(Topic ID: 293202)

DemoMan - Every switch in column causes row short for that row?

By Frax

3 years ago



Topic Stats

You

Linked Games

#1 3 years ago

Yeah so...I've found quite a few wonky things while working on this game, but this one I'm at a total loss.

Was working on the flippers, power off. Literally all I did was replace the left flipper bat, and the right flipper bat and pawl+plunger assembly. I had disconnected the trough optos to get the wiring out of the way of the right side, then plugged it back in when I was done.

Powered up the game to test out the flippers...start button no longer starts a game. Well...crap...okay?

Go into switch test, and now EVERYTHING on column 1 causes a row short for the row it's associated with.

Start Button, Launch Button, inlanes and outlanes, and the handle thumb triggers (which are effectively tied to Start/Launch), and the tilt bob.

What in god's name could've possibly happened here? Circuit still had charge and wasn't bled off in the coil voltage maybe shorted to a switch? That's honestly the only possibility I can come up with, even though I didn't (as far as I know) let any part of the coil or coil wires touch anything. I've rebuilt flippers a ton of times, so I'm generally pretty careful with that stuff.

I had previously tested the CPU board with jumpers to test all the switch matrix while troubleshooting something else, and it was fine. Obviously if coil voltage got up there, I need to go test it again, but don't have the time to muck with it tonight. I'm just wondering if someone else can spitball this, as I've never seen anything like it before, especially from just working on the flippers. My soul is crushed right now..I'd already spent like 20+ hours isolating and fixing everything else I knew about.

I've got some LM339s on hand in case I have to go there, and sockets, and I can get ahold of ULN2803a and sockets if I need to go that route, but we all know traces on WPC boards are better left alone if at all possible...

#2 3 years ago

The one thing that immediately comes to mind is if column 1 was stuck low rather than pulsing then a row short would occur for every switch activation in that column.

#3 3 years ago
Quoted from Pin_Guy:

The one thing that immediately comes to mind is if column 1 was stuck low rather than pulsing then a row short would occur for every switch activation in that column.

And unfortunately I have no access to an oscilloscope to check that, much less a logic probe. Honestly, this is the first time I'm doing any serious work on a game in several years.

What would cause it to be stuck low? The ULN2803a?

#4 3 years ago

"The switch columns are controlled by a single 18 pin ULN2803 chip on the CPU board at position U20. The switch rows are controlled by two LM339 chips on the CPU board at positions U18 and U19. The direct switch rows are controlled by two LM339 chips on the CPU board at positiion U16 and U17.

Welp....guess I'm ordering a ULN2803a

#5 3 years ago
Quoted from Frax:

And unfortunately I have no access to an oscilloscope to check that, much less a logic probe. Honestly, this is the first time I'm doing any serious work on a game in several years.

That's ok, you don't need either to make this check as the majority of the time the column signal is at 12V so its measurable. You can check the column 1 pulse at either J205-1 or J207-1 whichever one doesn't have a connector on it, you should get a measurable voltage and it should be similar to the voltage on pin 2 of that connector.

If it reads 0, that's bad; disconnect the connector from J205 or 207 and measure again, if it still reads 0 then its CPU related.

Quoted from Frax:

What would cause it to be stuck low? The ULN2803a?

Yes, U20 can cause this.

1 week later
#6 3 years ago

I had a similar issue on a Williams Flash where a screw that held the spinner assembly had been replaced by a previous owner with a longer screw. The longer screw went through the bottom of the playfield and touched a GI bulb which shorted that entire column to ground.

I found this on the net. https://techniek.flipperwinkel.nl/wms11/index3.htm#switch
“When a column wire is shorted to ground, and any switch in that column is closed, the switch test will show ALL switches in the ROW of the closed switch as being closed. If no switches are closed, the switch test will show no switches closed. To find the location of the short, go to the end of the switch column wire on the playfield (the switches are "daisy chained" together for an entire column or row). Then break the daisy chain one switch at a time until the short no longer shows in the switch test.”

Have you checked to see if that column is shorted to ground?

Promoted items from Pinside Marketplace and Pinside Shops!
3,500 (OBO)
Machine - For Sale
Los Angeles, CA
$ 81.95
$ 10.00
Playfield - Decals
Metal-Mods
 
$ 37.50
$ 18.95
Playfield - Toys/Add-ons
ULEKstore
 
$ 329.99
Lighting - Other
Lighted Pinball Mods
 
$ 30.00
Playfield - Other
Lenticular Designs
 
$ 45.00
Lighting - Interactive
86Pixels
 
$ 40.00
Cabinet - Other
Rocket City Pinball
 
$ 30.00
Electronics
Yorktown Arcade Supply
 
From: $ 17.99
Eproms
Matt's Basement Arcade
 
$ 85.00
$ 39.99
Lighting - Led
Mitchell Lighting
 
$ 72.95
$ 35.95
Lighting - Led
Mitchell Lighting
 
$ 79.00
Lighting - Under Cabinet
Arcade Upkeep
 
$ 9.95
Eproms
Pinballrom
 
$ 54.95
Eproms
Pinballrom
 
$ 199.95
Electronics
PinSound
 
From: $ 17.99
Eproms
Matt's Basement Arcade
 
$ 35.00
Cabinet - Other
Rocket City Pinball
 
$ 18.00
Playfield - Protection
Volcano Pinball
 
Great pinball charity
Pinball Edu

Reply

Wanna join the discussion? Please sign in to reply to this topic.

Hey there! Welcome to Pinside!

Donate to Pinside

Great to see you're enjoying Pinside! Did you know Pinside is able to run without any 3rd-party banners or ads, thanks to the support from our visitors? Please consider a donation to Pinside and get anext to your username to show for it! Or better yet, subscribe to Pinside+!


This page was printed from and we tried optimising it for printing. Some page elements may have been deliberately hidden.

Scan the QR code on the left to jump to the URL this document was printed from.