Flash
Williams, 1979What it does is kind of quietly hum when it should fire...vibrate the tiniest bit.
4.5 ohms at coil
Verified continuity from brown and blue wire on coil all the way to driver board.
Tried it in game and during solenoid test.
I still have to check the diode on the coil.
If that tests ok do I just assume the transistor is bad? Is there a way to test it? What else could it be?
It moves back and forth freely. Actually it fired once yesterday during all the testing. Was weak though.
I would maybe try changing out the coil with one that works. I guess that might tell you if it was the coil is bad or not
Coil measures 4.5 ohms and diode measures 0.7 (well 700 on my meter I assume that is 0.7 as no decimal displays when set to diode setting).
Pretty sure coil should be good with that reading...right?
I guess pull the driver and reflow edge connector? Not sure what else to try. Besides replacing the corresponding transistor which is fine but I have to order it.
I have the exact same problem with my Flash. Replaced coil, sleeve, and still no succes. When it fires I just get a weak bump.
Would love to know the solution you find.
Just reflowed the edge connector and transistor...transistor tests good verified by testing nearby identical transistors. Will put back in and retest.
Any other ideas appreciated.
Quoted from mwsmith:How much DC voltage is at the coil when idle? Should be between 28-38V.
You know I had trouble measuring the DC voltage on not just that coil but all the coils. Numbers always bouncing around. The numbers were kind of all over the place but hovered around 19v DC...since all the coils I measured are similar I am thinking the voltage is there even though I can't get a good reading for whatever reason.
I connected test lead to negative side of coil and grounded it to metal side rail. Still just get the humming and light vibrations...
Quoted from crujones4life:Can a coil still be bad with a reading of 4.5 ohms?
Marcos coil labels have the DC resistance printed on them. Looks like your 4.5 ohms is good for a 23-900 coil.
So is it even possible for the coil to be bad with that reading? What's weird is that it responds with light humming and vibrations. Any previous bad coil I have had did nothing at all.
The coil at 4.5 ohms is OK, so is the diode with 0.7V drop. Does the knocker work if you short its driver transistor collector (tab) to ground? If it works then, you have a bad transistor - either the power transistor or pre-driver. If not, then check connectors for bad contact.
Quoted from Tuukka:The coil at 4.5 ohms is OK, so is the diode with 0.7V drop. Does the knocker work if you short its driver transistor collector (tab) to ground? If it works then, you have a bad transistor - either the power transistor or pre-driver. If not, then check connectors for bad contact.
I tried shorting the coil directly to ground and it still didn't fire. (Post #12). I verified continuity from coil to driver board as well. I guess maybe I can check the driver board chips? I thought shorting the coil to ground bypassed everything else so long as it is getting voltage. Is that not correct?
show a picture of your knocker assembly. You can assemble something wrong and it makes the coil really weak.... i forget exactly why tho.
Now that I see the picture I remember.... the plunger rod being installed upside down is what I was thinking of. Looks like you got it right, but make sure the nylon tip of the plunger is going to strike the top.
I'm sure this doesn't help, but I have never even heard the knocker fire in my Flash because it only gives sound effect when set up for free play. You have your machine set up for coin op, right? My understanding is that William's machines of that era did not use the knocker at all in free play.
Quoted from Calfdemon:I'm sure this doesn't help, but I have never even heard the knocker fire in my Flash because it only gives sound effect when set up for free play. You have your machine set up for coin op, right? My understanding is that William's machines of that era did not use the knocker at all in free play.
That's how my Firepower works. You wont here the knocker on free play.
Williams SS knockers seem to almost never work and when they do they make a dull thud you hardly notice.
I don't bother trying to fix them or make them louder. Just not part of the early Williams digital experience for me.
Game is not on freeplay. I didn't even know that was possible...lol.
Edit: I am pretty sure the manual states credits can be added from 1 to 99.
Are we sure Flash has free play?
Regarding the voltage...I for some reason cannot get a steady voltage measurement on any coil. Numbers bouncing around everywhere. Digital MM new battery. It is definitely seeing some voltage as it hums and vibrates. The readings were similar to flipper and drop coils so assumed (lol) was getting correct voltage. Will try to measure again.
On my system 6, I think if you set the maximum credits to "00" it will go into free play. Something like that.
Quoted from mwsmith:Have you checked for cracked solder at the pins on 3J3 on the power supply board? (lower left corner) Pin 7 at 3J3 feeds the 28V to the knocker & coin door coils. Also check the plug for burnt or corroded contacts.
Thanks! I will check this out tomorrow.
Solved! You guys ready for this one? The plate that the plunger rests on is magnetized! Feck!
My "fix" was wrapping the plate in electric tape. I ain't replacing the assembly. Thanks everybody for chiming in!
Well if barakandl hadn't flagged it as problematic, ironically I would have suggested flipping the plunger so the nylon tip prevents the magentic attachment. 
Congrats on figuring this one out.
Just remembered something. The bracket is supposed to have a rubber on the bottom for the plunger to rest on.
If you want a louder knock, try the mod I used on my Flash: https://pinside.com/pinball/forum/topic/knocker-sounds-weak-on-gottlieb-system-1-machines#post-3716952
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Cedar Hill, MO
Lempäälä
I'm gonna make a note on that one.