K200 B1 crackling sound [message #12833] |
Tue, 02 February 2010 01:51 |
real_to_reel
Messages: 11 Registered: September 2007 Location: Los Angeles
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Junior Member |
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The problem started in the 70's and, repair shop never could fix. The amp is possessed with crackling sound that starts when powered up. Polarity and tone/volume controls do not affect it. I would like to fix this as I am playing again. If anyone has a schematic for the B200 it would be greatly appreciated as I'm quite sure I'll be asking many questions and need to refer to it.
The best description is that it sounds like a bad guitar cord that makes a crackling sound when moved while attached to a guitar and amp. The B200 crackles for a minute - stops - starts again for 2 minutes - stops for 5 minutes - starts again. Nothing is plugged into the head.
The only other known issues are: bulb missing - needs to be replaced, the original AC cord should be upgraded and, I noticed a spark as I plugged the speaker cable into the head.
Thanks in advance for any suggestions to solve this.
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Re: K200 B1 crackling sound [message #12834 is a reply to message #12833] |
Tue, 02 February 2010 06:26 |
stevem
Messages: 4772 Registered: June 2004 Location: NY
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Senior Member |
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Hi.
The first thing to do is to look at the top of the two big mian filter cans that are clamped to the floor of the amp.
on each can you will see a little round area that when all is well will look like a dimple.
If it looks puffed up like a pimple than these are the first two items on the list to get replaced before any more testing can take place, and in fact there is a chance that bad filters could be adding to the problem.
If all looks well, continue on with what I have posted below.
Your amp is made up of five main sections.
Main power supply
preamp power supply regulator
preamp channel #1
preamp channel #2
driver/output stage.
We can go about using two different ways of at least removing the preamp channels from the problem list.
One way will involve unsoldering two wires, the other way will invole clipping two wires and butt splicing them back together.
Option #2 will not require you to dismount eitheir preamp board( left channel or right) off of the inside face of the amp.
Each preamp board has a three wires goind to it.
red
green
blue
The blue wire is the signal output which carrys the signal to the driver/output board mounted on the rear wall of the amp.
By clipping each blue wire somewhere along its lenght where it will be easy to incert a butt splice to get it hooked back up we can check to see if the noise stops.
If after clipping each blue wire you still fine you have the noise then each preamp board can be concidered ok.
Another easy test to make if you have a volt meterwould be to test the regulated 8 volt supply that feeds each preamp board.
This voltage is feed to each preamp thru the green and red wires.
The red wire carrys a +8 volts DC, and the green carrys a -8 volts DC, so these must be tested across each wire to ground not by placing the meter across the red and green wire.
These test should show a voltage of around 8 volts. It could be a spec higher or lower but it should be stable with the meters reading changing only down in the .001 descimal point area.
any big jump in the reading( a higher voltage) in time with the noise would mean a problem in the regulator circuit on the rear mounted circuit board.
Try these test and post your findings and we will continue with the search for the root of the problem if these things have not narrowed it down.
[Updated on: Tue, 02 February 2010 06:32] Report message to a moderator
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Re: K200 B1 crackling sound [message #12842 is a reply to message #12833] |
Tue, 02 February 2010 12:19 |
chicagobill
Messages: 2006 Registered: April 2003
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Senior Member |
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Welcome to the place.
It sounds like a power supply or power amp problem. As Steve mentioned, there are many places that the problem could be located.
I'm not familiar with the B200 model, maybe you have a K200B? If that is the case, you will need to tell us which model K200B that you have so we can help you get a schematic.
Again Welcome.
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