Hello. I have a Boss MT-2 distortion pedal. It will not power up with the adapter or battery. Wondering what could be wrong. Any suggestions on what to look for? Thank you!

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Battery is not the problem.
It could be transistors, IC, elco etc. It must be checked.
This electronic parts, could be almost breakdown. At the beginning of the device is turned on, it work fine, but after a while it became hot, then the value is changed, then the circuit was not working.
Can also occur on the DC input, the diode and the elco (D006,C019,C40,C41). View image.

See the full diagram here :
Boss MT 2 Metal Zone distortion pedal schematic
.

Make sure you are NOT using a TRS (stereo or three conductor cable) type cable. PLugging into the input should turn the pedal ON, not off. The switch on the jack may be broken or soldering to the circuit board may be broken OR worst case, there is a crack in the circuit board.

There is a switch contact that connects the battery when you unplug the AC adapter. These commonly get sprung and cease to make contact leaving the battery disconnected when adapter is unplugged, resulting in no power. Verify the battery is being connected and see if the unit works properly. If so the adapter is either the wrong one or defective.
In other words, there may be two problems.

Check your power adapter or battery if you are using a battery.

A few things to try....

Usually the adapter will over ride the battery when used.
1) Make sure your 1/4" cables are working properly without the pedal "in-line".

2) Take out battery, and use just the adapter only. Make sure it is the correct and proper adapter that works with Boss. Usually the PSA-120. If you are not using a Boss Adapter, make sure yours is a direct replacement with same specifications. 9V/200mA. And "tip negative". DO NOT use Radio Shack stuff, nothing against them, but there adapters just don't mix well with Boss products and the like.

2) Try just the battery, no AC adapter. Remember to unplug the input when not in use. Saves battery.

Basic rule of thumb...when using correct AC adapters for all your pedals all the time, and all sounds good, then take out the batteries.

If you still experience problems, it would be an internal IC chip most likely. From there post another question maybe.

Distortion is a very HIGH gain operation and any hum on the input will be amplified many times.

Check your guitar AND input cable for ANY hum at all at high gain settings on the amp WITHOUT the pedal in line to assure that the source is not before the pedal.

ADDITIONAL cause could be a poor power adapter for the pedal or even a bad filter cap in the pedal.

First and foremost , check your signal chain. By that, i mean put the pedal aside, ...just unhook it and take it out of your signal path. Using the same cables , guitar , amp, other pedals - borrow a friends MT-2 if you can get one , and try THAT to see if THAT works , OR any other kind of distortion pedal. If another one works ok , it's YOUR MT-2. Boss pedals are pretty rugged , but sometimes the little actuator (on/off switch) underneath the treadle (where you push your foot down) will become faulty. That's a high-gain pedal - are you using a basic Strat or other single-coil pickup guitar? If so , are you playing close to any flourescent lights? SIngle coils are noisy around those lights. Will cause a hum / buzz if using a heavy dist. pedal. You can check that by moving around as you play.

If you are using battery power, the answer is to try a new battery.

If you have an adapter for power, make SURE you are using the right one.

Make sure the in and out cables are connected correctely.

A subtle problem can be a bad power inut plug.

i got d same problm. i fixed it myself.. check all the op amp ic's if they're all gud. if youre not sure, replace all 4 rc4558 ic's. in my case, i still felt a very small output signal from my pedal (equalizers, vol n gain ctrls r gud since they vary when i change the setting) so i suspected that one or 2 of my ic's were damaged. i only replace d last two op amps which my signal passes thru. i also had this problm with my marshall drive master. same diagnosis and solution. check your schematics