by Rob-NYC »
Thu May 31, 2012 9:51 am
"Moose" Here are few tips:
Credit unit: as Ron pointed out some dopes bend the cancel ramp, others though run a jumper from the center slip contact on the credit wheel to ground. See if that is the case here.
Stepper: The basics include cleaning the stepper wafer contacts and wipers of tarnish and -lightly- lubing them. A drop of oil on each stepper bearing and pawl too.
make sure that they will "home" easily from even just one, or two steps up. There are contacts that ride on a roller on top of the first stepper wheel (Letters). These must transfer during the second pulse that arrives. I set them so that the roller follows the wheel downward but puts no pressure on it, just stays lightly on to keep it in the groove.
There is a large 5mfd non-polarized capacitor that is critical to accurate operation of the stepper. This will need to be replaced. I make the value up with several mylar caps. You can also use electrolytic caps in back-to-back (AC) configuration, but as recent experience reminded me, they are often much higher in capacity than marked.
There is a 100 ohm resistor in the 2050 plate circuit. Often these are burned from wallbox contacts have shorted the signal line. I use 100 half-watt to act as a fuse and protect the stepper coils.
The 2050 requires a minus voltage of approx 28VDC to keep it in cut off except when a box pulses. Replace the small filter cap on that circuit and be sure the voltage is there before putting the tube in. Having a thyratron tube conduct before it's cathode is fully warmed up causes stripping of the thorium and wears it out sooner.
Wallboxes: Connect an ohmmeter from signal (blue wire) to chassis ground and slowly turn the pulse wiper noting the resistance on each rivet. jiggle, but don't press the buttons at each rivet and again note resistance. If it jumps more than a few hundred ohms there is a good chance it will give wrong selections due to dirty keyboard contacts. Whenever I place these back into commercial service I wash the whole box and we can go into that later if needed. When used regularly they tend to keep better contact.
Rob/NYC
"If we believe absurdities, we shall commit atrocities" -- Voltaire