Taito Space invader problem

[mammyrat]

I just obtained a nice Taito Space Invader Trimline (mini). It works great with one minor problem. When the game starts the man moves all the way to the right and will not return. Even if I unplug the control panel. What could be the problem?
Thanks.

[jay]

The joystick is simply 2 switches. It sounds like one is stuck, but if the control panel is disconnected I would look for a short in the harness.

[mammyrat]

Thanks, I will check it out and post my findings.

[mammyrat]

I pulled the wire from the PCB connector and the base still goes to the right.
I assume this means something on the boards. I pulled the boards, didn't notice anything obvious. I cleaned them with a nylon bristle brush and compressed air, cleaned all the connections for the harnesses and jumpers and it still does the same thing. Any ideas?
Thanks

[li_gangyi]

I would start by probing around the 74153s (multiplexer) and 7414s (inverter), that come after the inputs. See if on any of them the output is stuck for some reason.

A logic probe / oscilloscope will be real good for this, failing that, a DMM might work.

[mammyrat]

Thanks, I'll get out my scope and see if I can figure something out this week. Is a logic probe a handy device to have even if I have a scope? If so , can you recommend a good one to get?
Thanks,
Alfred

[li_gangyi]

If you have a scope that'll be better than a logic probe usually, because now you can see the quality of the waveform and fast changing signals... I prefer my oscilloscope to a logic probe.

For a logic probe, anything that'll do tri-state (High, Low, and High-Z or no signal), is what you are looking for, some of the cheaper ones don't do the High-Z (no input, totally disconnected etc.) and show a false reading (usually high).

[mammyrat]

Finally got around to working on the S.I. The I replaced 7414 coming off the right joystick switch and the game works great!
Thanks for the help.

[channelmaniac]

Sweet!

Thanks for taking the time to let us know!

RJ