It's late & I'm tired, and I'm in a hurry to prep games for a show, so this is just a sanity check.

I've been working on a shadow. Did a bunch of repairs (replaced brick wall drop target, replaced plastic under left phurba ramp, replaced mini playfield IDC connector, fixed a pulled wire from another mini playfield connector, fixed disconnected wire from mongol target 52).

I was doing a final play test, everything went fine. Then I lifted the playfield, went to eject the balls, and row 4 shorted to gnd.

So, in switch test, all row 4 switches are closed.

If I try to activate any other switches, that entire row fires off all its switches.

With the switch connectors disconnected from the MPU, except for j205, no closed shorts in the edge test.

When I try to step through the rows & columns by jumping connector pins on the MPU, columns 1 & 2 fire off a bunch of switches. All other rows/columns only activate a single switch.

So, I'm assuming blown U20?

Potential problem areas:

Mongol switch on the left side of the left phurba ramp. One of the wires was broken off. I'm assuming this was supposed to be the correct arrangement.

Battle drop target micro switch--diode with long leads may have shorted on bracket. I repositioned the diode so there's no danger of touching. Not my work--someone else installed that diode.

Left opto for left furba ramp. I put some mylar on the inside of the ball guide so that the wires/contacts of the opto wouldn't short on the ball guide.

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I inspected everything, and that diode near the bracket was the only thing I didn't catch earlier.

I replaced U20 (it was already socketed).

Column 2 was unresponsive when jumping the connector pins, but all other rows & columns worked.

I tried a second ULN2803 just in case the first replacement was faulty, but same result.

I would imagine something else in the board blew as well.

[edit]: I think I'll go ahead and replace U14 74LS374.

Well, I desoldered u14 74LS374, put it in my chip tester, and the chip tested good.

I don't have a WPC-S MPU schematic handy, so I'm not sure what might be the next likely candidate.

Bingo--U23 74HC4514 tested bad.

I'm not sure that it's a chip that I actually have on-hand. I'll have to double check.

I'll certainly take a closer look on what column 2 switches may contact a coil, but nothing immediately jumps out at me.

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In other news, it does not appear that I have a u23 chip.

Nor does it look like I have a wpc-s board I can swap in or steal u23 from. I do have quite a number of wpc89 mpus, which doesn't really help.

I ordered a few chips from marco with overnight shipping ($$$). Maybe they'll get here in time...who knows.

I probably have a couple hundred chips on-hand for doing repairs. Unfortunately, since I never needed to do any significant work on WPC-S MPUs, I never stocked up on any of the components specific to that board.

[edit]: The shipping label was printed. Tracking hasn't shown that fedex has it yet.

I checked it, and it seems fine. No exposed wire on the coil, and the lugs don't seem to touch anything even when wiggling it around. However, as an extra precaution, I put some gaffers tape on the coil wrapper, and over the coil lugs.

I went over the wiring pretty well, but I didn't see anything cut/damaged/worn/frayed.

I even cut open the plastic sleeve on the coin door harness, but that wiring was fine too.

I wiggled each coil to see what the range of motion was, and none looked even close to touching anything with the eyelets or lugs.

I'm really not seeing any obvious areas that could be an issue.

The chips I ordered are "in transit". Whenever they get here, I'll pop one in and see what happens.

Well, the package got here, but I got the wrong chips...
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Marco's product photo shows the 2.54mm chip, not these wider ones.

herbertbsharp was kind enough to supply an MPU, which had the chip socketed. Thanks Herb!

The game fired right up, played fine, and didn't seem to develop any shorts. So, hopefully, it will last the duration of the show.

Well, the game lasted a full day at a show without incident. If a game can survive a show, I consider that a win.

Thanks guys