JCM800 2204-bass control has no effect any more

Shwing · 09-24-2008, 03:52 PM

All of a sudden when I turn the bass knob is has no effect on the tone...the knob is attached firmly and it rotates freely
I bias all my amps, but have never encountered this before
what should I check for?
The amp has recently had a PTP board installed, along with the Lee Jackson Volume 2 mod as well as his Tube Buffered FX loop, it was all working fine, I had a nice bias at 39...then one day i noticed a significant loss of volume, this was traced back to a power tube moving around in it's socket...this has since been fixed
Thanks In Advance

Shwing · 09-25-2008, 03:43 PM

anyone?

Shwing · 10-02-2008, 06:40 PM

pretty please ?

bobbyramone · 10-13-2008, 03:34 PM

deoxit didn't work either, I also noticed the presence control has no effect on tone as well :-(

these are all new components, brand new ptp board ect...

here is a page on the build of my amp:
Ivabiggun/JCM 800 fx loop - Photobucket - Video and Image Hosting

here are the boards he makes:
eBay Store - HurlesSound Amplification: 100 watt boards

mmorse · 10-24-2008, 06:17 PM

I had a similar issue just happen with my 2204. I had a power tube go out and sometime after, I noticed my mid pot no longer functions. I checked it and it seems to be fried. I've got one ordered.

bobbyramone · 11-01-2008, 02:29 PM

finally! I nailed the problem down, a solder connection has broken
I took a bunch of pic's of the amp so you can check it out

link to pictures of the Marshall :
http://www.divshare.com/download/5722033-5a0

It is a 1986 Marshall JCM800 8104 50 watt chassis with the following mods
PTP board with Sozo's
Lee Jackson Marshall Mod Volume 2 Mod
Lee Jackson Marshall Tube Buffered Effects loop
25/50 watt Mod
BIAS points installed at the back with lockable adjuster

NOW I have a bigger problem
I guess one of the kids was playing with my multi meter, I didn't check and it was set to ACV750!
I leave it at DCV200m
I herd a pop and I might have seen a flash, not sure though

Now the amp constantly blows the Mains T3A fuse
Where should I start looking?
I'm ready for the bad news....sigh :-(

Thanks Again

09-24-2008, 03:52 PM	#1 (permalink)
Shwing Junior Member Join Date: Sep 2008 Posts: 3	JCM800 2204-bass control has no effect any more All of a sudden when I turn the bass knob is has no effect on the tone...the knob is attached firmly and it rotates freely I bias all my amps, but have never encountered this before what should I check for? The amp has recently had a PTP board installed, along with the Lee Jackson Volume 2 mod as well as his Tube Buffered FX loop, it was all working fine, I had a nice bias at 39...then one day i noticed a significant loss of volume, this was traced back to a power tube moving around in it's socket...this has since been fixed Thanks In Advance Last edited by Shwing; 09-25-2008 at 10:58 PM.

09-25-2008, 03:43 PM	#2 (permalink)
Shwing Junior Member Join Date: Sep 2008 Posts: 3	Re: JCM800 2204-bass control has no effect any more anyone? __________________

10-02-2008, 06:40 PM	#3 (permalink)
Shwing Junior Member Join Date: Sep 2008 Posts: 3	Re: JCM800 2204-bass control has no effect any more pretty please ? __________________

10-13-2008, 03:34 PM	#4 (permalink)
bobbyramone Junior Member Join Date: Jan 2008 Posts: 2	Re: JCM800 2204-bass control has no effect any more deoxit didn't work either, I also noticed the presence control has no effect on tone as well :-( these are all new components, brand new ptp board ect... here is a page on the build of my amp: Ivabiggun/JCM 800 fx loop - Photobucket - Video and Image Hosting here are the boards he makes: eBay Store - HurlesSound Amplification: 100 watt boards

10-24-2008, 06:17 PM	#5 (permalink)
mmorse Senior Member Join Date: Nov 2006 Posts: 122	Re: JCM800 2204-bass control has no effect any more I had a similar issue just happen with my 2204. I had a power tube go out and sometime after, I noticed my mid pot no longer functions. I checked it and it seems to be fried. I've got one ordered.

11-01-2008, 02:29 PM	#6 (permalink)
bobbyramone Junior Member Join Date: Jan 2008 Posts: 2	Re: JCM800 2204-bass control has no effect any more finally! I nailed the problem down, a solder connection has broken I took a bunch of pic's of the amp so you can check it out link to pictures of the Marshall : http://www.divshare.com/download/5722033-5a0 It is a 1986 Marshall JCM800 8104 50 watt chassis with the following mods PTP board with Sozo's Lee Jackson Marshall Mod Volume 2 Mod Lee Jackson Marshall Tube Buffered Effects loop 25/50 watt Mod BIAS points installed at the back with lockable adjuster NOW I have a bigger problem I guess one of the kids was playing with my multi meter, I didn't check and it was set to ACV750! I leave it at DCV200m I herd a pop and I might have seen a flash, not sure though Now the amp constantly blows the Mains T3A fuse Where should I start looking? I'm ready for the bad news....sigh :-( Thanks Again Last edited by bobbyramone; 11-01-2008 at 07:31 PM.

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