Mark IIC to C+ Steps Required for Upgrade

[jrb32]

So I've been going through the steps required to the C+ upgrade on my '83 IIC with the RP10A and I just wanted to share how ridiculous these are! I have no idea what Mike B was on back then but if you think it's just a few component changes or an FX loop/Reverb swap think again.

I've counted just under 40 steps from looking at pictures of an upgraded RP10A and comparing them to some schematics of the IIC I based on the chipaudette ones to try and get my head round it all. I also drew up a corresponding board layout. It involves V2A and B being swapped around completely, traces being destroyed on the board, jumper wire and hook up wire everywhere.

I don't really want to post a step by step guide, especially for those in the US who can send this to Mike B (sending to Petaluma is not really a viable option for me), but definitely everyone appreciate the hard work and effort required to do the + upgrade and the genius that went into this creation.

I'll stick up a board layout and schematic for the RP10A and RP11A boards for maintenance and general information in the next few weeks. This is for the C and the C+ for the RP10A and the C+ for the RP11A (I don't have any information on an RP11A C and would be guessing). If anyone wanted to do the mod work themselves (or even downgrade to a C if you wanted) you can analyse them both but I'm not doing a step by step for dummies guide or anything to stop people destroying their amps if they don't know what they're doing. I just think it's nice to document these 30+ year amps as much as possible for the future.

 

[JD]

That would be very cool

 

[jrb32]

RP10 IIC Schematic: https://drive.google.com/open?id=1mpJFsu2gHA2gIiNmg6FGbC81rlggkt6M
RP10 IIC Board View: https://drive.google.com/open?id=1Lx0AofY9eI34mGY3RbgNDSV5IgEUf5cS

RP10A IIC+ Schematic: https://drive.google.com/open?id=1dyC8zXSQ8Ta8Gg-TDZPpQb3j4_4PnjHk
RP10A IIC+ Board Layout: https://drive.google.com/open?id=1Z0-2LdLlP0GLd5otlq_kVX8XQX49nUWV

Hope that helps someone out there do some maintenece/repair if needed.

If you're looking into doing a C to C+ upgrade there are a load of wire placements and moves you need to sort too so don't think you can just do these changes to the board it'll work. It won't. Don't even try unless you know what you're doing. ALWAYS send it to Mike B if possible.

Cheers,

Jon

 

[jrb32]

RP11A IIC Schematic: https://drive.google.com/open?id=1_KWgnYKephAlJAnfH8IL9El8qHdo5nji
RP11A IIC Layout : https://drive.google.com/open?id=1CALqxt8hsJK_ghfb4ZnNmY8LQ627h54b

RP11A IIC+ Schematic: https://drive.google.com/open?id=1SRE-Dthwda_-Wq0oRresd9D8matOy4qY
RP11A IIC+ Layout: https://drive.google.com/open?id=11AstDiHmxnD4zt-o7hp-OfKH6Vb7VAwj

The IIC schematic for the RP11 is the best I can get it without tracing one first hand. Looks like there is some weird stuff going on with the Lead Pull Bright as opposed to the RP10 board, but is very similar to the RP10 preamp wise apart from that. It also has all of the EQ, automatic treble shift, V2A/B rearranged and power section already at IIC+ specs. Like it was designed with the + upgrade in mind. It would make sense from a production point of view that the RP10 was the one that Mike B and Doug West originally modded and made the RP11 easier to upgrade with a lot of C+ features already done. That way the customer could choose easily between the C or the C+ far easier. There's the SP10 and SP11 boards as well but they seem similar in layout to the R versions (R meaning Reverb) from what I have seen. I've written on here that it doesn't really fit the Winter 83 timeline and makes more sense this would have been done Summer 83 in time to get a PCB redesign put into production (the IIC RP11s appear from around October 1983 with a lot of the + features already done). Could just be coincidence though and something that was being developed at the time but it seems unlikely. Just my thoughts! I'm probably wrong.

 

[TiPiMods]

thanx, great info & schematics

 

[aiyiadam]

Thank you for the valuable information.

I am planning to do a IIC+ conversion on a RP10 board. Am I right to assume that the conversion won't be possible without taking the PCB out?

 

[Henz]

Thank you for the valuable information.

I am planning to do a IIC+ conversion on a RP10 board. Am I right to assume that the conversion won't be possible without taking the PCB out?

Jrb32 is rarely on here now.

 

[aiyiadam]

Jrb32 is rarely on here now.

Thanks.. Maybe somebody else could answer..

However, I will probably need to pull the PCB out anyways. Some unprofessional looking was done on the amp and I should take a look at the traces on the bottom side.

 

[JD]

I have done a few C to C+ upgrades there is no need to remove pcb just be careful with the soldering/heat on traces

 

[Henz]

Thanks.. Maybe somebody else could answer..

However, I will probably need to pull the PCB out anyways. Some unprofessional looking was done on the amp and I should take a look at the traces on the bottom side.

BoogieBabies is on here more frequently. He's very knowledgeable. I want to lift my Rp11A pcb but holy geez! Major pain eh!? Have you worked on your amp? Via that pict, it appears that the two 220uf filter caps are missing or replaced with shorter ones maybe black F & T's ?

 

[Henz]

Oh how I wish someone would help me! Am I checking correctly for Leaky DC voltages in my orange drops?🕵

 

[aiyiadam]

BoogieBabies is on here more frequently. He's very knowledgeable. I want to lift my Rp11A pcb but holy geez! Major pain eh!? Have you worked on your amp? Via that pict, it appears that the two 220uf filter caps are missing or replaced with shorter ones maybe black F & T's ?

Not my amp, I am trying to service this old beauty. I had serviced a Mark III before, but this amp will probably be much more difficult..

The lead channel isn't working. Looking at the tube broken socket lugs, the board was lifted a couple of times.. Two 270uf radial caps (Epcos brand) are glued on the chasis instead of the 4x220uf caps.. Some resistors and caps are changed, etc..

JD said that I don't have to remove the board, but maybe I should see if there is any damage on the bottom side. When I am at it, I could also change the sockets with broken lugs.

 

[Henz]

Not my amp, I am trying to service this old beauty. I had serviced a Mark III before, but this amp will probably be much more difficult..

The lead channel isn't working. Looking at the tube broken socket lugs, the board was lifted a couple of times.. Two 270uf radial caps (Epcos brand) are glued on the chasis instead of the 4x220uf caps.. Some resistors and caps are changed, etc..

JD said that I don't have to remove the board, but maybe I should see if there is any damage on the bottom side. When I am at it, I could also change the sockets with broken lugs.

What have you troubleshooted so far? I made up these lil mirrors , kinda like what dentist use, to look underneath where I can.

 

[aiyiadam]

What have you troubleshooted so far? I made up these lil mirrors , kinda like what dentist use, to look underneath where I can.

Don't know if it will work here, but the dentist mirror is a good idea. It surely would help, when you are working on a Marshall with a ST1 board.

I have decided to find the problems of this IIC before doing an upgrade..

What I have found so far: Couple of LDRs. The 100n cap in the tone stack was dead an there was round 90VDC on the pots. The 1M resistor in the lead input wasn't there. The lead output was wired to V2B instead V2A. The 22/15uf cap in the reverb circuit was damaged and not connected.

What I have done:

• Changed the LDRs (I am putting them in heat shrinks to increase their dark resistance a bit. And I read about 10K, when they are on.. Maybe I can increase the current on them? )
• Changed the tone stack cap/reverb circuit caps, corrected the errors in the lead circuit.

What still needs to be done:

• The reverb tank.. It seems okay with a multimeter, It looks okay inside. When you shake the thing, you can hear it. And there is still no reverb.
• The lead master pot doesn't work.
• There is a lot of hum in the normal channel, which increases uncontrollably with my 220V fed LED lights.
• And the lead channel doesn't sound okay. It tends to oscillate..

This amp is a lot of fun..

 

[Henz]

Don't know if it will work here, but the dentist mirror is a good idea. It surely would help, when you are working on a Marshall with a ST1 board.

I have decided to find the problems of this IIC before doing an upgrade..

What I have found so far: Couple of LDRs. The 100n cap in the tone stack was dead an there was round 90VDC on the pots. The 1M resistor in the lead input wasn't there. The lead output was wired to V2B instead V2A. The 22/15uf cap in the reverb circuit was damaged and not connected.

What I have done:

• Changed the LDRs (I am putting them in heat shrinks to increase their dark resistance a bit. And I read about 10K, when they are on.. Maybe I can increase the current on them? )
• Changed the tone stack cap/reverb circuit caps, corrected the errors in the lead circuit.

What still needs to be done:

• The reverb tank.. It seems okay with a multimeter, It looks okay inside. When you shake the thing, you can hear it. And there is still no reverb.
• The lead master pot doesn't work.
• There is a lot of hum in the normal channel, which increases uncontrollably with my 220V fed LED lights.
• And the lead channel doesn't sound okay. It tends to oscillate..

This amp is a lot of fun..

I know, right!? Aren't these amps sooo much fun to troubleshoot. Whoever was last in there, with all of the erroneous schematics floating around, I dont know if he/ she can be blamed. But that 1meg grid stopper is a given. Changing that100nf bass cap is tight on the pot side. How'd ya get to it? Let me ask you if I may, I'm troubleshooting my C+. I'm a DIY learner. What method do you use to test for bad LDR's? Thanks for your time!, Jim

 

[meesa_jarjar]

Don't know if it will work here, but the dentist mirror is a good idea. It surely would help, when you are working on a Marshall with a ST1 board.

I have decided to find the problems of this IIC before doing an upgrade..

What I have found so far: Couple of LDRs. The 100n cap in the tone stack was dead an there was round 90VDC on the pots. The 1M resistor in the lead input wasn't there. The lead output was wired to V2B instead V2A. The 22/15uf cap in the reverb circuit was damaged and not connected.

What I have done:

• Changed the LDRs (I am putting them in heat shrinks to increase their dark resistance a bit. And I read about 10K, when they are on.. Maybe I can increase the current on them? )
• Changed the tone stack cap/reverb circuit caps, corrected the errors in the lead circuit.

What still needs to be done:

• The reverb tank.. It seems okay with a multimeter, It looks okay inside. When you shake the thing, you can hear it. And there is still no reverb.
• The lead master pot doesn't work.
• There is a lot of hum in the normal channel, which increases uncontrollably with my 220V fed LED lights.
• And the lead channel doesn't sound okay. It tends to oscillate..

This amp is a lot of fun..

10k is way high, I would also check the circuit feeding them power when 'on' if you've already replaced them. They should be in the tens of ohms at most when turned 'on'.

 

[aiyiadam]

I know, right!? Aren't these amps sooo much fun to troubleshoot. Whoever was last in there, with all of the erroneous schematics floating around, I dont know if he/ she can be blamed. But that 1meg grid stopper is a given. Changing that100nf bass cap is tight on the pot side. How'd ya get to it? Let me ask you if I may, I'm troubleshooting my C+. I'm a DIY learner. What method do you use to test for bad LDR's? Thanks for your time!, Jim

I am also learning.. To remove the cap I have bent the capacitor legs as much as I can and used some fresh solder for getting it loose.. I have replaced it with a 630V mallory 150, which is much smaller.

10k is way high, I would also check the circuit feeding them power when 'on' if you've already replaced them. They should be in the tens of ohms at most when turned 'on'.

It is high, but the circuit seems to be okay. I have replaced the 680 resistor (which measured actually about 750R) with a 5W wirewound type and the 470 cap.. I am reading about 1.65V, when the circuit is on. And one of the old vactrols seem to work fine.

I am using those cheap chinese LDRs. Maybe those need a higher voltage/current.

 

[Henz]

Great move on that 680R. They take a pounding! Factory installed 2 watts was too low. And my amp suffered. Burnt up and took part of the pcb with it. I've read where 3 watt wire wound is common now. 5 watt even better. What about the Zener diode? Is it ok?

 

[aiyiadam]

Great move on that 680R. They take a pounding! Factory installed 2 watts was too low. And my amp suffered. Burnt up and took part of the pcb with it. I've read where 3 watt wire wound is common now. 5 watt even better. What about the Zener diode? Is it ok?

I didn't test the diodes, but the voltages look good.. I still suspect my cheap LDRs and will build a supply circuit similar to Mark II for testing them. We'll see, if they will perform similarly.

There is another optocoupler brand called silonex, which looks promising. I want to give it a try.

 

[aiyiadam]

I think, I have done it.. The photos, layouts and schematics were very helpful. Thanks to all, who have shared their experience on this forum..

I did remove the board to inspect and repair some missing traces.. There was a resistor under the board, which didn't belong there.. Swapped the tantal caps with newer ones. Used cheap 1W metal film resistors and 2/3KV ceramic caps , which usually work fine.. Used Silonex NSL32SR3 LDR's.

The amp sounds actually very nice. I expected a much noisier amp.

There is a small problem though.. On lower lead master settings the sound level increases for a few seconds when I switch to the clean channel. The lead master pot measures 140K. I will install a larger value, but this will stay as a problem. This is probably normal?