(Topic ID: 285977)

Black Knight player 3 and 4 commas stuck on

By solarvalue

9 months ago


Topic Heartbeat

Topic Stats

  • 12 posts
  • 2 Pinsiders participating
  • Latest reply 9 months ago by Schwaggs
  • No one calls this topic a favorite

You

Linked Games

Topic Gallery

View topic image gallery

0D7E2612-5949-4754-AED6-ABDCE2FD1AC3 (resized).jpeg

#1 9 months ago

Hi all,

I have an issue with my BK. The commas in the player 3 and 4 displays are always on. Anyone come across this before?
I can see in the schematic that IC36 on the MPU is associated with the commas and there is also a capacitor C82 which is for the player 3 and 4 comma outputs. Do you think either of these components may be causing the issue?

Thanks

#2 9 months ago

The caps on the MPU board are filter caps and rarely fail. To test if the problem is on the MPU or Master Display board, unplug J8 from the MPU board and see if the commas turn off. If they do, I would suspect the MPU. If they don't, I would suspect the Master Display board.

#3 9 months ago
Quoted from Schwaggs:

If they do, I would suspect the MPU.

Yep, no commas with J8 disconnected.

#4 9 months ago

That points to IC36 6821 PIA being the culprit.

Is it and another PIA on the MPU or Driver board socketed by chance? If so, you could swap them around to see if the problem follows the chip.

#5 9 months ago
Quoted from Schwaggs:

Is it and another PIA on the MPU or Driver board socketed by chance? If so, you could swap them around to see if the problem follows the chip.

Not socketed unfortunately, but I will put a socket in if I need to replace it. Is there a way to test the chip with a logic probe?

#6 9 months ago
Quoted from solarvalue:

Not socketed unfortunately, but I will put a socket in if I need to replace it. Is there a way to test the chip with a logic probe?

You can test pins 16 (comma 3-4) and 17 (comma 1-2) on IC36 to see if they are HI when the commas should be on and LOW when the commas should be off.

Pin 16 is probably stuck HI

#7 9 months ago
Quoted from Schwaggs:

You can test pins 16 (comma 3-4) and 17 (comma 1-2) on IC36 to see if they are HI with the commas should be on and LOW when the commas should be off.

Pin 16 is probably stuck HI

Great, but since I am a beginner with the logic probe can you please give me a few pointers? Where is the best place to get power and ground for the probe and should the probe be set to CMOS or TTL?

#8 9 months ago

You can connect the power connections to the test points on the MPU board (see the circles on the picture I attached). Set the switch on the probe (if it has one) to TTL and touch the probe to the leg of the pin you want to test. Try not to bridge 2 pins together.

0D7E2612-5949-4754-AED6-ABDCE2FD1AC3 (resized).jpeg
#9 9 months ago

Thanks, 16 is stuck HI, 17 is pulsing HI and LO as it should in attract mode.

#10 9 months ago
Quoted from solarvalue:

Thanks, 16 is stuck HI, 17 is pulsing HI and LO as it should in attract mode.

Looks like you found the smoking gun!

#11 9 months ago

Replaced the chip today and it fixed the problem. Thanks for your help Schwaggs , even though we suspected the chip from the start, it was good to go through the process of ruling out other issues. In the past, I have just blindly started replacing perfectly good components before narrowing down the problem.

#12 9 months ago

Awesome! Congrats on the fix!

You are welcome, I’m happy to help!

And in this case, the problem could easily have been one of the AND gates or the 7180 on the master display board. As you said, nice to know for sure before replacing perfectly good parts. It will be especially important as these parts are used up.

Hey there! Got a moment?

Great to see you're enjoying Pinside! Did you know Pinside is able to run thanks to donations from our visitors? Please donate to Pinside, support the site and get anext to your username to show for it! Donate to Pinside