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Hi guys, I've got an EHX Micro Metal Muff which won't receive power via jack socket. To make things simple, I'm going to list all the relevant info I can;



-Using a one spot power supply (centre negative) as per the pedal's requirements. One spot is fine with all my other pedals (including other EHX models of the same age).
-Pedal works on battery power with no issues as it should do
-When using DC jack, LED doesn't light and no audio when effect engaged. Bypassed is fine.



Now to me, it would make sense that the DC jack has gone and needs to be replaced. However, testing jack with a multimeter yields the following results;



-With power adapter plugged in, multimeter still reads 9v going through.
-Judging by the datasheet located here, terminals 2 & 3 have continuity as should be expected.




Going by this additional info, I believe that the jack socket is working fine, and that the issue actually lies further down the line. The vast majority of the board is SMT, however there are a few through-hole components.


Am I going in the right direction at looking at other components? I can't see that any of the through-hole ones have shorted/burnt out, which makes me think it might be an SMT component has gone, which pretty much means this is unrepairable.

Or is it possible that it could infact be the DC jack socket and I'm being an imbecile by looking elsewhere?



If requested, I'm happy to supply pics, my only reason for omitting them is that I don't think they would supply much info.

Many thanks in advance for any help and advice!

I'm not %100 sure how you performed the tests but I think you have a bad power jack. I don't know if you had the cable inserted to the input jack when you measured the voltages. I also don't know where you ground probe was in relation to your input jack. it is possible that the power jack got fixed right when you went to test it then went back to being broke. there are some moving parts to the power jack just like 3PDT switches. when they fail they usually manifest weird problems that are inconsistent making them hard to find. this is a good reminder why I usually avoid switching power entry jacks in favor of the two terminal style.

Thanks for the advice, all testing was done without any cables plugged in, with exception to when I had my one spot plugged in to the power.


Going by what you've described to me, I think I'll replace the power jack with a new one and see how that goes.


I mean, thinking about it if I do replace the power jack with a new one, then it can't really hurt anything, right? If the new one works, great, if it doesn't, then I'll go back to hunting for the issue again.


Thanks for the advice

umm you need the guitar cable plugged to the input to test power buddy. maybe that is why it did not work.

Sorry, I should probably clarify how I tested the power jack;

Based on the datasheet I posted above, I attached my multimeter (on voltage mode) to terminals 1 & 2, which showed approx 9 volts going through the pedal with the power supply plugged into it.

I assumed this meant that the power jack itself was receiving 9volts input, and therefore was not at fault?


I would imagine I'm being an idiot and have gotten something wrong in my understanding of testing voltage, so apologies!

no your not being an idiot. you did the right thing. you didn't give up. you got your meter out and tested the power first! that is what I would do. usually the battery does not have more than 2 wires. one of those is always at the switched power entry jack. the other one is either at the PCB ground or the input ring or input sleeve or chassis ground (if you do not have plastic jacks). after confirming that the barrel connector has +9v and 0v, I would test the battery terminal on the power jack to make sure I have two different voltages. this means the power jack has disconnected the battery properly. on a 3 digit meter it is highly unlikely that you would get the same reading 9.51v barrel and 9.51v for the battery. you can also do this test with a dead battery. if the battery reads 0v, at the power entry jack, chances are good that you do not have a cable plugged to the input jack to make the pedal turn on or you have faulty power wiring in that pedal. you also need to test the switching mechanism on the power entry with the barrel power removed. you should get the same battery voltage on either + terminal of the power entry jack.

So I'm not being an idiot? That's a pleasant surprise


Seriously though, thanks a lot for the advice, really appreciated. I'll give it a go later, and go from there.