Quoted from pincity:
Has anyone ever had any issues with using a reset generator on an 80B board? Here’s why I’m asking:
When I got my Monte Carlo, the board in it was toast from corrosion and I rehab’d it as a learning experience.
I had the board booting, playing, etc. but every few startups, the roulette wheel and some computer controlled lights would lock on, sometimes would kick a ball into the shooter lane. Restarting, everything was back to normal. Swapping in a known good MPU, it ran very reliably every time, so the driver board seemed good.
I used an MCP130 generator in the reset section. Somewhere I read that it changes the reset delay from something like 50ms to 150ms, which increases the “thunk” and that thunk can cause weirdness in different games depending on the solenoid setup (like the roulette wheel).
Given it happens intermittently at startup, I was considering rebuilding the reset section back to original spec to see what happens but wanted to see if anyone’s had a similar issue before doing so.
Why do you use an
because usually we put an
The difference between the MCP100 and the MCP130 is that the first is a "normal" output and the second one is an
The original reset circuit uses a 4081 whose outputs are not open collectors.
Indeed, if we look closely at the 4081 documentation, we see that the outputs are driven to "+" and to "-" by two transistors. Luckily, CMOS technology is quite resilient to short circuits, and an output accidentally set to the wrong potential does not necessarily burn the output transistor.
The additional RESET card that was added (later for the first SYSTEM-80s) does not really help. Moreover, its implementation is doubtful, because despite the addition of a diode acting as open collector, it prevents that in case of reset, the output of the 4081 will be short circuit! Admittedly, it works, but it's still a DIY "made in Gottlieb".
Poor design, but the main thing to note is that
there is no pull-up resistance on the RES line
So, if you use an
, don't forget to add a pull-up resistor, otherwise, the RES line will be unstable.
Both MCP100 and MCP130 have a reset delay of 350 ms, that is not abnormal.
The "schlank" at startup is due to another misconception or the driver board. Not visible on the very first SYSTEM-80, it became obvious when they started using lamp outputs to drive coils. There are several solutions to remedy this problem, one of them using MCP100 has been described on our site: