I recently took a look over a Bride of Pinbot pinball machine and noticed the head mechanism was malfunctioning. When you shoot a ball up the left ramp and into the face, it should rotate to the next face in the sequence and then return to the previous face for the next player. This wasn’t working correctly. The face was rotating, but rarely to the correct one.
Having never worked on a pinball machine before, this seemed like a good fault to get my feet wet. However, what started out as intending to fix a single small problem, snowballed…
After reviewing the manual and running through the test procedure for the head unit, it was clear the CPU wasn’t able to determine the heads current position. Reading over posts for similar issues on pinside there was a post about switch D67.
The head unit has a small micro-switch with a roller on the end of an arm that sits in one of three indentations when the head is on three of the four faces. Between faces it’s forced out of the indentation and the switch closes. The CPU can use timing between indentations (combined with the longer timing for the side with no indentation) to perform a calibration and determine which of the four faces is currently showing.
With the machine in the switch test mode and the face plate removed I activated the switch manually and saw no response. A continuity test confirmed the switch was dead. This should be an easy fix, just solder in a new micro-switch and tweak its position to ensure the switch doesn’t activate whilst in the indentations.
Unfortunately that was not the only issue.
Whilst in the test section of the interface, I decided to run through all the available tests. All the switches passed fine, numerous GI lamps were dead and two of the flasher lamps, more concerning however was the solenoid test.
Solenoids are used to trigger the flippers, pop bumpers, slingshots and a variety of other items on the playfield. The first tests for solenoids 1-7 all went without issue, but then everything went quiet. Tests 9-14 didn’t trigger a single one.
Several coils not working sounds like a blown fuse. Most of the fuses are on the various boards in the back cabinet of the machine. Opening this up revealed the cpu, audio and power driver board and…
clear signs of damage.
A couple of transistors and resistors look destroyed.
In addition the 0.12 Ohm resistor R224, seen in the second photo near the top left just below the two bridge rectifiers and to the right of the set of fuses has blown apart. The bare wire is exposed rather than a solid ceramic shell. The remains of one half can be seen just below the wire.
The hits keep coming
The damage doesn’t end there, further inspection of the board revealed a couple of fixes by one of the previous owners.
The headers on the PCB for these two sockets had melted in places and the molex connector had welded itself to the header. Both sockets and housings will need replacing.
To cap it all off, the battery holder on the CPU board showed clear signs of acid damage, although thankfully just the holder. No sign of any damage to the board/components.
Also for some reason the sticker that covers the glass window on the UV erasable ROM had been removed. Odd, but nothing a bit of insulation tape doesn’t fix.
I’ll have to pull the CPU and Power Driver board’s and sort this all out, but first things first, photos and lots of them, with close ups of every single connector. Just in case there’s any confusion when reconnecting anything.
I’m going to have my work cut out and that’s before looking at the play-field issues and what may be lurking under the hood.
to be continued…