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Hi all
Got a right pig here. Customer said he turned on the amp after a short break of using it. No Sound. His friend who is probably a Plumber, who also fancies himself
as a amp tech.
said he will have a look. Changed all the tubes still no sound. He dicked about with it for a bit. then handed it back.
This was all done 1 week ago and some details have been wiped from my brain
When i got it . i was told very low sound. I used the sig gen and up full you could only just hear it.I did notice a cable not connected. i think it was CON 04
I used the scope and started to trace the signal. It was not making sense. Nothing at PI tube and seemed to be one channel working
Found the signal at C23 from V2 was correct and after that was reduced and distorted.
I started to think about that connector and i checked the others to find they didnt match up with the schematic i had . I think it was 2 or 3 connectors in the wrong place.
Then i got both channels up and this time i could hear it . still quite. Then started to trace the signal. Found then that R1 had gone open on V3. Changed it.
Turned it on working perfectly. So i thought. I found then at any sort of volume it would make some awful sound like a machine gun with distortion and mains tx was making a stressed out sound.. Checked the tubes biased at 25ma
changed them still the same. Soldering checked. I thought I'll better remove the main board and check underneath. All looks ok. Some repairs to bias board before.
At this point i put it down as i was busy. Sorry to be abit sketchy on the details and the lack of voltages. want to get the schematic before i start and the label on the end of the chassis say JCM2-20-16 think made in 2008
So what im looking for is the correct schematic for this model. Can anyone help
I just want to be sure that the leads are all connected up correctly
BBB
Got a right pig here. Customer said he turned on the amp after a short break of using it. No Sound. His friend who is probably a Plumber, who also fancies himself
as a amp tech.
said he will have a look. Changed all the tubes still no sound. He dicked about with it for a bit. then handed it back.This was all done 1 week ago and some details have been wiped from my brain
When i got it . i was told very low sound. I used the sig gen and up full you could only just hear it.I did notice a cable not connected. i think it was CON 04
I used the scope and started to trace the signal. It was not making sense. Nothing at PI tube and seemed to be one channel working
Found the signal at C23 from V2 was correct and after that was reduced and distorted.
I started to think about that connector and i checked the others to find they didnt match up with the schematic i had . I think it was 2 or 3 connectors in the wrong place.
Then i got both channels up and this time i could hear it . still quite. Then started to trace the signal. Found then that R1 had gone open on V3. Changed it.
Turned it on working perfectly. So i thought. I found then at any sort of volume it would make some awful sound like a machine gun with distortion and mains tx was making a stressed out sound.. Checked the tubes biased at 25ma
changed them still the same. Soldering checked. I thought I'll better remove the main board and check underneath. All looks ok. Some repairs to bias board before.
At this point i put it down as i was busy. Sorry to be abit sketchy on the details and the lack of voltages. want to get the schematic before i start and the label on the end of the chassis say JCM2-20-16 think made in 2008
So what im looking for is the correct schematic for this model. Can anyone help
I just want to be sure that the leads are all connected up correctly
BBB
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