How do I troubleshoot the coin switch on a 742A?

[Simple Sam]

My 742A isn't registering coins when dropped in the machine.  They are going straight into the hopper without registering.  When I opened the door, I tried to manually register coins by pressing on the wire of the coin switch; nothing.  I've had this happen before and it turned out to be a bad fuse at the 50 volt, 3 amp fuse.  I replaced the fuse but it didn't clear up the problem.  What should I check next?  I have a multimeter but I've never used it so I'm not clear on its operation.

[DavidLee]

Hold the handle release lever forward then pull the handle.
Thus cycling the machine.

Check the payout step up unit to see if its been reset.

This Low tech technique might help.
Using the the plastic end of a screwdriver in a hammer fashion,
tap the switch in question 2-3 times.

[Jim]

depending on your meter, there might be ohms scale x1, x10 etc.  or just the greek symbol for ohms.  place your indicator on the scale for ohms,  touch the two probes together, this should cause the meter to zero or indicated zero ohms, complete meter deflection .  your switch has three posts on it, one is labeled common, the other n/o  or normally open,  the other n/c  normally closed.  normal operation of the switch is: from the common terminal to the normally closed terminal you should read zero ohms, or the switch contact is closed, when you depress the trip wire the contact should open and you will read no ohms or open,  check the common to normally open contact , it should read just the opposite, no ohms when normal, zero ohms when the trip wire is depressed.

this is a way to check all three terminal switches for proper operation.

hope this helps

Jim

[wolftalk]

just to make sure on jim's write-up ... you do that with the power off.


there's a gotcha tho if you are testing a switch in the game - you will likely measure resistance going through other paths like the coils and transformer regardless of the switch position.


if testing in game, what you care about is a zero vs non-zero reading on the meter.   zero = switch closed, non-zero = switch open.  A few ohms when the switch is closed means a dirty switch. 


you may be able to open it to clean or just squirt electrical cleaner/alcohol in it and toggle the switch a bunch of times.  Let it evaporate before turning on the game.


if testing a disconnected switch non-zero = infinite.


the 742A is also an early design where the coin switch only needs two terminals.  There may be a 3-terminal switch in there, but you are checking for zero ohms between yellow wire 30 and blue/red wire 21-1 when the coin tripwire is held down.


there's lots of variations of the 742A, but generally closing the coin switch should power the coin relay.  If you stick a voltmeter on the 50V fuse or the orange wire on any 50V coil, then put the other probe on the blue/red wire on the coin switch, you should see 50V when the coin switch is depressed.


if you do and the coin relay is not powering, check the switches on the coin relay.  The blue/red wire goes to the middle/moving blade on a switch, and it should connect to a blade with a black/yellow wire 83 when the relay is not powered.


that switch is a rarity ... the middle blade is supposed to be "make before break", meaning the middle blade should be contacting BOTH surrounding blades during the switch movement.  It only disconnects from a blade on either side when the armature plate is all the way up or down on the coil top.


if that doesn't make sense, the idea is you want to maintain the connection between the 21-1 and 83 wires as long as possible to ensure the coin relay powers completely and the handle release coil trips.

[Simple Sam]

Hold the handle release lever forward then pull the handle.
Thus cycling the machine.

Check the payout step up unit to see if its been reset.

This Low tech technique might help.
Using the the plastic end of a screwdriver in a hammer fashion,
tap the switch in question 2-3 times.

I hand cycled the machine but I don't know what the payout step up unit is or had to tell if it's been reset.  Sadly, tapping the switch didn't help.  I do wonder if the problem is something related to the hopper as it stopped working when I pulled the hopper out to get some coins.  The previous time when the fuse had blown was also after I had pulled the hopper.

[Simple Sam]

depending on your meter, there might be ohms scale x1, x10 etc.  or just the greek symbol for ohms.  place your indicator on the scale for ohms,  touch the two probes together, this should cause the meter to zero or indicated zero ohms, complete meter deflection .  your switch has three posts on it, one is labeled common, the other n/o  or normally open,  the other n/c  normally closed.  normal operation of the switch is: from the common terminal to the normally closed terminal you should read zero ohms, or the switch contact is closed, when you depress the trip wire the contact should open and you will read no ohms or open,  check the common to normally open contact , it should read just the opposite, no ohms when normal, zero ohms when the trip wire is depressed.

this is a way to check all three terminal switches for proper operation.

hope this helps

Jim

I have a Klein MM400 multimeter. When I set it for Ohms, it read OL when I connected it to the switch wires.  When I triggered the switch, it read 0.

[Simple Sam]

you may be able to open it to clean or just squirt electrical cleaner/alcohol in it and toggle the switch a bunch of times.  Let it evaporate before turning on the game.

I didn't realize the switch was serviceable.  Maybe I can try that later.


there's lots of variations of the 742A, but generally closing the coin switch should power the coin relay.  If you stick a voltmeter on the 50V fuse or the orange wire on any 50V coil, then put the other probe on the blue/red wire on the coin switch, you should see 50V when the coin switch is depressed.

Is this something I do with the power on? I'll have to look for a conveniently located 50 V coil. Looks like the fuse is pretty easy to get at with the hopper out.



if you do and the coin relay is not powering, check the switches on the coin relay.  The blue/red wire goes to the middle/moving blade on a switch, and it should connect to a blade with a black/yellow wire 83 when the relay is not powered.


What is the coin relay?  I'm looking in the Bally Manual 100 and don't know where to find it.  I just got started and still don't know what all the parts do or where there located.


that switch is a rarity ... the middle blade is supposed to be "make before break", meaning the middle blade should be contacting BOTH surrounding blades during the switch movement.  It only disconnects from a blade on either side when the armature plate is all the way up or down on the coil top.


if that doesn't make sense, the idea is you want to maintain the connection between the 21-1 and 83 wires as long as possible to ensure the coin relay powers completely and the handle release coil trips.

[DavidLee]

Payout step up unit is located on the left side hopper.
A coil plunger on the lower left side of the unit behind the contact board resets the unit to zero.
This can be manually depressed in to reset the unit.


Another low tech maneuver is to move the hopper in - out, left and right about 1/4 inch.
As there might be a bad connection with the beau plugs in the back.
Sometimes plug pins or sockets get pushed out of place resulting in loss of continuity, and or can also cause a short.

[DavidLee]

Payout step up unit photo.
Mechanical step up type.

[wolftalk]

the coin switch may or may not be openable.  The older it is, the more likely to be assembled with screws or the lid can pop off when you take out the mounting screws.  Modern ones are usually welded shut so the best you can do is try and get some solvent in it.  I usually remove it, dribble some in, shake, operate the switch, try and shake out the solvent and let it sit/blow air into it until nothing comes out when shaking it.


the game needs to be on when measuring voltage and the meter should be set for measure AC volts.    Power off when measuring resistance (ohms), or you can damage the meter.


grab the bally 400 manual from http://bingo.cdyn.com/slots/bally_manuals/ ... it has exploded parts diagrams.  If your lucky, you'll find what you want using a text search...but in this case you aren't lucky.  It should be items 48-66 on page 64, which is the only coil device on the left side of the reel mechanism.  It's a "trip relay", so when the coil powers and pulls in the armature plate, the switches flop to a new position and stay there until the reels are spun and the relay is mechanically reset.


in other words, depress the coin switch and you should hear that relay click once as it trips.  It will not do anything on repeated coin switch closures because one of the switches on the assembly disconnects the coil until the relay is reset by the spin.


there's multiple switches on the stack on the relay assembly, so use the wire colors to figure out which switch you care about.  You can also just check them all.


if you aren't familiar with cleaning/adjusting switches, yell.   Key things is don't file off metal if you can help it, make sure there's a bit of "overtravel" after the contacts touch so the contact faces slide across each other a little, and you almost always adjust the non-moving blades to create the overtravel and gaps.


having said all that, 0L on your meter means infinite, which is a little suspicious if the reel mech is installed.  Pull the 50V fuse and use the ohmeter probes on the ends...you should get 0 ohms.


what is the model number of your machine on the plate under the handle?  The top number is the model, the bottom the serial number.

[Simple Sam]

I think I found the problem!  Do I just solder the disconnected wire to the same spot as the other orange wire?

[DavidLee]

Payout relay latch coil.
This is a good lesson learned.
Broken wires are sometimes hard to spot.
When checking components it’s a good habit to take a good look at the solder joints.
Besides wires completely off.
 There is a possibility of wires hanging on by one or two strands.
 Completely broken, but just resting on there respective joint or one close by.
 Broken contact leafs / blades, Blades can also be cracked within the switch stack wafers / separators.

[wolftalk]

I think I found the problem!  Do I just solder the disconnected wire to the same spot as the other orange wire?

yup, attached the busted wire to the other orange one on the coil lug. 


That's wire 70 - the 50V power wire.  It daisy chains all over the place, so many of the spots it's connected to have two wire segments soldered to the same place. 


looks like someone in the past cut out a coil and replaced it with another cut out coil using those inline crimp connectors.  I guess they didn't have a soldering iron.

[Simple Sam]

It's fixed!   After I soldered the wire back in place, I tested the machine.  I was initially dismayed that the coin hopper wouldn't stop after hitting a winning combination.  I poked around the hopper pretty sure that I had somehow screwed up the coin counting mechanism.  It was making a kachunk, kachunk sound as it ran non-stop on what should have been a two coin win.  Apparently I poked the right thing because it is now working flawlessly.


Thanks all for the advice.  When I first got the slot machine, I thought it would be a cheap project to try to learn about EM machines.  I quickly decided I was over my head and got a pro to fix it.  I thought that once it was working, I could hopefully troubleshoot it when the inevitable problem popped up.  With all of your help, I was able to fix the first problem.