Yamaha EMX3500 repair - help needed

[djbon]

Dear all,

I have a strange problem with my Yamaha EMX3500 powered mixer.

Whenever I connect the power amp module to the TA7317P protection circuit, the DC offset jump to 12V DC. This makes the protection circuit kick on.

But, if I disconnect either one of the amp module from the protection port, there is no DC offset (very small) and the relay is turned on.

Checked both amp module (when only one is connected to the protection circuit) and no DC offset.

Interchanged both port with either one of the module connected and no DC offset presents on the speaker output.

Have changed all the electrolytic caps for the protection IC (TA7317P), and the IC itself but nothing help.

Another thing is when I disconnect the audio signal from the mixer to the amp module, the DC offset is even higher (almost the same voltage with the power rail).

Anybody in here can help?.

Regards,

Djbon

[sakis]

some of your grounds is disconnected

doublecheck everything

[djbon]

TQ sakis,

Will check again the ground to see if there is any disconected ground.

Anybody having the schematic (or service manual) for this model?. Have searched the net and they requires $$$ which is in USD. In my money, that will spell 3.6 times and I simply can't afford it

BTW, there is 2 nos of connector pins (TP1 & TP2) protruded on the amp PCB. Not sure what the heck is that thing for (no schematic and somebody has dismantled it before being sent to me for repair).

Anybody please?.

djbon

[sakis]

will probably be some test pin where you put your multimeter in reference with ground so you may get some reading that will apply to idle setting .....

idle setting can be done in many other ways so its not really anything critical ....

all this will require scope signal generator and multimeter to make perfect ....

[djbon]

Have check all ground and seems to be okay.

But the is something I have discovered which might be the culprit (???).

There is another small transformer (KS960712a - HY) other than the main transformer, which I believe supplying low voltage to the PSU.

There are 3 different color of cable from the secondary winding:-

1) Red to Black ---> shorted
2) Black to Yellow ---> No shorting

Not so sure how the transformer is being built, hence cannot make any conslusion from this discovery.

Oh my.. what a headache....