Diagnosis: Pinball!

Still no DIA today... the auctions go off tomorrow. The mpf is up to $77, and the others are still at their opening bid. Honestly, I don't expect them to go any higher, but I wouldn't be adverse to being pleasantly surprised.

As I've mentioned before Pinball Wizards is approaching fast, so since this is the last weekend before the show, it was time to get off'n my bottom and figger out what's wrong with my games. Last night was a particularly good night to do it, since my wife took a break from the TV, so I wasn't in danger of being distracted by a particularly good episode of the Fairly Odd Parents or something (that sounds snide, but I am very easy to distract, and the Fairly Odd Parents is actually pretty good).

First stop, Doctor Who. Most of my tests used my latest diagnostic technique, the continuity check on my multimeter. First I checked the wires for the mpf opto switches, hoping there would be an obvious break, but there wasn't. In addition to my own game, I wanted to show that the optos on the mpf I'm selling were working so it would hopefully attract more bidders.

But the biggest problem is that switch column, so I tackled that next. I looked around for loose wires &tc. No luck. I beeped through the wires and found no problems between one of the outlane switches and the pin where the column enters the CPU. Then I used the diagnostic in the switch section of the repair guide to test the columns. That demonstrated pretty clearly that the problem is on the CPU, which it says means I should probably replace the chip at U20.

Then I got the bright idea to try my other CPU board in the game. That's the one I got from eBay from England a year ago that turned out to mostly work until you plug it and the display board in to the multistop ribbon cable. I was hoping to determine if the column worked entirely by sound... possibly the way Tommy would fix pinball machines (though I know, he's deaf too, so the analogy doesn't entirely work). I was able to get the game to boot, but not start... maybe it knows the display isn't there? And the switch levels test -- it cycles through all the closed switches, beeping as it goes -- beeps with the same tone, so you can't tell if there's been a change. So that was disappointing. I did, however, glance as the dreaded J202 connector and noticed that the solder seemed to run between the pins. Looking at the picture, the two pins in the top left are fairly discrete blobs of solder, whereas the ones after that seem to have some cohabitation action going on. Some quick continuity testing indicated that most of the pins in the upper row are pretty much in bed with each other, which is not good for precision electronic devices. Most likely, the English Guys I bought it from tried to resolder the connector and botched it, so they gave up and put it on eBay. Another interesting thing I learned from this board was the underside around the U20 chip has scorch marks, which makes me think the U20 fails a lot. If/when I get around to fixing mine, I should definitely put it in a socket for easy replacement.

That was pretty much it for Doctor Who... I put it all back together and played a game, which is not as much fun without that column of switches. You can't transmat without the bumpers, you can't get all the Daleks in multiball, and you can't get an Extra Ball or as many Hang Ons. And sick as I was of it, I was surprised at home much I missed "Quick, Ace, it's a Second Chance!", which the outlanes trigger in many cases.

Next up was the feature lamps on Eight Ball Deluxe. I used the lamp diode test described in the repair doc -- I just love those things, don't you? -- and after initially finding nothing I ended up with a handful of diodes that didn't respond. I can try replacing those as soon as I level up my soldering skills to boards... and 1980 Bally boards are much easier to start with than 1990 Williams boards by a long shot.

When I was done with the testing, I played a few games... they were a lot more satisfying than DW, but was off my game... I didn't exactly come close to beating the high score.

This morning I decided to make another assault on the optos in the mpf up for auction. After a couple of failed attempts, I detached the opto boards from the unit, plugged them in to the game, and powered it on. Then I used the digital camera, because they can see the infrared -- thanks to the repair guides again, man they're awesome.