Dbox2 power fault

rooky

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Hello
i have got nokia dbox2 and im facing the following problem,after each soft or key update when i have to restart the dbox2 it stops at the boot (lcd) screen and it doesnt boot to the prog at all.The bizzare is that if i'll wait for 1hour and plug the main supply again the dbox boots normal without any problem....
 
Thats a known problem.
Some capacitors for the processor are not fully functional and the processor get the reset signal only if the whole thing is cooled off.
Enable the standby mode and don't do a reset.
 
thats what i do,but when i have to update the img is the problem.....is it possible to ,if yoy know,which capacitors must be replaced where are located .I have solderind skils to do the job...

thx in advance
 
TN1 and TN4 near the dbox buttons.
Those are smd transistors not capacitors, sorry.
 
I have found it very hard in the past to try and identify faulty capacitors,

You would have to take each one out of the circuit and measure the capacitence with a tolerance for what it says it is etc eg 20F (fareds)

What you could try but it can be all for nothing! try powering it up, then unplug it and drain the caps by putting a resister over the live and neutral, or if you have a multimeter measure the voltage at the live and neutral (to try and drain the power from it. If you drain the power over and over again it is possible to try and bring to life the faulty (dried out caps) if you need any help with this get back to me.

:)
 
polarised electrolytic resin filled caps - such as those used for smoothing the output of smps (switching mode power supplies) can be tested in curcuit quite easily. you need an isolated soldering iron (24ac weller is perfect) now power up the curcuit and press the iron to the top of the capacitor can. the remaining resin will become slightly fluid and retunr the cap to working order while the heat is present. i.e if problem goes away you have found the cap. this is common practice by many in the repair industry with smps power supplies.
i should also point out that we also use fully isolated mains supplies to power the powersupply. this method is fast and effective.
the second method is the squeeze the cap with a pair of long nose pliers < this can be procarious LOL as it sometimes results in a bang - i know peeps who do this but i am not one. i use the heating method it is quicker and more reliable.

ceramic caps are a different breed - the don't use a fluid isolator. these fail due to insolation breakdown - fortunately this often causes a conductive track to form between the 2 layers resulting in a short curcuit. these go short curcuit when they fail, they are also of very low value in capacitance to begin with. this makes them perfect for absorbing sporadic energy spikes of very low duration, as well as removing dc current from signal lines while still passing the signal through them when connected in serial configuration as apposed a parallel configution. in very very rare instances they can go o/c - these can usually be identified with a signal generator in curcuit without removing them.

this is general electronic information not directly relating to dboxes and should be treated as such.

TBC
 
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