Missile Command Cap Polarity

[tb lilley]

My Missile Command went down last night. Been running problem free for about 3 years.

Voltages all tested good. So, was in process of cleaning and reseating socketed chips when I noticed that the cap at C42 only had one leg connected to the board. Looks like the cap had been soldered in very tight up against the PCB.

Cap is .22uf 25V radial.

I'll order a replacement that'll go in here:

But I've no idea which way round the cap should go in, as there's no polarity marking on the board.

Diagram doesn't help either:

So ... Any ideas which side way around the cap should go?

 

[PaulSwan]

Isn't that blob on the left of the "22" the + sign?

You can also verify from the schematics - use a meter to determine which pad goes to which point on the schematics and that will tell you which way round it should be.

Paul.

 

[tb lilley]

Thanks, It's a dot (0.22) rather than a plus. Anyway, turns out its a ceramic disc cap (which are non polar) so I'm told. So will be good to go.

 

[RaveN]

If it's the same as C41 then it's not a ceramic disc cap, looks more like a mylar, Polypropylene or film, although it shouldn't matter too much. If it is, and you've used a ceramic, ideally it would need to be a slightly different value but it's not vital as it's just a supply bypass cap. I would have thought the game would work without it, just not 100% reliably.

None of those caps use polarity.

Andy