Smoke and weird voltages

A project log for E-Ink Display Adapter

Using a replacement Kindle screen with an Arduino/whatever

sapirsapir 06/19/2016 at 00:174 Comments

I got my pcb some time ago and tried soldering it. I seemed to manage most of it except for the connector. It's hard to even try to solder the connector without touching and melting the plastic, or maybe I need a smaller soldering iron tip. If I order more boards, I'll be making the pads longer.

So while ruining four of my five connectors, I decided to solder everything else, if only for practice. Finally I powered it up with 2 AA batteries - not 3.3V but hopefully close enough. And got a thin column of smoke from somewhere. Turning it off and on gave the same result again, and the smoke seemed to come from somewhere around the LT1945.

After giving it a rest for a few weeks and looking at the board visually, I noticed that some of the LT1945's pins were shorted (VPOS_CTRL and GND, but I didn't check at that point), so I fixed that and tried again. Still smoke. One of the inductors wasn't soldered properly, so I fixed that, and cleaned or melted some brown stuff (flux?) next to a nearby component. No more smoke after that. Somewhere along the way, I noticed the batteries weren't giving 3V anymore, so I replaced them and finally got out the DC/DC power converter I bought from Seeedstudio a while back and got a much nicer 3.28V.

But the output voltages are all off - I'm getting +0.66V or +0.2V instead of +22/-20V. So maybe the LT1945 really is broken.

I don't really know how to continue debugging from here.

Anyway I ordered more spare parts so I can try doing it all over on a new board.

edit: I forgot but some of the LT1945's pins on the other side also looked shorted at one point, so of course I fixed that. Could maybe better explain what went wrong.


j0z0r pwn4tr0n wrote 06/26/2016 at 14:47 point

Having the same connector in my project, I would suggest using a reflow oven for that. You can use a hotplate if you don't have a dedicated oven. Also the LT1945 might have a ground pad on the bottom that would be better to be reflowed

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sapir wrote 06/27/2016 at 17:46 point

Thanks! I don't have an oven or a hotplate :/ I tried hand-soldering the fifth connector today, and so I'm now out of non-broken connectors. I think I should have made the footprint's pads longer for hand-soldering. I'd just copied the footprint from the datasheet (intended for reflow) but when the connector's on the pads, you can't really get at them with a soldering iron.

I don't think I saw a ground pad on the LT1945 but anyway the footprint I used on the PCB doesn't have one, so I can't solder it now.

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sapir wrote 06/26/2016 at 00:22 point

Turns out the diode footprints on the PCB are all backwards. After turning them all around (and some more debugging) I'm now getting +22V, -20V, +15V and -15V. I messed the LM358 up so no VCOM but there's no FPC connector attached yet, either.

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sapir wrote 06/27/2016 at 17:48 point

Tried again with a new LM358 and now VCOM works, too. Only thing left is the connector. I ruined my last connector today so I'll have to wait for my parts order before I try again.

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