FIXED: Tech: Williams System 3/4 Hot Tip (SS) Won&#039;t Boot

Quoted from barakandl:
Crystal is likely going to be fine since the CPU is doing "stuff". Check CPU pin 37 for 0.8mhz square wave. It is the clock (logic probe pulsing good enough).

I've twice come across boards where the crystal was running st the wrong frequency (verified with logic analyzer, was only about 100KHz). Boards worked, but lights and displays flashed brightly and switches were missed, solenoids would be pulsed for too long.

Agree with barakandl though, check all the replaced sockets to make sure they're good. Leon's test ROM should give you some more info.

#18 6 years ago

ZAC

zacaj

OP
Quoted from wxforecaster:
OK, here's an update. I logic probed everything and was getting signals everywhere. Crystal had a nice pulse signal so that's not it. Reset circuit starts low and goes hi as it should, so that's not it.
So then I basically grabbed the multimeter and started doing continuity tests on all the main chips. That's when I think I stumbled onto something. Data Bus line D2 seems to have continuity to like EVERY OTHER PIN on the board. Running backwards from the 40 pin connector where I noticed the problem....
D2 "ends/starts" at Pin 16 on the 40 pin connector and runs back to pin 11 on the game/flipper ROMs (IC14/17/20) where it's socketed. From IC14, it goes to IC10 pin 10. And the other direction is goes to the 5101 RAM chip at pins 13/14...and surely a lot of other places.
Am I correct that having continuity to like nearly every other pin is a sign of a dead short on the D2 line? I'm getting continuity from it to like every other data/address line, etc. Trying to understand the electrical flow that could allow this to occur. What am I looking for to resolve it?

I assume the other data lines don't? pull all the socketed chips and see if it changes?

#20 6 years ago

ZAC

zacaj

OP
Quoted from wxforecaster:
Correct. All the other data/address lines have continuity only to themselves, except D2. The test was done with the chips out of socket. What could cause one signal line to be connected to all the others? That's what I'm not understanding electronically. If it were solder bridged to ground, what would that have to do with the other lines buzzing to it? Obviously a very simple explanation I'm not visualizing, but I've been up since 6AM.

It seems impossible for one line to have continuity to every other, but every other not to. Unless a diode is involved? Have you tried using the diode test? If there's continuity you should get 0V. See if there's 0V both ways or if it changes

#22 6 years ago

ZAC

zacaj

OP
Quoted from wxforecaster:
Maybe you're misunderstanding me. D2 line seems to have continuity to everything. Everything else (let's say D0, D1, A1, A2, A3, etc..) has continuity only to its own line (and of course D2).

D2 has continuity to D0, D1, etc. but D0 doesn't have continuity to D1? But If A is connected to B and B is connected to C, then A is connnected to C, so shouldn't D1 have continuity to D0 as well?

3 weeks later

#34 6 years ago

ZAC

zacaj