As most of the folks here know, I love the high brow K-200's, and having fixed all of mine, I'll tell you where to look first.
If I understand it correctly, your amp powers on, but you have no power? If so, then first check the large cap on the small driver board that is located on the back panel. It is cap number C203 on the schematic that Steve will send you. It is a 500mf electrolytic cap. Depending upon how old your amp is, it probably is a black plastic cylinder, about 1/2 inch in diameter and 2 inches long. If this cap opens up or drifts too low in value, it will cutoff the driver transistor and your amp will lose power or not make any sound at all. To replace it correctly you will need to un-mount the board by removing the two attached power transistors. If this is too much for your skill level, either refer service to a qualified pro, or just clip the leads off the cap and solder the new one to the old leads above the board. Not too pretty but it will get the job done. I prefer undoing the transistors, as this allows me to clean and re-grease them. Remember that this cap is polarized and must be installed in the right direction, or it may blow up (literally!).
As long as you are at it, you'll find another one of these same caps on the reverb board on the left side of your amp as well. It too should be replaced, as it has also probably drifted out of spec as well.
carlc Messages: 143 Registered: July 2006 Location: Summerville, SC
Senior Member
Bill,
Thanks for the advice. You are correct, powers on, but at full volume I'm not getting much. Yeah, this thing is about 40 years old (since I bought it new it makes me REALLY old) so I know many of the components need replacing. Cleaning and re-greasing the power transitors is a definite. I'll also check the reverb. I liked seeing Steve idea about boxing the springs in with cardboard. Sure would like to see a picture of it.
I was a navigation electronics technician for 24 years in the Navy so repairs are not a problem. I've been away for quite a while and the theory stuff has faded some.
Carl:
You should go ahead and re-mount all of the output devices while you're in there. Removing the back perforated panel will probably take the most time.
When you get into it, you'll find that the Frankenstein heads have a ground loop problem in the reverb tank circuit, that causes a hum. If your tank is original, both RCA jacks are grounded to the metal tank. Both of the cables also have grounded shields causing a ground loop. If you unhook the ground on the drive cable you should find that the hum will drop quite a bit. I believe that the factory tried to fix this by attaching the short ground wire that connects the metal reverb tank with the amp chassis, which actually made the problem worse.
Also, with the way that the tank is mounted inside the top of the case, I don't know if the cardboard encasement will work.
carlc Messages: 143 Registered: July 2006 Location: Summerville, SC
Senior Member
Steve,
The fax number I gave you is my wife's office. She said she got it yesterday. She also said it was really small and today is going to try to blow it up and see if it's readable.
Carl:
Don't ya just hate it when life gets in the way of one's hobbies!
There could be a few different reasons for the wrong color on your id tag. But, if you've owned it since it was new and it has never been out of your hands, then a factory error is probably the explanation. It's not difficult to switch cases and if your dealer needed a red head to go with red cab, then he may have made the switch.
I remember reading a few posts here, about Bud Ross telling stories about the old days when factory repairs may have really been exchanges. Or at least that's what I remember.
carlc Messages: 143 Registered: July 2006 Location: Summerville, SC
Senior Member
Hi again guys.
Well, I made some repairs. Looked at C203 (500ufd) and the other just like it. They were right on spec. What was way out were the 2 4500 ufd capacitors (C2 and C3) on the driver regulator board. They both read about half value, so I replaced them. The hardest part was figuring out how to use the old clamps with the new, smaller caps.
Everything else appears OK. I now have a lot more volume and the background hum is even reduced greatly.
Carl:
Congrats on getting it up and running again. There is still a lot of life left in these old amps.
A question for you... I don't own a Frank-PA, and I know this has been asked before, but I can't remember if it was ever answered: Are the 0.005 "HIGH" input caps removed from the PA heads? I know that the front panels are not marked high and low, and I would assume that they are not installed on a PA, but maybe you could let me know for sure.
stevem Messages: 4733 Registered: June 2004 Location: NY
Senior Member
You know what bill, have a the PA head and I can not recall, so as I sit hear I am looking at the schematic for all the frank heads which are on one sheet as kustom provided it, and yes the caps are common to all versions due to that input board being used on all versions.