Hi all
Amp came with burned power supply. 70n06 mosfets with 47ohms gate resistor and two pnp A1266 drivers. I changed them with 3205.
Amp is pulling too much current on idle. I removed mosfets belongs to one transformer the other transformer that is producing small voltages works good Amp came on and gave good output oscillations.
But as soon I replace mosfets for next transformer amp pulls plenty current. I removed one mosfet from each bank of the same transformer and amp works good. So it driving 2x2 mosfets good but can't drive 3x3 mosfets. What I can do to solve this issue.
Amp came with burned power supply. 70n06 mosfets with 47ohms gate resistor and two pnp A1266 drivers. I changed them with 3205.
Amp is pulling too much current on idle. I removed mosfets belongs to one transformer the other transformer that is producing small voltages works good Amp came on and gave good output oscillations.
But as soon I replace mosfets for next transformer amp pulls plenty current. I removed one mosfet from each bank of the same transformer and amp works good. So it driving 2x2 mosfets good but can't drive 3x3 mosfets. What I can do to solve this issue.
How do the drive waveforms on the gate legs of the FETs compare between the FETs of the two power supplies?
Attaching pictures of waveform when 2x2 mosfets and when 3x3 mosfets.
First picture when 2x2 mosfets are used same waveform in both banks. Second waveform is of one bank when 3x3 is used. Third is from another bank when 3x3 is used.
Attachments
You have serious drive circuit problems for the second 2 images.
What's it using for driver transistors?
Are the PNP drivers leaking/shorted?
What's it using for driver transistors?
Are the PNP drivers leaking/shorted?
It using total 4 A1266 pnp transistors.
1 was short and i changed it. I also tried with BD140 no change.
Where does the signal degrade, starting at the outputs of the TL494?
Where does the signal no longer look like a clean 50% duty cycle square wave?
Where does the signal no longer look like a clean 50% duty cycle square wave?
Ya signal is same on the TL494 output pins also. When amp power up I get good frequency about 40khz. Then suddenly transformer starts to make noise and frequency goes 80khz and signal goes bad too.
Post a good quality photo of the drive circuit, including the 494, drivers and the gate resistors.
Is R19P1 within tolerance?
Do you read 1k ohms from gate to source for ALL of the PS FETs?
Is the burned area under one of the missing gate resistors conductive?
Do you read 1k ohms from gate to source for ALL of the PS FETs?
Is the burned area under one of the missing gate resistors conductive?
R19P1 is the culprit. Value was little high but I did not expect that will interfere so much.