Rock-Ola 460 Credit Unit

My Rock-Ola 460 quit registering credits. It is on coin play and the coin switches have been working fine, but I flipped the service credit switch on the credit unit (50225-A) to play it while the dome was open. That one played, but since then the unit will not register credits. The 1/4-amp slow-blow fuse is good, and so are the three breakers on the power supply, but now neither the coin switches nor the service credit switch will establish credits. Looking at the wiring on Page 16 of the service manual, it appears that everything passes through this service credit switch, then on to the accumulator. How can I test this switch, and what else should I be looking at? This machine is also connected to a 507 wall box through a 1769 stepper. Credits at the 507 work O.K. and will make selections (actually it plays whatever it feels like through the wall box, but I'll get around to that later). Selections made manually at the 460's selector unit play just fine.
Patrick.

Patrick,
Since I can't see it--
Is the credit wheel at zero, or above. Does it spin freely, if you manually "pull" a coil lever? is the credit switch open or closed ? are any of the"pushbuttons" on the keyboard locked down (suspect the last played combination here) ?
Did you use a meter to test that fuse ??
Ron Rich

Ron: thank you for your reply. Before it gets obvious, I've got to admit I don't know much about credit units. Been pretty lucky until now with them. I pulled the unit out for a better look. I don't know what position the credit wheel was in. The three wheels would click back until, I think, credits were maxed out. The switch is a momentary switch, and all of the push buttons were good; none stuck down. I did use a meter on the fuse, out of the holder. Blown. Yesterday I'd tested it in the clip. Since you can't buy slow-blow fuses around here (I've ordered a package) I installed a fast-acting 1/4 amp fuse. Worked O.K. with the coin switches, but when I tried the service credit switch it vaporized the fuse! So that switch is probably the cause, although there's got to be a better way to test it.

Patrick,
It would be my guess that the fuse is blowing because you are holding the switch too long--or, one of the coin coils is defective ? Did you try all coin switches prior to vaporizing it ?
BTW--a fast blow is an adequate replacement for the same sized slo blo--however, a slo blow is never a replacement for a fast blo--
Ron Rich

Ron: I tested the coin switches individually with the rest of the fast-acting fuses. Dropping a coin is working fine in all four, but holding one down even briefly pops the fuse (makes sense). But the service credit switch is not working properly. It's a momentary, spring-return switch but it takes out the fuse dependably. I'll either have to replace it, or just simply not use it. I've got it all back together with the proper slo-blo fuse and everything's working fine. I'll just keep a couple half dollar coins near the credit unit so I wont be tempted to try my luck with that switch. Thanks for your help.
Patrick