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I have successfully repaired a connection which was either anisotropic or monostropic conductive film which connected an LCD display on a central heating thermostat (Honeywell CM901). I made a tool that applied heat and pressure. Details of what I did are on my website. https://lesjhobbies.weebly.com/repairing-honeywell-cm901-display-fault.html
I found very little information about how these connections are made on the web. The temperature (135 Deg. C) and pressure (30 KG per sq cm) that I used was about all I could find. I doubt that this will be any help to you.
Thank you for your reply:
At your website you writes: I found I needed between 10 and 11 volts to raise the temperature to about 135 Deg. C (About 22 watts ) With the two pieces of aluminium not touching I raised the temperature to 135 Deg.
How did you calculate those 10 and 11 volts to raise the temperature to about 135 Deg. C?And how soon did you reach that temperature?
(I would have expected mains voltage to be needed.)
Thank you.
I did not calculate the voltage. I held a very small thermocouple against the heated plate and adjusted the voltage to get a temperature just above 130 Deg. C I did not think it worth while setting up a closed loop temperature control system for a one off job. (Or experiment as it was at that stage.) I only quoted the voltage so anyone else had an idea of the power required as they would probably use a different heating element which would be goverened by what they had in their junk box or could obtain easily.
Les,
Thanks for your reply.
If I understood, in a correct way, you waited till you reached 130°C and only then started bonding.
I would expect bonding to start as soon as the temperature starts raising (not after the temperature is reached.)
But you were successfull, so your method was correct.
You also mentioned you had found some info how it was made in the factory. Do you have a link?
Thank you.
I did not make a note of the link when I found the information and I have not been able to find it again. This is a copy of the screen shot I captured.
**broken link removed**
Before attempting to repair the bond I had found the voltage that gave a steady state temperature of just above 130 Deg. C After applying the pressure I waited a few seconds then switched off the power and directed compressed air at the plate to cool it.
Long time ago i had a big problem with one of these elastomeric connectors too. It was for a digital volt meter that i liked but the display was missing some segments (LCD). When i looked into it, i found the connector was not making good enough contact with the glass on the LCD. When i pressed slightly it worked, but when i released it it did not work again.
The fix was to install a small black binder clip, which kept pressure on the connector at all times. After installing, the silver metal 'handles' of the binder clip are removed, and what is left is just the black spring part of the binder clip. That lasted for many years, but eventually the whole meter started acting up so i junked it. I got another 10 years or more out of it after the fix however.
Hi MrAl,
The problem I had was where the film strip connected to the PCB. Not where it met the LCD glass. From looking for a fix on the web for this range of thermostats (Honeywell CM901, CM921, CM907 and CM927) this seemed to be a common fault. There was no mention of problems with the connection at the LCD end. I suspect that the LCD was supplied to Honeywell with the strip bonded at the LCD end and Honeywell did the bonding to the PCB. It looks like their method is not as good as the LCD manufacturers. From reports on the web some people managed to repair the connection using a hair dryer and applying pressure to the connection. I first tried this method but using a hot air soldering station set on a low setting instead of a hair dryer. This made the problem worse in my case.
Oh yes, heat could be a problem due to the material reaction to heat.
Now that you mention it though i cant remember if it was the connection between the glass and connector or connector and board that was bad, but in my case it didnt matter that much because all i did was used some pressure from the binder clip to help keep the connection solid enough for the tiny currents required for the LCD.
Some people i have talked to in the distant past recommended getting a new connector piece, that is, the elastomeric part that goes between the board and the LCD glass. They said that sometimes that's the only way to fix it. I have never tried that though becasue i had already junked the meter and never tried to take one apart again in that manner. Not only that, i am not sure i would know where to get one for some specific product anyway.
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