I recently bought a Dirty Harry from a friend of a friend. It was his first pin and he just didn’t catch the Pinball bug. It was working at his place when I picked it up. I played a game and could tell it needed some love and a good shop job, but it fully functioned.

Got it home, set up and then 30 seconds into the first game it slam tilts. Played another game for a few seconds and slam tilt happened again. Then upon powering back up it just said “slam tilt switch stuck”.

Long story short, the slam switches were not stuck. I reseated all the connections to the MPU. That didn’t help. Went to bed annoyed, woke up, turned the game on and it played fine again. However, now it randomly and quite often thinks the enter button is being pressed while I’m playing. It beeps like I’m in the menu and says “open coin door to use buttons”. Also, it randomly slam tilts still but not very often.

I installed new connectors on the MPU at J212 and J205 since they looked pretty corroded, but the same problem remains. (See pic). The MPU doesn’t look terrible to me but I’m wondering if these symptoms point toward battery acid damage. I can see a bit of acid damage near the resistors but it doesn’t look that bad to me. The underside of the MPU has no signs of corrosion or cold solder joints.

Thoughts on how to diagnose this problem?

052A8407-AC22-466C-A506-49F1FF861DFC.jpeg6444A48C-492E-4C6E-9B9B-CDA1376CE928.jpeg

I was afraid you guys would say that. I think I was trying to talk myself out of the inevitable. Unfortunate, but it is what it is.

I do have a DrWho, World Cup 94 and a Bram Stokers Dracula. Could I swap MPUs with one of them just to confirm? Obviously I would have to swap game ROMs as well but is there anything else?

Yup, I’m thinking I’ll go with the rottendog MPU replacement, then eventually get this original board repaired so I have an extra for testing purposes down the road. Who’s the go to for MPU repair?

I did try unplugging J5 from the opto board like DumbAss mentioned. When I power the game up the dmd says “check fuses f115 and f116, j112 and opto 12v supply”. It’s been sitting in attract mode like that for 20 minutes now and I haven’t gotten that phantom beep yet. However, I cannot start a game and only the escape button inside the coin door works.

I’ve also checked the coin door interface board for cold solders and it doesn’t have any.

Well, forget what I just said about not hearing the phantom beep. Literally seconds after posting that...it started phantom beeping. Lol.

ChrisHibler I've ordered a rottendog MPU replacement. I'll be contacting you soon about repairing the original board. Thanks for offering and sending the instructions!

Also, thanks to everyone else that has helped in here. I can't wait to get this game fully functioning so I can start the teardown/deep clean of the playfield. It has bubbling mylar everywhere but looks like there's a perfect playfield underneath.

Followup:

You guys were right. Looks like the MPU was the problem. I installed a new MPU from K's Arcade. The game has been on and playing now for an hour straight without any problem. As an added bonus, the MPU came installed with a more recent code version.

Thanks for all the help!