New to me JCM900 MKIII issues

[Deftone]

Just picked up a JCM900 MKIII and It's got issues. Mostly just loud static and popping noises when I turn the MV. I can faintly hear guitar coming through at times. Same on both channels.

Seller said it's been sitting in storage since Covid.

I can take it to a tech but any suggestions first?

 

[Beryllium-9]

Did you try other tubes? Spray the sockets?

 

[Deftone]

Did you try other tubes? Spray the sockets?

I'm on it. Thank you.

I just tried putting a patch in the loop as @Tatzmann suggested and it worked wonders. Still scratchy and popping but much less and I'm getting guitar sound out of it. Needs to go to 3 on the MV to be about as loud as 1 on my SL-X (both are 50w and both are switched to "high")

 

[Tatzmann]

Its normal on the mkiii that the volume comes up at about 3 to 4 on the masterscale, same with the 900DR cleanchannel-master.

 

[Dogs of Doom]

I'd also just do a visual inspection on the boards, just to see if anything obvious stands out, like bulging cap's, or something looks fried. Any soot or burnt spots...

 

[Deftone]

I just plugged my board into the loop, everything is working great now. Just need to be used I guess. It sounds killer. It's brighter than my SL-X, on par with my '90 2204...in fact I A/B'ed the MKIII and the '90 2204...they are close. I'd pick the 2204 but after fresh tubes and bias, that could change.

Definitely going to pull the chassis out and spray everything with DeOxit, check for bulging caps and burnt spots, as advised. Thank you all for the suggestions.

The chassis is pretty dusty....what's best way to clean off the grime?

 

[Tatzmann]

Just tongue it down, oh wait, your tongue is still sore from todays meat-up, isn't it?

Little hoover and brush should do i'd say, mine had quite a bit of dry dust too, but the inside was like someone had licked it clean.

 

[fitz]

The chassis is pretty dusty....what's best way to clean off the grime?

 

[Central Scrutinizer]

The chassis is pretty dusty....what's best way to clean off the grime?

I get the WalMart microfiber towels in the Automotive Dept.

They work great!

Also use them for dog hair in my trucks. Works wonders.

 

[Leonard Neemoil]

The chassis is pretty dusty....what's best way to clean off the grime?

View attachment 147183

Sandblaster?

 

[shredless]

Deoxit should cure tha mv issue...lm surprised it wasnt mentioned till you said it

 

[Leonard Neemoil]

Deoxit should cure tha mv issue...lm surprised it wasnt mentioned till you said it

Nope... real men use sandblasters...especially for the tubes.

 

[Beryllium-9]

Tie it to the roof of your station wagon and drive through the car wash! I think that is a self biasing circuit..

 

[Central Scrutinizer]

I’d try to get at least one crop out of it, before you get rid of all that topsoil.

 

[Dblgun]

Tie it to the roof of your station wagon and drive through the car wash! I think that is a self biasing circuit..

Then you can use that wiper blade to squeegee it off!

 

[Deftone]

Ok, everything has been douched with DeOxit. One 12AX7 was slightly discolored at the top so I swapped it out. Put it all back together and plugged it back in and zero issues now. Sounds killer.

 

[Dogs of Doom]

congrat's! & HNAD!

 

[Kutt]

Congrats. I too got the same amp very recently. Love it.

 

[Kutt]

Everything cool with your fuse holder there, or is it just an illusion?

 

[Deftone]

Everything cool with your fuse holder there, or is it just an illusion?


View attachment 147240

Good eye. I noticed that too and asked the seller if the fuse was missing. Turns out it's there, just looks weird in the pic. The back panel is long gone though.

Couple of gut shots....