Y electronic gadgets stops working after drop, even 0 physical damage to them (6.5MB)

[khankll]

hi
the title says it all,y electronic gadgets stops working after drop,even no physical damge is done to them ,i.e no break/tear on the body or circuit..i cant remember now more instances of such happenings but one such thing is my calculator..
its casio fx-991es scientific calculator. it was droped .. and then it stopped working .. i opened it there was no damage wither to the lcd or board or anything.. battery is giving proper volts ,tried new battery , rboard is properly seated..also it does'nt seem to have any magnetic material ..

pics are below


http://img4.imageshack.us/img4/1164/picture010xh.jpg



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[Resqueline]

This gadget employs 3 unreliable (in my experience) technologies. Listed in order of unreliability:
1: epoxy-blobbed bare chip bonded straight to the PCB.
2: carbon-stripe ribbon bonded to PCB & LCD.
3: carbon-paint through-hole "plating".

All you can do to test it is:
1: measure & inspect if the battery voltage makes its way all the way to the chip.
2: measure & inspect if the ON button works & has continuity all the way to the chip.
3: measure if there's any high-frequency activity on the small capacitors near the chip (while trying to turn it on).
4: try to apply some pressure on the epoxy blob while trying to turn it on.

 

[(*steve*)]

My guess is that you managed to disconnect the LCD from the PCB.

Looking at that first picture, the LCD is not exactly aligned with the PCB. Those things (the horrible zebra stripe connection) rely on the parts never moving and several acts of god to keep them working. I hate them.

Taking the calculator apart was not the wisest move. I would have started with some mild pressure applied to various parts of the board to see if something had been jarred slightly out of position.

 

[khankll]

thanks for ur replys.
the above calculator works on either solar and cell .. the cell is registring proper 1.5 volts tried in another device [ not calculator] worked there ... tried that device cell in this calculator nahhh nothing happens..i mean no display..

however in either case the points labeld BT+ and BT- gives proper 1.5 volts reading... the solar panel voltage SP+ and SP- i checked it in the evening was giving me .6 volts which is obvious..

the lcd is connected properly .. i checked in another calculator of the same sort it was the same there .. it is not stripped/loose..

not expert but how to check the button is working ? [ i will search about it and will post results or any questions if i cant get it into my mind]

however i checked the capacitor voltage it was .6 [ point 6 volts] whareas it [cap itself ] was labeled as 6 volts..

looking forward for solution this ailment ..

 

[(*steve*)]

6V is the maximum voltage the capacitor can withstand. Any voltage less that that is fine.

If the buttons are simple contacts, measure the resistance across the switch and press it. It should go from a very high value (perhaps completely open) to a very low value (possibly 0).

The LCD appears to be at an angle, and the tape below it has a slice in it. Is there some sort of flexible connector between it and the PCB?

 

[khankll]

i have checked the lcd connector it is ok.. it appears as being cut but that is only so after taking pic.. there is no cut and all the contacts are fine..

capacitor i measured it its capacitance was 23 uF and it is labelled as 22uF.. [ i didnt remived it from circuit,, it was still on pcb]

 

[Resqueline]

Never mind the big capacitor. I was referring to the 9 small ones. At least one of them is involved in an oscillator that determines the speed of the processor.
The DC voltage on the cap's is only partially interesting. You'll have to make an RF-probe attachment for your DMM if you're to figure out if the processor is running.
And measuring BT+ and BT- only is no guarantee that the battery voltage makes its way all the way to the chip. Sometimes the cracks in the tracks are too small to see.