Driver boards tested and fixed

So I put together the little address selector tool that Leon designed on his website (see my links) and used it to test both the Pinball Champ ’82 and Devil Riders driver boards.

Driver board test tool

I used a LED to test each input individually for the eight possible addresses.

Driver board test setup

I had to do it on the PC82 since I don’t have an independant 5V power supply anymore… really need to fix that!

The Devil Riders driver board was in perfect condition. This machine is turning out to be just a case of bad switches and dirt, lots of dirt… excellent!

The Pinball Champ driver board was another story. I had intermittend faults on connector CN21 while signal that came for the same SCR’s on CN18 where perfect. After a more thorough visual inspection of the board I noticed this:

Bad connector seating

As the solder didn’t appear broken and I had a very hard time desoldering this connector, I suspect it had been put together this way 29 years ago… So now it’s reseated properly and I replaced four SCR’s that were faulty, this board is now in tip-top shape as well.

I’ve also tested the Devil Riders CPU board with Leon’s test EPROM and it’s also in perfect condition. I’ve also found some discrepancies in the way the Pinball Champ CPU board functions compared to the Devil Riders board. I’ll get into that next as it’s the only thing that needs to be done before I can really get into the Devil Riders.

Wish me luck!

Progress report

Well, the playfield is almost done!

I’ve cleaned out the cabinet and head.
I’ve installed the new microswitch (#52) that let’s the machine know the ball is on the 2nd level playfield.
I’m still missing a few rubbers, but they are in the mail.
The 20A fuse on the transformer box burned out while I was working on the playfield. I stuck a new one in and that burned out too. So I removed all the lights and measured the wiring to look for shorts. There were none. I stuck the lamps back in one by one and now everything works… Weird.

The guy I bought the ZM1550 display modules from mailed me to say he is abroad for work and will send them next week.

I still have the CPU board problem though… I’m going to swap out IC’s 8, 19, 31 and 37 for good measure. The way the CPU reacts to the DIP switch 4 position looks like it’s unable to read the settings once PROGR is off. When I put the switch back in PROGR mode, I can read all the settings, which to me means the RAM is good.
I’m also writing a extensive memory test program that will write alternative 0x55 and 0xAA’s to every memory position between 0x1800 and 0x1BFF. When a test fails it will show which test failed in which nibble at which location on the Player 1 display. This way I should be sure if the memory is good and I can test with both positions of DIP switch 4.

I’ll keep you updated.


Still debugging CPU problems…

As I stated in an earlier post, the pinball machine will only work when it is in PROGR mode (DIP switch 4 to ON position on the CPU board).

When the machine is in normal mode (DIP switch 4 to OFF position), al the displays show 0’s and that’s it. Sometimes not all displays will light up at once and it will take up to 30 seconds for all of them to turn on.

Lights on the head and playfield will stay on or off at random (changes every time I restart the machine).

When actuating the Test-Advance button in the door, it will go to test #1 and all the displays will test correctly showing 0’s, 1’s, 2’s, etc… up to 9’s and back to 0’s, but after that, there’s nothing I can do to stop that test, go to the next test or whatever.

Also, when I start the machine on normal mode, the error LED on the soundboard lights. Actually it always lights and never turns off. I noticed it takes a little time to turn off when the machine is turned on in PROGR mode, so I guess it’s the CPU not initialising the sound card.

I’ve tested the IC’s 31, 37, 19 and 8, but they all do what they’re supposed to do…

The PROGR circuit. The PROGR signal comes from DIP switch 4.

What you can see here is that the PROGR signal enables addresses 1C00 to 1C7F (or 1800 to 187F, since AB10 is not used but the software holds it high for RAM access) for writing when it is LOW. When the switch is put back to the OFF position, this memory range becomes read only.

So what’s next? I’m not really sure. There’s a few options:

  1. Maybe the TMS40L45-45NP is not a good substitute for the 2114L. I found some people who still have these, so I’ll get me one and see what happens.
  2. I write a test program than constantly writes to RAM when the CPU board LED is on and constantly reads from RAM when the CPU board LED is off and follow the R/W signal with my logic probe.
  3. Call Mulder and Scully to find the ghost in my machine…

Anyway, as always I’ll keep you updated.

All electronics fixed, but still problems…

The mailwoman came with goodies this morning; four 3081 chips! So I put them in the CPU board and ran Leon’s test EPROM again. Victory!

Two new 3081's

So I mounted the board back into the pinball machine, connected everything and switched it on. Not so good… The sound was weird, only a few cracks and screeches would come out of the speaker.

I disconnected the sound board from the CPU board and ran the test and all went well, so clearly there was a problem with the communication between the CPU board and the sound board. I checked the schematics and the only thing that could be wrong was the entry stage behind CN7.

Using my multimeter I immediately found that all the data lines where shorted to the +5V. So only the resistor array ICR6 or the 74LS244 could be the cause. So I started with desoldering the resistor array, but that wasn’t the problem. So I desoldered the 244 and found the culprit!

Off to the store I went. Bought a couple of BF422’s and a 4042 as well for the two display driver boards that needed them and even went round to the hardware store to get some screws, there’s a lot of screws missing in the cabinet and head.

Back home, I put all the components where they should be and succes! I have sound!

A new 74LS244

The two display driver boards got their components too and now I have 4 working displays.

A new 4042.

Two new BF422's

Four working displays, one to go...

Next week my ZM1550’s should arive and then I can fix the last display.

And that’s it for the electronics… OR IS IT???

The game still won’t start. No flickering lights, no sound, no highscore showing, nothing… just all 0’s on the displays and that’s it.

When I put DIP switch 4 in PRGM mode, the soundboard now makes the annoying warning sound and I can do all the tests, reset the accounting and set all the options. So I set the options, resetting the ones that already had a good value, clear the accounting and do the tests. All tests are fine. The displays do their thing, the lights go on and off, the solenoids scare me and the sounds are played in order. But then there’s the button test (test #2) that just shows 18. And whatever button I press, it doesn’t change. I guess I’ll have to go through the wire harness and measure what signals I do get.

Guess that’s my queue to end this article and get back to work!


Back home and back to work!

Finally back from Sweden. There were quite a few packages waiting for me! Unfortunately, the TMS40L45 wasn’t one of them, so I couldn’t start work on the CPU board.

Or so I tought…

I started Leon’s test EPROM again and started testing all the outputs since I skipped over that test to find out if the memories where good. Well, I found two 3081 chips that are dead… that kind of explains why the LED on the soundboard always comes on when I attach it to the CPU board. So I’ve ordered a couple of those 3081’s and they should be here in a couple of days.

I also saw that all the signals on the CN14 connector for the displays were there, so I started fooling around with the idea of writing a little program to see if the displays still work. I guess I can’t wait for the CPU board to be fixed so I can use the built in tests. And it does keep me out of other trouble 😉

Anyway, I’m waiting for my EPROM to be erased to put the 3rd try on it. I have a good feeling this time… But then again, I had a good feeling every time.

If it works, I’ll let you know and post the program and some pictures.