Pwavey CS800X

[bsco]

Just going through this amp and found some parts gone....The 10A relay has continunity but will not pass AC....I only get 3V out of it.....Jumped it out...with the light blub limiter and I get approx 120...Found some transistors blown.....There are five gone in total...Dead shorts...on all three elements...I de-soldered all 20 of them in order to check them...the bad ones are all on the same side....Also checked the SBS14...good......Checked the SAC187.......It reads about 67ohms across the outer two leads.....this is on both sides of the amp...So I would say that this is ok??? I also checked all the emitter resistors...they all read .6 ohms but my meter leads measure .2 ohms so they all seem fine as well.... Also, the amp is filthy.....It needs a very good cleaning and probably some fresh thermal grease on ALL the transistors......and maybe even some new mica washers...while I have it apart I will check any electrolytics for excessive esr as well....if there is anything else I should be checking, fire away....
Cheers......
P.S. Sorry about the typo in the header....I can't get back in to fix it....

[Enzo]

Um, relay won't pass AC? The only relay I see is in the speaker lead, not the mains wiring. What do you mean you "get 120v"? Do you have 120vAC right at the transformer primary or not? Blue and black wires. There is a large triac that turns the amp off and on, that may have failed. Usually they fail shorted, which doesn't hurt anything, but you cannot then turn the amp off with the powr switch. If it fails open, you can't turn it on. There are three terminals on that triac, the small one is the gate, the larger ones are the main terminals. SHort the two main terminals together and the amp is in the on condition.

The two leads in question on the SAC187 are pins 2 and 3, not 1 and 3. The thing to do is measure the output bus to ground on the inboard side of the speaker relay. It is shorted to ground or not. The amp will run without the SAC187 during test, replace shorted ones after repair is complete. In the last 29 years I still have never seen a bad SBS14

May I assume the problem you are fixing is the amp blows the main breaker. Wait, do you mean the 10A circuit breaker when you say relay?

I'll be surprised if the caps are tired.

If you have blown outputs, they need replacing, but each row of four outputs also has a driver and a predriver on that output board. Check those. So also check the 22 ohm emitter resistors of those. And when outputs blow do not overlook that little 330 ohm resistor base to base on the drivers.

[bsco]

Sorry Enzo....I was referring to the 10A circuit breaker......I did find 5 transistors shorted...the 22 ohm resistors checked fine...I will check the 330 ohm resistors like you suggest....The caps I was referring to are the ones on the preamp boards....they all tested fine....I did notice on the pre-amp boards that there is a resistor labeled R113 on the pictorial of the board layout...a 22k 1/4W which has been scorched on both preamp boards......which I will have to replace....I am going to pull the SAC187's and test them off board....Sorry for the confusion......
Cheers

[Enzo]

If R113 on the driver board is burnt, then it is a good bet that Q101 it connects to is bad.

[bsco]

If R113 on the driver board is burnt, then it is a good bet that Q101 it connects to is bad.

I just checked that out downstairs....the resistor measures the correct resistance but has a scorch mark in the center....I'll pullQ101 and check.....
Cheers,
Bernie
I have to ask....there was a LOT of old flux residue on the board especially on the power transistor CBE connections....really bad....and where this unit had so much dust and dirt in it, is it possible that this created leakage paths on some of the transistors causing them to short...all the other parts that you suggested I check test ok......I cleaned off ALL this old flux resude from the board and when I re-install parts I will be cleaning all the new flux away again....just to be sure.....Thanks for your help.....
Cheers

[Enzo]

I don't worry about flux.