I saw smoke from the jfets so I know they are toast. If I replace the ones in the bad channel do I also have to replace the ones in the good channel?
I saw smoke from somewhere else and I thought it was from a mosfet. Nothing on the board looks toast.
Looks like I need to track down two matching jfets.
Amway to test mosfets with a VOM?
It will be awhile before I can do anything. The diyaudio store is out of matching jfets for the F6.
I just tried but I blew my last fuse. The bias got to 5V before the fuse went and it went faster then I could adjust. I looked over the board for shorts and did not see any. What direction do I turn the bias pot to maximize the resistance?
No matter what I do I can not bias the output mosfets. It's acting like an adcom I once had that has a blown output transistor.
1) Check all solder joints
2) Buy a manufacturers tube of IRFP240, and start matching your own parts.
These are my building tips
1) Study amp circuit to get a good enough understanding of how the bias and dc offset circuitry works.
2) Carefully compare pcb with circuit diagram
3) Always have circuit diagram open when stuffing pcb
4) Double check all components have been installed correctly
5) Remove solder flux and inspect all solder joints with lighted magnifying glass
6) Use light bulb tester for testing power supply in isolation from amp circuit.
7) Use lab power supply with current limiting to test amp circuit in isolation from power supply.
8) Reduce bias to half the specified value then connect power supply and amp circuit rebias to correct level. Use two multimeters in tandem, one measuring dc offset and the other measuring bias level.
Never had a failure following this method.
Always test power supply and circuit in isolation from each other.
2) Buy a manufacturers tube of IRFP240, and start matching your own parts.
These are my building tips
1) Study amp circuit to get a good enough understanding of how the bias and dc offset circuitry works.
2) Carefully compare pcb with circuit diagram
3) Always have circuit diagram open when stuffing pcb
4) Double check all components have been installed correctly
5) Remove solder flux and inspect all solder joints with lighted magnifying glass
6) Use light bulb tester for testing power supply in isolation from amp circuit.
7) Use lab power supply with current limiting to test amp circuit in isolation from power supply.
8) Reduce bias to half the specified value then connect power supply and amp circuit rebias to correct level. Use two multimeters in tandem, one measuring dc offset and the other measuring bias level.
Never had a failure following this method.
Always test power supply and circuit in isolation from each other.
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That is some fantastic advice! Thank you
Last night the JFETS and MOSFETS came in so I got back to work on the amp. I installed the JFETS correctly this time and I replaced both MOSFETS. No smoke but also no bias voltage, I do have DC offset though. At the moment I am assuming that when the jfets went they took out a resistor but nothing on the board looks fried.
Check all solder joints around biasing circuit.
Check voltage across Zener diodes.
Measure voltage between gate of mosfet and ground.
Possible issues
Bad solder joint somewhere
Bad trimpot (wiper is cactus)
Bad Zener
Zener installed backwards
Maybe the smoke you saw was either from the Zener or Trimpot.
Check voltage across Zener diodes.
Measure voltage between gate of mosfet and ground.
Possible issues
Bad solder joint somewhere
Bad trimpot (wiper is cactus)
Bad Zener
Zener installed backwards
Maybe the smoke you saw was either from the Zener or Trimpot.
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