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Post by jukerocks on Jan 4, 2021 16:46:07 GMT
The 464 would trip the CB just as the gripper would release the record (A-side only; B-side, no problem). After some time with the manual and verifying micro switch cam positions throughout the cycle, I removed the readout wiper and found the A-side hammer coil several shades darker than its twin and not testing anywhere near for continuity. I replaced it with old old stock and, upon selection, found it continued to trip (stuttered) after hammering the lever during record play. I "solved this by manually tripping the reset coil in the control box. All good. I made and cancelled several selections and all was working well. So I fired it up and let it play, checking a couple times and ignorantly thinking I'd accomplished something.
After nearly a hundred plays it came to a grinding halt mid-record. Two things had happened simultaneously: the circuit breaker tripped and the A-side coil went up in smoke. And I found out the hard way that it was pretty hot. So, where does the problem lie? I know it's the A-side coil because it was playing a long series of A-side selections at the time. But does this look like a fault in the trip or reset coils in the control box or does this look like a problem with one of the micro switches? And how to order a new coil as opposed to another 50-year-old replacement?
Patrick
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Post by Ron Rich on Jan 4, 2021 19:08:03 GMT
Hi Patrick, It's not a fault of the coil ( BTW-- if you put un-cooked bacon on it, you will smell t cooking prior to the coil cooking ! ) If this was my phono, I would replace that CB, first, with a 1/2 amp SB fuse ! 2nd, L@ k at the schematic-- what's the difference in operation of a cancel coil from the A to B side ? Replacements ? Where are you located ? See our FAQ's section-- the Hi Newbies", and the "books--parts, where----" posts. Ron Rich |
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Post by jukenorman on Jan 4, 2021 19:41:16 GMT
There's a diode in series with each hammer coil (after the A/B snap switch) - it would be worth checking it's not gone short circuit.
Norman.
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Post by jukerocks on Jan 4, 2021 19:47:56 GMT
Ron: thanks for your reply. I don't think it had anything to do with whether it was the A or B side. I just happened to be playing a lot of A sides. When I look at the sequence of operation, I see micro switches 2A and 3 and the two relays in the control box affect the hammer coil. But if it stays energized, which part isn't doing it's thing?
Patrick
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Post by jukenorman on Jan 4, 2021 20:29:16 GMT
Hi Patrick,
When micro switch 2A operates to its normally closed position, a circuit to the hammer coil is made through the A/B snap switch, switch 2A and a contact of the interlock relay. When micro switch 3 then operates to its normally closed position, it energises the interlock release coil which opens the above contact of the interlock relay relaxing the hammer coil. So you have a fault to ground somewhere on the ground side of the hammer coils (including switch 2A and the interlock contact) or the interlock relay contact isn't fully opening when the interlock release coil operates allowing current to flow through the hammer coil. Sequences 18 & 19 in your manual refer.
Norman.
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Post by jukerocks on Jan 13, 2021 14:35:08 GMT
Ron, Norman: thank you for your input. This thing crashed right at the end of my vacation so I didn't get back to it right away. I removed micoswitches 2, 2A, and 3. All tested OK with an analog meter. The comm lead on 2 and 3 were blackened. I cleaned and burnished them. The wire connectors all looked good. I treated all with Deoxit and reassembled. I then pulled the control box. The contacts on the relays were also blackened, so I burnished them, them cleaned with Deoxit. The 15 ohm standee tested OK. I replaced the burned out hammer coil. All appears to work OK. I observed the coil hammer and release a couple dozen time them let it run through quite a few plays. So far, so good.
Patrick
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