Q'Bert...Knocker

uuv8217

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Hello,
Would someone know, knocker wont work, replaced my coil and I have 32 volts dc, made sure logic switch #6 is on and fuse is good, but still no luck ,anyone have a clue or what to check.

thanks in advance
 
Hello,
Would someone know, knocker wont work, replaced my coil and I have 32 volts dc, made sure logic switch #6 is on and fuse is good, but still no luck ,anyone have a clue or what to check.

thanks in advance

with power off and disconnected.

did you ohm out the coil to make CERTAIN it is not open (broken wire in coil).
 
q'bert

yes, replaced the coil and have a 11 ohms, with the new one, i have 30 volts but no knock, just to check the coil, put external power and the coil worked
 
yes, replaced the coil and have a 11 ohms, with the new one, i have 30 volts but no knock, just to check the coil, put external power and the coil worked

Maybe a bad driver on the motherboard. Does this coil have a diode? If so, was it wired correctly?

Edward
 
Do you have a switching power supply installed in it? I've heard that switching power supplies don't work well with the knocker.
 
Q'Bert

Power is wired correct and no power switching sypply, for the driver are you talking about Q2, yes for the diode and its good

thanks
 
If the circuit looks the way I think it does, if you ground the collector and the knocker works, all that really tells you is that your power supply can power the knocker. It can rule out a switcher that can't take the load, but not much else.


It goes supply -> knocker -> collector of Q2 -> emitter of Q2 -> ground, right? In that case: If you want to rule out Q2, apply a small voltage to the base of it (I don't know QBert, but you want to be somewhere between Vces and Vcb). If the knocker kicks, Q2 and your supply is good and your problems are further up the circuit. If it doesn't kick, rule out the supply by temporarily bypassing Q2 with, say, a tweezers. If that makes it kick, yes, replace Q2.
 
Knocker

Is there anyway to keep the knocked working, and not use a switcher.. As I've got a qbert with a rebuilt ps and the knocked pops a fuse every once in awhile..
 
Is there anyway to keep the knocked working, and not use a switcher.. As I've got a qbert with a rebuilt ps and the knocked pops a fuse every once in awhile..

The answer to that is:
The ONLY way to keep the knocker working is WITHOUT a switcher.
 
i have the arcadeshop PS and my knocker still works. its only getting 12v instead of 30v which makes it a lot weaker sounding.
 
Wow, all this looks vaguely familiar from a previous post. Has anyone ever given this a try. My Q*bert is still out of commision for now.

Something I would try but don't have a working q*bert to test. Maybe someone could double check my calculations or test this please let us know. Q*bert uses a A-5195 coil. Two things you could do if you have a new switching ps w/ a conversion kit.

1. Take the wrapper off the coil. Desolder the outer winding and un-wind about 50 turns. Check the resistance and that point. Don't go below 5 ohms. Resolder the winding back on. This will lower the resistance and make the coil "more powerful". We do this in the pinball world all the time.

2. According to my calculations, the current draw through the coil circuit is about 2.5 amps. Now, it's only protected by a 1A sloblo fuse (it can handle that for a fraction of time, that's why it doesn't blow for a coil). The transitor that fires it is a 2N6044. It can handle 8A. Looking at the A-5195 coil, it has a resistance of about 12.3 ohms. Under the normal 30v, that where I get about 2.5amps. A gottlieb A-5194 coil only has a resistance of 4.5ohms. That will give you about 2.6amps with the switcher only supplying 12v. If it blows the fuse, which it shouldn't, use a 1.5amp slo-blo. The extra can easily be handled by the 2N6044 (8A) and the switcher 12v which looks like it can handle 4A.

#2 is the way I would go. No hacking involved and can easily be documented and put back to the original state.
 
Q2 on the logic board appears to control the knocker. Test it, and if it tests good trace the signal back to A8.


I am having the same problems as per OP, coil is Ok, and have changed the Q2 could the A8 (74LS377 Flip Flop) be bad?

I also have another problem where when you land on the spinning disc or getting the small green ball the whole screen warps, which must be something to do with background colour on the screen changing as its more noticeable when you get the small green ball. (I should put this in another thread apologises)
 
Q'Bert

Hello,

Changed that bad boy Q2 and it did the trick, the knocker works fine now, thanks for everyones help, If you changed Q2 and no luck ,measure the voltage for 32vdc ,no voltage power supply or fuse ,if good go for the flip flop, or replace the coil or check the diode on it
 
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