So I was a naughty boy and was fiddling with a non-working pop bumber on my TAF with the machine on and blew out F115. Disconnecting J114 the fuse stays ok so that led me to the MPU. I checked the 4 LM339 using a multimeter (red on ground, black on each leg) and each one was short on the vcc leg. That isn't good right?
I also checked the ULN2803a and this was also short on the vcc and also had a diode voltage drop reading of only 0.06 on leg 16 (I think). The fuse remains ok with the 2803 removed.
Is it possible that I took out all the chips even though the fuse holds with just the 2803 removed? Does all that make logical sense?
Would be grateful for any pointers. Really annoyed as it was working nicely!!!
P.S. Also, when I buy a replacement for the ULN, I can't see that there is any difference between a 2803a and a 2803. Could someone kindly confirm if they are exactly interchangeable? Many thanks.