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Riddles 16th February 2013 09:23 AM

Mos-Fets replacement

I'm currently repairing a Yamaha YST-SW800 subwoofer and have found some of the Mos-Fets to be dead but am unable to locate the ones that i require.
This is what the service manual says and the parts that i need-

Q16- V5877200- FET- 2SK2378
Q18- V5877200- FET- 2SK2378
Q19- V5877000- FET- 2SJ406

Are there alternatives to these?

pergo 16th February 2013 10:25 AM

2SK2378 ---> IRF640
2SJ406 --> IRF9640

for the IRF640, choose the non-N version or the -A version (IRF640 or IRF640A, not the IRF640N)

Riddles 16th February 2013 10:40 AM


Brillaint thank you, have found the IRF9640 but all the IRF640 seem to be N-Channel although have found a IRF640A so think might be in luck.


pergo 16th February 2013 10:43 AM

you can also use FQP19N20 & FQP12P20

jlithen 1st October 2017 07:13 PM

Are you guys sure IRF 640/9640 work in these amps?
I just soldered in a parallel pair of IRF9640 in the same subwoofer and the amp now seems to operate fully in class-B I think.
Not switching. Of course something else may still be blown in it.
From the datasheets it can be seen that IRF has much higher VGS than 2SJ/2SK at least...

And yes all IRF640 are N-channel, but an IRF640N is a bit different from IRF640. That is what was meant earlier in the thread :)

jlithen 2nd November 2017 09:59 PM

For the record I bought some from aliexpress for 0.60€ each, fake, could be noticed from VGSth being high.
Bought some from UK for 10.20€ each, fake, RDSon was skyhigh at VGS= -4V
Sooo, back to trying with IRF.

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