G'day Bob,



08 Jun 96 11:51, Bob Lawrence wrote to Rod Gasson:



 RG>>> So far it has blown about 5 of them (over a 3 week period). It

 RG>>> has also blown 2 micro's in the same timeframe.



 RM>> know ) I'd suspect overvoltage, possibly caused by a power

 RM>> supply regulator going strange, maybe by losing a 0V reference.



 RG>> Tis possible, BUT I don't think so.. The last time it blew, I

 RG>> had a meter hooked up to both the 5v supply for the micro, plus

 RG>> another of the 12v supply to the drive chip. They were both

 RG>> rock steady at the time of failure.. I got it on tape :-)



 BL>   It's almost certain to be voltage, probably a 12V spike with lots



Or excessive current.



 BL> of current behind it, but I can't imagine what would do that.

 BL> The electro should soak it up. Maybe there's a broken track around

 BL> the main 5V electro or something.



Or something :-(



 BL> A meter would not read a sudden spike.



True, but I'd have expected to see the needle at least give a flicker

at the moment of failure.. I didn't.  (Yes, I still use an analogue

meter for some things)



 BL>   I'd be inclined to leave the blown ICs in place and bash the hell

 BL> out of the power supply looking for a flick upwards on the 5V rail

 BL> (or 12V or whatever is blowing ICs). The other possibility is a weird

 BL> earth return that breaks and puts current where it should not flow...

 BL> either way, you shoud see a flick on the 5V when it happens.



Heck, even with new chips and the machine working, no amount of

bashing, heating or cooling will invoke the fault.  :-(



 RG>> I don't relish the idea of forking out another $80 just to

 RG>> confirm/reject this possibilty.. but it is certainly on the

 RG>> cards if/when I get other ideas as to the actual cause of it

 RG>> all.



 BL>   When in doubt, modify. Add the big zeners and get rid of it.



I've already gone this way..  the bustard keeps coming back though. :-(



 BL> Let some other poor bugger fix it.



That's still a problem...  I'm the silly bunny that tends to get the

machines that other places around here have given up on.  Not wishing

to blow my own trumpet, but if I'm at a loss I can almost guarantee

that no one else around here would have any success with it either. :-(



It's a worry isn't it.



Cheers,

Rod



___ QWKRR128 V4.50 [F]



--- FMail 0.94