Burnaby, BC
Looking into a problem with our Roller Coaster Tycoon where the game would cut out the lights and coils for up to a second at random intervals. This would happen perhaps once or twice every day or two.
Digging into the game I noticed that the Dallas supervisor chip used in both the original Stern MPU and the Rottendog replacement Driver Board (SDB004) both left pin 3 (LOP) floating (clipped). Now this pin selects the Vcc tolerance - if grounded it is 5% and if tied to Vcc it is 10%. However the schematics now show pin 3 as floating.
Sega Service Bulletin SB112 (June 7, 1999) had recommended cutting pin 3 (to floating) on both Dallas DS1232s (MPU & Driver PCBs) where the factory (at that time) had connected pin 3 to Gnd(5%). Sega, then Stern continued this practice of either cutting or leaving pin 3 floating. Rottendog also did this on their replacement SDB004 White Star Driver Board.
http://arcarc.xmission.com/Pinball/Stern%20Service%20Bulletins/sb/sb112.pdf
I was curious what would happen and if this idea of cutting the leg or leaving it floating was recommended by Dallas. So I pulled up both the original Dallas documents and the Maxim Application Note and in neither case did they suggest that pin 3 should be floating - no connection.They said it was to be connected to either Gnd or Vcc.
https://datasheets.maximintegrated.com/en/ds/MAX1232.pdf
https://pdfserv.maximintegrated.com/en/an/AN581.pdf
I then asked Maxim (who now make Dallas Semi chips) to comment on what happens when pin 3 is floating - they replied today (Nov 25, 2019):
-------------(quote)--------------
Thank you for contacting us.
It is not recommended to leave the TOL pin open since it is a digital input and noise can make it oscillate, there is no internal pulling resistor, so please do indeed connect it to GND or Vcc.
Regards,
Javier Monsalve
Maxim Applications
---------------(end quote)---------
We had already tied pin 3 to Vcc (+5) as of Nov 23, 2019 to check my assumption that floating was wrong, and the intermittent cutting out problems had indeed disappeared!
The game has been running for days now with no hiccups and we shall be leaving it running at least one more day before sending it to its new home. We are monitoring the Vcc with a Mooshimeter logging 5V, to see if Vcc drops below any reasonable threshold and a Heathkit logic probe monitoring the R (pin 5) of the DS1232 as the Heathkit logic probe stores momentary state changes (turns on a 'memory' LED).
Therefore, based on our tests, and the advice from Maxim, the manufacturer of the DS1232 IC Supervisor chip, we can now say that you need to tie pin 3 of the DS1232 to Vcc! Do NOT leave it floating as per Sega Service Bulletin SB112!
Hope this helps!
John :-#)#
