Testing a defective touchscreen (resistive)

Hello, sometimes I leave one of my tablets in hands not so accustomed to “well-done” works, so this afternoon, I received back, from a technician, one tablet with “some defect in touch screen”. Obviously, when the tablet went out from my laboratory, it was fine, but now it isn’t. Ok, resistive touchscreen is very simple device. In order to understand what happened, I detached the flat cable from its socket and put it in another one, coming from old, used circuit. I soldered 4 wires to such used connector to measure the touchscreen resistence with a simple multimeter. In the picture below (a little bit out of focus, sorry), you can see the touchscreen’s flat cable withdrawn from the “natural” socket and inserted in the testing one.

Touchscreen flat cable removed from its socket and plugged in a wired one.

Touchscreen flat cable removed from its socket and plugged in a wired one.

The following picture one is a particular of the wiring. The four soldered wires are the X and the Y resistors of the touchscreen.

Particular of the wiring; upper two for X, lower two for Y

Particular of the wiring;  upper two are for X resistor, lower two for Y.

In the next picture you can see the multimeter, set to range 2K Ohms, that shows left positioned “1” and it means over range resistence. The multimeter cables, actually, are connected to the couple of wires at the left (upper) side of my connector. The over range indicates that the circuit is open, and it’s right, ‘cause I’m NOT tapping the touch screen in any position.

Multimeter showing out-of-range measurement (high resistence)

Multimeter shows out-of-range measurement (high resistence)

Next picture shows the multimeter measuring a value of  825 Ohm ; good, ‘cause I’m pressing with my finger approx in the middle of touchscreen, now.

reading 825 Ohm value

reading 825 Ohm value,  pressing the touch screen around the center

Now, I repeated the test moving my multimeter cables from the left two wires to the right two (the other axis of the touchscreen), but this time NO LUCK. The value read is always “1” (out-of.range) even with touch not pressed and even if pressed. So, probably the flat cable has an interruption and the touchscreen is unuseable. Looking with optical power magnifier, I noticed that “someone”, closing the tablet after hardware modding, has damaged the small flat (micro interruption) and now there is only to look around on the Internet for a spare part 🙁
Ok, hope this will be useful for someone. Bye…