Complete Mark III Schematic

[>Photi G<]

Well, it's about time we had a legible schematic for this amp. I'm aware that the only one available up to this point in time was both illegible and inaccurate. I am happy to say that this fixes both of these problems! It is completely accurate, and readable. This is for a Blue Stripe MIII, but all the others should be similar. The only thing is that I'm not sure about the pot values, and some of the bypass capacitors. PM me with any corrections, PLZ.

EDIT: The old link was dead, so I tried uploading the file again. Linkage: http://www.filedropper.com/markiii

Enjoy, fellow Boogie Boarders

 

[chipaudette]

Hey that's a lot of work you did. Wow. Thanks for sharing!

A couple of questions for you, though:

1) On P1.pdf, does the optional C30 really go to ground? On my Mark IIC(+), it goes up to the power supply rail (ie, it jumps around the 274K plate resistor on that tube stage). Does it really go to ground on the Mark III?

2) On P1.pdf, coming off V1B, you've got a 0.047u coupling cap (fine) followed by a 274K resistor in series. Branching off, you've got a 3.3M to ground (via relay) and another 2.2M to ground (via a different relay). Is this right? Based on the Fender lineage and based on my Mark IIC(+), I would have expected either that 3.3M or the 2.2M to have been the one in series and the 274K to have been to ground. Is what you're showing correct for the Mark III?

Thanks again for sharing! Do you have any knowledge of what makes the other stripes different from the blue?

Chip

 

[>Photi G<]

1.) Yes, C30 goes to ground, at least in the Blue Stripe it does. I've scoured the PCB for days to make sure I got all the connections right

2.)I can't say I got the Rhythm 2 circuit exactly right, as some of the traces disappear underneath the relay itself (there is only one relay, BTW, but it has 2 halves), but the component values are correct. The Blue Stripe was designed with a hotter R2 channel in mind, so that 2.2M resistor (or was it 3.3M?) was subbed for 274K to feed more signal to V2A, the R2 tube/mixer.

3.) as far as the other stripes, I think just component values are different, as they all share the same board. The date stamp on mine says Copyright 1984, and the amp was made in 1988, so I can say that with confidence. Also, some components, like C30 in the lead channel, and C26 in the Graphic EQ have been removed altogether to change the sound. The problem with the Mark III is that the changes in each stripe were not documented, or publicly released, for that matter, so there's no telling what changed, and what did not, unless you spoke to Mike B, who has built/tested each one of them.

And I'll probably post an updated version. I'm planning on measuring some reference voltages sometime soon. The PT secondaries and B+ voltages have ? marks next to them because that's what the original schematic implies, or my calculations show; but then again, it comes down to that grain of salt. I need to buy a multimeter, and replace my filter caps first, as one of the 220u's has a small leak, and the others are at least 23 years old. :lol:

 

[McBarry]

+1 for thoroughly great work.
Appreciated ++.

 

[okgb]

Is there a way to download it without having to sign up & pay for file dropper ?

Good effort btw , and with so many revisions of the mk III , i would think it hard
to make a definitive schemo unless you made all the versions
[ which , perhaps everyone can use this one to compare to their & post it ? ]

Being that i haven't been able to down load it , were you able to
put the part designators [ C30 , R214 , etc . ] onthe schematic ?
that would be a bonus to refer a number to a part value to the circuit

forgot to say , thanks for the hard work

 

[Jameson]

Hi there! I have been a silent reader of the forum for almost a year but now I'm posting here The forum is a real grail of valuable info, thanks to all! >Photi G<, thanks for sharing the schematic, it looks pretty accurate in terms of values and corresponds well with my own investigations about Blue stripe.

I have the Purple stripe schematic which is made by one member of SLOCLONE forums, it is also very detailed. When I modded my Blue stripe to III+ I took the sheet of paper with that schematic and noted there the differences between Purple and Blue stripes (but only for the preamp). There are not so many of them and they are all related to cap and resistor values except for the C32 cap which is connected by one pin with ground in Blue stripe and with the cathode of V3A in Purple stripe.

But in Purple stripe that C30 cap is installed across 270K plate resistor exactly as in IIC+. In Blue stripe the placement on the PCB really looks like it should be run to ground by one pin... In my Blue stripe I installed this cap exactly as in Purple/IIC+ and I like the results Haven't tried to put the other pin to ground...


okgb, there is a large gray button labeled "Download This File"... at least for me this works

 

[okgb]

O.k. thanks i got it , once you avoid all the other download buttons
otta say i've alway hated the way they go right to left !

Do you have a link to the slocone mk iii ?

 

[Jameson]

Yeah it's always hard to find the right download link in a bunch of "Login", "Sign-up" and "Give us your money" stuff :mrgreen:

This is the topic: http://www.slocloneforums.com/viewtopic.php?f=14&t=2739
(you need to register there to view anything)

The guy's name is msi (probably he also presents here on this board? if so, thanks to him for the schematic )

 

[okgb]

He did a pretty nice schemo as well, thanks too

 

[pdub]

I have been looking for this! Thanks for sharing!

 

[stevebeige]

Filedropper doesn't seem to be working for me. I have a blue stripe mkiii and would really appreciate if someone could email me the schematic?

Yours hopefully

Steve

 

[daveg62]

can't seem to get the link to work for me either. i really could use this right now. My Mark III is giving me a really loud hum. Tried all the obvious, tubes, cleaned pots, jacks. It goes away if I plug a cable in the return jack so I'm guessing there's a problem in the preamp stage somewhere.

 

[daveg62]

Ok, this time I went back and it showed me a different page and let me download the files. Weird :?
Awesome job on this!

If anyone has an idea of what could be wrong with my amp, please let me know.

 

[Restless Rocks]

can't seem to get the link to work for me either. i really could use this right now. My Mark III is giving me a really loud hum. Tried all the obvious, tubes, cleaned pots, jacks. It goes away if I plug a cable in the return jack so I'm guessing there's a problem in the preamp stage somewhere.

One of the most common problems I see is the FX return jack itself gets sprung open.

 

[daveg62]

can't seem to get the link to work for me either. i really could use this right now. My Mark III is giving me a really loud hum. Tried all the obvious, tubes, cleaned pots, jacks. It goes away if I plug a cable in the return jack so I'm guessing there's a problem in the preamp stage somewhere.

One of the most common problems I see is the FX return jack itself gets sprung open.

Thanks, I wish it was that easy but that's not the case. It meters out ok. I've checked over the circuit board the best I can using a multimeter and a magnifying light. Can't see any obvious problems with connections, burnt or open resistors, loose grounds or any other obvious problems. I don't have or even know how to use a scope so I guess I'll have to get it to a repair shop. It's already had the power caps replaced so I don't think its them. Doesn't look like any authorized service centers near here, maybe I should just send it to mesa. I live in PA, wish it was easier to fix problems like this.

 

[&gt;Photi G&lt;]

Thanks, I wish it was that easy but that's not the case. It meters out ok. I've checked over the circuit board the best I can using a multimeter and a magnifying light. Can't see any obvious problems with connections, burnt or open resistors, loose grounds or any other obvious problems. I don't have or even know how to use a scope so I guess I'll have to get it to a repair shop. It's already had the power caps replaced so I don't think its them. Doesn't look like any authorized service centers near here, maybe I should just send it to mesa. I live in PA, wish it was easier to fix problems like this.

If you believe that it's an FX loop problem, 99% of the time, if you replace the jacks, the problem is usually solved. On a side note, Where in east PA do you live?

 

[daveg62]

If you believe that it's an FX loop problem, 99% of the time, if you replace the jacks, the problem is usually solved. On a side note, Where in east PA do you live?

I don't think it's a loop problem , I think it's in the preamp section. When you plug into the return you are bypassing the preamp and going right into the power amp. I can use my processor (fractal axe-fx) into the effects return and it sounds great, dead quiet.
I live just south of reading, pa.
I emailed this guy, maybe he can take a look at it
http://www.jouleelectronics.com

 

[mak009]

Hi-I can't get the link to work either.
Could someone kindly post the schematic on a more user friendly download site
Many thanks
MAK

 

[&gt;Photi G&lt;]

Ok, everybody. I've been getting complaints about dead links, and an overall bad experience from Filedropper. It turns out, with a free account, they delete the file after 2 weeks. So, I am now hosting the file at UploadIt.org, and we shouldn't have any problems from hereon out. I haven't had much free time lately, so this is not a revised version. I would expect to have it done in late April.

New download link: http://premium1.uploadit.org/pRPLbLNs//MARK-III.zip

 

[jedmon01]

many thanks