CJ MF2500 fault - smoke

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bambadoo
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CJ MF2500 fault - smoke

Post by bambadoo » Wed Apr 19, 2017 5:26 pm

Hi, have had this for a while but have never tried it
Anyway - replaced all fuses (3 were blown) just to test. On fuse on the back and 2 on the pcb.
Connected a DMM on each loudspeaker terminal and fired up.
Left channel showd 72Vdc - Right channel ~100mV.
After some seconds a bit of smoke appeared somewhere on the board.

It is late here now and bed time... I will take some pictures on a later occasion.
Any initial typical faults that I could be aware of? Blown transistors maybe?

Looks as one or two resistors are blown but I guess it is a reason why that has happened?
I know this is not much to go after....

Some pictures.

First is a overview of the amp.
Second is the area which I saw smoke. However I cannot visually see a problem there.
Third I noticed afterwards that what seems as a cap or resistor has been toast.

I will take everything apart on a later occation.
cj1.jpg
cj2.png
cj3.jpg
CJ wasalso kind enough providing me with schematic.
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bambadoo
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Re: CJ MF2500 fault - smoke

Post by bambadoo » Fri Apr 21, 2017 6:25 am

A loose fuse holder (only soldered at one end to pcb) Q12 (mpsu60l), Q23(nsdu57) and R12 (100r) minimun are broken on left channel. Waiting for some equipment so I can du some more digging..
Probably more that is broken.

bambadoo
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Re: CJ MF2500 fault - smoke

Post by bambadoo » Sat Apr 22, 2017 7:55 am

Only one pair of output transistors were gone.
1 2sc3282 and 1 2sa1302..

Anyone know where to get a couple of genuine Toshibas?

bambadoo
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Re: CJ MF2500 fault - smoke

Post by bambadoo » Mon May 01, 2017 3:08 am

Q13 (small signal) mje340 on the left channel was also gone.
CJ has stopped responding. Anyone know where to get a service manual?
After it is finished I will chech bias dc offset and so on.

Also did a recap of the psu and changed one fuseholder there.
ImageImage




Sincerely

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