K 300 [message #18950] |
Sun, 07 July 2013 21:07 |
mrg2u
Messages: 34 Registered: July 2013
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I have a Kustom 300 P.A. head and I can not get any sound out of it. everything inside looks good, caps are not swollen, nothing seems burnt,. i can not find any thing listed as 300. Is this similar to other models and can I use a different schematic to check it out. The main problem is the power switch. the wiring on this i white, white w/a black stripe and red. i can not find any such colors on any of the schematics I have found. It did work until the switch went bad. Thanks in advance for any help.
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Re: K 300 [message #18954 is a reply to message #18950] |
Mon, 08 July 2013 11:57 |
chicagobill
Messages: 2006 Registered: April 2003
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I believe that the red wire you are talking about is for the pilot lamp inside the switch. The white and white with black stripe are the ac power wires.
If you look at the polarity switch there will probably be a green wire added there for its' pilot lamp.
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Re: K 300 [message #18957 is a reply to message #18956] |
Mon, 08 July 2013 15:17 |
chicagobill
Messages: 2006 Registered: April 2003
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Senior Member |
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mrg2u wrote on Mon, 08 July 2013 13:30A distinct pop when this should be powered up but no sound.
Do either of the pilot lamps in the two front switches light up? If you are hearing the amp power up, then the lights should light up unless both lamps are burned out.
If you have electronics experience, try using a voltmeter to read the power supply voltages at the filter caps and see if you have plus and minus 40 volts.
If the voltages are there, then try and send a signal directly into the power amps to see if they are working.
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Re: K 300 [message #18962 is a reply to message #18950] |
Mon, 08 July 2013 16:48 |
chicagobill
Messages: 2006 Registered: April 2003
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Senior Member |
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The power amp board should be marked PC5029. The input hot is an orange wire that comes from the mixer-reverb board. Black is ground, Blue wire is speaker output and the pink wire is the tape/monitor output.
Do not unhook the black ground wire during testing. I can't remember if the input of the power amp is capacitor coupled or not, so be careful with whatever you use to inject a signal into the power amp.
When you were testing power supplies, did you test the plus and minus 12 volts preamp supplies as well?
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Re: K 300 [message #18964 is a reply to message #18950] |
Mon, 08 July 2013 17:41 |
chicagobill
Messages: 2006 Registered: April 2003
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Senior Member |
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Did you test the 12 volt supplies?
Put everything back to normal and turn up the master reverb control. Shake the reverb tank, does it make any sound through the speakers?
Keep working forward through the circuits to find out where the signal stops.
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Re: K 300 [message #18969 is a reply to message #18950] |
Mon, 08 July 2013 22:05 |
chicagobill
Messages: 2006 Registered: April 2003
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Senior Member |
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Why are you trying to bypass the reverb tank? Try pulling the RCA plug from the tank output and then with the amp on and the reverb turned up touch the tip contact. If the circuit is working you should hear a buzz, just like when you touch the tip of a guitar cord plugged into the front of the amp.
If there is no buzz or no reverb, then there is no output from the mixer board. Again check the low voltage power supplies and check the output chips on the mixer board.
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Re: K 300 [message #18974 is a reply to message #18950] |
Tue, 09 July 2013 12:15 |
chicagobill
Messages: 2006 Registered: April 2003
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Senior Member |
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Please explain in more detail, as I don't understand what you are saying about the missing power.
Did you get correct dc voltages at the two main filter caps of plus and minus 40 volts dc?
Do you have the correct low dc voltages for the preamps of plus and minus 12 volts dc?
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Re: K 300 [message #18977 is a reply to message #18950] |
Wed, 10 July 2013 13:11 |
chicagobill
Messages: 2006 Registered: April 2003
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Senior Member |
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I'm glad that you found some sort of problem. Hopefully that will fix it right up.
If the amp is original, the only bridge rectifier that I know of in the amp is mounted directly to the chassis. It connects directly to two of the wires from the power transformer. Is this what you are talking about?
It is made up of 4 diodes not resistors, so be sure that you get the right parts as replacements.
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Re: K 300 [message #19416 is a reply to message #18950] |
Thu, 26 September 2013 12:09 |
chicagobill
Messages: 2006 Registered: April 2003
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Senior Member |
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It sounds like the power amp and the mixer boards are working to some degree. Have you tried all of the individual pre-amp channels? Are they all low in volume?
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