so I have been loving my demo man and modded it quite a bit (color dmd, lots of custom lighting, home roms, custom time delay police light topper, etc.). I was devastated to turn it on after soldering in the leads for my latest project (adding a home built shaker) to get a ground short row 1 message. I have read the most common threads diagnosing the handles (j205, j209 connections) to no avail. It seems to somehow have multiple row ground shorts suddenly.

Rows 1 through 7 all list as ground short in test report along with claw motor error (on start up, the claw just makes a short electrical grunt noise and doesn't move, or move all the way towards back only). 24 (always closed) reads row short. 37 not used reads row short. 75 not used reads row short.

The following switches work in test:

Left and right coins d1 & d3
All test switches
18 Right outlane*** (shows open, then when closed it reads as row short)
28 not used shows open
The standups***(same as r outlane show short when activated)
48 Right loop***same
68 not used shows open
88 Lower rebound***
F1 r flip eos works fine
F2 r flip but works
F3 l flip eos works
F4 l flip but works
F6 ur flip but (on handle) works fine
F7 ul flip eos works
F8 ul flip but (handle) works

Also, looking at the cpu board, there are 3 red leds: d19, d20, d21 (top to bottom). D19 is not lit, d20 is flickering, d21 appears lit (though dimly maybe, see pic). Light are right to left in pic.

Any help would be greatly appreciated as this is my favorite machine and I miss it already.

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Edit: forgot to mention the first thing I tried was removing all the wiring I had added (of which 95% had been extensively tested and was working perfect for many games). No dice.

UPDATE: In test mode, the claw will move left and right, but it is allowed to move outside of the normal range (i.e.: run into side of cabinet). Could bad opto board on the claw cause this ground short issue or am I grasping at straws?

So checked this morning (thank you Classe for the response) and got some odd behavior. With all unplugged, nothing is closed (including 24). See first pic. With j212 and j207 in, rows 1 and 4 are closed (2nd pic). With j207 and j209 in, all rows 1 to 7 are closed. How do I even go about systematically finding the wiring issue? Thank you again.

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So assuming I'm wrapping around for pin 10 (1st pic), I'm reading .012 on my meter set to 2M (2nd pic). Assuming U20 is toast, everyone agree? Are there any other chips I should check while I'm doing this (and how to check them)? Are there specific things I may have done that caused u20 to fail? Thank you

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Thank you PinballManiac40

Using correct locations now reading 0.022 with meter set to 2k, so 22 ohms? Just for clarity, I am measuring with all the "j" connectors removed (not sure if that makes any difference).

Awesome and thanks guys. Any idea best place to source u20 chip and that resistor in US? Going to dig into shirring issue. Any chance that column is related to the right ramp flasher? Having trouble deciphering the flasher stuff. That one had never worked correctly for me.

Found the resistors. New question. Is the Toshiba ULN2803APG the same as the ST ULN2803A?

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I'll let you know my mileage then with these.

Am I missing something or is there no detailed schematics or wiring diagram for the cpu board on the manual? Looking for the diagrams like I found for the 8-driver board on pages 128 & 129 (3-24 & 3-25). Really just want to increase my own knowledge and understanding to verify how you guys know that R71 is tied to column 5?

Thanks again for all the advice as I'm learning a ton.

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Thank you PinballManiac40 found it!

Update: I just found a common link to something I need to try and check. I think I shorted out the diode on switch 54 (upper rebound) and plan to check when I get home. Would this cause the column 5 frying of the resistor (and subsequently U20)?

There's a diode on the connection for switch 54 under the playfield (it's a leaf switch). I think I had a crossed current from high power coil circuit hit it by mistake.

Definitely will do.

In the spirit of full disclosure and owning up to my boneheaded mistakes in the hopes of learning from them as much as possible, I originally had hooked up a poorly designed circuit to trigger my homemade shaker motor project. I have a switching relay that closes when it gets signal from the desired source and sends a 12v trigger signal to a time delay relay that runs the motor (same idea for the police light topper). My problem here was I was now looking to relay trigger from multiple sources, and didn't realize until afterward that I would need a separate trigger relay for each source to keep their circuits independent and isolated (doh doh doh, I know). Basically wired the pop bumpers to that leaf switch on 54 and I'm sure turning the game on at that point certainly did some level of this damage.

Again, I am not ashamed of admitting my stupid mistakes and it has forced me into a situation where I am exponentially increasing my knowledge of working on these machines.

New u20 and new resistor at r71 and we're up and running again! Diode on switch 54 checked ok. Started to uncover my right upper ramp flasher issue as previous owner had the J3 cable plugged into J109 on the power board! New issue is the right handle button (launch) seems to be stuck closed and there are several flashers that are just remaining lit like GI. After this though, I'm confident I'll be able to rectify those correctly. Thank you everyone for all the advice and help. I think i did ok for my first ever PCB repair.

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Since you guys were such an awesome resource here (PinballManiac40 and zaza especially), any chance you'd take a quick peek at my 8-driver board flashers issue:

https://pinside.com/pinball/forum/topic/demolition-man-8-driver-board-flasher-on-issue