Marshall JCM800 2203KK Rebuild

[GuitarGoat]

Figured I'd share one of my latest projects for anyone interested here. With a little more time at home the past few months, I figured it was a good time to start digging into this Marshall. I bought a JCM800 2203KK Kerry King Signature last year sometime as a project. It looked like there was extensive water damage, but I figured how big of a deal could it be? It turned out to be more than I thought. After digging into what was working and what wasn't, I found the low voltage gate and boost circuit was not working, the bias circuit wasn't working, the preamp tube sockets were arcing...basically a whole host of problems. I ended up depopulating everything but the power tube sockets and replacing all board components as well as having to cut the PCB support posts and redoing how the board is held in due to the screws basically being fused and crumbling into dust as I tried to get this thing apart. This post is a little preemptive as I'm still waiting on the potentiometers to come in, but then all should be good!

As always, I should have taken way more pictures, but here's a few:

After getting the main PCB out - note the two resistors tied together for the screen resistor...it looks like someone had tried some repair in the past but I'm assuming gave up:

A close-up of the board where a lot of the wires come in from the power transformer - note the corrosion on the fuse...was chasing that issue for a little while wondering why I wasn't getting proper voltage when the transformer was measuring fine:

Close-ups of the smaller PCB for the potentiometers, boost and gate circuits (after depopulation, but before clean-up

Corrosion around the bias circuit resistors:

The guts now - might change the wire nut to a crimp cap before I button everything up:

The chassis:

The potentiometer PCB just waiting for potentiometers - I also socketed the ICs in case those gave any issues so they'd be easy to swap:

Like I said, at this point just waiting for those potentiometers and ready to let 'er rip! Voltages look good now so hopefully nothing unforeseen! If anyone needs any help with one of these, shoot me a note as I've been studying the schematics and PCBs quite a bit over the past few months.

 

[thenine]

Wow, that’s awesome. Good job man. I admire your effort here, really well done!

 

[controlled_voltage]

respect!
it's sad to think someone let such an amazing new-ish amp get that fucked up !

 

[GuitarGoat]

Wow, that’s awesome. Good job man. I admire your effort here, really well done!

respect!
it's sad to think someone let such an amazing new-ish amp get that fucked up !

Thanks! After all is said and done, it would've been a lot easier and maybe cheaper to have just bought one of these that was functional, but it's a fun project and it saves this one from the dumpster so I think it's worth it. Hopefully everything goes smoothly once the pots come in.

 

[Mailman1971]

Awesome man. That amp by far is my favorite Marshall amp out the box.
Glad your saving it. Was it submerged totally under water?

 

[shredhead7]

Was this from the Nashville flood? I hope that you paid next to nothing for it. Amazing skill that you have though, it will be interesting to hear it when it's finished.

 

[shredhead7]

Was this from the Nashville flood? I hope that you paid next to nothing for it. Amazing skill that you have though, it will be interesting to hear it when it's finished.

 

[GuitarGoat]

Awesome man. That amp by far is my favorite Marshall amp out the box.
Glad your saving it. Was it submerged totally under water?

It doesn't look like it to me. There were defined areas on the chassis that were rusting pretty bad. Transformers all measure okay, so hoping I don't run into unforeseen lingering issues related to those.

Glad to hear you liked it...a lot of people with good ears have said similar things about these amps, which is why I wanted one in the first place!

 

[GuitarGoat]

Was this from the Nashville flood? I hope that you paid next to nothing for it. Amazing skill that you have though, it will be interesting to hear it when it's finished.

Very well could have been...I don't remember where it shipped from as its been sitting in my basement until I had time to mess with it. After wiring up a patchbay I figured this would be a good project.

Thanks for the kind words though, it's actually pretty simple (just time-consuming) after I realized almost everything had to be replaced. At first I tried diagnosing what was working and what wasn't and it just made more sense to replace everything. I also debated replacing the main board with a turret board but ultimately decided against it after getting things working well.

 

[John4021]

Thanks for saving a great amp.
Made me think I'm glad all my amps
are a few feet or more off the floor.

I bet Dan the Male (stripper) man has those Daisy Duke shorts up on a shelf.

 

[wIsEbLooD]

Nice work man.
That is my favorite amp, I love mine.

 

[Dopethrone]

Thanks for saving a great amp.
Made me think I'm glad all my amps
are a few feet or more off the floor.

I bet Dan the Male (stripper) man has those Daisy Duke shorts up on a shelf.

BAAAAAAAAAAAAHAHAHAHAHAHAHAHAHAHAHHA!!!!!

 

[GuitarGoat]

It’s alive! Finally got the potentiometers in a week or so ago and got those populated. I was still having an issue with the Beast circuit working, but it ended up being a little more corrosion on the +15V connector causing the THAT4301 to not get the proper voltage. Appropriately named for sure; this is a beast.

The Beast circuit seems to add a fairly flat boost to the front end, so one thing I noticed when staring at the schematic (for way too long) and now playing through is that you can use the preamp gain control along with the Beast circuit to dial in the voicing of the amp up front. If it’s too bassy, try keeping the preamp gain lower since there’s a bright cap and crank the Assault control. If you want the less defined low end of more bass early in the circuit, try the opposite.

This has been a fun project...would I pursue this kind of basket-case again? Maybe not...then again, we’ll see if the right amp pops up that needs some rehab. Thanks for taking a look!

 

[311splawndude]

Wow

Just wow.

 

[rottingcorpse]

Dibs. Text you tonight.

No,you don't have a choice.

 

[SpiderWars]

Very cool refurb. Well done!

 

[Meeotch]

Man what a great thread, this makes me happy and thankful. You deserve mad props for your efforts, and I hope this one turns out to have serious mojo. I've been thinking about buying my first Marshall...was leaning towards one of those Jubilee reissues but this story may have changed my mind.

 

[GuitarGoat]

Man what a great thread, this makes me happy and thankful. You deserve mad props for your efforts, and I hope this one turns out to have serious mojo. I've been thinking about buying my first Marshall...was leaning towards one of those Jubilee reissues but this story may have changed my mind.

Thanks to all for the kind words...I appreciate it! This thing sounds great, so I'd definitely recommend one if you can find it. I need to to a little more side-by-side comparisons with my other Marshalls to determine if this unseats any of the others as the favorite, but I've been impressed so far. Just don't let it get too wet...

 

[Pentatonic Wanker]

Wow.....nice job! Does my heart good to see such a professional salvage operation completed on such an awesome amp.

Bravo!

 

[GuitarGoat]

Got the beast back in the headshell and rocking. Ended up reversing the Beast switch because I had it backwards where pushed in was “off” and the switch out was “on”. Also ended up removing some of the push-on connectors on the board to the transformers as I was getting some crackling and drops in voltage due to bad contacts from the connectors. Sounds great now! Was comparing to my VTM60 and this has a lot of nice low end through a Marshall 4x12 with Blackbacks. I need to compare this to my JCM800 combo through the same cabinet and see how it compares to that but from what I can tell this sounds very full and maybe a bit thicker than I’m used to. Loving it so far!