would be with those capacitors. You just need one of those values listed. I use the 0.047uF.
If you have junk boards around, the 0.1uF will be plentiful.
The TLx94 ICs rarely suffer damage because they only drive any significant current positive (to 12v). When components like PS FETs fail, they short to the positive supply which doesn't stress the TLx94. There will be times when the PNP driver transistors fail and that can damage the IC but that's relatively rare that the IC fails.
If you have junk boards around, the 0.1uF will be plentiful.
The TLx94 ICs rarely suffer damage because they only drive any significant current positive (to 12v). When components like PS FETs fail, they short to the positive supply which doesn't stress the TLx94. There will be times when the PNP driver transistors fail and that can damage the IC but that's relatively rare that the IC fails.
Thanks for the info. I decided to install the fets since the ic seemed ok. I installed the fets and powered it up with 10 volts and limited to 3 amps. The amp was unhappy and appeared to be trying to pull high current, It kept cycling between power and protection. I removed the rectifiers and the power supply appeared normal it pulled .5 amps and had good square wave. I’m assuming there is a short somewhere in the output section. The output transistors are removed. I’m not sure where I should be looking next.
Some amps don't like being starved for current.
Are any of the output FETs heating up when it won't start (rectifiers in the circuit)?
Are any of the output FETs heating up when it won't start (rectifiers in the circuit)?
I did not not have the output fets installed when I powered it up. Ill reinstall the rectifiers, install the new outputs fets and check them for heat.
Are you saying that it wouldn't power up with no output FETs installed?
If so, could you have had solder bridges?
If so, could you have had solder bridges?
No output fets installed and it will not power up. I currently have the power supply fets and the rectifiers installed. It rapidly cycles between power and protect. I upped the voltage to 14v and 5 amps and nothing changes. Without the rectifiers installed the power supply seems normal and it will power up. I was going to remove the caps and check for shorts, is that a good place to start?
I went back and tried it again, it powered up and seems stable. I think you were right about the voltage, I think the caps just needed to charge.
Thanks I’m good. I soldered in the output fets and everything looks good, square waves look good it’s drawing about 2 amps. I’m going to fully test with it in the heat sink. Thanks for your help, I really appreciate it !!!