Monochron Contrast Issue

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stinkbutt
 
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Re: Monochron Contrast Issue

Post by stinkbutt »

Would you look at that. Manually running a wire from the pot to the pin fixes the problem. Now, I'm not going to suggest this is a design flaw, since I'm pretty much the only person who appears to have experienced this issue, and it's likely it was merely a fabrication issue with the original trace. (I'm going to blame China, not my heavy hand with the Weller. At least it's pretty to think so.)

Thanks for the quick replies, Ada. They very much helped me clarify my thinking and isolate the problem.

adafruit
 
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Re: Monochron Contrast Issue

Post by adafruit »

hmm, we have not heard this problem before so it is interesting to hear. you could look for a splotch of copper shorting it. that would be interesting to see. the PCBs are made in the USA tho :)

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stinkbutt
 
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Re: Monochron Contrast Issue

Post by stinkbutt »

Next time I open the case I'll examine the PCB, put it up to a light, report anything unusual.

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w1sby
 
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Re: Monochron Contrast Issue

Post by w1sby »

I'm having the same issue... I'll be watching with interest.
Received the kit today, assembled this evening.

73 de Allen, W1SBY

adafruit
 
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Re: Monochron Contrast Issue

Post by adafruit »

hey w1sby, can you do the same tests? we hope we did not receive a batch of icky PCBs or pots :(

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w1sby
 
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Re: Monochron Contrast Issue

Post by w1sby »

I'll get on it tomorrow evening :D

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stinkbutt
 
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Re: Monochron Contrast Issue

Post by stinkbutt »

BANNED' awesome! I'm the Bob Woodward of the Monochron!

(I'd be the Leonard Berstein but I don't like music enough.)

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w1sby
 
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Re: Monochron Contrast Issue

Post by w1sby »

OK, I did the tests as requested, all was as it should be.

I am sure it is a defective board. I pulled the pot and checked from the middle pad to ground and had continuity. Not good.
I used a dremel tool to clean up the area around the middle pad as the traces are quite close. Didn't help.
I ended up cutting pin three of the display board and using the same kludge as stinkbutt (love that handle LOL). and Shazzam! I have a display.

I hope you don't have a ton of boards with a problem out there...

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Re: Monochron Contrast Issue

Post by adafruit »

:( thanks for doing these tests. We will examine the PCBs we have immediately. we had them tested so its a little strange there should be such a problem.

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stinkbutt
 
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Re: Monochron Contrast Issue

Post by stinkbutt »

The fix for this issue is very easy:

1. Don't clip the leads to the adjustment pot after you solder it in. This is to make it easier to pull out if you discover this issue. If it's not an issue for you, no big deal, just clip 'em afterward.

2. If you do have an issue, desolder the pot out and take the middle pin and bend it up, so it points towards the center of the board when you seat the other two pins of the pot.

3. Solder a wire to that pin. Solder the other two pins of the pot back in, with the wire hanging loose.

4. Remove the third pin from the bridge between the board and the LCD. It's pin #3. You should see the trace that leads to it on the bottom of the board, but more importantly, the pins are clearly numbered on the LCD.

Be careful - This is the only tricky point! I used one of the Adafruit flush diagonal cutters to nip the male headers at the two thin points around pin #3. Big mistake. I nearly pulled the entire header out of the LCD. You're better off using a box cutter or an exacto to saw your way down. Provided you can avoid slicing open your finger. I don't own a Dremel but I imagine there's got to be some sort of attachment that'd let you slice your way through.
lcd12864black.jpg
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5. Take the other end of your wire and solder it to the recently removed terminal.

You're done.

c_4
 
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Re: Monochron Contrast Issue

Post by c_4 »

I just got my Monochron kit and it has the same problem: the contrast adjustment is shorted to ground on the PC board.

I had to cut the trace at the pad on both ends (at the pad on the connector to the LCD, and at the pad at the trim pot) in order to get an open circuit reading, so it's the trace in between these pads that is shorted somewhere..

Since cutting the trace at both ends isolates the shorted trace, I don't have to cut or pull pins: just tack on a short piece of wire between the pads and everything will work fine.

I'd suggest checking the PCB layout files- there's probably some little place where the geometry is such that the etch is not complete and there's a little copper whisker that's causing the problem.. If you just widen the clearances all along that trace, it should totally resolve the issue..

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Re: Monochron Contrast Issue

Post by adafruit »

We went through all the PCBs last night and found that 1/10 had a short from the pot to ground. It was a mistake made by the PCB factory :( we took out all the bad PCBs from kits but some already made it out. If you find this problem you can fix it pretty quickly with a BANNED blade / xacto knife by cutting the little copper trace. we're sorry about that - its a very rare occurrence and we'll have full electrical testing from now on. if your kit is unassembled we can also just send you a new PCB
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