JCM 2000 DSL100 ISS 5 TO ISS 20 REBUILT

Guido X Salas

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I purchased a used JCM 2000 DSL 100 - ISS 5 version for $150.
I thought it may be of interest to some people, the process and encounters I will experience during my deep dive it to the restoration of the amplifier. Please realize I am NOT an expert at this, I just have OCD, this is just a personal hobby.
It may also be of assistance to some members who may be pondering the idea of purchasing one, given the well documented faults with the PCB circuit board issues.
The symptoms:
When I purchased it from a young man, he mentioned that he had it in his garage for some time and it would not power on. He did not know what was wrong with it, he was not very good at the workings of the amp.
Approach: I did not know too much about this model and or version issues either. I started by researching the model and known issues, first as a general Google search. I found several YouTube videos and also treads on this site discussing numerous issues with the PCB board, thank you all who contributed.
One item that is not properly covered is how to determine the PCB board (ISS) revision number. The confusing part to me was that some boards note several revisions such as in mine 4, 5, each in a separate square box. What I presumed and I think I am correct is the numeration indicates that revisions 4 & 5 were both intergraded into this one PCB board release.
I am in the process of upgrading the PBC to revision ISS 20. I considered Dr. Tube Stable Bias Mod but I was uncertain of all the issues with the current board, I figured upgrading from ISS 5 to ISS 20 will provide additional benefits (I hope).
I am closely inspecting the other two boards within the head to see if I can find any other visible issues that may require repair prior to installing the new ISS 20 board once it arrives.
Findings:
1) - I found two of the Marshall 11mm Potentiometer - A1M, on the JCM2-61-00, ISS 2, 3, 4 & 5 PCB board, position VR1 & VR2 corresponding to Classic Gain Channel A were damaged, probably someone hit it with something.
2) - On the main PCB JCM2-60-00, ISS 4 & 5 (THE MAIN ISSUE) I visually inspect and found a hot (burnt trace) near V8 (EL34) Tube pin socket 3 & 4, that leads position R76 (1K 5W Resistor), position C46 (22 pF ±10% 500V Ceramic Capacitor X7R Radial). This appears to coincide with some black overheat residue visible on two of the EL 34 tubes.
1657978657802.png
1657978818672.png 1657979059532.png
3) - The EL34 tubes were two different manufacturers and some displayed evidence of red plating (overheating, black smoke like stains around the interior top portion of the tubes).
4) - The Specified ECC83 tubes (4) Preamp were found to be a mix of Ruby 12AX7WBC, JJ ECC803S (2), Generic China 12AX7B tubes.
5) - The installed fuse were a mess, wrong amp and type installed (can be catastrophic). Please read your schematics for proper fuse required. Realize there are different "Type" and dimensions of the same AMP rating, they will not fit properly into the AMP holder.
Approach:
1) - I ordered a new P-H219 Marshall, Replacement Board ISS 20 revision, from AmplifiedParts
2) - I ordered new JJ ECC83S and JJ EL34II tubes from TubeDepot, they had the best prices.
3) - I ordered new grill cloth to replace the existing that had glue of some sort, as well as a new Marshall emblem 11".
3) - I ordered new Marshall 11mm Potentiometers - A1M from Studio Sound Electronics Item # P-VKG
4) - I ordered new glass fuses, goodness this can be very time consuming to find. I will save you a lot of time go to Digi-Key Electronics and purchase the following:
Digi-Key Part Number507-1531-ND
Detailed Description4 A 250 V AC DC Fuse Cartridge, Glass Holder 3AB, 3AG, 1/4" x 1-1/4"
Digi-Key Part NumberF2677-ND
Detailed Description1 A 250 V AC DC Fuse Cartridge, Glass Holder 5mm x 20mm
Digi-Key Part Number507-1254-ND
Detailed Description6.3 A 250 V AC DC Fuse Cartridge, Glass Holder 5mm x 20mm
Let me know if you need any specifics on my progress, I will post photos soon need to reduce size wont upload.
Update 7-2-2022:
A few experiences I would like to share since starting this project.

Circuit Board Supports:
Circuit Board Supports
are not provided when you purchase a replacement board and are quite an issue. The old ones are brittle from heat, the treads for the #4 screws that support the spacers from the metal plate are warned. When you install Valve/Tube V1 it creates sufficient downward pressure that eventually the plastic treads give way.
Buy new ones, it will prevent you from having to remove the boards (all of them) a second time, like I am having to do.
I will save you hours of research, the original "Self Retaining Spacers" are obsolete (Digi-Key Electronics Code # 30502-4-N). The replacements I found in Digi-Key Electronics that appear to be a good match are
SSRS4-8-01. You will probably need to purchase new #4-40 screws of the appropriate length for the new spacers.

Marshall Communication:
I contacted Marshall via email and eventually communicated with a Dave Wittering (Senior Service Engineer) to discuss a few issues. First I needed the schematics for the new JCM2-60-00 ISS20, I could not find it anywhere on the web, Dave emailed it to me (Thank you very much Dave).

Tube Biasing:
Second item: I asked Dave Wittering (Senior Service Engineer) about proper Biasing of Tubes/Valves for the JCM 2000 DSL100. I mentioned that I found a Marshall Service Bulletin on the Dr. Tube site that indicates the DSL100 - mV Setting at 90mV. Dave mentioned that Marshall recommends a Bias Setting of 80mV, it will save tube life and works much better with Marshalls.

Marshall Recommended Tubes/Valves:
Third item: I asked about what tubes Marshall Recommends, I mentioned that I recently purchased JJ brand tubes. Dave mentioned that Marshall use only Tung-Sol, they work better with Marshall Amps.

I must add that one of the four JJ ECC83S, I purchased lost its vacuum within the first 15 minutes during the Biasing stage of the JJ EL34II. I contacted TubeDepot to request a replacement. They immediately forwarded me a UPS return authorization and within three days I was notified that a new replacement was on its way.


Update 7-3-2022:

POTENTIOMETERS:
They are available through Studio Sound Electronics, you will need the following;
P-VKG (5-PCS) Marshall 11mm Potentiometer - A1M - $6.95 EA.
P-VKG (3-PCS) Marshall 11mm Potentiometer - B20K - $6.95 EA.
P-VKG (1-PCS) Marshall 11mm Potentiometer - B200K - $6.95 EA.
P-VKG (1-PCS) Marshall 11mm Potentiometer - B5K- $6.95 EA.


BOARDS (PCB):
I wanted to provide the following information regarding the PCB Boards.
There are three (3) large PCB boards and three (3) small ones.
The main PCB is labeled as "JCM2-60-00, ISS20" is the latest revision. The schematics note it as JCM2-60-02, ISS20.
1657975654879.png


The front control PCB is labeled as "JCM2-61-00, ISS5". The schematics note it with the same numerations as printed on the PCB.
1657975245715.png


The rear output PCB is labeled as "JCM2-62-00, ISS5". The schematics note it as JCM2-62-02, ISS3.
Two of the small PCB's are not numbered, and are intergraded in to one schematics "JCM2-63-02 REVERB/MAINS INPUT, ISS6".
1657977318178.png 1657977528214.png
1657979676730.png


The third small PCB board is the Bias Board, JCM2-64-00, ISS1.
 
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Guido X Salas

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Dr. Tube Stable Bias Kit will save this
$#@! amplifier from the bin.:p
I did research it, it addresses the issues with runaway bias, if that is the only known issue. Being a recent none operational unit I figured I would spend the additional $150 and have a clear working point.
 

Leonard Neemoil

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I did research it, it addresses the issues with runaway bias, if that is the only known issue. Being a recent none operational unit I figured I would spend the additional $150 and have a clear working point.

You also have to do the speaker ground mod if it hasn't already been done.
 

mrrstrat

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Sounds like fun! I found that the DSL pots do not cleanup well and need replacement in heavily used amps. The green pots are hard to find - I think its the 5K I had to order from the UK as I could not find it in the USA (forget which one). The blue pots are not bad but for aesthetics I liked the green (not even sure if there was a qualitative difference that matters).

My JCM2K DSL was literally free and had the flyback cap burn out and take out the one of the power tubes and a few components. Replace the power section resistors - I have both installed and not installed the fly-back cap. I think the ones I stock are 10KV rated. I don't believe I have one on my current amp as I struggle with the benefit over the risk of having it.

Or just buy the power board for $200: https://www.tubesandmore.com/products/board-marshall-replacement-jcm-2000-dsl-100

I restored mine to brand-new and replaced the 220K grid stoppers with 5.6K - the later releases of the DSL power board come with the 5.6K and even Marshall appears to have abandoned using the terrible sounding 220Ks.
 

Guido X Salas

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mrrstrat:​

It so happens that I was inspecting the condition of the potentiometers today. I decided to replace them all. Originally I ordered two, after having to remove the PCB boards for the second time I figured I same me having to take the board out again later so I order the remaining ones.
I am also going through and checking the resistance on all of the resistors. I am finding a few that are out of tolerance, but what is a person to expect from an amp that is 25 years old.
 

Leonard Neemoil

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Guido X Salas

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Good morning everyone, I hope you all are having a great day.
I need a bit of assistance please.
Perhaps someone can assist with an issue I might have found on the JCM2-61-00 ISS5 (Front Control Board). Capacitor C9 is noted on the schematics but it was never "Fitted" on my board. I wonder if it has any negative effects on the performance of the system?
Do any of you have any photos of the front board that you can share, I would like to see if your amp is fitted with the C9 capacitor.
1658061670969.png
1658061739104.png
 

Pete Farrington

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I think C5 was intended to mitigate the imperfect performance at high frequencies of electrolytic caps. A belt and braces thing, to make sure that general interference didn’t cause spurious effects on the switching circuit function.
But if the amp’s function / channel switching is fine, glitch free, even with an old ecap, I suggest not to be concerned that C5 hasn’t been populated.

 
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Guido X Salas

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I think C9 was intended to mitigate the imperfect performance at high frequencies of electrolytic caps. A belt and braces thing, to make sure that general interference didn’t cause spurious effects on the switching circuit function.
But if the amp’s function / channel switching is fine, glitch free, even with an old cap, I suggest not to be concerned that C5 hasn’t been populated.
Thank you very much for your response. Would it be a negative idea if I install the C9 cap? I have one and the board is out. If you do not think it would matter I can leave it out.
 
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Leonard Neemoil

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Good morning everyone, I hope you all are having a great day.
I need a bit of assistance please.
Perhaps someone can assist with an issue I might have found on the JCM2-61-00 ISS5 (Front Control Board). Capacitor C9 is noted on the schematics but it was never "Fitted" on my board. I wonder if it has any negative effects on the performance of the system?
Do any of you have any photos of the front board that you can share, I would like to see if your amp is fitted with the C9 capacitor.
View attachment 111386
View attachment 111387

I think C5 was intended to mitigate the imperfect performance at high frequencies of electrolytic caps. A belt and braces thing, to make sure that general interference didn’t cause spurious effects on the switching circuit function.
But if the amp’s function / channel switching is fine, glitch free, even with an old ecap, I suggest not to be concerned that C5 hasn’t been populated.

Thank you very much for your response. Would it be a negative idea if I install the C5 cap? I have one and the board is out. If you do not think it would matter I can leave it out.

I'm confused.

The picture shows c9 but now you're talking about c5.

Which is it? :)
 

Pete Farrington

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JohnnyChimpo

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Been busy re caping and refinishing my Carvin x100B lately, was going to get back to my TSL100 right after. Following!
 

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