1980 MXR Distortion+ Repair

[Steve Mavronis]

Back in January, my daughter's boyfriend gave me this old broken MXR Distortion + pedal:



It is the version before they added the LED and power jack. Since taking this picture I've added 2 new MXR knobs. The Distortion knob pot (CTS) date code says 1378049 and the Output knob pot says 1378012. So that means the pedal was made either late 1980 or early 1981. Here is a picture of the PCB trace side. The orange gain pot wire broke off but that is not the main problem It appears the trace from the red V+ connection burned off the board? I'm guessing the trace line goes straight down to a resistor hole you can see below. And there should be another trace going to pin 7 of the 741 op amp that's missing too as well as from pin 6 to a cap. It looks like it took quite a hit although you can't tell by looking at the component side parts.



Does anyone have a good trace side PCB photograph as reference so I can re-create the board or repair it?

[Steve Mavronis]

I found what I needed here:

http://www.pedalarea.com/mxr_distortion.htm" onclick="window.open(this.href);return false;

Thanks anyway.

[jcm800nut]

Wow, thanks for that link!

That has to be the ultimate mxr dist+ page for sure, even has comparison clips for all the different versions.

Awesome.

[Steve Mavronis]

Here's the PCB etched and tinned made from my ExpressPCB layout which is a 1:1 copy of the MXR Distortion+ circuit board. I still have to clean up the board edges.Tonight or tomorrow I go over my father's to use his drill press to get the holes done. Then hopefully I can use this to replace the old fried one so I can refurbish and repair my broken pedal. I can't wait to hear how it sounds! I'll post a picture this weekend of my fixed pedal if I'm sucessful.



Hey I have a question about those 5 wire pads at the top of the board. When I first made the replacement board layout I had the normal wire holes there. I forgot the real MXR board doesn't have the wire strands going through the board to the other side. I've since corrected the PCB layout I made in PDF format not to have holes there. On my board replacement, you won't see the hole spot since the wire and solder will cover it over. What is the best method to 'contact' solder wires directly to the pads? Should I just drill them through and solder the wires normally? Thanks.

Here's a complete schematic thatI traced and verified (the standard PCB circuit is inside the dashed lines) including all of the offboard wiring - http://home.comcast.net/~snmavronis/mxr ... ematic.jpg" onclick="window.open(this.href);return false;

[Tone Slinger]

I tell ya, the MXR Distortion + is probably the BEST distortion/overdrive circuit EVER !

This is the pedal that you find the most 'blown battery acid' in. I've owned and/or played through more of these than any other pedal (yes, even tube screamers).

I got 3 that sound the 'bestest'. A old script, an old hybrid (bottom plate is 'script' top paint is block, and an early block (which resides in an old black JH-2 round fuzz face enclosure (lots of interest in this pedal from others ).

The hybrid '78 (the case and paint were 'mismatched' MXR used the remainer of thier 'script cases, BUT, with their NEW BLOCK paint). This was in '78)is the best of the lot.For some reason,maybe the fact that my father bought it for $ 3 dollars down in a South Carolina flea market, combined with me having to clean out all that battery acid and soaked grey foam, I had to properly clean it up before I dared put a 9 volt in it. Regardless, it sounded/sounds very warm,,, big and dynamic. THIS is how it should sound !

My script logo is not as fat or gainy. The early block (in the Fuzz Face shell) is VERY close to the hybrid. I also prize this because BILLY BATZ of this forum (who hasnt posted much at all the last couple of years) sent it to me. I didnt use it for some time. Finally did and am very glad I did ! Great circuit/board.

[Steve Mavronis]

So you like the '78 hybrid the best? Do you attribute that to anything different with the components?

I'm just restoring this one to original condition to refurbish it. With the new PCB replica I made, trying to use close to what was in this 1980 unit. The op amp IC is a '80 Texas Instruments UA741CP with Malaysia stamped on top. In my stock of parts I do have is a Texas Instruments UA741CP with M701 (not sure if that's a date code) and Malaysia underneath so at least that is close. I have two small 1uF tantalum caps except they're yellow instead of blue. For the four ceramic caps I may try to re-use the originals since they don't appear to be damaged. I have two 1N270 germanium diodes that look identical to the originals.

After I get this together hopefully Sunday and hear how it sounds, not sure if I should go beyond repair and mod the pedal to feature a red LED and DC jack. Maybe I'll keep 1980 spec integrity and if I want those added features, a complete separate clone pedal could be possible.

[Tone Slinger]

The script (not a bud box) is a '77. It and the hybrid (script on bottom plate block on top) have the same Malaysian UA741cp Texas Instruments op amp. I also have a '79 block (both block on bottom plate and the top) that has this same op amp.

The later board (in the fuzz face shell) is still a non battery adapter model, but I do not know the exact date of it because I only had the component loaded board of it (no pots). It has a slightly different layout. I am assuming that it's early '80's ?

It has a 8752A LM741CN op amp.

Funny thing is how the battery acid 'smudged' and rubbed off some of the bands on the resistors (on my '78 hybrid).Still has JY initialed on the circuit board. I guess that was the person who assembled/soldered/ tested this unit ?


The '77,'78 and '79 all have the 'solder' traces. The early '80's has copper clad pcb. Still 'band aid' colored on the component side, but green on the other.


I'd like to hear a very early Distortion + that is the bud box version (or the one's with those large carbon comp resistors) Maybe the Distortion + was never in the Bud box ? Not sure.

[garbeaj]

Mine doesn't have a Bud designation anywhere on the box...it has a very small cursive or "script" MXR logo on the lower right hand corner of the outside (painted side) of the back plate. I'm not sure what year mine is...I have the original foam inside covering everything up and I don't want to mess with that to get to the pot codes. Of course the foam is all dry rotted and crumbly inside the unit. It works though, you can hear it on my version of the Live Without A Net solo...

[youtube]http://www.youtube.com/watch?v=W443_DdglYk[/youtube]

Is there any other way to tell the date without getting to the pot codes? I reckon mine is an early 80s unit going by the block logo...

[somethin'else]

ok, i just officially quit playing guitar. selling everything. (kidding)

nice friggin' job there, garbeaj. didn't sound like garbeaj to me.

[garbeaj]

ok, i just officially quit playing guitar. selling everything. (kidding)

nice friggin' job there, garbeaj. didn't sound like garbeaj to me.

Thanks! It was all the fault of my old MXR Distortion + really!
I used my '65 Super Reverb with the volume on "3" so it was really clean without the Distortion +...That clip is a really good example of what the pedal really sounds like completely unadorned. The only other effect I used was my original 1979 Electro-Harmonix Deluxe Memory Man for the delay on "Cathedral". I didn't even have any reverb from the Super Reverb!

[Tone Slinger]

Man I tell ya from what I can remember of it (Live Without a net solo) you pretty much got it down.

I was confused about 'bud' boxes. That was simply a company that made the earliest MXR enclosures ('75 early '75 I think) They are aluminum and lighter in weight than the ones MXR went to by '75 or so (zinc I believe).

MXR went to using the block logo paint by '78. If yours has the script mxr on the bottom of the plate but has the block paint on top, then yours is a '78 'hybrid' like my favorite one is.MXR had a certain amount of enclosures left with the script 'MXR' stamped on the bottom plate. I guess they didnt want to waste these and went ahead with the 'new' paint (block logo).

By later into '78 the bottom plates (new batch of enclosures) were stamped with the BLOCK logo on the bottom as well, though they went to putting a thin foam on the bottom plate. I have a '79 that is 100 % block logo.

Its funny but I wonder how long it took for the pots to be used for a particular pedal ? Like if a pot denotes that it was made the 20th week in '78, I wonder how long it was until it was used in a pedal ?

[Steve Mavronis]

Its funny but I wonder how long it took for the pots to be used for a particular pedal ? Like if a pot denotes that it was made the 20th week in '78, I wonder how long it was until it was used in a pedal ?

One of the two 1980 stamped pots in mine is dated 4 weeks to the end of the year. So it's questionable if it's 1980 or early 1981. Also look at the date code on the 741 chip. If it's Texas Instruments it might be a 3-digit Y-WW date code.

I soldered parts onto my replica PCB. It was a pain but I de-soldered the four ceramic caps and put them on the new PCB. The pain part was one of them flipped out of my hand and it took me an hour crawling around on the floor until I found it! Anyway, the replacement PCB is ready to be attached after I clean the solder flux off the other side:

[garbeaj]

I was confused about 'bud' boxes. That was simply a company that made the earliest MXR enclosures ('75 early '75 I think) They are aluminum and lighter in weight than the ones MXR went to by '75 or so (zinc I believe).

MXR went to using the block logo paint by '78. If yours has the script mxr on the bottom of the plate but has the block paint on top, then yours is a '78 'hybrid' like my favorite one is.MXR had a certain amount of enclosures left with the script 'MXR' stamped on the bottom plate. I guess they didnt want to waste these and went ahead with the 'new' paint (block logo).

By later into '78 the bottom plates (new batch of enclosures) were stamped with the BLOCK logo on the bottom as well, though they went to putting a thin foam on the bottom plate. I have a '79 that is 100 % block logo.

Its funny but I wonder how long it took for the pots to be used for a particular pedal ? Like if a pot denotes that it was made the 20th week in '78, I wonder how long it was until it was used in a pedal ?

Wow! Thanks for the great info...I have a rough idea of the lineage of my pedal without tearing into the guts of it:)

[Steve Mavronis]

Well that's it for this thread I suppose. The verdict is in - It works!!!



New DIY replacement board and refurbishment successful. Long live MXR Distortion+

I made a little write-up on this page - http://sites.google.com/site/snmavronis ... nd-repairs" onclick="window.open(this.href);return false;

Steve

[garbeaj]

Just a brief sidetrack...does anyone know where I can find replacement screws for the back plate on the MXR Distortion + and MXR Phase 90? I've only got two on my Phase 90 and my Distortion +...