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Old 09-21-2018, 09:16 AM
vortalexfan vortalexfan is offline
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1952 Zenith Bugeye AM/FM Clock Radio

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.
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File Type: jpg Zenith Bugeye Radio.jpg (51.4 KB, 56 views)
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Old 09-21-2018, 10:42 AM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by vortalexfan View Post
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!
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Old 09-21-2018, 10:55 AM
WISCOJIM WISCOJIM is offline
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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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Old 09-21-2018, 12:32 PM
vortalexfan vortalexfan is offline
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Quote:
Originally Posted by dieseljeep View Post
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.

Last edited by vortalexfan; 09-21-2018 at 07:15 PM.
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Old 09-21-2018, 12:37 PM
vortalexfan vortalexfan is offline
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Originally Posted by WISCOJIM View Post
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.

Last edited by vortalexfan; 09-21-2018 at 07:12 PM.
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Old 09-25-2018, 05:58 PM
vortalexfan vortalexfan is offline
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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.
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Old 10-01-2018, 06:27 PM
vortalexfan vortalexfan is offline
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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.
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File Type: jpg DSCF3216.jpg (113.8 KB, 30 views)

Last edited by vortalexfan; 10-01-2018 at 06:46 PM.
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Old 10-02-2018, 10:06 AM
dieseljeep dieseljeep is offline
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Originally Posted by vortalexfan View Post
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.
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Old 10-02-2018, 10:56 AM
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Electronic M Electronic M is offline
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I'd remove or replace those line to chassis caps if you plan to have that radio plugged in unattended for any length of time...They are time bombs at this point in their lives.

I'd try variacing it the chassis out of the cabinet and see if it smokes again and where...If it does not smoke look at all the wiring on the chassis and clock and see if anything could be moved by flexing or bumping into something during installation in a way that could cause a short. Magic smoke can come from anywhere so finding the general vicinity of the source is key to diagnosis.
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Old 10-02-2018, 12:42 PM
vortalexfan vortalexfan is offline
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Originally Posted by dieseljeep View Post
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.
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Old 10-02-2018, 01:10 PM
vortalexfan vortalexfan is offline
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Originally Posted by Electronic M View Post
I'd remove or replace those line to chassis caps if you plan to have that radio plugged in unattended for any length of time...They are time bombs at this point in their lives.

I'd try variacing it the chassis out of the cabinet and see if it smokes again and where...If it does not smoke look at all the wiring on the chassis and clock and see if anything could be moved by flexing or bumping into something during installation in a way that could cause a short. Magic smoke can come from anywhere so finding the general vicinity of the source is key to diagnosis.
How would I variac the radio out of the cabinet? I can't run the radio outside the cabinet because of how the interlock plug is made on this radio.

Also I had figured out that the diode I wired into the radio to replace the selenium rectifier shorted because I wired it in backwards unintentionally because I was wiring it up how it was on the selenium rectifier which had the cathode marked with a (+) sign which made me think it was the anode side because of how it was marked.

But the only thing is that when I replaced and properly wired in properly, there was no audio but the tubes were lit.

What would be going on?
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Old 10-02-2018, 06:21 PM
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init4fun init4fun is offline
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Originally Posted by vortalexfan View Post
How would I variac the radio out of the cabinet? I can't run the radio outside the cabinet because of how the interlock plug is made on this radio.

Also I had figured out that the diode I wired into the radio to replace the selenium rectifier shorted because I wired it in backwards unintentionally because I was wiring it up how it was on the selenium rectifier which had the cathode marked with a (+) sign which made me think it was the anode side because of how it was marked.

But the only thing is that when I replaced and properly wired in properly, there was no audio but the tubes were lit.

What would be going on?
Having the diode wired backwards could have damaged your electrolytic caps , but first things first there is usually a resistor between the rectifier and and the filter caps , that's the first check you should make and hopefully if that resistor smoked it saved your filter caps in the process .

Also , if at all possible when replacing a chassis mounted multi cap with single caps , it's best to mount a terminal strip and use that to install your new caps .
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Old 10-02-2018, 07:49 PM
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I agree. If you powered it up with the diode backwards you likely ruined the lytics. If you don't have a leakage tester that can test them at full working voltage it is probably best to change them again.

Do you own any clip leads? You can bridge the interlock with those. IIRC when I changed the power cord on mine you can unscrew the female phenolic part of the interlock from the back and grab those terminals with your clip leads... Be careful not to mix up the connections or you could release more smoke... even the least serviceable designs can be worked around with a bit of enginuety.
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Old 10-02-2018, 08:13 PM
vortalexfan vortalexfan is offline
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Having the diode wired backwards could have damaged your electrolytic caps , but first things first there is usually a resistor between the rectifier and and the filter caps , that's the first check you should make and hopefully if that resistor smoked it saved your filter caps in the process .

Also , if at all possible when replacing a chassis mounted multi cap with single caps , it's best to mount a terminal strip and use that to install your new caps .
I didn't have a resistor in line with the diode on my radio... I just wired the diode straight up to the radio because I didn't realize you needed a resistor online with the diode, so yeah the capacitors are probably toast, but would that cause there to be no sound to come out of the speaker or the tubes not to light?
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Old 10-03-2018, 10:35 AM
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init4fun init4fun is offline
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Originally Posted by vortalexfan View Post
But the only thing is that when I replaced and properly wired in properly, there was no audio but the tubes were lit.
Quote:
Originally Posted by vortalexfan View Post
I didn't have a resistor in line with the diode on my radio... I just wired the diode straight up to the radio because I didn't realize you needed a resistor online with the diode, so yeah the capacitors are probably toast, but would that cause there to be no sound to come out of the speaker or the tubes not to light?
Your sending contrary messages , in one post you say "No audio but the tubes were lit" and in this post you say "The tubes not to light?" , , , So , which is it , ARE the tubes lit or are they not ?

Now , to get down to the troubleshooting , we need to talk about troubleshooting itself and what it means to diagnose and repair vacuum tube circuit electrical failures . The "Shotgun" method of replacing parts on a vague "It could be this part" notion is not the right way to go . A LOT of perfectly good parts end up replaced that way at great cost till the bad part is finally changed by the luck of the draw . Yes indeed changing out the failure prone electrolytics was a good action , but now that you've had the episode of reverse polarity and have no sound the best course would be to start over completely .

Were this my situation to rectify I'd start by replacing the filter capacitors again because as Electronic M and I have said , they very well could be damaged . Consider mounting a terminal strip to the chassis and attaching the new caps to it as in my picture . I'd put the Selenium rectifier back in the circuit (polarized correctly or you'll REALLY learn what it means to "let the magic smoke out"* !!!!!) and then with a DC voltmeter on a scale of 300 volts or higher , and the schematic diagram , see exactly where B+ voltage actually is and isn't . This of course presumes that the tubes ARE lit and you have no sound . If the tubes aren't lit , start with an AC voltmeter on at least 200 volts scale and using your schematic follow the tube's heater AC path till the open is found .

A multimeter , a schematic , and about 5 minutes are all it should take you to diagnose this , once you replace the filter caps and put the rest of the circuit back to original status . Once you've got it running if you want to eliminate the Selenium rectifier , fine , but DO install the proper dropping resistor for the excess voltage of the silicon diode , circuits have "as designed" operating voltages for a reason , and especially in electronics "somewhat higher" is just about never equated with "better" .

* If you don't already know , an overloaded or shorted Selenium rectifier lets out a noxious smoke that smells like a bucket of rotten eggs X 10 , so make damn sure you polarize the Selenium rectifier correctly , and also using your ohm meter mode of your multimeter make sure that the new caps you install are wired correctly and aren't presenting any kind of short circuit to the rectifier BEFORE you power it on again .....

Last edited by init4fun; 10-03-2018 at 10:50 AM. Reason: Clarify a point
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