Help me to save the Crest FA1201

[xiaof_99]

Dear all,
My friend took a output stage fired crest fa1201 to me and want me to help him make it alive.

I moved all the output 2sa1302/2sc3281 and changed all the parts that burned. When i power the amp without the output stage again, the output line see the voltage -80V . It seems that the drive tr 2sa1006bq is saturated or short. But it is not short when i test it when power off.

The amp use old IC as STK3152III and LA2500. I have no idea to test them and how to judge they are OK or bad IC.

I need your help!

Service manual or test solution is very appreciated.

More information about the schemaitc,please refer to the attachemt.

 

[ifrythings]

This is very common with these stupid chips, they like to latch to rails or stop outputing on one channel. I just fixed a JVC amp that uses that exact IC, there only $12 from Main Electronics (search for STK3152 on there page).

I would just change it, it's almost always IC that dies.

Check between pins 5,6,7and 9 for shorts, Here's thedatasheet for it.

 

[Burnedfingers]

Change the LA2500 also. Its a bias IC. Change the STK3152 also because its only $12 and it could fail if it hasn't already.

 

[gmphadte]

If the resistor that biases the STKs input circuitry (about100 ohms)becomes open, this will happen. The best way to check whether the STK is working is to check the input pin voltsge. If both show nearly same voltage, then the IC is good.

Gajanan Phadte

 

[xiaof_99]

Thank you very much!
I have got the STK3152III IC but LA2500 is difficult to buy.
So i want to change the it with normal multi_Vbe circuit. Is it possible? Could masters suggest some good circuit? Thank you in advance!