Just got this and started fixing it up. It was filthy so I cleaned it all. Took power transistors out so they would'nt get soaked by cleaning. Checked the Pt's and all were good. Found a ballast resistor with broken lead fixed that new three prong. DE ox all boards. Replaced 10k pot. Fired it up and popped the fuse. I did not fire it up before doing all this because of the shape the power cord was in. Kinda scratching my head now. Ant help will be apreciated. Thanks.
stevem Messages: 4733 Registered: June 2004 Location: NY
Senior Member
I can't see why you pulled out the 4 output Transistors just to spray things clean, but I bet that when you reinstall them that was the cause of your popping fuses issue, assuming that you put the slip on connectors back on right.
One easy test is to remove the slip on connectors and ohm test the red wire and the both the Emitter and Base lead to ground, you should not see any low resistance reading.
A low reading on the red wire means that the case of the Transistor is shorted to the chassis.
Are the leads to the bias tracking diode in the clip between the output Transistors?
The leads break easily and if that circuit goes open the amp will pop fuses also.
To save you power transformer from harm until you get this issue cleared I would only do test with a 1.5 amp fast blow fuse in the amp.
It was that filthy. This stuff needed some scrubbing. As far as I can see they look correct. The chassis is drilled to place them correctly isn't it. Thanks o will check again. Thanks
I have looked it over and searched on line for pictures that show the wiring. The pictures I have found it both ways yellow blue or blue yellow. It doesn't seem that the way the wires were trained fits this. I also had taken pictures after I had taken them out and wires at rest would show the blue yellow placement.
stevem Messages: 4733 Registered: June 2004 Location: NY
Senior Member
You said you worked on the dropping resistor ( ballast resistor) that feeds the pilot lamp, are you sure that's not shorting to something?
I would first do a ohm check to ground from the red wire and the green wire on the power supply filters, as a reading of less then 1000 ohms would indicate a short on that power supply rail, and then we need to dig deeper!
stevem Messages: 4733 Registered: June 2004 Location: NY
Senior Member
Now I see!
The resistor you speak of is not a balist resistor , it's a Emitter resistor and if the lead wire failed due to heat then you have At least one bad output transistor and maybe a bad driver transistor that feeds that output transistor also, and this is what's popping your fuse.
I had all of the transistors out and tested them they were all good. I will take them back out again and test them. I will take the power board out and start with the drivers. I think I will change out those resistors as well.
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I have a variac. Its probably going to slow down till I get all my parts. On another subject I have another K200 that I am working on. Someone did a botch job on a 3 prong install. Anyway went to fire this up this p.m. thru my variac. And nothing. I re did the 3 prong install. When I was writing it up there was a jumper between center prong on the top of switch to the bottom prong of the switch. I unsoldered it and went along. Fast forward. Hooked up every thing started to bring up voltage. No pilot light. Checked all again. Nothing. Then I thought that jumper was getting power thru that. Checked voltage. Sure enough that is it. I am guessing the switch is bad. That's all some people.
stevem Messages: 4733 Registered: June 2004 Location: NY
Senior Member
First off as long as the amp is unplugged from the wall outlet you do not have to drain out the filters as there's only 40 volts sitting on them and that amount will not harm you unless you put your tongue across the terminals!
Also driaining any power supply filter out by just shorting them to ground can damage them as they need to be drained out through a resistor slowly.
These amps are not easy to work on since most everything is on that one main board that hangs off of the face of the amp, so things have to taken apart enough to get that board out and well clear of the amp.
If your ok with digging into the amp that far then we can continue, if not thent take the amp to a repair tech, and preferably one that does audio repair and is good with SS amps and not just a half Assed tube amp guy!