1970's Radio Repair - Page 1
Forum section: electronics / repair

author: vidarr
author_rank: Frequent Contributor
timestamp: October 20, 2018, 07:29:41 pm
content: I am trying to get a bunch of projects finished, or scrapped, while my wife is gone. Here are the guts of her cat/kitty (feline) alarm clock and AM/FM radio from when she was a kid. It is ridiculous in an old, Brazilian kind of way that makes it kind of interesting. Anyway, I identified the transformer to be a "vintage" Stancor WF-35 and found it in an old, Stancor Transformers 1952 catalog. But, I cannot find the voltage for it. Maybe I don't know how to read the catalog correctly? Does anyone happen to know the voltage? Or maybe a source I could find it?I have this link only:http://tubebooks.org/file_downloads/stancor_1952.pdfThanks!

author: capt bullshot
author_rank: Super Contributor
timestamp: October 20, 2018, 07:41:54 pm
content: The transformer shown in your picture is a simple mains power transformer with several output voltages, I suppose.The vintage WF-35 is an output transformer for a valve amplifier as far as I can see from the catalog, something quite different.

author: vidarr
author_rank: Frequent Contributor
timestamp: October 20, 2018, 08:43:20 pm
content: I see. That was the only thing I could find with those markings. Odd coincidence they have the same number. Oh well.How would I go about testing this transformer for proper voltage then? What would "proper" voltage be? I am totally clueless about this.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 20, 2018, 08:57:38 pm
content: I don't understand your question.From what I can see, I'd guess it has an attached mains cord that you could plug into a wall outlet, then measure the output voltages.From the markings I'd guess it's for 117V mains voltage. Output voltage(s) are expected in the 6V ... 12V range for such kind of radio.

author: vidarr
author_rank: Frequent Contributor
timestamp: October 20, 2018, 09:08:37 pm
content: Yes. That's what I wanted to know. The device has a nine volt battery hook up, but I do not know if that is just a backup power to keep the clock going.I cannot figure out how to get the voltage tested right. It has four wires coming out of the transformer. Red, White, Black, and Blue. The Blue comes out of the same side the mains (117V) goes in. The other three come out the other side. What wires do I test in pairs? Red/Black... Blue/White... or some other combination? Does that make sense? I am really bad at this sorry.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 20, 2018, 09:37:53 pm
content: That's just guessing, or reverse engineering the circuitry.The blue wire seems a bit strange, maybe it is a tap on the primary to get the line frequency for the clock - that would be rather useless for any other application.For a first step, do not apply power and measure resistance between the wires in any possible combination. The actual resistance isn't that important, more a simple decision if there's an open circuit (very high resistance) or a winding in between (low resistance).Check if the blue wire is connected to the mains side, if so, leave it alone.Then apply power and measure voltage between the wires that were not open circuit.You may find one secondary with a (center) tap, or two secondaries that aren't connected or something else.From your photo, I can see two diodes that might be the rectifier, so my guess would be one secondary with a center tap.You'll measure the nominal voltage from each end to the center, or double the voltage from end to end.Yes, most probably the 9V battery was intended to keep the clock running in case of a power outage.

author: commongrounder
author_rank: Frequent Contributor
timestamp: October 20, 2018, 10:11:36 pm
content: One thing I notice right away, looking at the photo, that concerns me, is the condition of the transistor to the left of the blue electrolytic capacitor and 2200 ohm resistor (red, red, red code). The photo is not super sharp, but it appears blown.What caused you to assume a faulty transformer?

author: james_s
author_rank: Super Contributor
timestamp: October 20, 2018, 10:15:52 pm
content: Are you sure the transformer is bad? I don't recall ever seeing a power transformer in a clock radio fail.

author: vidarr
author_rank: Frequent Contributor
timestamp: October 20, 2018, 10:16:58 pm
content: Continuity testing: Blue to mains is nothing -- no buzz. Blue to black gives 039 buzz. Blue to the other two gives 043 buzz. Everything else gives 000 buzz.What does that mean?

author: vidarr
author_rank: Frequent Contributor
timestamp: October 20, 2018, 10:18:45 pm
content: Quote from: james_s on October 20, 2018, 10:15:52 pmNo, I do not know where the problem is. I just thought I would start at the beginning.

author: james_s
author_rank: Super Contributor
timestamp: October 20, 2018, 10:23:04 pm
content: The blue and brown mains wires should show some small resistance between them, those are the primary. The other wires are the secondary winding or windings, each of them will show a small resistance to at least one other, I suspect you have at least two separate windings, one or more may be center tapped. Does the transformer hum or get warm when you plug it into power? Can you measure any voltage on the outputs? I doubt there is anything wrong with it.

author: Nusa
author_rank: Super Contributor
timestamp: October 20, 2018, 11:18:46 pm
content: Wow, I didn't realize transformers were so expensive in 1952! (Multiply 1952 prices by about 10 to get today's dollars.)I agree, that transistor package doesn't look whole in the picture. Take a closer look at it, with a magnifying glass if you need one.The place to start would be to diagram the circuit, at least the part you're working on understanding. With single-sided boards like that, it should be easy to determine what is connected to what.With small transformers like yours, if the input is correct and the outputs produce sensible voltages, it's probably the correct voltages.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: October 20, 2018, 11:39:08 pm
content: It doesn't work. What are the symptoms? Does the clock work but radio doesn't? Does it come on but you can't change anything? Any information you can provide on this will help in diagnosis.I agree with others about the suspicious looks of the transistor. Also there might have once been a component just up and left from the transistor that has blown completely away, leaving just a portion of a lead and some smoke traces.The small circuit board at the top left looks like the contact pads for the control switches. The buttons themselves have (or had) a bit of conductive rubber on the bottom. I have found radios of this vintage where the conductive rubber no longer existed or served its function. Might be one source of non functionality.

author: vidarr
author_rank: Frequent Contributor
timestamp: October 21, 2018, 12:23:05 am
content: Yes guys, that transistor is toast. There are several problems here. I was going to swap out the transistor because I have a match, but I found some other problems. All the contacts for the clock changing times etc all fell out (little metal round pieces like flat pads). I have no idea where to get new ones. I could make my own I guess. The wiring is all corroded and came disconnected too (mostly on the radio side). In fact, almost all the wiring is coming apart. It is all repairable, but not the kind of project I had in mind. Interestingly, the clock counts up in seconds forever. I am going to make a box for it and keep it as a conversation piece for when I am waiting at the airport. Just kidding.If I re-purpose this transformer, how do I determine what wires go together? I took pics of the testing of all four wires, plus the blue wire to the mains. I will post them, but the site only allows a couple at a time.Thanks guys.

author: vidarr
author_rank: Frequent Contributor
timestamp: October 21, 2018, 12:33:41 am
content: And the last two wires.... 003

author: CatalinaWOW
author_rank: Super Contributor
timestamp: October 21, 2018, 01:17:53 am
content: maybe the way to keep a happy wife is to replace the entire contents. Just keep the exterior looking original. Might be quite a bit smaller project than repairing the original guts.

author: james_s
author_rank: Super Contributor
timestamp: October 21, 2018, 01:45:50 am
content: If the clock lights up and does anything then the transformer is almost certainly fine, don't even worry about it. Start with the obvious stuff, replace the burned transistor, re-attach any obvious wires. If the buttons are what I'm thinking about, those little metal domes that are usually taped over pads on the PCB, I don't know what the proper name is but I've seen them in lots of similar devices so you could probably salvage some out of some other junk. I don't think this clock should be too hard to repair.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 21, 2018, 03:01:46 am
content: Quote from: vidarr link=topic=146027.msg1908245#msg1908245esistance date=1540073818It means that "continuity" isnotthe appropriate range to use for these tests, as the primary winding may have a higher resistance than can be tested with continuity, & still be OK.For instance, I just checked my similar (230v) clock radio, & found the primary is 334 ohms.(If you have 127 v Mains, it will probably be about half that)Continuity range will see that as "open", so use the "ohms" range instead.*From your first photo, it is quite obvious that the brown & blue wires are the primary, as they come out to the Mains power cord.Those colours are pretty much the standard for Active ("hot") & Neutral ("cold"), respectively, everywhere except North America, who like to go their own way!If you hang across the pins of the plug on the other end of that cord, you will be looking at the transformer primary.*I don't know why so many people on this forum are so enamoured with "continuity", which is mainly meant for testing large numbers of cable connections in awkward spots where it is hard to look at the DMM display.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 21, 2018, 08:42:06 am
content: If you just want to repurpose the transformer,cut the wires from the PCB, then plug it into mains and measure the output (AC) voltages.Anyway, you don't really need to cut if off, as it's working and the clock shows some display.As a first guess, connect the black wire to the COM of your DMM and measure the voltages on the red, white and blue.From what I can see, the red and white wire are the "outer" ends of a center-tapped winding, the center tap (my guess) is the black wire. I'd expect around 3...5 Volts from red to black and also from white to black (and double that for red to white). The blue wire might have a somewhat higher voltage (maybe 6...9V) to black.I've seen this from the layout, red and white are going through a diode and a resistor to supply the LED display, a rather low voltage is required here. The blue wire might supply a somewhat higher voltage to the rest of the circuit, but I cannot see this from the pictures.Don't expect any substantial power from this small transformer, this one might be good for some 0.2A on the red / white wires, and maybe 0.1A on the blue.

author: SeanB
author_rank: Super Contributor
timestamp: October 21, 2018, 11:42:46 am
content: Those typically are a secondary made from a 6-0-6VAC winding, and this us used to provide the AC power for the LED display ( the LED display has 2 common anode connections, and each half of the display is driven by alternate cycles of the AC mains voltage, reducing the number of pins for the clock chip to have to drive the cathodes, so each digit drive will switch between 2 states so as to allow 2 LEd units to be driven from 1 pin) along with part of the power for the clock itself. The other wire on the transformer is a 9VAC winding, common to the oV on the transformer, used to give roughly 12VDC after a half wave rectifier to run the actual radio side.http://www.paulanders.com/G5-LED/ver1/datablad.pdfThis is the most likely chip in your radio, which also has the transformer layout and how it works.

author: vidarr
author_rank: Frequent Contributor
timestamp: October 21, 2018, 08:08:48 pm
content: Quote from: SeanB on October 21, 2018, 11:42:46 amFirst, thanks everyone for your comments! Yes, everyone, the transformer is fine. I don't know why, I just thought I should start where the power starts and go from there piece by piece. The first broken link is the transistor that looks like it popped. But, I don't know if I am going to move on with the project yet. I think I am going to do what someone above suggested and put something else inside the box. I think it might be a lot more interesting. There is no chance this will ever be a collectible clock radio, so...Yes, it is the LM8560. The circuit also has the TDA1083. I downloaded the datasheets. I am not going to throw any of this away. This will go in the future projects bin. I have a tiny motor I am salvage/turning into a cooling pump first. Almost finished.Thanks everyone.

author: james_s
author_rank: Super Contributor
timestamp: October 22, 2018, 02:49:11 am
content: The correct approach to repairing something is to take a close look at the symptoms and then think about what could cause those symptoms. If the clock is lighting up at all then the transformer is obviously ok so there's no point in looking into it further. Next look around for any obviously broken or damaged components.

author: tkamiya
author_rank: Super Contributor
timestamp: October 22, 2018, 05:26:40 pm
content: I would look at where the transformer attached to the PC board. It has to go into some kind of rectifier and filter circuit. Draw that out. What winding is needed to produce voltage out of that should be obvious. Capacitors for consumer electronics are often used awfully close to the rating. That can be a guide to what voltage are coming out.I recall having a wire that connects to the transformer itself is common. It's usually blue or brown.