Randix Collector's Edition Radion No 0287

[Plecotus]

I am trying to repair one of these for a friend. Not my thing at all really but it was her mother's and it has sentimental value so I got talked into it

Anyway, having been sat on the bench for a few weeks, I took a look at it today. The primary of the mains transformer is open circuit. I can't see any other, obvious damage so perhaps that's the only problem....we shall see.

The transformer is a centre-tapped type. There is no indication of the secondary voltage. I've not removed the PCB (and I'd rather not if I can avoid it!!) but, looking at the components, it appears to feed a bi-phase half-wave rectifier.

Would anyone either have a suitable transformer or be able to suggest what AC voltage I might need from an alternative? The only marked IC I can see is a Toshiba TA7640AP which looks, from a datasheet I found on line, to be a 5V device but there is also a cassette drive which has a motor marked at 9V so perhaps the transformer should be 5-0-5 or 6-0-6 volts?

As I said, I don't normally work on this kind of stuff so would appreciate any advice and commentary from those who do.

[snowman_al]

We have all been given jobs like this...

Sorry I know nothing about the unit, but as no one else has commented, there might be a clue if you look at the voltage rating of the smoothing caps straight after the rectifier. The 'normal' / target supply voltage should be lower than the cap value.

If you have access to a variable bench supply you could power it from that, prove it works and work back to the transformer voltage needed?
Good luck! Alan

[Silicon]

Make sure the power supply is not designed to supply something like 0-9V and 0-18V from the two windings.

[Mr Moose]

Hello,
Is this the right Radio? https://www.radiomuseum.org/r/swing_...ion_radio.html If so there is a circuit which you can download. It doesn't give the output voltage from the transformer but the smoothed output from the rectifiers is connected across the cassette motor so presumably should be 9V. You could try a 6-0-6 transformer if you have one but the voltage could be a bit low.
Yours, Richard

[Plecotus]

Originally Posted by snowman_al

We have all been given jobs like this...

Sorry I know nothing about the unit, but as no one else has commented, there might be a clue if you look at the voltage rating of the smoothing caps straight after the rectifier. The 'normal' / target supply voltage should be lower than the cap value.

If you have access to a variable bench supply you could power it from that, prove it works and work back to the transformer voltage needed?
Good luck! Alan

Good advice but the caps are all 16V and I'm guessing they will be a little over-rated. I thnk a variable supply is the way to go though - thank you.

[Plecotus]

Originally Posted by Mr Moose

Hello,
Is this the right Radio? https://www.radiomuseum.org/r/swing_...ion_radio.html If so there is a circuit which you can download. It doesn't give the output voltage from the transformer but the smoothed output from the rectifiers is connected across the cassette motor so presumably should be 9V. You could try a 6-0-6 transformer if you have one but the voltage could be a bit low.
Yours, Richard

Hi Richard,

It's a different model but it looks almost identical with the exception of the cassette deck being on the oppsoite side to the one of my bench. Looking at the circuit diagram, I am 99% sure that the electrical design is identical. I'm going to try powering it up with an adjustable DC suppy, starting at 6V and going up to 9V. The cassette motor is stamped 9V so I reckon that's my target. If that works, I will make up a new PSU from one of the many wall-wart units I have knocking about.

Thanks for the link to the diagram and to everyone who commented. I will let you know how it goes.

Cheers,

Denis