I believe my K200 A5 PA may be overheating [message #18831] |
Sun, 09 June 2013 15:10 |
janalex
Messages: 11 Registered: May 2013
|
Junior Member |
|
|
Hi,
Just got a Kustom A5 K200 PA it sounded great for the first 2 hours of rehearsal through twin Kustom PA towers however after a little over 2 hours of moderate volume use (5-6), it started to sound raspy and quiet through all channels. I shut it down. I waited an hour and turned it back on and it worked fine for a quick test. Today I will try to keep it on idle for a few hours and see what happens. Is this a common issue with Kustoms? Any ideas what may need replacing? Cap job?
Thanks
|
|
|
|
|
|
Re: I believe my K200 A5 PA may be overheating [message #18835 is a reply to message #18831] |
Mon, 10 June 2013 07:11 |
stevem
Messages: 4772 Registered: June 2004 Location: NY
|
Senior Member |
|
|
Vintage Kustom amps like yours where built with a thermal circuit breaker mounted next to the bias diode that Pleat spoke of.This breaker ( hooked up to the two black and white striped wires) is made to go open at 185 degress F and save the amp from truly burning up its output section, but if your diode is out of its clip, or one of its two leads have broken off, problems like you are having will take place.
Make sure this round black breaker that is held down with two machine screws is still in your amp, as I have worked on many that the breaker has gone bad, and someone just jumped it out!Let us know how you make out.
[Updated on: Mon, 10 June 2013 07:18] Report message to a moderator
|
|
|
|
|
Re: I believe my K200 A5 PA may be overheating [message #18840 is a reply to message #18831] |
Mon, 10 June 2013 12:12 |
chicagobill
Messages: 2005 Registered: April 2003
|
Senior Member |
|
|
I will add a few things here.
The bias diode that Pleat mentioned is designed to lower the bias to the output stage as it heats up. If it isn't thermally connected to the output transistors (it comes loose from the clip) the amp can start to overheat. When this happens, the power amp can start to distort and act as you have described.
If the output transistors get hot enough (185 degrees) the thermoswitch will shut off power to the entire amp until it cools off. When the thermoswitch opens, nothing will light up and there will be no sound from the amp. The thermoswitch will reset itself once the amp has cooled down.
When checking the thermoswitch, be sure to unplug the amp, as it is connected directly to the ac line.
Be careful when handling the bias diode, as the leads after all these years are somewhat fragile. If the one of the leads should break, there will be no bias voltage and the power amp will blow up.
[Updated on: Mon, 10 June 2013 12:20] Report message to a moderator
|
|
|
|
Re: I believe my K200 A5 PA may be overheating [message #18905 is a reply to message #18831] |
Mon, 24 June 2013 07:17 |
stevem
Messages: 4772 Registered: June 2004 Location: NY
|
Senior Member |
|
|
Unfortunaly the fact that the amp was still outputting sound means that the thermal breaker was closed and that the power output stage atleast was not overheating, how hot was the chassis of the amp when it failed, over 150 degrees?.
That being said it would seem that the amp has a thermal problem somewhere.
One easy frist thing to check is that the screws on the rear of the amp that bolt down the pre-driver/driver board are all tight, as one or two of those screw (6/32") make the boards ground connection.
You may also first want to dismount that board and check for bad solder connections.
One thing is for sure, and that fact is since all the channels are acting up it will not be a problem with eitheir of the 4 channel preamp boards, your problem is on the reverb board, or the driver board, or maybe something weird with the output stage.
One thing you cab do before the next rehersal would be to get a can of cool down spray from radio shack, then take the amp out of its case and cover it and do the reshersal, when the amp acts up, take the freeze spray and spray it across these two boards slowly, when the amp clears up your on the right board.
It would also pay to have a hair dryer handy set on low to get the problem to reapear.
In this way you will atleast pin down what section of the amp the problem lies in. You can than report back to us and maybe we can help you rectifie the issue.
Good luck to you.
[Updated on: Mon, 24 June 2013 07:20] Report message to a moderator
|
|
|
|
|