Help needed Yamaha YST-SW800 faults

[samurai_x47]

Ok, and just touch the coil on both it's underside pins? with the red probe I guess? Same as the resistor on just a pin?

 

[Nigel Goodwin]

Ok, and just touch the coil on both it's underside pins? with the red probe I guess? Same as the resistor on just a pin?

You don't need to go underneath, the pin of the inductor (and the resistor as well) is clearly accessible on the top.

 

[samurai_x47]

All done, no voltage reading at all, I set the meter to 200v just incase, then worked my way down to 200m and it read only 0.00 as you can see.

Have I been very lucky and only caps and a few transistors have blown?

 

[Nigel Goodwin]

I presume it's plugged in the mains and turned ON while you're doing these tests?, and that the black wire is making a good contact?

Make sure things are running, check the HT rails - be aware they are +/-110V - just in front of the row of transistors on the heatsink, there are three big wire jumpers labelled JY1, JY2, and JY3 - check the voltages on JY1 and JY2 - JY1 should be -110V and JY2 +110V, keep your meter on the 200V range.

 

[samurai_x47]

Ok

 

[samurai_x47]

And yes, all powered up.

 

[Nigel Goodwin]

Ok

So you've got + and - 110V (or so) on those two jumpers?.

 

[samurai_x47]

I found 1, safe to say it's shot! Just finding the others ...

 

[samurai_x47]

I can see the other 3 you mean, look ok, just going to test them, but that other one is burnt out....

 

[samurai_x47]

Safe to test while that one is blown?

 

[samurai_x47]

I got the other board from my other amp back plate and it's a J53

 

[Nigel Goodwin]

If it's any help, here's the layout of the PCB. JY1 and JY2 are at the top, just below Q18. If the link J52 has blown, then something nasty has happened, as pieces of wire don't often blow.

 

[samurai_x47]

Ok, cool. It's safe to test them still with power on? Wish I had the device to just run a much lower load through it.

 

[samurai_x47]

Just going to test them...

 

[samurai_x47]

0 volts on all 3

 

[Nigel Goodwin]

You've got no power to the board then.

 

[samurai_x47]

Ah damn...

 

[samurai_x47]

So, ESR meter then cap testing, transistor testing?

 

[samurai_x47]

Just bought, Pro soldering station (mine was cheap) ESR meter, Fluke multimeter, determined to fix it think once they arrive I'll take out all the caps, transistors, diodes and resistors... But start on the power board first.

 

[Nigel Goodwin]

So, ESR meter then cap testing, transistor testing?

As you've got no power you need to move back to the power supply, and find out why.

You don't repair things by randomly removing components and testing them, that way lies disaster.