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(Topic ID: 213292)

Tech Help Needed : Bally Medusa $20 fix me challenge


By EEE

2 years ago



Topic Stats

  • 12 posts
  • 6 Pinsiders participating
  • Latest reply 2 years ago by Puffdanny
  • Topic is favorited by 3 Pinsiders

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IMG_1103 (resized).jpg
Bally_Medusa_Tech_Chart.pdf (PDF preview)
Medusa_coils (resized).jpg

#1 2 years ago

I have a strange problem with our Medusa. What I thought was an issue with a weak trough kicker is something different and more complex.

When the outhole kicker wiring is removed, the machine plays properly. I pulled the apron and I manually move the ball into the shooter lane. All solenoids and switches appear to be running properly.

If the outhole kicker is soldered into place (yes, correctly) the machine becomes possessed. The upper bank of drop targets randomly drop and reset, the knocker fires with virtually any switch closure, the zipper flippers seem to get confused, and the machine seems to have a problem at the end of the boot up process with the sound continuing to play.

At this point, I have a new mpu (thanks barakandl), I have swapped in a known working solenoid expander board, I have swapped out the outhole kicker coil.

I am stumped. Any suggestions?

#2 2 years ago

Check all of the coils associated with the solenoid expander board. They should all have two diodes. I can almost guarantee someone replaced one at some point with a single diode coil.

Medusa_coils (resized).jpg

#3 2 years ago

Thanks dothedoo...

Why two diodes? I seem to think that they are three lug coils with two wires attached and one open leg.

#4 2 years ago

As you can see in the red box above, the solenoid expander switches between two solenoid busses. A coil on one buss shares the same ground line with a coil on the other buss. The solenoid expander determines which coil will fire (i.e. which of the two coils will have power) when a given driver transistor on the SDB is turned on.

The second diode prevents power from reaching the inactive buss. Looking at the diagram above, if the buss with the outhole coil is powered, as is shown by the solenoid expander relay, power will pass through the second diode on the outhole coil, through the coil and reach the ground line (A3J5-10). Since the outhole and saucer coils share the same ground line, power will also appear on the saucer coil. It will pass through the coil and if there wasn't a second diode to block the power it would reach the inactive solenoid buss, which causes all kinds of strange problems with the wrong coils firing at the wrong times.

Quoted from EEE:

Why two diodes? I seem to think that they are three lug coils with two wires attached and one open leg.

Yes they should all be three lug coils with two wires, one open lug and two diodes on the coil.

#5 2 years ago

Driver and pre-driver transistors may be damaged too due to the stress from handling the current of two coils firing at once. After you find and replace the incorrect coil, if any coils are still weak you'll have to replace their associated transistors.

#6 2 years ago

Ok, I will dog into that tomorrow and report back. Clearly you are on top of this.

Thanks

#7 2 years ago

Yes, I concur.
I've made a Tech Chart for Medusa.
Maybe that will help a bit.
The coil for the outhole needs to be an AT-26-1200 (with 2 diodes).
All the other coils are also listed on my Tech Chart.
The file is on my website www.inkochnito.nl, but here is a copy.
The coils are also listed in the manual on page 20.

Peter
www.inkochnito.nl

Bally_Medusa_Tech_Chart.pdf

#8 2 years ago
Quoted from dothedoo:

Driver and pre-driver transistors may be damaged too due to the stress from handling the current of two coils firing at once. After you find and replace the incorrect coil, if any coils are still weak you'll have to replace their associated transistors.

Well just as soon as I lifted the playfield I saw a two lugged coil on the upper saucer. You earned your $20 very quickly, dothedoo!

I will swap a correct replacement in and circle back with the results.

#9 2 years ago

Just happen to have my playfield up.

IMG_1103 (resized).jpg

#10 2 years ago

The results are in. Swapped in the correct coil and wired it properly (thanks rack-em-up) and the machine works properly.

I owe dothedoo $20.

#11 2 years ago
Quoted from dothedoo:

As you can see in the red box above, the solenoid expander switches between two solenoid busses. A coil on one buss shares the same ground line with a coil on the other buss. The solenoid expander determines which coil will fire (i.e. which of the two coils will have power) when a given driver transistor on the SDB is turned on.

The second diode prevents power from reaching the inactive buss. Looking at the diagram above, if the buss with the outhole coil is powered, as is shown by the solenoid expander relay, power will pass through the second diode on the outhole coil, through the coil and reach the ground line (A3J5-10). Since the outhole and saucer coils share the same ground line, power will also appear on the saucer coil. It will pass through the coil and if there wasn't a second diode to block the power it would reach the inactive solenoid buss, which causes all kinds of strange problems with the wrong coils firing at the wrong times.

Thanks for a great informative post.

#12 2 years ago

Some of you techs are simply amazing

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