1952 Zenith Bugeye AM/FM Clock Radio

[dieseljeep]

Originally Posted by vortalexfan

Hello Everyone, earlier late last year I had found at Goodwill for $5 a 1952 Zenith Bugeye AM/FM Clock Radio that was in really good shape yet and still worked without hum on its original power supply capacitors.

It recently though had one of its power supply capacitors fail, but what's weird is that it only affected part of the radio's function, the alarm/radio mode is the only part that hums, the radio on mode doesn't hum and neither does the sleep mode.

Any ideas as to why it would of failed that way or is it just random?

Some Pictures of the unit in question below.

Are you sure it isn't the mechanical buzzer alarm?
Make sure the alarm set button is pushed all the way!

[WISCOJIM]

The schematic is available online (thanks Bill J.) for anyone that wants to take a look.

https://app.box.com/s/e22uy20wf2slx63b8hlm

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[vortalexfan]

Originally Posted by WISCOJIM

The schematic is available online (thanks Bill J.) for anyone that wants to take a look.

https://app.box.com/s/e22uy20wf2slx63b8hlm

.

Thanks, I just downloaded it and I noticed it is slightly different than mine but not by much, but it'll work.

The Chassis on my radio is 7J03 and the service manual you linked to me was for a 7Z03 which I'm not sure what all the differences are exactly but there must of been some other wise they wouldn't of revised the chassis design from the 7J03 to the 7Z03, but from the looks of it one of the differences was possibly the addition of an extra knob of some sort to the side of the radio cabinet, which mine doesn't have.

[vortalexfan]

Well I have a good head start in recapping this radio, I have all but 3 of the coupling capacitors replaced (2 of them I won't bother with becuse they're just going across the AC Input to ground, one on each side of the AC plug hookup on the chassis, and they don't look like they are in that bad of shape, so I won't bother replacing them for right now).

The power supply caps might be a little trickier to place in the radio because there isn't very many places for one to place the new filter caps under the chassis as far as grounding the negative leads of the filter caps to.
Also the wires and resistors and capacitors that were connected to the original can capacitors leads don't have much in the way of leads on them to go by for connecting them to the new capacitors.

And I replaced the old selenium rectifier with a 1N4007 rectifier diode under the chassis, but left the old Selenium rectifier in place for appearances sake, same for the old can capacitor.

[vortalexfan]

OK so I finally finished recapping the radio and went to plug it in and something made a sizzling noise in the radio and it started smoking so I quickly turned it off and unplugged it and took it apart to see what happened and nothing looked burned inside the radio, all of the filter caps were fine (they none of them were reversed) the 1N4007 Diode still looked good and it wasn't reversed and like I said nothing else looked burnt inside the radio, component wise.

The clock and the neon pilot light still work but the tubes aren't glowing so I don't know if maybe a tube failed or what, but either way its kind of got me stumped because nothing inside the radio looks burnt and none of the stuff that I thought of that could of caused that issue was the cause.

Any ideas as to what could of happened?

See photo below for the finished recap job.

[dieseljeep]

Originally Posted by vortalexfan

OK so I finally finished recapping the radio and went to plug it in and something made a sizzling noise in the radio and it started smoking so I quickly turned it off and unplugged it and took it apart to see what happened and nothing looked burned inside the radio, all of the filter caps were fine (they none of them were reversed) the 1N4007 Diode still looked good and it wasn't reversed and like I said nothing else looked burnt inside the radio, component wise.

The clock and the neon pilot light still work but the tubes aren't glowing so I don't know if maybe a tube failed or what, but either way its kind of got me stumped because nothing inside the radio looks burnt and none of the stuff that I thought of that could of caused that issue was the cause.

Any ideas as to what could of happened?

See photo below for the finished recap job.

You'll have to do some circuit tracing. I never reassemble a set until I'm satisfied it's working properly.
I have almost the same radio that I have to get back to.

[vortalexfan]

Originally Posted by dieseljeep

You'll have to do some circuit tracing. I never reassemble a set until I'm satisfied it's working properly.
I have almost the same radio that I have to get back to.

The only problem is that with the way this radio is built I have to put it back together in order to test it because it uses a funky 4-pin safety interlock plug on the back of the radio for the power cord, and a normal two pin safety interlock plug won't work on this radio, so that's why I had to put it back together to test it which was how it got smoked, because something in the radio wasn't hooked up right or something and it blew out some magical smoke, that was pretty rank smelling, it smelled like burnt rubber almost.
So it's kind of hard to test the radio chassis outside the case.

[vortalexfan]

Originally Posted by dieseljeep

Are you sure it isn't the mechanical buzzer alarm?
Make sure the alarm set button is pushed all the way!

Nope, I already checked that, in fact that's what I thought it was at first, but when I hit the button to turn it off the humming coninued and it was coming out the speaker (kind of sounded like the way Sony did their alarm for their Digimatic alarm clocks for years where they would produce a 60 Hz hum out of the speaker for the alarm buzzer, rather than a mechanical buzzer).

The funny thing is that when I test the old capacitor's leads they test normal, no shorts or anything, charge up to over 15 Megaohms and then slowly discharge like they're supposed to.

I might put it back together and see if it was maybe just a fluke.

EDIT: just put it back together and tried it out again, and it seems that now the power supply cap is completely shot as now its humming in all 3 different power settings not just the alarm/radio mode. So it seems I will definitely have to replace the power supply caps in this radio, as well as the paper caps in there.