Short in 4.3 LCD/Button Board


 
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Eric Bishop

New member
I just finished assembling a HeaterMeter 4.3 kit. Having read some of the troubleshooting threads and having zero confidence in my rusty soldering skills, I decided it might be a good idea to do some testing with my multimeter before powering everything up. The good news is that everything that I checked on the main board looked fine. The bad news is that there seems to be a short between ground and 5V on the LCD/Button board.

I looked everything over as close as I could and wasn't able to identify any solder bridges. I tried lightly scrubbing a few spots with isopropyl alcohol and a toothbrush to no avail.

I guess my next step is to buy a solder wick and start pulling things apart until the short disappears. Any sage advice from someone who's been down this road before?

Here are some assembly photos from my phone. If it would be helpful, I could post some higher resolution photos tomorrow.


https://photos.app.goo.gl/j3PRfzKAwhSF77h92
 
My guess is you added to much solder on the header pins and the plastic piece is covering up the solder bridge. The 5v and gnd are next to each orher.
 
That's crazy because I am looking over that board and it looks really good, if anything it could use a little more solder in some places! I've looked over your photos and I can't see anything where solder is even close to touching. Are you sure about the short? I'm sure that is a dumb question but I'm at a loss as to where it could be. The two places where GND and 5V are adjacent are on the top right pins of the right input pin header, and the left pins 1 and 2 on the LCD. Those would be my best bet for where the issue could lie.

I get about 6kohms resistance between 5V and GND on my LCD/Button board sitting on my desk here, if that helps at all.
 
I thought the same thing, solder looks nice on the LCD header (and great job on the pics!). The only place that looked heavy on solder was the contrast pot, since it does have 5v on it and is surrounded by ground plane that looked like the most likely place for a short. You do have a good point though, what makes us so sure we actually have a 5v short to ground in the first place?
 
Thanks for all the quick responses.

My multimeter has a continuity testing mode that beeps + shows short on the display or conversely shows open on the display. I measured several points that are either ground or 5v and see 0.2 Ohm resistance between them.

I think Ralph was probably on the right track with contrast pot. I checked all three legs on that and they are also showing a short to ground/5v. I had a hard time getting the first leg soldered on, so I think I probably just overheated it. My desoldering kit just arrived, so I'll start there and move on to the header pins and the LCD header if that's not it.

Reading through the soldering tips from WBegg, I think I probably spent too much time on a few pads. That combined with the 20 year old RadioShack soldering iron were probably my undoing. I have a feeling this is going to be one of those cases where my frugality ends up costing me time and money in the long run.
 
I put together the first HeaterMeter with a Radio Shack! Yes they are not so great. Still, it would be unusual to damage a pot while soldering it so that seems strange but perhaps the power of The Shack compels it. The potentiometer should be pretty easy to desolder due to it not actually going through the PCB. You can just start with the top leg, heat it until the solder flows then apply a little force on the plastic part and the leg should lift from the pad. Then apply heat on one of the other legs (not the ground one probably) and give it a little twist to lift that leg. Finally, do the ground pin and just pull the part free while the solder is hot.
 
It turns out the pot is undamaged. I pulled off the set of header pins that have 5v and gnd adjacent and didn't see anything unusual under there. I also decoupled the LCD board from the button board and didn't find anything there. After all that the short persists.

At this point I'm pretty sure I've damaged the PCB somewhere. I think it's time to call this one dead and start fresh. I'm also going to retire the RadioShack soldering iron. It was probably 99% me bungling around with that first pot pin and 1% this iron being too hot, if I'm honestly assigning blame. But I may as well make it easier on myself by using proper equipment.

So far everything is working well on the main board. It's hooked up to the RPi, reading temps from a thermocouple and thermistor, and sending 12v to the blower.

Thanks for all the help.
 
Well that stinks, it is a shame it wasn't as easy as just being the potentiometer. If you want, you can either mail me the board and I can take a look at it for you, or if you want to give it another go I can give you a half off store prices deal on the parts you need. If you think the LCD is in good shape, that's like 1/4 of the price right there. If either of these sound good just email me at heatermeter@capnbry.net and we'll see what we can work out. And before I can even hit post you've already ordered a set of boards. I'll email you this in case you want to go a different way.
 
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