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Why the radios stop working

babulio
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Re: Why the radios stop working

Postby babulio » Sat Jul 30, 2016 8:42 am

old del boy wrote:I might have had a go it it were just replacing that diode but it's what's on the other end of the blown track that confuses...

Derek..


Why not do it then?
As said - that might be all it needs. If not - then leave it.
The other end of the blown track is the power supply.
It is what is beyond the diode that is unclear at present.
1995 Suzuki Baleno 1.6 GLX

old del boy
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Re: Why the radios stop working

Postby old del boy » Sat Jul 30, 2016 10:53 pm

babulio wrote:
old del boy wrote:I might have had a go it it were just replacing that diode but it's what's on the other end of the blown track that confuses...

Derek..


Why not do it then?
As said - that might be all it needs. If not - then leave it.
The other end of the blown track is the power supply.
It is what is beyond the diode that is unclear at present.


''why not do it then ? ''

Well for one thing , my soldering is a bit hit and miss and i've no doubt i could end up blowing something that isn't blown yet , having said that what you say makes sense so i looked for the part and found this , is this correct ?

http://www.ebay.co.uk/itm/201600595801? ... EBIDX%3AIT

What would you suggest i bridge the track with ? would some thin gauge stranded wire do ?

Derek..
'93 4.0L Daimler, solent blue,
'93 4.0L Daimler, Westminster,
'85 2600 Rover sd1 vdp oporto.

babulio
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Re: Why the radios stop working

Postby babulio » Sat Jul 30, 2016 11:19 pm

old del boy wrote:''why not do it then ? ''

Well for one thing , my soldering is a bit hit and miss and i've no doubt i could end up blowing something that isn't blown yet , having said that what you say makes sense so i looked for the part and found this , is this correct ?

http://www.ebay.co.uk/itm/201600595801? ... EBIDX%3AIT

What would you suggest i bridge the track with ? would some thin gauge stranded wire do ?

Derek..


You do not need the diode to run the set up on a (nice clean 12V) car battery - it just conditions the power supply. Just cut one of its legs so it is no longer in the circuit.
I would avoid stranded wire if possible - a bit of solid conductor from some lighting twin and earth should be easier to work with and less messy. Make sure your work does not leave anything sitting too proud of the rear of the board that could short on the case when the set is reassembled.
If it then works from a car battery (that is the diode was shorting the supply) then see if you can get the whole part number of the diode (I can only see part of it from your photo) and check against the eBay item. That is likely the right one though.
Cutting the diode may mean you won't need a pump to clean the joints up before removing it. Heat and a gentle well timed tug should free each lead one at a time.

Tin the bit (to get decent contact) then heat the work and feed a minimal amount of solder onto it. Get someone else to hold the wire in place (not with fingers) or use some cloth tape while you fix it to the pads.
Last edited by babulio on Sat Jul 30, 2016 11:40 pm, edited 2 times in total.
1995 Suzuki Baleno 1.6 GLX

old del boy
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Re: Why the radios stop working

Postby old del boy » Sat Jul 30, 2016 11:38 pm

So i can re connect that track , cut the diode and it may still work ? , does it matter which end to cut ?

Derek..
'93 4.0L Daimler, solent blue,
'93 4.0L Daimler, Westminster,
'85 2600 Rover sd1 vdp oporto.

babulio
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Re: Why the radios stop working

Postby babulio » Sat Jul 30, 2016 11:42 pm

old del boy wrote:...does it matter which end to cut ?Derek..


No - so long as it is a clean break - the diode cannot then conduct.
1995 Suzuki Baleno 1.6 GLX

old del boy
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Re: Why the radios stop working

Postby old del boy » Sat Jul 30, 2016 11:51 pm

Right , i'll give it a go , i can't understand for the life of me how it all works but i'll give it a go ;)

Derek..
'93 4.0L Daimler, solent blue,
'93 4.0L Daimler, Westminster,
'85 2600 Rover sd1 vdp oporto.

babulio
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Re: Why the radios stop working

Postby babulio » Sun Jul 31, 2016 8:35 am

Image
A diode should normally let current flow in only one direction through it (indicated by the orientation of the triangular symbol).
In your radio the diode normally sits reverse biased across the supply - that is non conducting.
If the diode had broken down - and was conducting a lot of current backwards through it then the PCB track supplying it (and the rest of the radio) - the little frayed red thing - could get too hot and melt. This would prevent current flowing further into the rest of the radio.
Removing / cutting the diode (that is the short across the supply) and fixing the melted track would therefore restore power to the electronics.

...anyway - make sure the set is fused (5A might be more sensible than 10A) when you test it out in case the duff diode theory is wrong and something else in the 'rest of the radio' is lunching on all that current.
If your repair to the track is beefier than it was originally - and there is still a fault, somewhere else will heat up instead and you want it to be a fuse - not something important!.
1995 Suzuki Baleno 1.6 GLX

nlcrane
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Re: Why the radios stop working

Postby nlcrane » Sun Jul 31, 2016 1:11 pm

Derek you have to think of that bulky diode as an overvoltage protection, any voltage spikes on the power supply will be effectively be blocked by it, unless the value of that surge is greater than the inherent avalanche (breakdown) value of the diode (20 Volts in the case of the MR 2535). Just as a fuse protects us against over amperage until the specific fuse value has been exceeded and then it will melt, break the circuit and thus help to protect any downstream components from over current. This is why we should never put in a higher value fuse in an attempt to resolve a problem of a circuit that is blowing. This could result in cooking even more expensive stuff downstream as Babulio points out.
ImageImageImage
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old del boy
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Re: Why the radios stop working

Postby old del boy » Sun Jul 31, 2016 11:19 pm

Ok , i've got it , so somehow i have to incorporate a 5 amp fuse in the track repair or would a thin gauge wire do which would blow instead ? , i say this as i have some very fine [ 0.40mm and 1.08mm ] gold wire that my missus use to use back in her electronics job for track repairs to circuit boards , a quick google on wire diameters for amp reckons about 1.7 amps for the thinner wire and 10 amps for the thicker wire so would the thinner one be ok ?

Derek..
'93 4.0L Daimler, solent blue,
'93 4.0L Daimler, Westminster,
'85 2600 Rover sd1 vdp oporto.

babulio
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Re: Why the radios stop working

Postby babulio » Sun Jul 31, 2016 11:35 pm

babulio wrote:replace the blown track (possibly with a fuse on some flying leads at first) and try it out?


I'd probably do it as above - but it's possibly easier / simpler - depending on what you have to hand, to bridge it with a single bit of your 10A wire and add the fuse somewhere else.
A fuse attached to the battery +ve will be fine.

Mrs. Derek sounds ideally qualified for this job.
1995 Suzuki Baleno 1.6 GLX


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