Digital Radio Formats

[Musicmanager]

Hi Guys

Firstly, a reminder I'm a complete Idio..... novice !

In an effort to gain some experience of circuit analysis and the like, I've been buying faulty DAB radios on Ebay ( average 99p )to see if I could identify the problem and repair them. Those I've managed to repair I've given to the local charity shop to make a few quid out of.

I've been reasonably successful when the problem has been a power supply problem but I have two that power up OK but there is no output, at least, not that I've been able to find. I've tried looking for numbers on the chips and going for datasheets, but of the numbers I've found most arn't recognised so I guess, they're 'in house' components and also many of the chips have no numbers on them at all.

What I wanted to ask .. .. . I guess there is a roughly common layout to these radios that would at least give me a clue of where I should expect the signal to go - something like a block diagram - a schematic would be too much to hope for - I've tried googling but there are so many variations on the theme it's more confusion than help.

Any suggestions ? ( There isn't a pier in Birmingham )

S

 

[Les Jones]

I would not attempt to fix a DAB radio other than the power supply or audio amplifier. I think the RF section and decoding is done in a special function chip or a DSP (Digital signal processor. - a special type of micro controller.)

Les.

 

[ericgibbs]

Any suggestions ? ( There isn't a pier in Birmingham )

Pity about no Pier in Brum, Wigan has a famous Pier where you could catch a DAB.

Serious note, I would go with Les on this repair limit.

E

 

[Musicmanager]

Hi Guys

Yes, thanks for the sound advice Les .. . Oh, excuse the accidental pun !
I guessed there was a point where it became an encoded process and impossible to do anything without some very specialised knowledge and equipment.

No matter, I bought 11, repaired 9 and I'm going to rip a few bits out of the other two and bin the rest. Total cost to me about £20, I've learnt a lot and the charity shop in the village is quids in !

Result !

Thanks guys

S

 

[JimB]

No pier at Peterhead, but there are a couple of breakwaters protecting the harbour entrance, maybe you knew that already.

On a more positive note, why not show some pictures of the DAB radio boards?
The meaningless numbers may mean something to somebody, and it may be edifying for those of us who have never seen inside a DAB radio.

JimB

 

[Musicmanager]

Morning Jim

No pier at Peterhead,

No, but there may be a Peer in Stuartfield ! Now there's an image to conjur with !!

I'll do some photos and post them, although I think the chances of getting numbers to show up are a bit slim - very tiny. Good idea though .. .

If it goes no further, it will have been a very useful exercise .. . I've learnt quite a lot about PSU's from it .. . and the bloke in the BHF shop in the village can't get his hat on !

S

 

[Musicmanager]

Hi Guys

By popular request, and for your edification, no less .. .. here are some pics of the inside of a Digital Radio -

There's nothing in them really !

S

 

[Les Jones]

You can sometimes replace faulty LCD displays. Some are standard units with standard drive electronics. I even replaced one that was just the display with no electronics. It was for my brother in law who managed to get the display on ebay.

Les.

 

[Musicmanager]

Hi Les

The LCD's seem OK. I've got two left unrepaired .. .. both the same problem .. .. there was no power which was only a duff solder joint under the white connector you can see in the pic.. .. .and now the power led flashes. which the instructions say is 'stand-by' mode, but the 'standby button' nor any of the others has any effect. I expected to find either a voltage or gnd on one side of the button and the other side connected to a pin on the chip, so that pressing the button would either pull high or low, but I can't trace either.

My question was only to see if there was a generic format to these things that might help me trace the circuits, but I'm not concerned if they get binned. I've learnt quite a lot from the experience and charity has had a good day .. .. .

Thanks for your help

S

 

[Les Jones]

You will probably find that the buttons are (Electrically) connected in a matrix. As you have 17 buttons that I can see then one might go directly to an input and the other 16 wil be in a 4 x 4 matrix. The X axis will be driven with 4 sequential pulses and the Y axis (The X and Y may be the other way round) connected to 4 inputs.as only one X line of buttons is powered at a time then the controller looks to see which one of the 4 lines from the Y has a signal on it. As it knows which X axis line is being driven and knows which Y axis line has an output it knows which button is pressed This is repeated for the other 3 pulses. It could also be a 4 x 5 matrix with not all the points on the matrix populated with buttons. If you trace out the tracks you should be able to work out how the buttons are laid out on the matrix. You should be able to work this out with a meter on the ohms range by just connecting to pins on the buttons. (Although there are 4 pins on the buttons there is only one set of contacts.) When you have worked out the matrix if you look at the lines of the matrix with a scope you should see the sequential pulses on one axis and no signals on the other axis until a button is pressed. If there are no pulses then the main controller chip is probably not running.

Les.

 

[Musicmanager]

Wow ! Thanks Les. .. .

I'll have a go at that .. .. a good excuse to make proper use of my new 'scope at last !

Thanks very much

S

 

[JimB]

OK, this is my inspired guess on these things.

If all else fails and you decide to junk it, save the LCD display.
At a first quick look, it appears to have the standard interface for an LCD and can easily be driven by a PIC, if you get that far with PICs.



The RF module, takes the off-air signal and converts directly to base-band, ie audio and data for programme information.
The RF module will use a direct conversion technique to convert the RF (about 200Mhz) to baseband.

The chip which I have indicated as Baseband Signal Processing, looks a though it may have a Googleable part number.
My guess is that this chip splits out the audio and data.
Data goes to the microprocessor, audio to the audio amplifiers.

There will be control signals from the mirco to the RF Module.
These signals will select the frequency to which the radio is tuned.

All the above is based on inspire guesswork after Googling "DAB Radio Chipset", and finding the following useful information, as per the attachments
JimB

 

[Musicmanager]

Hi Jim

Thank you very much for all that information.
I've printed off the two documents and I need a bit of time to read, mark, learn and inwardly digest .. .. .. .
Also, the outline on the picture is great and helps a lot .. .

I'm a little concerned that you were able to google and find some very relevant information in the space of a few hours when I'd been looking off and on over several days and found very little .. .. . maybe interesting use of the word 'chipset' but that's a poor excuse.

After taking the pics this morning, I re-assembled the board back into the case, so I'll need to dismantle again to look further .. .. I think the BSP chip has a blue paint dot over the number which I haven't attempted to remove because I think it will fetch the number off with it, but I'll have a go tomorrow.

Finally, I will master PICs, if it's the last thing I do !!

Thanks very much, again

S

 

[KeepItSimpleStupid]

For more fun reading try "software defined radio:". Here's your first Cookie: https://en.wikipedia.org/wiki/List_of_software-defined_radios

Not too bad, fixing stuff without a schematic.

 

[b.james]

You could take them back to india when you go . You'll make thousands

 

[Musicmanager]

You could take them back to india when you go . You'll make thousands

Sorry BJ, you've lost me there ??

 

[JimB]

I am guessing that he thinks that you are from India, or are otherwise of Indian origins.

JimB

 

[Nigel Goodwin]

I am guessing that he thinks that you are from India, or are otherwise of Indian origins.

It's not like he looks very Indian

 

[Musicmanager]

More like a cowboy, I'd have said


Yi Hah !!

 

[atferrari]

Hola MM,

Any prevailing failure in those radios you managed to repair? Do they work on baterries only or on 220 AC as well?