1956 Zenith Cobra-Matic Stroboscope Changer Transition

[Hi-Fi-Mogul]

I'd like to power up the motor.

Here is the wiring diagram.

It appears that I would attach AC to
Pin 1 and Pin 2 to directly wire the motor ?

Then to test the changer switch, attach AC to
Pin 4 and Pin 2 ?

Thanks !

[electra225]

Pin 1 and Pin 4 will also let you test the phono motor switch.

And, if I may ask, what format do you use to post schematics and drawings on the forum? You do such a nice job, I just HAD to ask.....

[Hi-Fi-Mogul]

Pin 1 and Pin 4 will also let you test the phono motor switch.

And, if I may ask, what format do you use to post schematics and drawings on the forum? You do such a nice job, I just HAD to ask.....

Thank you Greg.

Re: schematics & drawings:

What I usually do is open up the pdf file of a schematic,
then I take a screenshot photo.

I then use some free photo software "Pix" to crop, focus, or
whatever to make the photo better.

[TC Chris]

I think you're right about pins 4 and 2, remembering the switch in series, but also remember that you'll be powering up that transformer too.

Chris Campbell

[Hi-Fi-Mogul]

Okay, the motor checks out good.

The neon bulb works, and the switch has
continuity.

I'll put back the rest of the parts and motor,
install the new belt to test, and await the donor Zenith.

Could this be an early clue to the new direction ? [: )

[William]

I'm keeping my fingers crossed!

Bill

[Hi-Fi-Mogul]

Big Day Today !

The owner's husband brought the
parts donor Zenith R566 this AM.

It must have sat in the San Angelo desert heat for
some years.

After 2.5 hot/humid hours of unpacking and dis-assembly,
I've got the two most important assemblies in the house.

The oscillating gear and spindle.

The gear is flat and straight, unlike the one in the
Stroboscope.

The spindle is complete with the missing little arm inside
that pivots to push the record off of the spindle shelf.

I'm happy as a pig in slop.

I also salvaged:

A 50C5 OPT
Nice spring loaded hinge from the lid.
Five tubes
Cobramatic tonearm with the ceramic cartridge mount
Drive wheel assembly
Idler wheel assembly
Record support arm
Changer base and mechanism
Two knobs and sleeves
Zenith metal ornamental escutcheon

The 2 pole motor has flaky asbestos covering on
the coil.
I cut its wires and put it in a zip lok bag
for safety.
I may keep the rotor from it.

The plastic Cobra changer cover and most of the
body of the radio/record player was badly
damaged.
So, its in the trash.

The record platter rubber is shrunken and not
salvageable. I'll keep it anyway for now, since
it's cast heavy aluminum.

I'll take a break for the rest of the day, and then
see about cleaning the spindle and oscillating gear
assemblies on SAT.

Idler and cartridge on order from Gary, hopefully the
last parts I'll need.

[William]

That's good news, Mr Mogul. I'm thinking you will be busy for a few days getting everything cleaned up and back together. Good luck, and I hope you will have another happy customer when done.

Bill

[Hi-Fi-Mogul]

Thanks Bill for the support.

I cleaned the donor spindle and oscillating gear
assemblies.
Lubed them and they are installed.

Last leg will be receiving the little idler and putting
it in, then re-assembly of all the other parts for
testing.

[electra225]

I've been watching the progress on this, Mr. Mogul. I haven't made a comment, since I am not familiar with what you are doing and didn't feel I could make an intelligent comment. Thanks for sharing this project.

[Hi-Fi-Mogul]

I had the amp, changer, and a speaker on for a
bench test.

The manual reject does not work.

So, I checked R4 220 Ohms, which reads 3 Ohms.

Would this affect the electromagnet circuit in a way
for it to not function ?

The e-magnet is crucial to engage the tripping
mechanism (reject function).

Help !

[electra225]

R4 is across the manual reject switch to common negative (ground). (The schematic doesn't indicate whether the "spade image" indicated chassis ground or common negative, so there is that). The reject switch provides a path to ground thru the relay. It seems to me that if that resistor drifts toward zero ohms, that might ground that relay and not let it work. I would suggest you try replacing R4 and note any difference. I assume you have confirmed that all the components in the electromagnetic circuit are good, other than R4.

[Hi-Fi-Mogul]

I cut one side of the 220 Ohm resistor and it reads 220 ohms.

I now see deep down in a connection to R4 220 Ohm
that there is a lot of oxidation powder there.

I had hoped I would not have to dis-assemble this birds nest
of wiring, but there you go.

Now to take reference photos, and start checking
the wiring and then the transformer voltage.

I'm glad I found a 220 ohm resistor in stock.

[electra225]

If R4 reads 3 ohms in circuit, but reads 220 ohms with one side lifted, one would think that perhaps the reject switch is dirty, sticking, or shorted, since R4 is across the switch to ground. Have you determined that you don't have an issue in the reject switch?

[Hi-Fi-Mogul]

Greg,
The reject switch is just a blade that the plastic button
presses down onto to contact a copper button on
the changer base.

I had already cleaned and checked continuity b/t
the blade and the button.

Yesterday I sprayed electronics cleaner and removed
all the oxidized powder wherever I saw it.

Today I measured the transformer secondary which I
finally found in the manual was to be 6.3 V.

It measured 8.5 V, so I know the transformer is
working.

When I tested the reject switch just now I heard
a hum.
I had to carefully lift up the changer to see the
electromagnet is now working !

Now for a mental break, and then set up the changer
for another full test with the platter on.

[electra225]

The drawing shows two switches with R4 across them. What am I missing?

[Hi-Fi-Mogul]

The drawing shows two switches with R4 across them. What am I missing?

This model is a 1956 one. The diagram shows the 1958 model that
has an added manual On/Off power supply switch.

Moving the record speed select slide from "Off" position allows the
underside plastic spring loaded lever switch to make contact which then
powers the motor and the electromagnet/transformer unit.

In photo, the left speed select lever is in the OFF position.
The right side lever is for record size selection.

I am making progress !!!!

I had to clean a lot of hidden oxidation off of the 2 trip switch levers
that make electrical contact when the electro-magnet is active.

I also had to bend each lever to make better physical contact.

When the changer is on its side, the levers align and contact well.

When the changer is upright, one of the levers sags slightly,
and was not making good contact with the other lever.

I think the tonearm is not positioned correctly in its mount.
It's not lifting high enough and other things.

It's a real pain to re-position it, as there is only a slight
vertical travel you can move the tonearm to access the
tonearm mount assembly.

[Hi-Fi-Mogul]

I got the tonearm on correctly.

I adjusted set-down and installed the new
ceramic Cobra cartridge which comes in
a 1mil D, 3 mil S dual tip plug-in cart.

I have some mono records that I'm playing on it.

Last item will be the record support arm replacement.

So far, so good !

This model continues the earlier Cobramatics design
in that it does not shut off after the last record.

The tonearm returns to play the last record.

You lift up the arm and set it on its rest, then
turn off the changer.

Depending on how my bad back feels the next
few days, I may put it all back in the cabinet.

And a photo of the tranny-e-magnet assembly.

[William]

Nice work, Mr. Mogul. I admire your persistence and patience which I seen to lack right now, heck I just lack the ambition to start any new project.

Bill

[TC Chris]

What's your appraisal of this design, in terms of function--is it stable in speed and rumble-free? I've wondered whether vertical idlers would be inclined to transmit more vertical noise to the platter. my old Lenco has a vertical idler as well.

Chris Campbell