Symptom 2: Record trips as soon as it starts to play.
The mechanism trip solenoid is used to trip from scan into play and from play into scan. Thus there are two circuit paths to energize the solenoid, one for Select Trip and the other for reject (or Mute) Trip. There are wiring differences between mechanisms used in the various jukeboxes, so I'll refer you again to the manual for yours. Generally, mechanism switch 3M12 is closed in play to complete the record reject path from the amplifier's Mute Trip Relay. Another switch, 3M11, is closed in Scan and Transfer to energize the Mute Trip Relay, which mutes the amplifier so that all the clicks and pops of record transfer are not heard. If either switch is misadjusted so that both are closed at the beginning of record play, the record will reject as soon as the tonearm sets down.
Switch S1103 is the switch mounted to one side of the Pickup Arm Cradle Frame. It closes when the pickup arm reaches the lead-out groove of the record, to begin the transfer cycle to put the record back into the magazine. If this switch is shorted, or the cabling between it, the reject switch in the Volume Control Assembly, optional PRVC, or the Mute Trip Relay in the Amplifier is grounded this can occur. To check for this, turn the power off and manually put the mechanism in play with a record on the turntable. Turn the motor coupling until the pickup needle just sets down, and rotate the coupling a few turns more to insure that the mechanism is completely in play while observing the movement of the 3M12 and 3M11 contacts. Make sure that 3M11 opens before 3M12 closes. If not, perform the appropriate adjustments as listed in the mechanism manual. Don't have a manual? You can get a copy from:
Always Jukin',
Victory Glass, or
Stamann Musicboxen for those in Europe.
Use your ohmmeter set for continuity to check between the non-grounded end of S1103 and ground. If there is continuity, either a switch is misadjusted, or a switch or the wiring is shorted. To narrow down the cause, eliminate the amplifier/volume control from consideration by unplugging the Mechanism cable (usually a 6-pin orange connector) from the amplifier. If the short goes away, the problem is in the amplifier, volume control, or PRVC (a likely candidate). Otherwise the problem is in the mechanism. If the problem is in the mechanism, first make sure the pickup arm is away from the magnet (or microswitch, on the older machines). If you still get continuity to ground, the problem is probably in the wiring.