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Mains/battery radios |
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#1 |
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Forum Member
Join Date: Dec 2010
Posts: 277
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Mains/battery radios
I have a couple of radios, neither of which work with the mains lead plugged in; however, one of them, a Panasonic, works with batteries in place. The other requires a PP5 battery which I'm not sure are still available.
I' m wondering if this is a common occurrence, I.e., radios not operating through the mains lead but working OK with batteries. What is the likely reason and is it something that can be rectified/repaired without too much expense? |
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#2 |
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Join Date: Jul 2005
Location: Herts
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Could be a fuse gone either in the plug or inside the radio else the internal power supply is probably at fault and likely to be beyond economical repair.
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#3 |
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Join Date: Apr 2006
Location: North Derbyshire
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Easiest (and probably cheapest) way would be to get one of those plug-in multi-volt mains supplies (make sure it's a regulated one), set it to 9V (assuming that's what the radio needs) and connect it directly in place of the battery.
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#4 |
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Join Date: Jul 2010
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with older radios more common for the actual radio part electronics to fail but power supply wd be a mains stepdown transformer and couple of rectifier diodes. nothing to go wrong there.
newer models will have a smps power supply. like everythng nowadays. if the inverter board fails then needs replacing. spare part unlikely to be available and in any case uneconomic to have repaired. as said if still working then you can power via the battery terminals. there used to be "battery eliminators" the exact size of a PP3 or whatever ......... if powering in this way, be VERY careful to get voltage polarity right way round or u might destroy the radio part ........ |
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#5 |
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Join Date: Jul 2010
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... i got a couple of really nasty chinese made mains powered clock radios at bargain price £5. invertor boards in both failed after a few days .......
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#6 |
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Join Date: Apr 2006
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Quote:
with older radios more common for the actual radio part electronics to fail but power supply wd be a mains stepdown transformer and couple of rectifier diodes. nothing to go wrong there.
![]() EVERY single part can (and does) fail in such a PSU - the transformers go O/C or shorted turns, the rectifiers go S/C (or VERY rarely O/C), and the large capacitor goes S/C or O/C (in pretty well equal percentages). However, they do tend to be more reliable than switch-mode supplies, which are of course far more complicated. Most common failure though is the transformer, often with an internal heat fuse failing - either just because it 'felt like it', or more commonly because of excess current consumption (shorted turns in the TX S/C rectifer. S/C capacitor). Usually though it's the transformer itself, that causes it - small mains transformers are far less efficient than large ones, so run a LOT hotter making them prone to failure. |
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#7 |
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Join Date: Jul 2010
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power rectifier diodes are sturdy things and rarely fail.
yes if you short cct the stepdown transformer secondary the enamel will start to melt, with some smoke and a nice sweet smell, and possibly a soothing buzzing sound as the laminated core shakes itself to bits ........ |
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#8 |
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Quote:
power rectifier diodes are sturdy things and rarely fail.
![]() Rectifier failure is a very common occurrence, and has been for many decades - even back before silicon rectifiers the previous 'metal' rectifiers used to commonly fail as well. |
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#9 |
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Join Date: May 2006
Location: Aberfeldy
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http://www.amazon.co.uk/Roberts-DAB-...b2+solar+radio
I have that radio if your looking for an update & comes complete with rechargeable batteries which is an optional extra in others it can take an auxillary input as well through a 3.5mm jack............... perfect for iPhone or streaming in the shower |
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#10 |
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Join Date: Jul 2010
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Quote:
You're showing your complete lack of knowledge about anything electrical again
![]() Rectifier failure is a very common occurrence, and has been for many decades - even back before silicon rectifiers the previous 'metal' rectifiers used to commonly fail as well. I doubt the radio being discussed has a copper oxide rectifier. Unless noah took it on the ark .......... |
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#11 |
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Quote:
I shall refrain from your tiresome style of name calling, and just say that rectifier diode failure is quite rare in old style power supplies.
Ask any service engineer who has done repairs over a few decades, they will tell you what fails and what doesn't. Back in the days before SMPSU's I use to order mains rectifier diodes in 100's because we used so many of them ![]() Even in modern SMPSU's the incoming mains rectifiers still fail just the same, although the secondary Schottky ones fail more often, |
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#12 |
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Rubbish.
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#13 |
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the old style power supplies were 2 rectifier diodes or bridge into "resevoir" electrolytic. so obviously if u shorted the diodes this destroyed them but they didnt spontaneously just fail !
maybe there was a 10 ohm resistor to limit initial surge but not enough to save the diodes of course. later on there was sometimes a voltage regulator with pass tranny & zener, which would current limit.obviously this arrangement makes lots of heat with other problems .......... small signal and low current diodes are different since they have a tiny junction area to limit capacitance. but old style rec. diodes have a large junction area for low current density and so r far less easily destroyed. input rec. diodes in smps are lower current higher voltage so come somewhere in between the 2 catagories. semiconductors in smps are obviously extremely vulnerable to transients unless "very generously" rated. |
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#14 |
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Quote:
the old style power supplies were 2 rectifier diodes or bridge into "resevoir" electrolytic. so obviously if u shorted the diodes this destroyed them but they didnt spontaneously just fail !
One possible cause is mains spikes, hence the inclusion of 1000pF capacitors in parallel with the diodes in many circuits, plus series resistors to limit surges - but in practice it never seemed to make much difference. |
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#15 |
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Join Date: Dec 2010
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Thanks to you all for the input. I think I'll just use the Panasonic on the batteries power. The othe requires a big square battery with top terminals, PP5 maybe; are these still available?
Last edited by ThePenkethPedan : 05-10-2014 at 01:43. Reason: Spelling |
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#16 |
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Join Date: Oct 2007
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Quote:
Again, you're showing you know nothing about electronics - they did (and still do) 'spontaneously' fail.
One possible cause is mains spikes, hence the inclusion of 1000pF capacitors in parallel with the diodes in many circuits, plus series resistors to limit surges - but in practice it never seemed to make much difference. |
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#17 |
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Join Date: Apr 2006
Location: North Derbyshire
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Quote:
I agree with spinny2 on this. Mains rectifier diodes rarely spontaneously fail, though of course they can be destroyed if something else fails.
![]() Try talking to anyone with decent servicing experience, rectifier failures were VERY, VERY common (and nothing else had failed - apart from the fuse, and occasionally the current limiter) - somewhat less so now with mostly switch-mode though. Quote:
The 1000pF capacitors were not for mains spike protection but for the reduction of RF interference that diodes could generate.
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#18 |
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Join Date: Oct 2007
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Quote:
Try talking to anyone with decent servicing experience, |
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#19 |
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Join Date: Apr 2006
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Quote:
You are.
![]() None of which have shown any degree of electronics knowledge or understanding?, perhaps you are referring to servicing something else?
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#20 |
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Careful Nigel - he'll have your post removed as offensive again.
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#21 |
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Quote:
Careful Nigel - he'll have your post removed as offensive again.
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#22 |
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Join Date: Jan 2011
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Oh dear - I can see us both disappearing again. Anyway, made a screen dump this time to preserve such gems for posterity.
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#23 |
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Join Date: Oct 2007
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Quote:
How can the truth be offensive?
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#24 |
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i am of course not saying that low voltage rectifier dodes hardly ever need replacing. only that the junction is destroyed nearly always by a short cct.
rectifier diodes in smps at 400 v are different and the junction can be easily wrecked by transients etc in badly designed supplies. i assume from nigels remarks he is talking mainly about sky boxes ...... |
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#25 |
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Quote:
i am of course not saying that low voltage rectifier dodes hardly ever need replacing. only that the junction is destroyed nearly always by a short cct.
Quote:
rectifier diodes in smps at 400 v are different and the junction can be easily wrecked by transients etc in badly designed supplies. i assume from nigels remarks he is talking mainly about sky boxes ...... Why on earth would you assume Sky boxes? - there's never been anything to even hint at Sky boxes - mostly I was referring to old TV's, radios, and record players - nothing switch-mode. |
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