Continental fuse blowing problems

[a4skyhawk]

I was researching that Arcolytic capacitor that is used for the PCR time delay. It looks like they were big in the 1970s and had a high failure rate so I should replace it. I think that this PCR pulse width is also what determines the pulse to the total play counter.

I found this on an Antique Radio restoration board:

Arcolytic cans weren't terribly different than other brands like Sprague or Mallory at the time.

Their individual tubular type electrolytics were another story, however. They frequently only lasted a year or two and were as likely as not to short out or become extremely leaky as a failure mode. I'm not surprised that those 8's are all leaky. I won't even apply power to any chassis I find now that has tubular Arcolytic electrolytics present........

I think I'll be replacing it!

Paul

[jukenorman]

Hi Paul,
Yes it's the same pulse. That electrolytic probably hasn't failed completely if it is still making selections but always best to replace it if there are any doubts. The other capacitors you mentioned will be there for noise supression and that banded component is a capacitor. I think we may have had some discussion of that before on Rob's Continental restoration (long thread). I think that I still have these banded caps in my Continental. Polyester would be fine for replacement although I generally use polypropylene (more expensive) just because I keep a stock of them for amp refurbs.

Postimages is good for embedding pictures in these forum threads.

Norman.

[a4skyhawk]

Thanks for all your help. I have ordered the capacitors, will replace all of them in the selector box and report back.

Paul

[a4skyhawk]

Hi - I said I'd report back once I had replaced the caps and I have now done that. 

Everything works well with one exception that has me stymied.  That one function isn't critical and that is the Total Play counter.  More about that later.

What I replaced was the 1000uF/50V capacitor in the main junction box where the power switch is.  I replaced that with a 3300uF/63V electrolytic.  This should add more surge current protection as I understand the circuit.  

I also replaced all the capacitors on the board to the right of the scan assembly.  These were all replaced with good quality capacitors of the same value and the same or higher voltage rating.  There are three polyester caps and one electrolytic there.

I was surprised having done that to find that the Total Play Counter would still not increment. The 100Ohm/150uF capacitor across the Pulse Control Relay should hold it in for ~100mS after the Sprag Relay is triggered, thereby generating a pulse to increment the counter at the same time the Latch Solenoid is actuated. At least, that's my understanding of the circuit.  I removed the Total Play Counter and put it on an external power supply which shows it increments reliably at any voltage over about 18V.

I tried adding back another 150uF in parallel with the one across the PCR which had the desired affect of doubling the pulse width - at least from my well tuned ear listening to the 'thump' of the latch solenoid.  However the Total Play Counter would still not increment.  I then checked resistances - checking there was a good ground on the TPC and that contact resistances were not too high.  What appears to be happening, without an Avo meter or scope to check, is that when the pulse PCR switches, the latch solenoid is pulsed and the 29V line voltage drops to under 10V.  Too low to trigger the Total Play Counter.  I added in a small bulb to the 29V supply and you can see the intensity drop significantly when the latch solenoid pulses. 

I'm not sure what else I can check. The 29V rectifier is not providing a robust enough supply - or the latch solenoid is pulling too much current.

Is this a common issue with a Continental 1?  Once again everything works - except the counter!

Paul

[jukenorman]

Hi Paul,
I probably said before that I don't bother much with things like total play counters. However as a matter of interest, I just looked in my Continental and the counter works! The electolytics have been replaced but are still the original values. All I can think of is that your counter must be less mechanically free than mine and consequently now fails to operate at prevailing conditions.

If you really want it working, you could replace the counter with an interposing relay, dedicated electrolytic capacitor and diode - small DC single pole relays are cheap! Charge the capacitor directly from the DC via the diode and use the contact of the new relay to discharge the capacitor to increment the counter. Do you understand?

Norman.

[a4skyhawk]

Yes Norman. Sounds like a good idea. At this point I am not sure if the fault is the Play Counter circuit or the jukebox's 29V supply circuit. It doesn't seem right to me that if I put a lamp on the 29V supply, it will extinguish when the Latch Solenoid is actuated. The pulse is only a fraction of a second so it's too fast for a DVM to register and I don't have a scope or analog meter so the bulb technique is a good one.

Paul

[a4skyhawk]

Here I am again! So after replacing all the capacitors and ensuring all the mechanism is well lubed and is free to move, the Box worked perfectly for a a couple of months, but then it was back to blowing the right hand mechanism 1A fuse. This happened right in the middle of a play session. Working one minute and not the next. I should preface this by saying that the box has a DC transfer motor/gearbox.

I diagnosed this as the transfer motor. The turntable was spinning, and the tone arm had tripped the mute switch. If I replace the fuse and monitor the voltage on the motor, it is at 22V, but the motor isn't moving. I loosened the three screws holding it in place and you can see through the slot in the top of the motor that it tries to move but it doesn't have the break-out torque to return the tone arm and operate the gripper to replace the record.

I did two things:
1) I removed the three mounting screws from the motor and was able to, with relatively little force, turn the driven gear on the gripper bow assembly to return the tone arm and the record to the carousel. The major force needed here was when the gripper lifted the bow assembly to the high point. Not initiating the return sequence and lifting the tone arm which is when the transfer motor 'stalls out'.

2) With the transfer motor removed, I reconnected it to the jukebox wiring and it ran very smoothly and quietly. It drew about 0.3A with no load and I could not stop the gearbox output shaft by hand. I also hooked up the motor to a bench power supply and ran it, in both directions. The motor starts moving at only 5V applied and draws about 0.23A at 21V.

Despite these positive checks I stripped the motor down, cleaned out all the old carbon debris and checked the brushed and commutator resistance to check for a bad armature segment. I lightly polished the commutator and there is no 'wear step' like on some motors I have seen. There was however quite a bit of caked yellow grease on the ends of the worm gear, which I soaked and removed. I re-lubed with lightweight watch oil and reassembled/ retested.

The motor still doesn't have enough break-out torque to start the sequence - lifting the tone arm. With the motor back in position, I tried powering it from a bench supply and with 25V applied, it was drawing over an amp and not moving.

The only thing that I can think of is that the camshaft switch assembly is lubricated with light oil instead of a graphite or Teflon based grease. It was recommended to me 20+ years ago only to use watch oil.

Is there something I am missing? I cannot see what would cause the motor to degrade in terms of producing lower torque.

Paul
Doylestown, PA, USA

[a4skyhawk]

Following on from this, I decided to take the transfer motor out again and clean the gearbox side of the motor.  There was a lot of caked on lubrication which I removed and now I have a question as to what lubrication to put on it.  In the past I have used watch oil but in reading the FAQ here there are a lot of diverse opinions as to what the best lubrication to use is.

A light coating of 3 in 1 motor oil (Blue)?

Paul

After cleaning:


Before cleaning:


Re-assembly:

[jukenorman]

Yes that motor oil is OK to use. I don't think it's the motor from what you've written, I suspect that camswitch 6 is maybe slightly late to operate when the record is placed on the turntable and it's then causing a jam - but not enough to blow the fuse before the motor stops.

Norman.

[a4skyhawk]

Thanks for the quick reply Norman. I admit that I do not have a good picture of the timing and operation of the cam switches. What is the adjustment setting for CamSwitch 6? I am a little confused by the procedure as described in RCS-22 of the manual. Maybe I should try turning the adjustment screw half-turn anti clockwise? I think that is the correct direction.

The reason I was homing in on the transfer motor is that:
A) I have witnessed the situation where 22V is being applied to the motor but it is not moving. The record is on the turntable and the tone arm in the center groove when this happens.
B) The motor is very sensitive to the position it is locked in. It seems to work better when all three bolts are somewhat loose to minimize friction between the grunion gear and the driven transfer motor gear.

I may be wrong in my troubleshooting conclusions!

Paul

[jukenorman]

Hi Paul,
The issue with the manual is that it covers an AC motor which always rotates in the same direction so the procedure given doesn't really apply. With a DC motor, what you have is the same arrangement as with an "I" or "J" which will jam if the motor overruns. You can wind the motor and transfer assembly by turning the armature with your finger (that's why the cover is usually missing!). If you can't do that, it's because it's jammed. And that the motor is drawing excess current pretty much points to that.

CS6 resets the selection pin, resetting the selection pin allows the stopping switch to relax which in turn stops the transfer motor so the motor will run a few milliseconds after the switch operates.

Edit - The "J" has open contact switches but the general method of adjustment should still apply and the manual states that the switch should be set such that the transfer action is complete with between two and six turns remaining on the motor armature before the motor begins to bind.

Norman.

[a4skyhawk]

Excellent. Thanks Norman. I have a much better on how it it meant to operate now. I am guessing one way of adjusting CS6 would be to move the mechanism by turning the armature to the point where I feel resistance as the mechanism locks up and then turn the adjusting screw on CS6 to the point it clicks and then another 1/2 turn or so.

Armed with this knowledge and a bottle of 3in1 Blue oil, I will re-assemble the box and try it today.

Paul

[tvtechrich]

Let us know if a late operating switch was the culprit ...I never thought of that .