1981 Bally Fathom Blowing Solenoid Board Transistors

[DRD]

My Fathom is developing a nasty habit of blowing power transistors on the solenoid board.

The saucer kick out fires and gets stuck on. When I first got this game about three weeks ago, it was fine for days, playing normally. The game managed to withstand 6 hours of intense league play last weekend without a fault. It managed about a dozen games last night. But then blew the troublesome transistor on its first game this morning.

This morning the saucer kick out just fired mid game (when it shouldn't have)

I did have the near fire when the wrong fuse was under the playfield. I changed the fuse and melted coil. But something caused the solenoid to lock on in the first place so I don't think I have found the cause of this problem

Any ideas please ??

Thank you

 

[stevebm1]

have you changed the diode and resistor that corresponds to the blown transistor on the solenoid driver board as well or tested them?

 

[DRD]

Hi. Thanks for the response

The resistor actually exploded, so that was changed !!!!!!!

I am today going to replace the solenoid board diode and the troublesome coil (which has 2 diodes) with a new Coil with 2 new diodes

 

[Johnnyo]

Hi DRD
That should fix it , do you know the recommend values for the under playfield fuses i have 3 on my mr/mrs pacman machine
at the moment they are all 4A fuses I was guessing they were one for each flipper but im probabaly wrong
do you kno what they should be?

 

[DRD]

Hi. My vector, fathom and paragon all have 1 under playfield fuse (by this I mean the fuse holder is attached to the underside of the playfield) these should be 1a slow blow. It is located in the middle of the game, about underneath the gap between the main flippers.

My fathom had a 4a in it and it nearly caught fire, so I suspect you will need to change this one !!!!!! I looked at an online manual for pacman and this said it should be 1a. When a coil locked on it detonated a resistor on the solenoid board and melted the coil under the playfield which was actually smoking

I do not know what the other 2 might be in your game, I think the rectifier board assembly should have the correct fuse sizes written on it, just take care here and unplug as there is High voltage on this board. If you have not checked them, do. 3 of the 6 fuses in my game were too high

Link to manual

http://mirror2.ipdb.org/files/1639/Bally_1982_Mr_Mrs_Pac_Man_Manual.pdf

 

[stevebm1]

don't always believe whats wrote on the rectifier board,games with 4 flippers need a higher rated fuse

 

[kevlar]

Have you traced every inch of the wiring from that solenoid to the board? It could just be short. On my Shadow after multiple transistor replacements for a certain coil I felt every bit of wire on that circuit and found a tiny nick in the insulation on one wire which with the playfield lowered was shorting on the cabinet speaker.

 

[Johnnyo]

Thanks for the reply DRD, well blow me I have been through that manual and thats the first time I have seen that ,Hmm will defo change that centre one
and also will change tha others to a lower rating rather underfuse than over. I cant even see these fuses on the schematics either.

 

[DRD]

@Johnnyo Just watch out for what @stevebm1 says.

I do remember seeing in one of my game manuals that you increase one of the fuse sizes for 3 and or 4 flipper games. So the manual effectively overrides what is printed on the rectifier board as they used the same board in 2,3 and 4 flipper games over the years despite the differing current draws

@kevlar thanks for the tip. I have today replaced the tranny, diode on the board, coil (including 2 new diodes). If the damned thing gives trouble again, I will go to the wring loom ! My game has had a hard life so anything is possible with it. Presumably you only need to trace one wire as it will be getting hi volts all the time, so it is just the switched ground that I would need to trace. This does sound a very plausible cause though. Thanks

 

[Johnnyo]

On your other observation about the kick out firing mid game i have a pop bumper that on occasion fires randomly during games
it happpens mostly when you hit the flippers it seems. I put it down to the age of the components and wiring cos I cant find what causes it,
tried adjusting switch gaps etc to no avail unless someone knows different

 

[backbox]

I think the melted coil in the 'smoking fathom' thread is an effect rather than a cause and that something is killing your transistors.
That resistor has blown from sudden high volts, not slowly cooked. The only high volts path is collector base shorted.

So either the transistor is being commanded to turn on for too long (switch short/software glitch/harness prob etc.) and being heated in to failure, or its a death spike from the solenoids turning off.
Either the catch diode open circuit across the right saucer coil itself or the one across the 2nd blue inline drop target could cause this.
Also, might be worth checking/replacing the cap across the transistor base/collector. This cap slows down the transistor turn off by feeding some of the rising collector voltage back to the base and so trying (in vain) to keep it turned on. The point is that the flyback voltage spike developed by the coil is directly proportional to the switching time. Slow it down, lower the voltage.

Also, from the other thread, yep, leaving the series diode off the coil will trigger solenoids from the other 4 pairs of the sol. expander circuit. doh!

 

[Nedreud]

I've got a random pop bumper on GOLD BALL just like @Johnnyo. It's always done it since I fixed the MPU. Very intermittent, sometimes not happening for days and dozens of games. But occasionally, and most noticeably during attract mode, the left pop bumper will start to hum like the coil is being partially powered. This will build up over a few seconds then snap! the coil fires. The pop bumper has been rebuilt and I've traced and tested everything I can. I'm going to replace all the driver components for that coil to see if that stops it.

 

[Johnnyo]

There is a very long post about this fault I was reading last night over
on pinside very in depth suggest you read it first, haven't got a link sorry at work at the moment
Basically he has changed almost every component on mpu and solinoid driver board related to data lines with no great success.

Haven't finished reading it yet but he seems to blame the design of the boards and the tolerance of the resistors on the boards.

 

[Moonraker]

Um, do you have a de-humidifier? I would use one first (and probably leave it for a week at 50% setting) before wading in to lots of fault finding... especially if there was 6 hours of sweaty bodies (!) in a confined space with the machine...

 

[pinballmania]

Check the solenoids are wired correctly. Fathom has the three terminal coils with the two diode arrangement. I once swapped one of these on a fathom for a single diode coil and had multiple transistor blows until I corrected the missing second diode on the coil. It serves to add additional protection against back emf up the power line.