| Re: Troubleshooting a 250 model 1 Bass amp [message #27397 is a reply to message #27393] |
Wed, 26 June 2019 13:29   |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Yes, welcome to the place.
With 43 mV dc on the output there is probably nothing major wrong with the power amp. Please try and refrain from changing parts to try to find a fix to the problem. It will only waste time money and may cause additional problems that will confuse the actual repair.
Good thinking on trying to send the output of the preamp to another amp. Now try and send a signal into the power amp and see what you get. There is a jack on the back of the chassis that connects to the input of the power amp through a 560 ohm resistor. Plug your drum machine in there nad see if the sound from the speaker is loud and strong.
If you look at the schematic for this amp, you should note that both of the preamp signals route through the first channel board, PC5066. So if both channels are dead or weak, I would start by checking that board first.
There is an IC chip at the output of the board IC1 that could be the problem. Try this, keeping all connector in place, read the dc voltage on the orange wire that connects the output of the preamp board with the input of the power amp (pin 3 of the power amp connector). There should not be any voltage there or at least just a few millivolts.
Good luck.
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