Line 6 Dm4 blown diodes

[Sheepy]

Hey, I have a line 6 dm4 which I use regularly, I was using it two days ago when it turned off and I noticed smoke coming out of the power supply input, I unplugged it instantly but the smell of fumes were strong. It looks like the d16 and d11 diodes have blown and I'm wondering if I could buy those diodes and repair it myself but I can't find any information about them online. I'll include pictures but I'm not sure if the board is repairable. Any help is appreciated, thanks!

[Slowpoke101]

Welcome to the forum.

The following diagram is for a DL4 but it is almost the same for a DM4 in the area that is toasted in your unit.



D16 = 3.6V 1 Watt Zener Diode
D11 = 1N4002 GP Rectifier

The failure appears to be in common with a short circuit on the +3.3V supply rail (this powers most of the fancy logic processing gear in these things. Usually U14, D15 and L1 are faulty and have caused an over-current situation which damaged D16 and D11. But there is a strong possibility that the +3.3V rail had a higher voltage applied before the magic smoke got out. This would not be good.

Have a look around and be prepared to do some tests. Hopefully you have a multimeter that is ready to use.

[Sheepy]

Thank you! So im not the best with circuit boards but I've worked with a few of them before, I phoned the company that repairs these pedals and they said these boards are pretty reliable so something else could of caused those diodes to burn out like you said, so how can I carry out a test to find out the problem if I replace d11 and d16? Also do you know any places which sell these diodes in the UK? I've had a look around but there's not to much info about them. I've taken a look at the board again and the L1 part is covered in glue, not sure if it's meant to be like that but I'll include a pic. Cheers

[Slowpoke101]

The picture that shows the MAX887 chip is extremely clear. Very helpful indeed and is somewhat encouraging as that chip usually blows its top off in an over-current situation.

Again, do you own a multimeter? Or have access to one?
Of course the next question is; Do you know how to use it? It's not a problem if you don't know as we can teach you without too much effort.

The first step is to remove the batteries (if you have any installed and assuming that this model can use batteries )
The next step is to make sure that the power cable is physically unplugged from the effects unit. Set the multimeter to a low ohms setting, short the two test probes together and confirm that the meter displays a reading close to 0 (zero ). If it does show zero then place the red test probe onto D12's cathode (the end of the diode closest to the edge of the circuit board ) and the black test probe the D12's anode (the other end of the diode ). The meter should display the same reading as if the probes are not touching. Then reverse the probe connections to D12 and measure again. You should see a reading that is much higher than zero but less than what the meter displays when the probes are not touching. If this is what you see, then things are looking a bit more encouraging. Let us know how you go.

Where to get electronics parts in the UK. I think that Maplin have bitten the dust so that's out. The next place would be Farnell. I think they have a public service desk (for non account holders ) that will do mail order. Perhaps another forum member will chime in with some other suggestions.

Edit: Got mixed up with D11 and D12. Fixed. Definitely D12 is what I was referring to.

[bluebunny]

Maplin is indeed toast (for us).  Even before its demise (and subsequent resurrection) it had long ago stopped being useful for most of our needs.

So try: Bitsbox (let's keep the little guys alive!), Rapid, Farnell (also CPC, part of the same outfit), RS, Switch.

[Sheepy]

Thanks for the replies! I can get my hands on a multimeter soon but I'm not entirely sure how to use them to test pedals but I'll let you know when I have it.

I'll look around for the diodes in the meanwhile and I'll update you then.

Thanks!