(Topic ID: 186616)

stern m-100 display self test errors

By creepykenny

4 years ago

Topic Stats

  • 7 posts
  • 4 Pinsiders participating
  • Latest reply 4 years ago by barakandl
  • No one calls this topic a favorite


Linked Games

#1 4 years ago

so, when entered into self test / display test, the displays should flash 000000, 111111, 222222 .... sequentially, but what i am actually getting is the zeros flashed twice, the the 2's flashed twice, then the 4's flashed twice - well you get the idea, no odd numbers are ever displayed, just repeat of previous number then a change to the next even numerals

replaced the 5101 & socket - no change,
unplugged the existing displays then plugged them in individually to eliminate the on-board decoders - no change
swapped the 6821's with known good units - no change

this also seems to be (is) affecting the scoring during gameplay as well so its not just limited to the self test, so since i don't really understand how the scoring is accomplished i am not exactly sure where to looks for the solution, game boots fine seems like it is mostly working correctly


#2 4 years ago

You'll have to look at the section of the MPU that is responsible for sending BCD number information to the displays. One of the 74xx series chips is probably bad, or there is a problem somewhere along the signal path between the 6821 and the header pins--could be the socket, could be a through-hole, could be a pad, a trace, cracked solder joint, corroded header pin...

#3 4 years ago

is this a display blanking issue ?

or latching issue?

#4 4 years ago

ha, i see, will check the gate at U20, oops stupid me put on glasses & U20 not involved, now that i can see the schematics yes, U10 is now in question

looks like a new socket is in order since traces all look good

will report back

#5 4 years ago

As ForceFlow hinted, you're missing bit 0 of the display BCD data from the MPU board to the displays. This signal is wired from pin 25 of connector J1 on the MPU board and goes to pin 19 at each display. It's used to select even/odd numbers at the displays (it appears the displays are seeing this signal stuck low causing odd numbers not to be displayed).

If you wiggle the MPU J1 connector, do the odd numbers appear?

This signal is "PA4" which comes from pin 6 of the U10 PIA chip on the MPU board.
This signal is also used to select feature lamps and is one of the switch strobes.
Are all feature lamps and switches working properly?

If you have a logic probe, check pin 19 at one of the displays connector. It should read high pulsing low and should be the same reading back at pin 6 of U10.
If you don't have a logic probe, try measuring the voltage with a multimeter at both of these points - they should read about the same. If they don't you need to trace where your open/short is.

#6 4 years ago

ok, with logic probe in hand signal PA4 is stuck low at MPU and at all displays
there is good continuity between mpu & all display connectors pin 25 to each pin 19 - and its stuck low even when all displays are un-plugged ... hmm seems like a short in the wiring

removed harness pin 25 @ J1 and of course pin 6 of U10 begins pulsing like mad, replace pin 25 and pin 6 is stuck low again

at least i know where to look, this should be a nice way to spend sunday afternoon

forceflow & quench thanks for the help!

#7 4 years ago

unplug the lamp driver board top left connector. PIA @ U10 port PA4 is multiplexed to do lamps and displays

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