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| |-+  JCM 800 2203, 2204, 2550, 2555
| | |-+  Problem with 2203 JCm		 « previous next »
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Author Topic: Problem with 2203 JCm  (Read 33009 times)
kevilay
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« Reply #15 on: January 13, 2010, 01:43:49 AM »
Yeah I did all that. I noticed when I measure from Pin3 to ground I dont get any voltage on the power tubes. Their directly connected to the OT plates, shouldn't i be reading some voltage?

Kevin
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cmoore
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« Reply #16 on: January 13, 2010, 02:33:39 AM »
Is your HT fuse good?  Otherwise you need to just backtrack from the screens ( Pin 4 ) and their resistors, across the choke, filter caps, rectifier, stand by switch, to the transformer.  It seems like you do not have any B+ supply, it must disappear somewhere.  Do your screens have DC voltage (Pin 4 to ground) ?
Is this EL34 or 6550 power tubes ?
Do you have a light bulb current limiter?
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kevilay
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« Reply #17 on: January 13, 2010, 02:50:21 AM »
Quote from: hired hand on January 13, 2010, 02:33:39 AM
Is your HT fuse good?  Otherwise you need to just backtrack from the screens ( Pin 4 ) and their resistors, across the choke, filter caps, rectifier, stand by switch, to the transformer.  It seems like you do not have any B+ supply, it must disappear somewhere.  Do your screens have DC voltage (Pin 4 to ground) ?
Is this EL34 or 6550 power tubes ?
Do you have a light bulb current limiter?

I have -42 volts at pin 4 with respect to ground. I have the EL34 tubes. At point E on the schematic Im reading voltage and it seems I am everywhere across the board. I checked my fuses with an ohm meter their both reading 0 ohms.

I have 0 voltage at K on the schematic and at both plate voltages. It seems my output transformer isnt putting out any power.

Kevin
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cmoore
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« Reply #18 on: January 13, 2010, 03:17:40 AM »
I am not sure what point K is, I assume it is right after the fuse where the choke and the OT meet.  If you turn the standby switch off (open) what do you read at the two HT wires?  They will be/should be high voltage AC, before it hits the solid state rectifier.
I am always a little confused by Zero ohms. Is that the same as continuity, is that what a new fuse would measure with your meter?  Just wanting to make sure your fuse is OK
« Last Edit: January 13, 2010, 03:33:06 AM by hired hand » Logged
kevilay
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« Reply #19 on: January 13, 2010, 03:27:17 AM »
well its not really 0 ohms that wouldnt be possible, its a very low resistance meaning its good. If it was broken it would read infinite resistance.

Kevin
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kevilay
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« Reply #20 on: January 13, 2010, 03:28:13 AM »
whats the HT point?

Kevin
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cmoore
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« Reply #21 on: January 13, 2010, 03:45:46 AM »
The two wires from the PT to the SB switch. That will tell you if the high voltage AC from the transformer is conducting. If that is OK, you can follow it across the SB switch to the rectifier diodes.  It is possible you have a bad SB switch. I just replaced a bad one that was grounding the B+.... so you never know.
Do you have your diodes oriented the right way?
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kevilay
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« Reply #22 on: January 13, 2010, 04:24:49 AM »
The diodes came assembled on the board and are facing the right way. It sends 242 volts through each of the transformer wires going through the SB switch and the switch works correctly.

Kevin
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kevilay
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« Reply #23 on: January 13, 2010, 04:30:54 AM »
I just noticed my 1A fuse is blown, I just replaced it with a new one cause my dad dropped it and it broke. I never though to check a fuse right from the store but maybe thats the problem. I followed to voltage and it stopped there. I doubt thats the problem cause i think it was good at one point. Im gonna stop at the store tomorro and buy a few fuses.

Kevin
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cmoore
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« Reply #24 on: January 13, 2010, 04:53:40 AM »
I am sure the fuse was good. I am starting to think you have a short somewhere in your B+ wiring.  Maybe in the rectifier diodes or maybe in the filter caps.
A light bulb limiter would help, saves on fuses, and is pretty easy/cheap to build.
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kevilay
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« Reply #25 on: January 13, 2010, 05:01:46 AM »
what is a light bulb limiter?

Kevin
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cmoore
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« Reply #26 on: January 13, 2010, 05:21:35 AM »
Basically you put a light bulb in series with the hot lead of a cord that attach's to another outlet. Plug your amp into that outlet so your wall supply is in series with the light bulb. If your amp has a short, the bulb will be bright, if the amp is good the bulb will be dim. I can send you a picture of mine along with a schematic link.
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kevilay
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« Reply #27 on: January 13, 2010, 03:14:38 PM »
that would be cool

Kevin
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kevilay
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« Reply #28 on: January 13, 2010, 08:26:53 PM »
Now its playing this loud squeel through the amp when you shut off standby and the volumes are all turned to 0

Kevin
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cmoore
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« Reply #29 on: January 13, 2010, 09:37:51 PM »
Try switching your OT leads.  I assume yours are Brown and Blue.  Those feed one set of power tubes to the OT.  Just swap them, Blue to where Brown is,  and Brown to where Blue is.
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