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(Topic ID: 265614)

1975 Bally Knockout: Relay acting like stuck switch (switch not stuck)


By SkyKing2301

6 months ago



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  • 12 posts
  • 4 Pinsiders participating
  • Latest reply 6 months ago by Sea_Wolf
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#1 6 months ago

I've been refurbishing a 1975 Bally Knockout, and I'm stuck on the very last issue (that I know of anyway) ... I've spent far too many hours on my own trying to knock this out (pun intended), so I'm finally throwing in the towel (pun intended again) and coming here for some help. I'll walk you through what I know and what I've tried.

Firstly, here's a look at area on the playfield -- I've circled the important switch in white.

pasted_image (resized).png

The schematic calls this the Top Center Lane Rollover Button (TCLRB from now on). Its associated relay has five switches on it, triggering up to 5 other relays:
A) 500 Points, always
B) Advance, when lit (advances bonus)
C) Right, when lit (lights red side pop bumper and rollovers)
D) Double Bonus, when lit (lights double bonus)
E) Left, when lit (lights green side pop bumper and rollovers).

Awards B thru E are lit at 'random' (really, just any of 10 different possible combinations based on a stepper unit which is advanced by any 10 point switch).

Here's a look at the section of schematic to show what triggers the Top Center Lane Relay:
pasted_image2 (resized).png

As you can see, the ONLY thing that triggers this relay is the TCLRB. It's also important to note that none of its switches are a Hold-type switch (the type that keeps the relay held on until some other switch breaks that circuit). Its five switches only trigger the 500 Point Relay, and when lit, the Bonus Advance Relay, the Double Bonus Relay, the Light Right Lane Relay, and the Light Left Lane Relay.

My problem is, intermittently, the Top Center Lane Relay sticks on.

[[[ Edit based on a reply below:
The star rollover is an obvious suspect, and it surely was fairly gunky. This has been exonerated, for two reasons:
1) I physically removed the star from the insert, and cleaned the star, washer, and insert.
2) During troubleshooting, to close the switch I'm often hitting it from below the playfield, bypassing the star completely, and still end up with the intermittent sticking relay. ]]]

The TCLRB switch itself would be the next most obvious culprit -- as it's the only thing that triggers the TCL Relay, so I keep coming back to that. However, that doesn't seem to be it, based on the following observations/troubleshooting:
1) I have physically observed -- and even manipulated -- TCLRB switch during the stuck relay. It is definitely not stuck closed. Maybe it's a short in the switch stack, right? Go to 2.
2) I desoldered the wire from the TCLRB switch and moved it to a different rollover switch. TCL Relay still intermittently sticks when triggered by the 'new' switch. That seems to exonerate the switch ... so maybe it's a wire problem, right? Go to 3.
3) I desoldered the wire from the TCLRB switch AND the TCL Relay, and this time connected them using a bypass wire on alligator clips. TCL Relay still intermittently sticks. That seems to exonerate the wire. So what else could it be? (Could the relay coil itself be defective somehow? This is the only thing I haven't tried switching out.)

Other observations/troubleshooting:
- This sticking can occur regardless of the 'extra' awards that are lit in the top center lane. (i.e., it can happen with any of the award configurations of Right/Left/DoubleBonus/Advance.)
- Physically unsticking (with a gentle touch) the TCL Relay stops the stuck behavior. (i.e., it's not behaving like it's being held on by some other closed switch)
- When the TCL Relay is stuck on AND Advance was lit (so Bonus Advance Relay is also stuck on), breaking the Bonus Advance Relay also results in the TCL Relay unsticking. (Perhaps this is a clue, but as I mentioned above, the TCL Relay sticking behavior also happens when Advance is NOT lit ... and I've confirmed that during TCL sticking when Advance is NOT lit, the Bonus Advance Relay is NOT activated.)
- The 500 point relay is triggered every time the TCL Relay is on (as it should be), so since this was the only other constant, I looked at this too. Attempting to break this relay while the TCL Relay is active is not possible (since the TCL Relay's switch is driving it), nor does forcing it cause the TCL Relay to release. I also looked at & cleaned Score Motor switch 8C (reference schematic below) which (if I understand it correctly) should break the hold on the 500 Point Relay. This function seemed to work fine anyway, since no other 500 point switch results in any problems.

- I've looked over all the switches on 500 Point Relay and the other four relays driven by the TCL Relay and they all look fine, open/closing as appropriate during operation.

Below & attached is a larger excerpt from the schematic, which does include the five other relays driven by the TCL Relay. Still, ultimately the problem seems to lie in the TCL Relay and/or the TCLRB switch, but I'm just not seeing how based on everything I've done so far. Thanks in advance for any help you can provide!

schematic_portion_annotated (resized).jpg

So I'm up against the ropes here (yup, pun intended again). Any help/guidance is appreciated. I have a full hard copy of the schematic (my excerpts are partial scans), so let me know if there's anything else you'd like to see on there. Thanks in advance!

#3 6 months ago

I should have mentioned this -- the star rollover was also another obvious suspect, as it was fairly gunky. This has been exonerated, for two reasons:
1) I physically removed the star from the insert, and cleaned the star, washer, and insert.
2) During troubleshooting, to close the switch I'm often hitting it from below the playfield, bypassing the star completely, and still end up with the intermittent sticking relay.

#4 6 months ago

you said you desoldered the relay ? does it still stick if manually actuated?

I wonder if the actuator plate is magnetized or binding somehow or the spring is gone

#5 6 months ago
Quoted from chas10e:

you said you desoldered the relay ? does it still stick if manually actuated?
I wonder if the actuator plate is magnetized or binding somehow or the spring is gone

I did desolder it temporarily when I was attempting the wire bypass. I didn't try manually cycling it during that time. Will attempt this later on tonight, plus whatever other ideas we've gathered by then.

#7 6 months ago
Quoted from chas10e:

Got a good video on how to finesse a relay

Hmm, maybe a tighter spring might help, since it didn't take much of a manual push to release it. I'll try that later too.

He also mentions slight divoting on the inner side of the plate that might be getting stuck on the top of the coil, I'll check for that also.

#8 6 months ago
Quoted from SkyKing2301:

Hmm, maybe a tighter spring might help, since it didn't take much of a manual push to release it. I'll try that later too.
He also mentions slight divoting on the inner side of the plate that might be getting stuck on the top of the coil, I'll check for that also.

Wasn't much divoting on the plate but I smoothed it up anyway. The spring, on the other hand, did feel noticeably weaker than the others. I swapped it out with a slightly stronger one and so far it's been working 100%. The family will put some games on it tonight before I declare it resolved.

#9 6 months ago

Well, after putting the stronger spring on there, I put it through about 30 cycles and it never stuck, and we put about 15 games on it since and it still hasn't stuck a single time. I'm going to call this resolved -- frustrating as it is that it was something so simple! But hey, I learned a lot along the way, and this was great practice for me on reading the schematics and figuring out how everything works.

Thanks chas10e for pointing me in the right direction!

#10 6 months ago

Glad to have pointed you to nicovolta 's video. It's great to have a guy like that in your corner for a game like Knockout

(pun intended)

#11 6 months ago
Quoted from chas10e:

Glad to have pointed you to nicovolta 's video. It's great to have a guy like that in your corner for a game like Knockout
(pun intended)

Haha, nice one! I sent him a PM as well, to thank him.

#12 6 months ago

Glad to see you got up off the mat and punched your way out of this.

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