Test issues in Temperature Sensor

Thread Starter

andrew74

Joined Jul 25, 2022
55
Hi!
I have some spare time and would like to try to figure out (possibly fix) why the LCD screen on this display doesn't work.
It's my first time doing something like this, so I'm the most inexperienced person of all.
I am attaching the photos.

- There is currently a battery that supplies about 1.8V, but the screen has not turned on.
- I opened it up and would like to test with the multimeter if there are any shorts between Vcc and GND, I will do that shortly
- I rotated the small potentiometer on the board with the screwdriver, thinking it was the screen offset ... but nothing happens

I have a few questions:
1) I don't understand how the LCD is powered .. there are those 4 wires that are connected to 3 buttons, so not to the display .. I circled with red color in the picture what I think is the connection to the LCD. Am I wrong?

2) Excuse my ignorance, there should be a microcontroller .. right? Where is it? That black plastic ball in the centre was glued with the front shell of the device to hold them together... but I see that a lot of tracks on the pcb go there... is there a micro underneath?

3) Perhaps the display lights up when it receives data from the temperature sensor? .. which is now disassembled and would be connected to the two white cables coming onto the board

What can I do to test where the problem is?

20220924_185204.jpg

1664039423948.png
 

MrChips

Joined Oct 2, 2009
27,112
The black circular blob is the MCU (microcontroller unit) commonly known as COB, computer on board.

First step is to remove the battery and measure the battery voltage.
It should measure close to what is indicated on the battery.

Next step is to insert the battery and measure the battery voltage again.
It should measure close to the first reading. Remove the battery.

Next step is to clean the gold plated contacts with IPA (not Indian Pale Ale but isopropyl alcohol. You save the former for celebration after a successful repair).

Remove the battery first. Connect the display then insert the battery.
Adjust the trimpot in case this is a contrast adjustment.
 

Thread Starter

andrew74

Joined Jul 25, 2022
55
The black circular blob is the MCU (microcontroller unit) commonly known as COB, computer on board.

First step is to remove the battery and measure the battery voltage.
It should measure close to what is indicated on the battery.

Next step is to insert the battery and measure the battery voltage again.
It should measure close to the first reading. Remove the battery.

Next step is to clean the gold plated contacts with IPA (not Indian Pale Ale but isopropyl alcohol. You save the former for celebration after a successful repair).

Remove the battery first. Connect the display then insert the battery.
Adjust the trimpot in case this is a contrast adjustment.
The battery has no problems, both off-load and connected it measures about 2V.

At the moment I only have denatured ethyl alcohol .. can I use acetone instead of isopropyl alcohol?
 

Kjeldgaard

Joined Apr 7, 2016
470
2 Volt battery, sounds a bit mysterious.

My guess would be either 1.5 Volt Alkaline in size AA or AAA, or some lithium with a voltage of 3 Volts.
 

Thread Starter

andrew74

Joined Jul 25, 2022
55
The black circular blob is the MCU (microcontroller unit) commonly known as COB, computer on board.

First step is to remove the battery and measure the battery voltage.
It should measure close to what is indicated on the battery.

Next step is to insert the battery and measure the battery voltage again.
It should measure close to the first reading. Remove the battery.

Next step is to clean the gold plated contacts with IPA (not Indian Pale Ale but isopropyl alcohol. You save the former for celebration after a successful repair).

Remove the battery first. Connect the display then insert the battery.
Adjust the trimpot in case this is a contrast adjustment.
Still doesn't work after these steps
 

Thread Starter

andrew74

Joined Jul 25, 2022
55
The black circular blob is the MCU (microcontroller unit) commonly known as COB, computer on board.

First step is to remove the battery and measure the battery voltage.
It should measure close to what is indicated on the battery.

Next step is to insert the battery and measure the battery voltage again.
It should measure close to the first reading. Remove the battery.

Next step is to clean the gold plated contacts with IPA (not Indian Pale Ale but isopropyl alcohol. You save the former for celebration after a successful repair).

Remove the battery first. Connect the display then insert the battery.
Adjust the trimpot in case this is a contrast adjustment.
Unfortunately, I don't have a multimeter that beeps when it detects a short between the two probes (red and black)... so I'm asking if I can somehow always with the multimeter but with another mode like diode mode, or low resistance .. check whether there is a short between the power supply and gnd.
 

MrChips

Joined Oct 2, 2009
27,112
What is the battery voltage when the battery is removed?
What is the battery voltage with the battery installed in the device?
 

MrChips

Joined Oct 2, 2009
27,112
The unit has an LCD.
How is the LCD electrically connected to the board?
It is common to use a conductive zebra elastomeric connection.

1665148333307.png

If this is the case, make sure that the zebra strip is clean and correctly seated between the LCD and the board.
 

Thread Starter

andrew74

Joined Jul 25, 2022
55
The unit has an LCD.
How is the LCD electrically connected to the board?
It is common to use a conductive zebra elastomeric connection.

View attachment 277881

If this is the case, make sure that the zebra strip is clean and correctly seated between the LCD and the board.
I have cleaned both this pink rubber and the insert in which it was mounted, but it still does not go.

I'm beginning to think that it would take me less time to make a new sensor (and print the pcb for it) than it would to try to figure out where is the problem.:D


WhatsApp Image 2022-10-08 at 15.49.34.jpegWhatsApp Image 2022-10-08 at 15.49.35.jpeg
 

Thread Starter

andrew74

Joined Jul 25, 2022
55
The unit has an LCD.
How is the LCD electrically connected to the board?
It is common to use a conductive zebra elastomeric connection.

View attachment 277881

If this is the case, make sure that the zebra strip is clean and correctly seated between the LCD and the board.
Here is the datasheet of the sensor I have to repair. I am reading it. If you find any useful information in the datasheet please write it down
 

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