Bush DAB Radio

[johnpalmer1963]

Hi all, I have a bush DAB radio, when it is switched on everything lights up as it should, it does its scan, finds all the channels and displays whatever channel you ask for and the display says playing radio one or whatever channel you select, the problem is no sound comes from the speakers. I have removed the board and had a good look, but nothing obvious has blown on it, so that said is there a component on it that makes the sound output? I have included 2 pictures of the board if anyone has any ideas on it, thanks....

 

[KrisBlueNZ]

The first board is just the display/control board. The amplifier is probably somewhere on the second board. Can you post an in-focus picture of it? And can you tell us which wires go to the speaker.

 

[johnpalmer1963]

Hi, hope this is a better picture, the red and black wires, (bottom left of the board) are spk + and - there is also the same at the top left of the board, though the wires will need re-soldering as they have come off whilst removing the board.

[Edited by a Mod]

 

[davenn]

OK after some editing, its a bit easier to see

those 2 chips 1/2 way down the left side are the audio output chips
what numbers are on them ?

do you have an oscilloscope or something else that can trace an audio signal ?, you are going to need it

once we determine what those chips are and hopefully find out the input and output pins we can check for audio at those points

Dave

 

[KrisBlueNZ]

OK, that picture is pretty poor as well. But you can see the two thick tracks coming from each speaker connector towards the two 8-pin ICs on the left.

Can you take a good clear picture of that area - those two ICs and all surrounding components - and post that? We should be able to tell you what to check. Make sure the markings on the ICs are readable and that you can follow the tracks on the photo that you upload. You may need to borrow a digital camera to get a picture with usable quality.

 

[profbuxton]

Do you actually have Digital radio transmission in your area? Don't laugh, I know someone who bought a digital radio and found it didn't work because there was no digital radio in the area.

 

[johnpalmer1963]

@ Profbuxton, yes we have dab available in our area, I have used a macro to take a close up of the 2 chips, hope this one is better, it says on the top of the 2 chips NS4148 M1342

 

[KrisBlueNZ]

OK, the amplifiers are type NS4148, made by "Nsiway". I found a data sheet; it's in Chinese, but the important information is there.



Start by checking the DC voltages. First, find a good connection point for the circuitry's 0V rail. Follow the track from pin 7 of either of the NS4148s. It will connect to some large copper areas. Find a place where you can make good contact with a multimeter probe, and keep your multimeter's black probe connected to that point.

Then measure some voltages on both NS4148s with your multimeter set to DC volts. If it's a manual ranging meter, set it to the 20V range.

Pin 6 of each NS4148 should have the supply voltage on it. It's probably around 5V. It must be between 2.2V and 5.25V, according to the NS4148 data sheet.

Pin 1 must also have the correct voltage. I'm not sure what that voltage should be, because the data sheet doesn't explain it, and uses conflicting names for the pin. My guess is that pin 1 needs to be low (between 0.0V and 0.5V) for the amplifier to operate, and if it's higher than about 0.8V, the amplifier will shut down and go silent.

If pin 1 is 0.8V or higher, you can safely bridge it to the 0V rail and see whether that makes the amplifier start working.

Once we know the voltages on those pins, we may be able to narrow down the area of the problem.

 

[johnpalmer1963]

Hi Kris, pin 6 reads 4.88 volts and pin 1 shows 3.2 volts, I have bridged pin 1 to earth but no sound comes from the speakers

 

[davenn]

Pin 1 must also have the correct voltage. I'm not sure what that voltage should be, because the data sheet doesn't explain it, and uses conflicting names for the pin. My guess is that pin 1 needs to be low (between 0.0V and 0.5V) for the amplifier to operate, and if it's higher than about 0.8V, the amplifier will shut down and go silent.

Pin 1 may well be a mute pin, grounding it via the switch as shown mutes the audio

 

[KrisBlueNZ]

Yes Dave, it could be either way round. It is named CTRL, either with or without an overbar. It is not mentioned in the text of the data sheet. So it's impossible to say which way round it is supposed to work.

It was at 3.2V, which should be considered high, and grounding it had no effect, so I will assume (for now) that it has been tested in both states.

John, what is the full model number for the radio? I would like to try to find some service information for it, if it's available (which I doubt).

 

[johnpalmer1963]

kris, Model number is Bush wooden DAB 141/4798(SG002D)

 

[KrisBlueNZ]

I can't find any service information for that model number. I suspect it will be difficult to locate the problem and to get replacement parts. I think you would be better to throw it away and buy a good quality radio.

If you want to keep going, try following the track on the underside from the via just west of R93 (this is the amp control signal) and follow the audio signal tracks from the vias next to C44 and C47. Trace them through to the IC that drives them, and post the pin numbers and the markings on the ICs. With luck we may be able to find data sheets for the ICs and suggest further checks. Do you have a signal tracer or an amplifier with speaker that you can use to test for audio on the signal lines?

(Also make sure the radio is tuned to an active channel! Does it have any indicator to show when a channel is tuned in? Does that indicator work properly?)

Cheap Chinese-designed equipment often uses components whose data sheets are not readily available - sometimes they're available in Chinese, but often they're simply not publically accessible - so don't be surprised if we come to a dead end.

 

[johnpalmer1963]

Thanks for your help so far, definitely tuned to an active channel as the display shows radio one etc.. playing, that said I think It will end up in the bin it as I don't have any specialized test equipment and it was only a cheap aquisition from a car boot, also if I buy another radio I will pay a little extra and get a better one, thanks again everyone

 

[Ronan]

I have the exact same problem with a BUSH Wooden DAB radio of the same model no. All picture and no sound. Thanks to the advice above its probably not worth attempting to fix it unless there is an accessible and obvious dry joint.

 

[des_tekki]

I have exactly this problem. There ARE however audio signals present at C44 and C47 so instead of throwing the radio away I'm going to install a stereo headphone amp and put a headphone socket on the case.