Damaged HeaterMeter Help - Which components are bad?


 

Robert Burditt

TVWBB Member
Hi, I built a HM for a friend of mine and it was damage by "dropping it" or something.

I am trying to figure out which components are problematic. Right now, everything works except for the LCD.

I replaced the LCD with a new one and it still isn't working. The only new thing that seems to have happened since I attached the new LCD is that the yellow and red LEDs are on the whole time. I did make sure it wasn't the brightness of the LCD being all the way off.

I don't know how all of the electronics work in order to troubleshoot and/or replace potential faulty parts. Can anyone help?

BTW, it must take mad skills to desolder! I tried for an hour or so with a wick and although I removed most of the solder, I couldn't get it to come off. I ended up with a dremel and a really tiny grinding sphere that was the perfect width to fit between the individual pins. There must be a better way.

Thanks!
 
Pics?

Bare HM or with rPI?

Could you log into it?

Maybe the fall broke a cold solder joint, but that should be easy to fix. Did you get the rPI to boot with it unplugged?

Multi-pin parts like the shift register are a real pain to desolder. You're better off cutting the legs of the IC, tossing it and desoldering each leg one at a time. Then use the solder wick to clean up the holes/pads. And you're gonna need a good iron for this.

Desoldering tip: solder is your friend! As counter-intuitive as it may seem, feed solder into the joint and then pop the component leg free. The extra solder aids in heat transmission to the joint. You can clean away the excess solder later.
 
If the HM was dropped I would pull the SD card and re-image it (assuming it's not a stand alone unit). If the SD card comes loose the program can get jacked up and all sorts of strange things can happen...
 
It is a HM with rPI. I can log into it. I can see it thru the web interface. The probes are reporting correctly. Everything seems to be fine except the LCD.
I previously re-imaged the SD card.

I did notice the shift register looks compromised. Could this be the issue? There looks like a small crack along the side of it. I don't remember this happening when I built it. Makes me really wonder what happened to it physically....Here are links to pics of it.

https://picasaweb.google.com/lh/photo/i3bPZvrj-j7l-F1BcvmlWNMTjNZETYmyPJy0liipFm0?feat=directlink
https://picasaweb.google.com/lh/photo/yWBAACtQM7RdoWb7NhuSrNMTjNZETYmyPJy0liipFm0?feat=directlink
 
I can't zoom into the pic, but that shift register shouldn't look like that. Do you have a spare on-hand? if so, just use some flush-cuts to nip off the legs and replace it.
 
I don't have a spare but I'll go ahead and remove it tonight. Radio Shack should have one so maybe I'll have another tomorrow. Do you know what it's function is for the HM? Is it for the LCD or other functions?
 
It sounds like this might be the problem piece then. Matt, thanks for the desolder tip. It was much easier removing the shift register than the way I removed the LCD. I'll post after I get the new sr installed.
 
I agree, it sounds like the shift bit register. A solder sucker also aids in removing solder and getting it free. It may take a few times but works better for multi-pin parts I want to reuse.
 
Ok, I finally picked up a shift register and installed it. I'm having the same problem. The backlight is on and so is LED 2 & 3. Everything works fine thru the web interface but no love with the LCD (other than the backlight). Before I scrap it and re-build the board from scratch, does anyone have suggestions for running down the problem? Is there anything I could check with a meter to isolate the issue? I rechecked my solder joints and they all look good.
 
take closeup pictures of the board and the display and then zoom in and follow the traces where you desoldered the display. Sometimes a trace can get broken and it can be hard to see with the naked eye. I had this happen to me early on when I was doing a lot of fiddling with my boards and display, ribbons etc. I tracked down the broken trace and jumpered with wire and havent had a problem since..... (also look for solder bridges while you are at it..)
 
Can't see your pic close up but looks like your solder joints are lacking solder it should flow through to both sides of the component leads. yours show hole with no solder showing on component side
 
If I had the schematic, could I use my meter as continuity tester between each of the different contacts to find the fault? I saw the 4.1 schematic in the github. Is the 4.0 still available?
 
Ok, it's all good now. It turned out to be a flashing issue. Not sure why. I'm positive that I tried it before too (I thought more than once). So even though the web interface was working fine, when I re-flashed it, the LCD came back to life. Thanks to everyone for the help.
 

 

Back
Top