Amazingly, a Medusa popped up right in my backyard last week. One of my wish list machines, I snapped it up. It's in generally good shape with a few minor issues.

IMG_1479 (resized).JPG

I could use some advice on the biggest of these issues, the 7-bank targets. When you start a game, they all reset up but then the single target drops and it starts on two targets. 100 points gets scored. The 3 and 4 group work OK. The 5 group misses the rightmost target. I haven't yet tested the 6 or 7 groups. So OK, let's go into solenoid test. All 7 drops work fine in solenoid test so I moved on to switch test.

Problem 1, switch test shows 41 in the display, Movable Flipper EOS. Looking at the Zipper Flipper mech, it looks like there is an EOS on both the left and right flippers but only one switch number is given. Does that mean they both share #41? I take it these should not be closed in switch test?

So even though 41 was blinking away I tried another switch and it briefly showed that one before returning to 41. So I tried the 7 drop targets - none appeared at all, just the 41 kept blinking. Should I have gotten switch closures with the targets down, or is it a quick, momentary sort of thing as they fall?

Let's start with that. There's also some issues with speech getting cut off and a bit of asymmetry in the zipper flippers when they pull in but we'll get to that later

Thanks!
Dave

Thanks Quench! That's extremely helpful and not at all obvious from the manual's diagnostic instructions.

I've been doing more research and it seems that coils without 2 diodes, in some locations, can cause this so I'll also be checking that out. I have a ton of diodes on hand so perhaps I'll just replace them all if the solenoid expander doesn't seem to be a problem.

Off to the basement!

Did a little more testing this afternoon after I had a friend stop by to move the playfield onto the rear lugs. Why didn't they just put rails in like everybody else?

Anyhow, the lamp on the Solenoid Expander was fine, blinking away in lamp test and toggling the relay. I closed up the zipper flippers and was able to test all the drop target switches. Each worked as it should. I did a full solenoid test and it was correct - firing the correct solenoid at the correct time. I'm replacing the solenoid driver and expander board with newer, modern stuff anyway so I'll wait to see what happens with the new hardware installed. If it's still acting up, I'll have to go through the diodes.

I'm not going to claim victory quite yet but I may have a lead on the drop target issue. I decided to begin cutting coils out of circuit one at a time to see if I could learn anything that way. There are relatively few coils driven by the SEB: outhole kicker, knocker, saucer, the 2 drop target bank resets, the 7 individual drop target releases and the zipper flipper open and close. I decided to start with the knocker as it was easy to reach. I clipped the single orange-green (74) wire and started the machine up. The single target stayed up! Went through the series and the targets acted as they should but I think I saw a problem with the zippers opening and closing. This is interesting because, as you can see below, that 74 wire controls both the knocker and the Open Zipper coils, based on the position of the SEB relay.

SEB Coils (resized).PNG

Maybe there's also another issue at play here associated with the SEB, getting its relay pulsed at the wrong times. It's also interesting to note that the original problem 1 drop target and the two zipper flipper coils are on the same side of the relay. I should have the new SEB replacement in hand by Tuesday to see if that helps any. In the meantime, two new diodes for that knocker coil and we'll see if the problem disappears.

For anyone who might search this thread out later, the problem with the progressive drop targets was indeed the diodes on the knocker coil, but not because one was bad. As I was getting set to pull the coil tonight to change the diodes, I was looking at the schematic, making notes and checking wire colors when it struck me - the coil was wired in incorrectly. Unlike most coils, where you have a wire harness lead going to each of the tabs with the thin coil wire attached to it, not so on these Bally dual-diode coils. In this case, the 74 wire was supposed to go to the unbanded side of the diode connected to one of the coil wires, and it did, but the 91 wire was supposed to go to the unbanded end of the other diode, which was the center tab on the coil, without the other end of the coil wire. Instead, it was soldered to the other outer tab. After reconnecting them the proper way, the drop targets continued to work properly, as they had with one lead cut out of circuit. YAY!

Now all I have to do is get these darned set screws to hold for the 4 new flippers and I'll be all set. Even blue loctite isn't doing it; may have to use the red stuff and hope I never have to do it again in my lifetime At least I can get new lower flipper cranks if I need them. Looks like the zipper flipper cranks may be unobtanium.

Besides the set screws, one pop bumper skirt to replace and 3 new translucent targets for the 7-target bank and she's good to go.