I report here the post made in VECTORLIST hoping someone here can help me:
Hi all,
I have 3 tempest boards. two work fine, while the third has a problem with the spinner direction.
using a Taito spinner all 3 boards work fine so I started to analyze the atari spinner behaviour first.
What I could see is one of the 2 square waves is "lower" than the other and this seems to have impact one one of the boards only.
Going to the board I can see both waves arrive to the MC14584B in E6 correctly but the lower wave doesn't exit from this component properly (pin 12). Inverting speed and direction pins, the problem persists (but in pin 6); so, the problem is definitely caused by the "lower" wave).
I replaced this component (with a 7414) but nothing changed.
So my questions are:
why this happens on this board only?
just in case, is there a good source for OPB2208 coupler? or is there a cheap replacement?