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(Topic ID: 257215)

DE TFTC not your standard switch matrix issue


By debaser

11 months ago



Topic Stats

  • 13 posts
  • 6 Pinsiders participating
  • Latest reply 11 months ago by kvan99
  • Topic is favorited by 1 Pinsider

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#1 11 months ago

Working on a DE Tales from the Crypt that is having an odd switch matrix issue. 2 switches in column 7 (switch 52 - Super VUK and switch 55 - Power Scoop) do not register a majority of the time as tested directly at the board with a jumper wire directly at CN8 & CN10 with those connectors from the playfield removed. All the other switches register every time you activate them with the jumper wire but 52 and 55 only register occasionally.

I've removed/reflowed the solder for the header pins at both CN8 and CN10. I tested Q49 and it was good but I replaced it anyways. I've tested the bussed resistor networks at RA6 and RA11 and they are good. I also swapped out the 74LS244 at 8J and the 6821 at 8H even tho both of those tested fine with my chip tester. RA16 tests good as well.

In looking at the schematics, switch 52 at CN10 pin 6 goes to the 4011 at 5J and switch 55 at CN10 pin 2 goes to the 4011 at 6J before the signal goes to the PIA, which I've already replaced. Is it possible that both 4011's have an isolated issue causing these two switches to not register most of the time?

#2 11 months ago

Do a diode test on D26-D33 with them still in the board. They should be between .4-.6v. In this case, D32 and D29 are the ones most interested in, but I always find it quick and easy to measure them all in case there is another issue that may not be noticeable through the other testing you did.

If any fall out of that range, replace them.

#3 11 months ago
Quoted from PinballManiac40:

Do a diode test on D26-D33 with them still in the board. They should be between .4-.6v. In this case, D32 and D29 are the ones most interested in, but I always find it quick and easy to measure them all in case there is another issue that may not be noticeable through the other testing you did.
If any fall out of that range, replace them.

I already tested those and they are good. At this point the only other thing I can think of would be 1 or both of the 4011's.

#4 11 months ago

I desoldered the 4011 at 6J and tested it with my chip tester and it passed. I installed a new one anyway and switch 55 is still not registering all the time.

Has anyone ever seen this issue before? It's a first for me.

#5 11 months ago

This part I am questioning : switch 52 - Super VUK and switch 55 - Power Scoop do not register a majority of the time as tested directly at the board with a jumper wire directly at CN8 & CN10.

If something is bad it will test bad everytime. Maybe you have a flaky switch or solder joint. Maybe a bad 1N4004 on the switch. Maybe the board is ok.
What do you get when you run the switch diagnostic from the coin door. Do the switches in question pop up as faulty?

I remember working on the supervuk on my TFTC and man was it in a place that was hard to reach!

#6 11 months ago
Quoted from luvthatapex2:

This part I am questioning : switch 52 - Super VUK and switch 55 - Power Scoop do not register a majority of the time as tested directly at the board with a jumper wire directly at CN8 & CN10.
If something is bad it will test bad everytime. Maybe you have a flaky switch or solder joint. Maybe a bad 1N4004 on the switch. Maybe the board is ok.
What do you get when you run the switch diagnostic from the coin door. Do the switches in question pop up as faulty?
I remember working on the supervuk on my TFTC and man was it in a place that was hard to reach!

Read my entire post. It’s not the switch because I’m testing it directly at the board with the playfield disconnected.

#7 11 months ago

Was there any corrosion on the board either currently or in the past? If you've replaced all the chips and verified the other parts the only thing left would be traces.

#8 11 months ago
Quoted from pinball_ric:

Was there any corrosion on the board either currently or in the past? If you've replaced all the chips and verified the other parts the only thing left would be traces.

No corrosion and no bad traces as I've got continuity from start to finish.

#9 11 months ago

What if you slow how quickly you are shorting it at the board. Does it register if you short it every 2 seconds vs 1 second?

Some coils are meant not to fire too often so it doesn't blow a fuse, especially in a case of a ball search.

#10 11 months ago
Quoted from PinballManiac40:

What if you slow how quickly you are shorting it at the board. Does it register if you short it every 2 seconds vs 1 second?
Some coils are meant not to fire too often so it doesn't blow a fuse, especially in a case of a ball search.

I'd like to know if that's the answer. Good call.

#11 11 months ago
Quoted from PinballManiac40:

What if you slow how quickly you are shorting it at the board. Does it register if you short it every 2 seconds vs 1 second?
Some coils are meant not to fire too often so it doesn't blow a fuse, especially in a case of a ball search.

No difference.

#12 11 months ago

I would check pins 8 and 4 on the PIA to make sure you're seeing the switch drive pulse reliably. If not work your way backwards toward CN10 to see if you can find where it's getting lost. Easiest with an oscilloscope but a logic probe would probably work too.

#13 11 months ago

I remember a confusing issue with a DE myself, I couldn't figure out why the switches were not registering., it turned out the connector was wired incorrectly.....did you check the manual to see if the connector's wire position is correct.

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