Re: Atari STUNT CYCLE - service bulletins?

Rodger Boots wrote:
> My God, that is one total abortion of what should be a simple circuit!!!
>
> I don't see any good reason a 5K pot shouldn't work, they don't
> mention what taper (linear, log, reverse log, etc.) the pot should be.
>
> What is the problem exactly, doesn't go slow enough, doesn't go fast
> enough, what? I assume (very dangerous) that it doesn't go slow
> enough. If that's the case maybe Q14 isn't grounding one end of the pot.

Hi Roger,

It IS a very nasty circuit...I've been trying to repair one here, can't
get it quite fast enough for jumping 21 buses, nor slow enough to crash
unless you use a little throttle to clear the starting 8 buses.

The theory of how it works is on page 8 & 9 of the operators manual.

R2 and R3 feedbacks are throttle voltage dependent and affect the lift
of the motorcycle vs speed, when you lift the front wheel the first step
it won't accelerate as fast as if the wheel is on the ground, and the
second lift step does not do much either, yet putting the 100KR pot in
place of R36 (as recommended by Atari) does affect the low speed and
also the maximum speed. It would have been nice if there was a
suggestion of tuning the circuit included with the page titled "Stunt
Cycle - Return Throttle Modification (B-0023)"

I've tried the recommended mods, but I do not have the original
transistor - 2N3565 and have tried a PN3565, 2n2222, and a few other 2N
NPNs - none of which worked much better than any other one. Reading the
manual and it uses a current amp for the 556 frequency change...not one
of my better subjects.

So, now it works, just not as well as it should. I've tried a few tricks
- changed a few resistances, but as I don't
 really understand the operation of this circuit I can't really do much.

Must see if I can turn up more service bulletins!

Darn.

John :-#(#

>
> On Wed, Aug 4, 2010 at 7:28 PM, John Robertson <pinball@telus.net
> <mailto:pinball@telus.net>> wrote:
>
> Well, not a lot of action on this mail list these days...sigh.
>
> Working on a Stunt Cycle and having trouble balancing the throttle
> - the manual and the two sheets about various mods don't help much.
>
> The schematic calls for a 5K pot for the throttle (works poorly
> with that installed), the board works better with the 25K pot on
> the CTS-1 that I use - so I put the 25K pot in (as was in when the
> game came to the shop), but the range of throttle is not
> satisfactory. I added the 100K trim pot in place of R68, and that
> allows one to adjust the minimum throttle and affects the high
> end, but there are no instructions about its adjustment...
>
> So, does anyone have any service bulletins for the game?
>
> Thanks,
>
> John :-#(#
>
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-- 
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames)
                 www.flippers.com 
"Old pinballers never die, they just flip out"
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