Hi all,
the above mentioned amplifier had two outputs blown and all power supply fets bad.
I have changed all fets to 3205 and gate resistors being 10ohm.
i have changed driver transistors.
and finally all the output fets on the same bad channel.
i have done this 2 times and the amplifier blows same way again.
i tested all the gate resistors and emitter resistors and all are fine.
When i replace all the above the amp plays good.
i have adjusted the bias also.
the above mentioned amplifier had two outputs blown and all power supply fets bad.
I have changed all fets to 3205 and gate resistors being 10ohm.
i have changed driver transistors.
and finally all the output fets on the same bad channel.
i have done this 2 times and the amplifier blows same way again.
i tested all the gate resistors and emitter resistors and all are fine.
When i replace all the above the amp plays good.
i have adjusted the bias also.
It dont look like any black or burn. But one place there is damage on insulation but the wires are not touching. Attaching the picture.
Attachments
Two of the output fets 1 irf9640 and 1 irf640 from same channel and all power supply fets with driver transistors blows.
Customer says it came on and start to play fine and as he tried to increase the gain he just heard pop and everything shutdown.
amp idling normal without any current change. 0.8Amp
yes fets clamped but what i notice is all the mehsa board is not touching the heatsink even though i tighten the screws good.
i use current limiter while troubleshooting.
i twisted the transformer good but no change in current draw.
the ground terminal screw does not tighten the wire good. is that any problem?
The ground screw will be a problem in that the terminal will overheat and cause damage ti it and the board.
You'll have to be able to duplicate the problem on the workbench to find the fault.
Sometimes a defective pot can cause a loud pop when adjusting it and that can cause an amp to fail.
If the amp failed when playing hard then being asked to play harder (increasing the gains), the warped MEHSA insulator could be the problem. To resolve that a clamp over the top may be necessary if you don't have another insulator.
You'll have to be able to duplicate the problem on the workbench to find the fault.
Sometimes a defective pot can cause a loud pop when adjusting it and that can cause an amp to fail.
If the amp failed when playing hard then being asked to play harder (increasing the gains), the warped MEHSA insulator could be the problem. To resolve that a clamp over the top may be necessary if you don't have another insulator.
i have done everything and going to test the amp on bench. attaching the picture of heat sings that i made to secure the fets.
the owner gave me another information that he used it in bridge mode. but i dont think it can be bridged. It has two separate gain knobs for two channels. Can it be bridged or is that the mistake the owner is doing all the time?
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if it is bridged then if one channel gain dont match with another channel gain will that cause problem. after bridging then how can i set gain because it has two gain for each channel.
If the signal level is VERY far off, the channel with the lower signal will heat more than the other.
Drive a low frequency signal into the amp. Measure the AC voltage across the individual channels and set the gains so that they're the same. They don't have to be within 1/1000 of a volt. Just get them close.
Drive a low frequency signal into the amp. Measure the AC voltage across the individual channels and set the gains so that they're the same. They don't have to be within 1/1000 of a volt. Just get them close.
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