Seeburg AQ160 random selections

Working on this,its been stored a few years.It regularly makes random selections only when scanning left to right.Does it even if I set it scanning and flick the switch into play.Receiver and pulse amp recapped.I borrowed a known good receiver and the problem is still there.Tried a seperate earth from TMU to pulse amp body.Any suggestions appreciated.
Mick

Hi Mick,
1. REMOVE the separate earth--you are just "jumping" around the fuse ! ( Do check, re-seat, ALL plugs that carry earth to the mechanism)
2. Examine the pins/plungers that ride the TMU. They must be flat, to slight dome, AND they MUST have silver on top.
3. Clean the rivets on the TMU with a safety solvent, apply a VERY light coat of 20 wt oil to both the silver bar ( which MUST still have silver on it), and a slight coat on the rivets, or you may leave the rivets non-lubricated.)
4. Adjust the contact block (aka "frog") so that the upward pressure is minimal. ( I look at the small black limiting pin thru the hole in the frog--I want it to NOT touch the top bearing plate when the mech is stopped with the plunger off a rivet).
5. Adjust the TMU so that when the mech is in play position, near the center of the record rack, the pin closest to you is dead center between two rivets.
6. Clean (check for silver content on contacts), and adjust the Detent switch as per the service manual--paying particular attention to the gap settings --
You should-otta be OK now--
Ron Rich

Cheers Ron,detent switch is set correctly but I will work through what you suggest thanks.Its weird happening when it does plus its almost always within maybe 20 record slots of the RH end.
Mick

Mick, where I disagree w/Ron is on the plunger ground return. It is a good idea to eliminate this as it does cause erratic tripping. However you -must- add a fuse inline (use no more than 1amp-fast) and disconnect the one in the mech. There is no electrical justification for the plunger return and it was eliminated years later during the LS series.

It is important to determine under what conditions these errors occur. If the mech trips at random when started with the scan switch (no selection been made) that is a ground problem as Ron points out.

If they only occur along with an intended selection and at the same points, it can be excessive write-in current or an overly sensitive pulse amp tube (12AX7) having hot spots. I also have one HVL with a slightly critical toroid in the "0"s that will sometimes flip when another 0 selection is made. It has been that way for 23 years and no one has complained about the extra selection so....

Rob

Thanks Rob,no selection needs to be made for it to trip.It can do it whilst scanning.
Mick

Hi Gents,
There was a justification for the ground plungers on the TMU--which, unfortunately I can't recall-but also, it was NOT changed on the LS models but 3 years earlier starting with the U-100 model. At that time the tubes were eliminated and the TMU wiring was slightly modified to eliminate the plungers ( part of the reason not to do this on tube type units)--plus, the whole system polarity was reversed on all future Solid State units, and the fuse was removed from the front of the mech on the ground side, to independent fusing on each o the "hot sides" of the frog.
Ron Rich