Roberts R250 / R550 – No Sound Faults

There’s no light in the R250 dial. Try following the suggestions in the post. If it’s not the volume control switch and power’s getting to the audio chip then it’s most likely the chip needs replacing.

Yes, it does matter, you need to replace the chip the same way round.
There’s a notch at one end so ensure this notch is in the same position.

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) Chip |
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1
The notch is on the left hand side and in the picture. Pin 1 is below the notch and pin 1 above.

Hi Justin, Roberts Revival digital series are not so forgiving when it comes to remote fault diagnosis. They either work or don’t so there’s not much of a clue and need more information. Is anything displayed on the LCD or just the back light?. Does it make a click sound through the speaker when switched on? Have you tried batteries and mains adaptor with same issue? Has the wrong power adapter been used?
If there’s nothing displayed is’s likely a logic board fault and probably needs replacing.

If it was an analogue R250 I’d suggest attempting repair as it’s a good way to learn about Electronics. Analogue is simple – there’s an audio chip that drives the speaker and an IF and RF chip that receive the radio frequencies and provide the audio signal. Components are mounted on standard circuit boards that can be repaired – no surface mounted devices.

With DAB radios it’s a little more complicated but not impossible if you have the time and determination. The 24v DC voltage, rather than 7-11 v that the adapters provide, will have damaged components – the pop you heard is likely to be a hole in the audio chip, or blown electrolytic capacitor or a regulator blown that provides lower voltage for the digital logic chips. Digital chips run on 3-5v and need a voltage regulator.

Roberts don’t include over voltage protection in their sets for the obvious reason – if you mess up it costs you a new radio or a hefty repair. The cost of over voltage protection in consumer devices is minimal but most manufacturers don’t care and don’t include fuses anymore.

I don’t have the circuit diagrams / schematics / service manuals for the RD50/60 series to hand but you could search for them and see what’s involved. You may be lucky and the pop is an obvious component failure that you could try to replace if you can read the numbering on the popped component. It requires soldering and if its a surface mounted device needs some skill in removal as the printed circuit tracks are very fine and close together – it’s too easy to solder adjacent pins together and it won’t work. A solder sucker or solder wick aids removal.

The obvious component failure may have taken out other devices that are not so obvious. So it may not work by simply replacing a blown regulator for example as the regulator supplies the main logic board components these too could have fried. Fortunately many regulator devices are designed with protection built in and hopefully will not have damaged further devices down the line. Diagnosing faults from over voltage is not easy without test equipment such as oscilloscopes as the clock speed of the signals runs at high frequencies that simple multimeter can’t read.

So my advice would be to look and see if the damage is obvious and if not return for repair. Roberts are unlikely to repair to component level and will replace the whole board or boards affected if they have the spares. It may be cheaper than buying a new radio and you have the satisfaction of avoiding a throwaway.

Let us know how you get on.

It’s 100Ω – looks like it feeds +v to the IF chip so maybe that will need replacing or one of the small buff ceramic caps has gone short circuit. Hope you get it working, the pastel colours were popular and if it’s the older R250 it won’t flake like the newer RD50/60 which disintegrate at a touch!

As you’ve found it’s best not expose electronic devices to high temperatures. Most silicon based semiconductors will operate up to 85℃. I measured temperature of 60℃ on the lawn in full sun yesterday although darker objects will absorb more heat. Older transistor radios, like the original Roberts R500, popular in the sixties used germanium semiconductors and these devices suffer from thermal runaway so could only operate at much lower temperatures – one reason silicon fabrication replaced germanium. So your silicon based R550 should have coped with the heat – the audio chip may be designed to shut down at high temperatures to prevent destruction and that’s why it sounded distorted and recovered on cooling. So guess you could say it’s expected rather than a common fault – in car audio works over a higher temperature range that household appliances without issue.