Lamp problem (Medusa, Bally 1981)

(Topic ID: 189125)

Lamp problem (Medusa, Bally 1981)


By nibre

1 year ago



Topic Stats

  • 9 posts
  • 6 Pinsiders participating
  • Latest reply 1 year ago by acebathound
  • Topic is favorited by 2 Pinsiders

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DSC_4196 (resized).JPG
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#1 1 year ago

Some insert lamps are on all the time and some are never on (they are not broken). When I look at the lamp driver board, the transistors in question even look broken (see image).

Is it as simple as this? I replace every transistor where there is a problem.

Should I measure the transistors first, and if so, do I check the resistance or use the diode test? Is it ok to do it while the board is still connected?

Could other components be broken? Can there be another underlying problem? How can so many transistors be broken at the same time?

Thanks!

DSC_4195 (resized).JPG

#2 1 year ago

How many lamps are on and how many are not? Do they work in diagnostic mode? (Flash on an off). You have corrosion on some of the transistors in the photo. This could be the source of some of your problems. Also did you replace the connectors on the lamp board, both male and female? Finally did you check the light sockets themselves?

Don

#3 1 year ago
Quoted from nibre:

Is it as simple as this? I replace every transistor where there is a problem.

Pretty much.

Quoted from nibre:

How can so many transistors be broken at the same time?

My guess is they did not break all at the same time. If they did, I'd look for another problem. I just replaced a bunch on a project I'm working on and the location of the board makes them very susceptible to alkaline damage from the batteries mounted above.

#4 1 year ago

On bally boards the transistors will need to be tested 2 ways.

For the larger square transistors:

1: On the diode test.
Put the black lead of your meter on the outside "cathode" leg (labeled "C")
Put the red lead of your meter on the outside "gate" leg (labeled "G") Your meter should read .4 to .6 volts.
Swap the meter leads. Now the meter should read 1.4 to 1.6 volts.

2: On the continuity test. Test the other sets of legs and make sure they are not shorted.

On the smaller transistors:

1: On the diode test.
Put the black lead of your meter on the "cathode" leg (labeled "C")
Put the red lead of your meter on the center "gate" leg (labeled "G") Your meter should read .4 to .6 volts.
Swap the meter leads. Now the meter should read 1.4 to 1.6 volts.

2: On the continuity test. Test the other sets of legs and make sure they are not shorted.

#5 1 year ago

The green gunk is from battery damage.
Remove and replace them is highly recommended.
Also clean you board with a 50/50 sollution of vinigar and water, just like what you should do with the mpu.
Check the bottom traces for continuity from thyristor to connector.

Good luck....

#6 1 year ago

Thanks for all the advice!

The machine was in this condition when I bought it and I don't know its history.

I have ordered components and will do the replacements and cleaning in a few days.

There is a new battery in place (see image below). Is this a type that can leak in the future? Are there any other, safer solutions?

DSC_4196 (resized).JPG

#7 1 year ago

Yep, this is the kind of battery that can leak over time.
Actualy it's not a normal battery (alcaline), but a rechargeable battery (nickel-cadmium).
The safer methode is a memory cap of 1F (not uF).
http://www.pinwiki.com/wiki/index.php?title=Bally/Stern#Installation_of_Various_Battery_Eliminators

Peter

1 month later
#8 1 year ago

I have replaced the transistors and now the lamps work as they should. I haven't replaced or moved the battery yet.

Thanks for all the advice!

#9 1 year ago
Quoted from nibre:

I have replaced the transistors and now the lamps work as they should. I haven't replaced or moved the battery yet.
Thanks for all the advice!

Yeah I'd cut that battery off ASAP.

NVRAM is $15 for a single module from a few sellers.

I sell them @ https://pinside.com/pinball/market/shops/1030-pinitech/00316-5101-nvram-battery-eliminator-for-high-score-save

I'm not usually advertising a ton when people post things like this, but your board is so nice compared to most that I'd really recommend going with someone's NVRAM product and ditching the battery so you can keep it that way. Any time I get a board in that looks like that, doesn't matter if the battery looks like it's been replaced recently.. it's gone! They're ticking time-bombs and anyone's guess when they decide to leak. Even brand new alkaline batteries leak often enough when their expiration dates are 5+ years in the future.

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