pa amplifer blows internal fuse!!! Help

[joka22]

my pa amplifier keeps blowing internal fuse on one channel this started hapening when i turned up the volume and blow up the speaker.
Now when I change the fuse and connect the input signal cable i can hear the large transformer making a funny sound like it bubbling and then it blows its internal fuse. This happens with the left channel only.

[Zero Cool]

sure sounds like shorted output transistors!

[joka22]

so do i just replace the toshiba 2n3773 transistors

here is an image of the circuit board and transistors. Their are more transistors but they are on the outside heatsink located on the ampilfier. http://img142.imageshack.us/my.php?image=toshibahy4.jpg

[Andy L. Francis]

My suggestion is to search a qualified repairer.
Do not try to repair an amp with zero knowledge, unless you want to cause more damage.

[joka22]

repair cost is too much the electricians over here tend lie about the extent of the damage and try to cash up so i thinking shall i just salvage the case power transformer and torriod and make gainclone.

[wg_ski]

Originally posted by joka22
so do i just replace the toshiba 2n3773 transistors

Yeah, with Motorloa/On 2n3773's. Those look like fakes. Real ones would have tolerated the overload when you blew the speakers. And of course check other collateral damage (drivers, bias stack, etc).

Any "real" Toshiba 2N3773's would have been made before 1985, with the OLD Toshiba logo on them and a very thick copper heat spreader. And more often, they were labeled "2SD873".

[joka22]

i have looked at the pcb cosmetically everything is normal no burnt reisistors no blown capacitors. I have used a multimeter and checked the reading on each resistors and checked thier color bands and matched it on the online reistors calculater. The transistors have got a number just below the model number of the chip which is: *9210 then says japan.

[wg_ski]

Just make sure no other transistors are open or shorted. They may *look* fine but be dead.

Those trannies have the new Toshiba logo on them - one that they started using about the time they quit making their plastic PNPs in the green case. A lot of the older TO-3 products were discontinued around the same time frame - like the 2SD424, and the JEDEC clones. Any original NOS from back then would have had the old logo.

[nigelwright7557]

Originally posted by Zero Cool
sure sounds like shorted output transistors!

Dont forget to check your speaker and leads for shorts before trying out your fixed amp !

I stripped down an amp to find a unreliable connection only to find in the end it was the speaker lead !

[joka22]

you know what i cant be asked repairing this amp now i got an excuse to strip it and use one of the two transformer for making gainclone since it got so much reviews on it. The large square transformer has these wires green, yellow, orange and purple which are shoreted and black and red these go out to the speaker outlet 100 volt line i think.

The toroid transformer has 5 pairs of wires which are: white/black, purple/green, grey/blue, red/yellow and orange/brown wires is wired to the power switch i think. what i want to know which wire is which for example v+ v- centre tap (i think it blue) or square vs toroid transformer.

i got mulitmeter to measure voltages but i cnt seem to find any info on which wire is postive or neg i know transformer is ac but how would i wire the transformer to let says gainclone modules.