On Thu, 13 Sep 2007 16:11:10 +0100 Eeyore
wrote in Message id:
:



robb wrote:

hello,
i have a 40 pin VFD driver chip SN755518N that three of the pins Q20 Q21
appeared to have gone quiet/died . Q24 seems to have its expected output
mangled.

I am trying to figure out wether i need to check out those lines (how and
what to look for) before i put a new chip in so that i do not fry the new
chip .

Could a faulty connection or other component connected to those lines fry
those pins ? or is it possible for the chip to just suddenly go bad ? is
there a typical reason for IC pins to go bad ?

what kind of test can i perform on the board to be certain that it is the
chip and not something connected to the chip ?

i put an ohm meter from grd pin to the dead lines and i get 25 MOhm reading
where other lines get 0 reading but that was not with chip disconnected
ffrom the board so i dont know if there might be a 25 MOhm short somewhere ?

Maybe it was killed by a fault in the VFD ?

I've tested and serviced several thousand of these, and never have I seen
a VFD kill a driver. A short on the other hand...