Dr who: How do I check a short on a row ?

(Topic ID: 220720)

Dr who: How do I check a short on a row ?


By jimy_speedt

76 days ago



Topic Stats

  • 11 posts
  • 4 Pinsiders participating
  • Latest reply 25 days ago by jimy_speedt
  • Topic is favorited by 2 Pinsiders

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#1 76 days ago

Hi,

I have a problem with my dr who. Row 2 is marked as short in test mode, these switches are not operational when a game is started. In test mode there are squares all over the row2.

Row 2 is driven by white/red wire:

Col 1, N/A
Col2, Coin door closed. I removed the connector from the micro switch, no change to the matrix
Col3, mini pf opto home. Is there any possibility an opto goes short ?
Col4, S target from escape, I removed the white red wires, all switches squares disappear in thest mode for row2, including optos.
Col5, E of escape, I replaced the target by a new one, no change all switches are lit in test mode (this is the end of the daisy chain)
Col6, right jet, I removed the whi/red wires, no switch at all lit in test mode for row2
Col7 mini opto bank. Any possibility that an opto goes short ?
Col8 playfield glass. I chevk the microswitch which looks ok.

Can anyone explain to me accurately what to do ? How can I determine a switch is wrong and triggers this problem ?

Thank you very much in advance

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#2 76 days ago

Remove the backbox connector that corresponds to those switches and see if the error clears. If it does, you have an issue somewhere on the playfield. If it persists, you have a board issue.

#3 76 days ago

Hi, thanks for replying, there is no board issue, I forgot to mention. Just wondering how to identify a short under the pf

#4 76 days ago
Quoted from jimy_speedt:

Hi, thanks for replying, there is no board issue, I forgot to mention. Just wondering how to identify a short under the pf

If you're sure it's not a board issue..... check the red/white wire looking for something that is pinching it against a metal part or a diode/switch assembly that is bent and touching ground. I've found both issues over time, even a frayed wire that was touching another frayed wire.

#5 76 days ago

the CPU is brand new, and if I remove the SM 20x connectors, no square is lit anymore. Same if I remove j3 from the opto switch 10 PCB. I do not see any wrong contact between lugs nor contact with the ground. I guess I could have continuity with the ground braid in that case. The only switches I have not tested are the 2 optos. As It requires the removal of the mini pf, I would like to check first if they can be faulty

#6 76 days ago
Quoted from jimy_speedt:

the CPU is brand new, and if I remove the SM 20x connectors, no square is lit anymore. Same if I remove j3 from the opto switch 10 PCB. I do not see any wrong contact between lugs nor contact with the ground. I guess I could have continuity with the ground braid in that case. The only switches I have not tested are the 2 optos. As It requires the removal of the mini pf, I would like to check first if they can be faulty

Look under the playfield, look at the coin door, look at the interconnect boards, look at the glass in place switch; check that every diode is installed the correct way with the NON-banded end toward the row wire (white with red stripe).

The row wire daisy chains from one switch to another, and is NOT wired in the order of the matrix, but is SHORTEST distance to next shortest distance. So the white-red wire may go from the MPU to the mini-playfield home opto, to the S switch in escape, to the E switch in repair, to the right jet, to the 5 bank right opto, to the coin door, to the glass switch. (only a guess, order may be different). Somewhere that wire is SHORTED to something else, or a diode is backwards.

If I were to guess, I'd try for the glass switch or the coin door closed switch as the location of the issue first. But it can be at any location even in between switches where the white red wire is pinched and now shorting to something else...

There is no easy way other than to take time and examine the entire sets of the white-red wire, and everywhere it splits and jumps from one switch to the next. In this case there are a number of connectors it will go through too...

You can try disconnecting it from each switch and see if the problem goes away, then you can figure out that that switch, or a downstream one, or downstream wire is bad. But examination of the wiring is the only way to find the issue.

If you've tried to repair something, or installed some modification or toy, check or remove that first.

The under playfield pic below shows SOME of the places the white-red wire lands and splits off to the next switch....

Inkedimage-5 (1)_LI (resized).jpgdrwho (resized).JPG
#7 72 days ago

thanks again for your help. Unfortunately (I do not know what happened) I burned the CPU, and blew F111, f112, I do not know whyh. I always do things right, but this is my luck with this pin. I ll remove the fuses related to solenoids and check.

I ll be away for 2 weeks but right after, I ll be back on that stuff

Disconnecting the coin door switch or the glass does not change anything to the problem, i.e. the row2 stays short in test.

For the 2 targets disconnected, all the switches from row 2 are shown open in test, even the optos. It means they must be at the beginning of the daisy chain. When disconnecting them the ones after no longer receive current (as you explained to me optos are normally closed. I suspect one of them to trigger the issue).

Thanks again Themadman for the time you spent.

1 week later
#8 61 days ago
Quoted from jimy_speedt:

thanks again for your help. Unfortunately (I do not know what happened) I burned the CPU, and blew F111, f112, I do not know whyh. I always do things right, but this is my luck with this pin. I ll remove the fuses related to solenoids and check.
I ll be away for 2 weeks but right after, I ll be back on that stuff
Disconnecting the coin door switch or the glass does not change anything to the problem, i.e. the row2 stays short in test.
For the 2 targets disconnected, all the switches from row 2 are shown open in test, even the optos. It means they must be at the beginning of the daisy chain. When disconnecting them the ones after no longer receive current (as you explained to me optos are normally closed. I suspect one of them to trigger the issue).
Thanks again Themadman for the time you spent.

see the board next to the upper left flipper under the playfield?

That is the opto to switch matrix interface board. All the opto's are wired to that board, and then it has 339 chips that convert the signal to the switch matrix.

Disconnect the wiring harnesses from this board and see if the short problem goes away.

The problem may be a pinched wire ANYWHERE in the machine past the MPU shorting to something else, a BAD diode, a REVERSED installed diode, or even just a simple single switch wire landed on the wrong terminal on ANY switch.

Since the short only shows up when you connect the row harness to the MPU, it is a short downstream of that harness. You just have to find it; finding it is WORK and Troubleshooting. There is no easy fix. If you are unable to locate it by visual, then divide and concur, remove the red and white wire from a switch, if problem goes away, it was that switch/wire or one physically wired "south" (toward front of machine) of that one. If problem stays, then a switch/wire physically "north" (back of machine) of that one...

Any backwards diode, a shorted diode, a frayed wire, or mis-landed connected (such as on the opto board) can cause your issue.

#9 58 days ago

Thanks a lot themadman, I ll be back home in 4 days. Will take care of this, I need the pin at the end of august for an event I organize in Belgium.

https://www.facebook.com/events/1794746423901781/

1 week later
#10 50 days ago

Sorry for being late to answer. Yes the problem disappears after the 2 connectors with white - red wire are unplugged.

3 weeks later
#11 25 days ago

LM339 was faulty on the opto board thanks all for your help

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