TM3030 V2 issue

[grizzle]

Hi all,

I am having an issue with my TM3030 V2 that I built years and years ago and has worked fine until I opened it up to measure the PCB. When I put the cover back on and powered it up it the power LED didn't come on and it didn't respond to any midi. I checked the 5.3v pad and it measures the correct 5.3v. I then checked all the LED's with my multimeter and they all lit up except for the power LED. I pulled that LED and it illuminated fine after it was removed from the PCB. I soldered another LED that I verified worked before installing and it also wouldn't illuminate once soldered in.

Does anyone have any ideas about what the issue could be or what parts to start checking? It is a strange one and is so far stumping me.

Cheers and thanks in a advance for any help,
Alex

[Synthbuilder]

Hi Alex,

Does anyone have any ideas about what the issue could be or what parts to start checking?

If the power LED is not lighting then this indicates that the +5V is not working. The +5V supplies the digital parts of the circuit. This is different to the 5.33V which supplies the analogue circuitry.

Measure the voltage between the + and - leads of C3. This should be around 15V although the actual value will vary depending on your chosen wall wart supply. If the voltage on C3 is 0V then check that R14 is properly soldered.

Now check the voltage across the pins of C8. This should be +5V but given the LED has gone out I would suspect it is much lower. Since it was working before you opened the unit, if you have your TM3030 in a metal case, it is possible that the problem is a short from the board to the case somewhere. Check that no wire sticking out from the underside of the board isn't touching the case.

Tony

[grizzle]

Hi Tony,

I measured 19v at C3 and 4.96v at C8. One of the LED legs was touching the case. I cut it and now everything works as expected. The odd thing is the case is non-conductive (metal but powder coated) so I'm not sure how it created a short. Either way it is working great again and ready for a proper case after all these years. Thanks a lot for the help!

Cheers,
Alex

[Schlumpfhut]

The odd thing is the case is non-conductive (metal but powder coated) so I'm not sure how it created a short.

The very most powder coatings are acutally some sort of porcelain or epoxy resin which can have microcracks within its structure or even be conductive. If such crack happens near to the said LED leg it might be enough to become conductive if not before
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