Electronics > Repair

How to fix/check LCD display from Jumo tstat

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ace1903:
I replaced Jumo thermostat at cookie factory on baking machine. Sadly no one remembers old temperature setting.
I need to fix old controller just to be able to read its settings. Currently I can read some segments but some are not shown.
To me it looks like that Epson SED1510 chip gets correct power and data signals since I can read error message when probe is disconnected.
But upper row is missing a lot of segments.
What can go broke on these TN displays? Used IPA to clean zebra strips and the panel but no improvement.
When I was young, I remember that one old repair men used multimeter on mega ohm range to test the segments on displays like this.
I tried but I am not getting any to be shown dark, even the ones that I saw working when connected to the controller PCB.
Mechanical contact on zebra strips seems good. There are no signs on mechanical damage on the glass.
Attached two pictures of the display part.



 

DavidAlfa:
What's on the LCD top right corner? Looks like a little chip came off.

wraper:
Apparently it's an overheating protection device, not a thermostat. So temperature setting should be a bit higher than max temperature setting on that oven. If you replaced it with the same device, you could try simply swapping LCD controller PCB/LCD  (should take only a few minutes on site), or transferring EEPROM IC to the new controller. As DavidAlfa said, it looks like LCD has a chipped corner.

james_s:
How feasible would it be to find another idendical thermostat with a good display? That's probably going to be the easiest, assuming that is a chip in the glass that it appears to be.

ace1903:
Checked and indeed glass is chipped on the corner. Conductive strip doesn't cover that part and there is no pad under it.
This device is already 20 years old and is replaced with new series with same name but newer hardware.

Main use it is to be safety device to limit overheating. But I think that designer of the machine uses one feature of the controller that is called warning temperature.
One can set warning temperature and the controller will open and close relay contacts with hysteresis around this temperature.
But if temperature goes above set alarm temperature relay goes off and never goes on unless manually reset.
This warning temperature and hysteresis around it is what I am trying to find out.

On the PCB there is connector to connect adaptor to PC and t read settings from the PC.
But since there are two versions of the hardware old plain TTL and newer with Modbus probably there are two versions of PC software.
I have one and can not connect and guessing that is wrong one. I am truing with simple ttl converter and I don't have old Jumo adapter. Lot of variables that lead to failure.

I can find old hardware on ebay but shipping time is month+ so not benefit from that also. One simple part replacement ended in endless story of cookies that are not good enough. But that is the price of 20years old equipment and no-one carrying to read parameters properly in those 20years.

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