Help with a clock radio

[lopaka1998]

I have an old ge clock radio from the early 80s. A filter capacitor shorted and killed the transformer with it.

The clock still works - I've used a temporary 9v transformer to test it (after removing the shorted cap) and everything works.

There are several filter caps with Rarcan brand, and one caps with rubycon brand with the following markings:

Rubycon
16v 470uF
CE W
8145
S.C.
85C M

There are ceramic disc caps for bypassing high frequencies in the areas that need it.

Is the rubycon also a general purpose cap? I was under the impression that all of the electrolytics would be basically for filtering purposes - but this one cap makes me question that - it's the same value as one of the other Rarcan caps, 16v, 470uf - but it is about 1/2 to 1/3 of the size. Why use a rubycon there? Would it be for size - or for maybe a different ripple current rating?

Also - should I replace the diode that all this current went though? I don't want to do the repair only to have a diode die shortly thereafter. It currently reads fine - open in one direction, 0.57 voltage drop in the other. Considering this is a 34 year old clock - would it be a good maintenance step? and if so - which ones should I use?

[stj]

Re: Help with a clock radio

any cap rated at 85' is general purpose.

[kaboom]

Re: Help with a clock radio

I have an old ge clock radio from the early 80s. A filter capacitor shorted and killed the transformer with it.

The clock still works - I've used a temporary 9v transformer to test it (after removing the shorted cap) and everything works.

There are several filter caps with Rarcan brand, and one caps with rubycon brand with the following markings:

Rubycon
16v 470uF
CE W
8145
S.C.
85C M

There are ceramic disc caps for bypassing high frequencies in the areas that need it.

Is the rubycon also a general purpose cap? I was under the impression that all of the electrolytics would be basically for filtering purposes - but this one cap makes me question that - it's the same value as one of the other Rarcan caps, 16v, 470uf - but it is about 1/2 to 1/3 of the size. Why use a rubycon there? Would it be for size - or for maybe a different ripple current rating?

Also - should I replace the diode that all this current went though? I don't want to do the repair only to have a diode die shortly thereafter. It currently reads fine - open in one direction, 0.57 voltage drop in the other. Considering this is a 34 year old clock - would it be a good maintenance step? and if so - which ones should I use?

Be sure there is a power transformer! GE was "infamous" for keeping to "transformerless" designs well into the solid state era. It wasn't till the Thomson buyout in '86 that they started with power transformers.

GE clock radios commonly had a 5 watt ceramic dropping resistor, in a "pocket" in the rear where the P-TX would usually be, that then fed the rectifier. The other end of this resistor connected to the AC line, either thru the alarm or function switches/linkages.

The speaker was either an odd 45-ohm type, or an 8-ohm unit with an audio matching transformer. Are you mistaking the output transformer for a power transformer?

You will not just have one diode if you actually have a power transformer- there's always a full-wave, or bridge, rectifier to keep net DC out of a power transformer, if used.

Take some pix of the top of this thing, w/o the cover.

[lopaka1998]

Re: Help with a clock radio

Be sure there is a power transformer! GE was "infamous" for keeping to "transformerless" designs well into the solid state era. It wasn't till the Thomson buyout in '86 that they started with power transformers.

Here are some pics. Maybe this is an exception. I'm seeing end of '81 era date markings on the caps and the original transformer. I'm sure it's a power transformer with multiple out taps. But I am still learning so correct me if I'm wrong. the transformer has been removed at this point, and is on it's side.

https://www.badcaps.net/forum/attach...1&d=1454028404

https://www.badcaps.net/forum/attach...1&d=1454028404

As far as I can tell, each of 3 taps has a single diode and a filter cap, so I think it's all half-wave rectification. Also - the highest rated cap is 35 volts, indicating a lower voltage than line voltage. The lowest voltage cap is 10v, as a dc filter to the speaker. The old transformer was a tamradio.

GE clock radios commonly had a 5 watt ceramic dropping resistor, in a "pocket" in the rear where the P-TX would usually be, that then fed the rectifier. The other end of this resistor connected to the AC line, either thru the alarm or function switches/linkages.

P-TX? What's that?

The speaker was either an odd 45-ohm type, or an 8-ohm unit with an audio matching transformer. Are you mistaking the output transformer for a power transformer?

I don't think so - but let me know if I'm mistaken.

You will not just have one diode if you actually have a power transformer- there's always a full-wave, or bridge, rectifier to keep net DC out of a power transformer, if used.

Take some pix of the top of this thing, w/o the cover.

There are 3 as far as I can tell (one for each used tap), and the transformer has 4 outputs and two grounds.

any cap rated at 85' is general purpose.

Thanks stj. Ok - I'll replace it with a KMG then. Love your avatar. Feeling is mutual

If anyone can send me in the right direction for rectifier diodes it would be appreciated.

The input on the case states the clock only uses max 4 watts... It works fine on 9v - I've tested it wiring up a transformer temporarily to see if it still functioned. I've found a 9v 750mA transformer that I think will fit the bill.

[kaboom]

Re: Help with a clock radio

Here are some pics. Maybe this is an exception. I'm seeing end of '81 era date markings on the caps and the original transformer. I'm sure it's a power transformer with multiple out taps. But I am still learning so correct me if I'm wrong. the transformer has been removed at this point, and is on it's side.

https://www.badcaps.net/forum/attach...1&d=1454028404

https://www.badcaps.net/forum/attach...1&d=1454028404

As far as I can tell, each of 3 taps has a single diode and a filter cap, so I think it's all half-wave rectification. Also - the highest rated cap is 35 volts, indicating a lower voltage than line voltage. The lowest voltage cap is 10v, as a dc filter to the speaker. The old transformer was a tamradio.

That's an interesting unit. Early 80's GE, but has more "cheap" looking PCB of the later stuff. Definately a power transformer- the audio output transformers were about the size of that tuning cap, except about twice as tall.

Even that far back, they used Tamradio...

P-TX? What's that?

Power transformer.

[lopaka1998]

Re: Help with a clock radio

I'm still looking for replacement diodes. The new transformer is 9v, 750mA, but I don't think the clock radio will use more than about half of that.

I was thinking of using a 1N4002 diode but I've never replaced a diode before so I'm not quite sure if the specs are ok.

Would 1N4002 diodes work for this application?

the audio output transformers were about the size of that tuning cap, except about twice as tall.

Even that far back, they used Tamradio...

I think I saw one of those the other day on one of the youtube videos I was watching of a vintage radio repair. It had a hole in the center for adjustments that was about the size of a pencil.

[stj]

Re: Help with a clock radio

1N4007 general purpose rectifier.
cheap and usefull upto 1a at 1000v

[lopaka1998]

Re: Help with a clock radio

1N4007 general purpose rectifier.
cheap and usefull upto 1a at 1000v

thanks stj.

I've got one last question. There are 4 ceramic capacitors for bypass at the transformer outputs that connect just before the diodes, so it's still technically ac. I want to replace them too as i'm not sure if any of those parts got overloaded (they do measure within spec though).

So my question: I've heard X7R shouldn't be used for pulses... Would a Z5U work in this case instead? I'm trying to find replacements for them but find myself confused after reading up on it.

3 of the caps read

R
103M
t

the other reads
al-5
471m
tdk-u

So the first three I think are 10nF or 0.01uF, 20%, and the fourth is 470pf, 20%

Could I use something like this?:

http://www.mouser.com/ProductDetail/...kmgfnHP8Zas%3d

[stj]

Re: Help with a clock radio

if they arent shorted, ignore them

[lopaka1998]

Re: Help with a clock radio

Arg.. .Just when I thought I was done, I've found another problem - an open inductor. Picture attached. It goes from the mains to the input of the transformer. It's got a red dot, a black dot, and a big brownish gold colored mark on it's right side. It's marked as L9 on the board.

When I patched a different transformer in there temporarily, I bypassed the inductor because I used the power cord already connected to the new transformer - thus I didn't spot this earlier. Anyone know how to read these old part values, and what a suitable replacement would be?

It's 120v/60hz here.

[xelectech]

Re: Help with a clock radio

That attachment didn't work for me - brings up this error "Invalid Attachment specified. If you followed a valid link, please notify the administrator"

[stj]

Re: Help with a clock radio

brownish gold isnt good enough, it's brown OR it's gold.
you need to decide.
codes are like resistors,
so red, black = 20
now we need the multiplier/divider digit

[lopaka1998]

Re: Help with a clock radio

That attachment didn't work for me - brings up this error "Invalid Attachment specified. If you followed a valid link, please notify the administrator"

Weird... it was working yesterday! Seriously

Here's attempt 2. I've reattached to this post.

The picture reasonably represents the 3rd color. Stj - it's sort of in the middle. I would guess gold but look at the picture and let me know what you think.

I've got two other opinions, one person thinks brown, one thinks gold. I guess this is the question of the day, for me at least.

[stj]

Re: Help with a clock radio

it's gold.
there is a brown one for comparison in the bottom of the foto.

so it's 2uH at whatever minimum voltage & current you need to put through it.

[eccerr0r]

Re: Help with a clock radio

That inductor looks like a primary noise filter... 120V mains -> inductor -> transformer.

I was wondering if there's a way to tell whether that is more sanely 200µH or 2µH as I am not an AC power expert... though I'd say either will probably work just fine.

[stj]

Re: Help with a clock radio

it probably doesnt even need it unless the power is noisy,
i suspect the clock uses the ac rather than a crystal for timing and doesnt want to get fooled by glitches.

[fzabkar]

Re: Help with a clock radio

Xc at 60Hz for a 200uH inductor is 75 milliohm.

Xc for a 2uH inductor would be 0.75 mohm.

I don't know which frequencies would be targeted by the filter. I guess that would depend on the capacitor (LC filter).

[lopaka1998]

Re: Help with a clock radio

it probably doesnt even need it unless the power is noisy,
i suspect the clock uses the ac rather than a crystal for timing and doesnt want to get fooled by glitches.

I want to put in in anyway. I would have replied sooner but there was a half-day power outage. A power spike from a previous outage is what actually took the end-of-life capacitor over the edge and short causing this problem.

The power quality hasn't been good lately as all the power transmission infrastructure hardware is past end of life.

The clock has a non-polarized plug, and each side has an inductor - but of different values. 2uH on one (open), and it looks like the other working one is rated 10uH (brown, black, black).


What do you think of this one?
http://www.digikey.com/product-detai...250-ND/2682541

Would it be ok with line voltage? I've measured between 7-8mm between leads on the old inductor - so I might have to bend one of the leads little bit on the one I picked. If you know of something better, I'm all ears. AC input to the transformer is 120v, with about 5 watt max so 0.0416 Amps.

To the person who asked about what's on the other side of the transformer, there are bypass caps (ceramic) rated at 0.01 uf, and then the diodes, then filter caps, etc...