Uh oh

[M29]

Boss MT-2 problem

Hello,

Well a while back I was doing a mod, (Montellums mod) on a Boss MT-2 pedal and on the last part of the mod my elbo slipped and I touched the wrong trace with the soldering iron. It went zap and I went into exile. I got the pedal for a pretty good price used and the mod was only 21 dollas so it was not too bad but I would like to get it going. I put it away about a year ago thinking I could use the case for something down the road. I brought it out today and took some pics to see if anyone here might have an idea on what parts to replace to get it going again. Nothing appears to be burnt or damaged other than the traces.

Here is a pic of the board with the burnt traces. I soldered jumper wires across to complete the trace but it does not put out any sound. The power light comes on but does not change sound when I push the pedal switch.

Here is a pic of the top side. I do not see any parts like resistors burnt. My thoughts are a transistor may be burnt inside. The sound does not change when I push the switch, I will take a look at the switch maybe that is the problem. I checked it as I did each mod. It worked up to the point that I burnt the traces.

Your time and help is greatly appreciated. :thwap:

M29

 

[duhvoodooman]

The two wire jumpers that you ran to repair the burnt traces--did you connect the wire ends to existing solder joints? If not, I'd be concerned about continuity, since soldering directly onto the copper trace can be very tricky. Check for continuity between an existing solder joint on each of the "reconnected" traces, but not the solder joint you used to connect each end of the wire. If you don't get continuity between the traces, then your repair job is the issue.

Couple of other questions:

• Is there a power indicator LED on the effect's PCB and does it turn on & off with the footswitch?
• Does the pedal work properly in bypassed mode? Is it a true-bypass pedal?
• I see what appears to be a reverse-polarity protection diode at D6, next to the AC adapter jack. Do you get a forward voltage reading through it, assuming your DMM has a diode test setting?

 

[M29]

Thanks Vood I will look into that. I do have continuity between my repairs checking solder joints back away from my repair points.

Thinking back...I think what happened is that after each part that I replaced I would check the pedal so I would know if the last part worked. This way I didn't get to the end and find out it did not work and then not know what part was bad. What happened is that I forgot to disconnect the battery and did the last mod and with the power on and the traces burnt. Yeah that is what happened. It has been a long time since I had this out. So the power was on when I laid the soldering iron to the trace. Maybe this will help diagnose this.

I have a couple multimeter's around here I think one can check diodes. I haven't messed with diodes and transistors in a long time.

Thank you for the help.

M

 

[just strum]

I feel as if I walked in on a Greek lesson - huh?

 

[M29]

I am sorry I should have done this through a PM but I did not know if anyone would have any idea what was wrong.

M

 

[oldguy]

Heck, don't be sorry..............look how much Strum's learning from all this.............:rotflmao:

 

[Kazz]

Yep...and it is only Greek to Strummy....I understand perfectly. These are the kinds of threads that really pique my interest.

 

[M29]

Well....OK I will keep going

*************************************************
Your questions DVM
* Is there a power indicator LED on the effect's PCB and does it turn on & off with the footswitch?
* Does the pedal work properly in bypassed mode? Is it a true-bypass pedal?
* I see what appears to be a reverse-polarity protection diode at D6, next to the AC adapter jack. Do you get a forward voltage reading through it, assuming your DMM has a diode test setting?
*************************************************

1, There is power to light the LED and I do get amph sound but no volume and it does not change when I push the switch.
2, The pedal does nothing different in by-pass mode. I don't believe it is tru by-pass but it is hard to tell. Any tips?
3, The D6 diode reads .505mv on the over voltage.

Thank you for your time and help DVM I really appreciate it.

M

 

[tot_Ou_tard]

Fret Rule #1) Always, always ignore Strummy (& tOt).

M29.Thanks for continuing. I love these kinds of threads & it'll be of help to some poor soul googling to try to repair his fried favorite pedal.

 

[duhvoodooman]

Your questions DVM
* Is there a power indicator LED on the effect's PCB and does it turn on & off with the footswitch?
* Does the pedal work properly in bypassed mode? Is it a true-bypass pedal?
* I see what appears to be a reverse-polarity protection diode at D6, next to the AC adapter jack. Do you get a forward voltage reading through it, assuming your DMM has a diode test setting?
*************************************************

1, There is power to light the LED and I do get amph sound but no volume and it does not change when I push the switch.
2, The pedal does nothing different in by-pass mode. I don't believe it is tru by-pass but it is hard to tell. Any tips?
3, The D6 diode reads .505mv on the over voltage.

Thank you for your time and help DVM I really appreciate it.

M

As usual, the answers to questions beget more questions!

• Are you saying that the stomp switch has NO EFFECT on the output sound? No change in tone or volume?
• Do any of the pedal controls have an effect when the pedal is engaged?
• Why is the C35 cap position open on the PCB? (lower right of photo)
• Which of the Allums mod kits did you buy?
• Are you sure the pedal work properly before you started the mod work?

 

[M29]

Sorry Strummy


*******************************************************
DVM,

* Are you saying that the stomp switch has NO EFFECT on the output sound? No change in tone or volume?
* Do any of the pedal controls have an effect when the pedal is engaged?
* Why is the C35 cap position open on the PCB? (lower right of photo)
* Which of the Allums mod kits did you buy?
* Are you sure the pedal work properly before you started the mod work?

********************************************************

1, The controls do not make any difference, engaged or not. There is a hum if I turn the amph up.
2, The only thing that happens when you push the stomp switch is the LED lights, there is no change in the sound just the same hum.
3,4, C35 is the second mod of the (Allums MT-2 Sustaniac Mod) it says to remove and (no jumper). The first mod is to remove C24 which cannot be seen in the photo. This is not to be jumpered either.
5, The pedal worked great before I started and it worked up to the last mod which was to replace C34 with one of their square yellow .047uF caps which can be seen just below R46.

M29

 

[duhvoodooman]

Hmm, this doesn't sound good at all. You're obviously getting power into the pedal, or you wouldn't be lighting the LED. From what I've read, these Boss pedals use a FET-based electronic switch as opposed to a mechanical switch. I'm thinking that perhaps you fried the FET or some other component in the switching part of the circuit, so the switch isn't engaging the effect circuit when operated. If the switch was working properly, you'd either get some degree of effect operation and working controls, or (if there was some serious problem in the effect circuit) no output at all. The fact that you're apparently getting the "dry" signal with the pedal on or off suggests that the effect circuit never actually engages at all. 'Fraid I can't give you much direction on how to go about fixing that kind of problem, if that is indeed the issue.

About all I can suggest would be to further pinpoint the problem by walking through the circuit using a signal tester in conjunction with MT-2 schematic & layout information. Sorry I can't be of more help, Barry....

 

[M29]

Thanks DVM, I got real frustrated back when this happened. I liked to jam hard with this thing, it was somewhat therapeutic.

One good thing though...I have a pedal housing that I can build into what ever I want. Maybe an A/B switch or something like that

It does kind of feel like a switching problem and I do not understand the switch. The switch that is actuated by your foot is a momentary switch. I wonder if the FET switch like you mentioned is replaceable? If they are not expensive I can replace some parts for the heck of it.

Thanks again DVM I really appreciate your time and help.

M29

 

[duhvoodooman]

FWIW, it looks to me from the schematic like one of the FET's is Q9, which appears to be right in the heart of the region where you fried your traces & had to do your repairs. FET's do have a reputation for fragility, so it might be worth replacing this FET just to see what happens. According to the schematic, this is a 2SC118Y type. I couldn't find that listed at Mouser, but they do list the NTE458 as a substitute. Not cheap at $3.80 apiece, but that's a whole lot less than a new MT-2....

 

[just strum]

I am sorry I should have done this through a PM but I did not know if anyone would have any idea what was wrong.

M

I thought I responded to this already (it must have been in the dream I was having about the beer girl)

Anyway, once I do my first mod, I plan on being in the thick of these threads.

A monster you have created - a monster with burnt fingers.

 

[M29]

Thanks Bob I was just looking over the schematics and layout images. Wow! What a difference to what Monte Allums sent me. The copy I got you can hardly tell what shape the board is let alone where everything is. It looks like it had been copied about 10 times and is real dark.

Thank you again for all your help. I think I am going to try the switch, I may be able to order it locally.

Strum,
I have built many kits over the years from old Harmon Kardon, Heathkit amps and TV's to Hafler stereo amps, 5 or 6 pedal mods and recently my GDS 18 watt Kit. I blame old age and ...well...old age and ...well...shoot what the heck was I just talking about...Oh...yeah amphs and girls and, wait a minute how did the girls get in there, oh shoot that was you that brought up the girls..... Shoot where did I put my..................

M

 

[duhvoodooman]

I think I am going to try the switch, I may be able to order it locally.

I don't think you understand what I'm saying about the FET "switch". It's part of the circuitry, right on the PCB. There a good description of how it works on THIS PAGE at Andreas Moller's excellent website.

All the mechanical switch does when you step on it is to complete a circuit and send a momentary "control pulse" through the pedal that causes the audio path through these FET's to open or close. This portion of your pedal obviously works fine, since the LED turns on and off.

P.S. Did you confirm that the effect acts the same way whether powered by battery or AC adapter? I can't imagine why it would be different, but stranger things have happened & it's easy enough to check.

 

[M29]

Bob,

I understand about the FET. I mistakenly called it the switch.

I had a surprise on that last note of yours. I plugged in my nine volt power supply, (1Spot) and the pedal works when the effect is (off) but when I push the switch it quits. That is weird it works on the power supply but not the battery. With the battery I get static noise and hum.

M