Strange portable, strange problem...

[darklife]

Got this radio from my grandmas house. It's a cute little radio and it is unique.
What you can't see in the picture is on the side of the radio it has two separate volume controls, one for each speaker, and one that has the on/off click built in. So in a way they are volume controls and also a balance control.

Problem is the thing doesn't go into stereo. The stereo light will not light up no matter how close and powerful the station and their pilot signal.
I opened it and checked for a faulty mono/stereo switch. It's fine.
Tried using the headphone jack to see if it was stereo only through cans, doesn't matter.
Checked for old dried out capacitors and any bad soldering joints and they all seem fine.

So what gives?

I have never seen another radio like this and would like to get it working. After googling for some time I can say that there is NO information, pictures or jack about this radio out there.

Brand: Tozaj
Model: TP 100, made in Hong Kong
AM: 530-1650Kc
FM: 88-108Mc
Dim: 6.5" by 3.5", 1.5" depth (it's little)
Built around the AN7420 chip.

AM reception on this little bugger is pretty darn good so I'd like to fix this.

[bob91343]

If indeed the set was designed to decode a stereo signal (you can't be sure unless there is a stereo switch), then the problem is in the decoder circuitry. Anything that old is pure analog, so you have to check for the pilot 19 kHz signal being detected and doubled (or synchronizing) to 38 kHz to achieve the L-R signal.

Maybe a simple alignment will make it work. Trace out the circuit and try to guess which alignments you need to tweak. Don't adjust anything unless you know what you are doing.

[darklife]

Originally Posted by bob91343

If indeed the set was designed to decode a stereo signal (you can't be sure unless there is a stereo switch), then the problem is in the decoder circuitry. Anything that old is pure analog, so you have to check for the pilot 19 kHz signal being detected and doubled (or synchronizing) to 38 kHz to achieve the L-R signal.

Maybe a simple alignment will make it work. Trace out the circuit and try to guess which alignments you need to tweak. Don't adjust anything unless you know what you are doing.

Well it is a stereo set. There is a stereo light and if you look at the picture closely you will see a stereo/mono switch.
The IC chip inside is a true stereo FM decoder.

So how do I go about tracing the 19Kc pilot? I have the IC chip pinouts and there is a filter to remove the pilot, and another to feed in the composite signal, and yet another to go into some kind of PLL setup.
I did peak a few of the FM detector coil boxes but I put them right back after trying it. Only difference that made was with reception anyways.
I don't understand the circuit that well. Reading the PDF on the chip doesn't give me much info...
http://pdf1.alldatasheet.com/datashe...C/AN7420N.html

I have a scope if need be used. Usually with something this cheap I could care less to fix it but I need a project lol.

[bob91343]

The easiest way is to just replace the chip.

[Electronic M]

I think that total was a walgrens electronics brand, but it has been awhile since I've bought any thing electronic from them (excluding video tape).

Tom C.

[Sandy G]

Unless you can replace the chip w/a generic one, you MIGHT just have to live w/it the way it is...Just looking at the set, I'd "mouth" it from the mid-late '80s to the early '90s. Be GLAD it has good AM performance. I'd also hazard a guess it was a checkout aisle/impulse buy proposition, it likely didn't set yr granny back a great deal. I'd say finding OEM parts would be a miracle on the order of the Loaves 'n' Fishes...My advice would be to just use it & be happy w/it, mono FM & all.

[AUdubon5425]

Tozaj was sold by Walgreens. Clocks, phones, radios and videotape from what I remember.

[jeyurkon]

Originally Posted by bob91343

The easiest way is to just replace the chip.

It's not clear that the chip is at fault.

The VCO center or freerunning frequency might be too far off. You could try tweaking the potentiometer (if there is one) that's in series with the resistor that goes to pin 4.

John

[Jeffhs]

The stereo FM capability of this radio (through its own speakers, anyway) is a joke, IMHO. The speakers are too close together to achieve any kind of stereo separation, although I suppose one could get fairly decent stereo through a pair of headphones.

One gets what one pays for, I guess, as these little radios couldn't have sold for more than $15-$20, if that much, when they were new. I think the word "stereo" on the front panel of the set was an advertising gimmick; although the radio is in fact equipped for stereo FM reception, that stereo decoder is wasted on it. I read (and agree with) another post in this thread in which it was stated that (in paraphrase), if the radio can be made to sing at all, in stereo or not, be happy you were able to get it working again.

These radios were built cheaply and were never meant to be repaired when they go bad. My best guess is that a lot of these sets were sold to teenagers with tin ears who would see the word "stereo" on the front and gush, "WOW! Stereo!" without giving a second thought to the fact that these radios are just about the poorest excuse for stereo radios there is. Larger boom boxes are an improvement, but again the speakers are too close together. Now, if it were possible to run the audio output from one of these small stereo FM radios through decent-size speakers, the sound would be much better, but it wouldn't work, the reason being that the amplifiers in the radio are nowhere near powerful enough to drive even high-efficiency floor-standing 2- or three-way stereo speaker systems to listenable volume levels.

[bob91343]

Well I remember in the early days I had one of those new fangled FM-AM portable radios, mono only, very small. I plugged my bass reflex hi-fi speaker, 12 inch, into the headphone jack and was very impressed with the sound. Not very loud, but fine for casual listening and certainly good enough quality.

[darklife]

An update:
After letting this radio sit to the side all of this time I got bored the other night and decided to give it one last try.
I noticed the (VCO) potentiometer inside was shifted far off center. After playing around with it and testing it with a ohm meter I noticed it was making bad wiper contact. Replaced the part and put it on a good strong signal, tuned the pot and voila stereo!
The stereo/mono switch also seemed to be dirty so that needed a cleaning.
Guess it was a much easier fix than I ever thought.

Also learned it's not Tozaj but rather Tozai. That I looks like a J on the label
I peaked all the slug tuned coils inside for best reception on AM and FM with the tuning at a station near the center of the dial.
Yes the stereo separation of those tiny speakers is a joke, but you plug in headphones and it really sings. Besides even those tiny speakers sound good for the tiny portable it is.
The audio of this little thing through headphones is really good for being a cheap radio. The AM end is nice and wide open giving clean bass and highs well up to the top 8-10kHz with a bit of usual rolloff.
FM sounds decent with little to no hiss on stronger signals. Oddly this radio will light up stereo with even the weakest signals making for the most distant stations give stereo with the obvious noise from long distance separation of the channels.

What amazes me about this supposedly cheap radio (and the cheapo brand) is how well it pulls in stations. I compared this radio to the common sony ICF S10MK2 and they are equal in reception strength, but the Tozai has much better audio through headphones even when in mono.
It seems to have a nice hot end, or maybe it's just because I really tweaked the little bugger

Anyways if any of you here see another one of these I recommend picking it up, you'd be surprised.

[Jeffhs]

Originally Posted by darklife

An update:
After letting this radio sit to the side all of this time I got bored the other night and decided to give it one last try.
I noticed the (VCO) potentiometer inside was shifted far off center. After playing around with it and testing it with a ohm meter I noticed it was making bad wiper contact. Replaced the part and put it on a good strong signal, tuned the pot and voila stereo!
The stereo/mono switch also seemed to be dirty so that needed a cleaning.
Guess it was a much easier fix than I ever thought.

Also learned it's not Tozaj but rather Tozai. That I looks like a J on the label
I peaked all the slug tuned coils inside for best reception on AM and FM with the tuning at a station near the center of the dial.
Yes the stereo separation of those tiny speakers is a joke, but you plug in headphones and it really sings. Besides even those tiny speakers sound good for the tiny portable it is.
The audio of this little thing through headphones is really good for being a cheap radio. The AM end is nice and wide open giving clean bass and highs well up to the top 8-10kHz with a bit of usual rolloff.
FM sounds decent with little to no hiss on stronger signals. Oddly this radio will light up stereo with even the weakest signals making for the most distant stations give stereo with the obvious noise from long distance separation of the channels.

What amazes me about this supposedly cheap radio (and the cheapo brand) is how well it pulls in stations. I compared this radio to the common sony ICF S10MK2 and they are equal in reception strength, but the Tozai has much better audio through headphones even when in mono.
It seems to have a nice hot end, or maybe it's just because I really tweaked the little bugger

Anyways if any of you here see another one of these I recommend picking it up, you'd be surprised.

I have a Zenith clock radio with stereo FM. The set has two small speakers (can't be more than 3"-4" or so) at either end of the cabinet and sounds fairly good, but the audio sounds 1000 times better when I listen with headphones.

I had a real surprise some time ago when I plugged a pair of stereo phones into my Midland weather radio with FM. Ordinarily, this radio's 3" speaker (might be smaller) does a good enough job reproducing the weather forecast, but not nearly so well with music -- in fact, FM sounds downright tinny, with almost no bass whatsoever. Connect a good pair of headphones to the external speaker jack on the back of the radio, however, and the sound is, as with my Zenith stereo clock radio, 1000 times better.

However, it must be remembered that this radio is primarily to be used a NOAA weather-warning receiver, not a hi-fi FM tuner. The designers intended this set to be used for reception of weather warnings over NOAA weather radio stations, not hi-fi FM, which is almost certainly why it was built with a small speaker. After all, who cares about high-fidelity FM if a severe thunderstorm (or worse) is headed for your area? As long as you can hear and understand the weather forecasts and/or warnings, that's all that counts.