My HM 4.1 was running just to test it, monitoring the temp of my house, and the LCD seems to have failed. The backlight is on, and at the right angle I can just barely make out text, I turned the variable resistor thing all the way left and right and it won't turn up any further so I suspect either the LCD or that resistor has failed, any idea how to troubleshoot it? I'm not sure I'm good enough to desolder the LCD and get it off, there are just too many pins to work loose too close together so I might have to start over or just live with it as is unless anyone has any ideas?
HM 4.1 LCD failure?
- Thread starter Philip_G
- Start date
Frank Giacinto
TVWBB Member
If the above does not work try this...
If you can see the text when held at an angle it is probably a contrast issue. If you have a voltmeter you can check the center pin of the trimpot to ground if you turn it one way the voltage should go down, if you turn it the other way the voltage should go up. The two outer pins should be 5v and GND, Check for cold solder joints.
If you can see the text when held at an angle it is probably a contrast issue. If you have a voltmeter you can check the center pin of the trimpot to ground if you turn it one way the voltage should go down, if you turn it the other way the voltage should go up. The two outer pins should be 5v and GND, Check for cold solder joints.
I'll check, but that sounds like the back light brightness, it's all the way up.
I'll check those pins, I thought the same and re soldered them to be safe but didn't know which pin did what. Thanks
backlight was up to 100% from me testing it, no change there.
The trimpot gets 4.88-4.9V to the outer two pins and the same to the center to outer pin when turned all the way up (there for testing, turning it down makes it worse) as soon as I figure out which pin carries power to the LCD I'll check that too, I think it's labled
The trimpot gets 4.88-4.9V to the outer two pins and the same to the center to outer pin when turned all the way up (there for testing, turning it down makes it worse) as soon as I figure out which pin carries power to the LCD I'll check that too, I think it's labled
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Bryan Mayland
TVWBB Hall of Fame
With the ground probe on pin 1 of the LCD, measure pin 2 and pin 3 of the LCD. Pin 2 should be 5V and pin 3 should vary when you turn the pot. The proper value for contrast, pin 3 should be around 1V. I must have a dozen of these LCDs around here and I've put them through all sorts of ill-advised environments and I've never seen one flake out.
Ah, I wondered about that, pin 1 and 2 measure the same voltage as the trimpot, 4.89. I wondered why changing the pot didn't change that. 1 and 3 measures 0.0 turned counterclockwise (this gives me the only slightly readable screen) and 4.9 turned all the way clockwise. it was somewhere near the bottom when it was working (counter clockwise)
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currently set to 1.15V no readability at all.
Whatever those matte black dome things are on the back of the LCD, one got hot enough to brown the paper label over it a little FWIW.
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Nope. I was pretty careful about that. I had one that was questionable so I heated it up and sucked the excess up with a desoldering tool before powering it up for the first time. I'll do the rest real quick just to be sure though.
Not the greatest soldering job but the joints are all working.
#1 and #2 don't touch, that's just a bit that sticks out up high, an illusion from the camera. if power and ground were shorted I'd probably know
I sucked it up anyway and retouched #6 and #10
I have good continuity between each pin space on the top unused row of pins and the back of the pin header thing on the back of the board, so those connections should all be good. Really bums me out, it was working perfectly. Might have to salvage the atmega and start over.
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Steve_M
TVWBB Guru
Using a solder sucker or some braid, it shouldn't be too difficult to get the display off. If you do it on the HM board side, you could leave the pin-header attached to the display and then just buy a new display and pin header.
Or if you have a dremel or something similar, maybe try and cut the pins between the display PCB and the HM PCB and then you can remove the remaining pins one by one?
Or if you have a dremel or something similar, maybe try and cut the pins between the display PCB and the HM PCB and then you can remove the remaining pins one by one?
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Bryan Mayland
TVWBB Hall of Fame
The contrast is one of the simpler connections to the LCD, it's just a simple path to ground through the trim pot. I can't imagine what else could be wrong, especially because your voltages all check out and read correctly. It seems like it might actually be that the LCD is toast.
I also have a very hard time desoldering things. I'd give it a try, even if you have to destroy the LCD. I mean $15 to get a new one is a lot better than a whole new HeaterMeter right? If things go very poorly, send me a message and I can probably hook you up with a v4.1 board single.
I also have a very hard time desoldering things. I'd give it a try, even if you have to destroy the LCD. I mean $15 to get a new one is a lot better than a whole new HeaterMeter right? If things go very poorly, send me a message and I can probably hook you up with a v4.1 board single.
Well, thanks for all the help. I'll try to desolder it but my experience is the sucker doesn't get all the solder out and you end up with a really thin joint that sets as soon as it cools if you can't pull the pin out while it's hot, but I'm not super skilled at it either. I have nothing to lose so I'll give it a shot when I get back into town. A local guy has a spare board so I can get one if I need it, he bought three and I got one, he got one, I'll just buy the third no big deal, if I have to start over the next one will be soldered better anyway.
I originally built the hm to monitor temps on my pellet grill cooks but I want to build a uds to use it in more of its full capacity, it's a really neat little device I'm really impressed.
That could work, if I cut the plastic between the header pins I could push them out under heat one at a time, good idea thanks
Steve_M
TVWBB Guru
I actually removed the LCD tonight. Went through 3 rounds of solder sucking of the short side of the pins on the HM board, then I clipped the pins as close to the board as I could and did another round of solder sucking. At this point I was able to wiggle the screen back and forth and was able to remove the display.
I'm really liking the transflective display.
I'm really liking the transflective display.
Bryan Mayland
TVWBB Hall of Fame
Awesome! Yeah I really like the transreflective displays too. Which one is that, the NHD-0216K1Z-FSW-FBW-L or NHD-0216K1Z-FSW-FTW-FB1 (fixed contrast)? I was going to add it to the LCD Color Gallery in the wiki if you don't mind.
Bryan Mayland
TVWBB Hall of Fame
ha HA! I bought an orange one a few weeks ago. It's not bad, but I prefer the "pure green" still. Maybe I like the white too. The red is really hard to read for me for some reason so I don't recommend it. One day I will have seen all the colors!