[Yaesu] FP-1025 Power Supply, Schematic?

[Steve]

At 06:57 PM 3/7/2013, you wrote:
>Anyone know of a source for the schematic for this power supply?  I 
>have looked everywhere online.  Looks like a basic switcher inside 
>not unlike a computer power supply, but it would be nice to have a 
>schematic to troubleshoot this thing.
>
>It suddenly died, although not entirely, but only has 3v output when 
>turned on.

Most equipment dies due to a capacitor, usually electrolytic but any 
modern film capacitor is also suspect, going away. You might find the 
problem by checking every electrolytic with a good capacitor tester. 
Check for every characteristic you can measure; if no-go, then try 
removing the cap and subjecting it to an external power supply 
running at the cap's rated voltage. I once had to find the failure 
mode of several switching power supplies. All caps checked out, as 
did all resistors, diodes and transistors. Finally, out of 
desperation, I removed the electrolytics then built an RC-time 
constant test fixture to operate the caps at their rated voltage. 
Voila...  one in particular was breaking down and becoming a 
quasi-zener at around 1/2 rated voltage. When this was communicated 
to the distributor of the power supplies, they had another lab do 
further tests upon the physical construction and chemistry and were 
told the caps in the new supplies, which had been dying, were built 
using a foil that was RoHS-compliant but also was problematic for 
encouraging a chemical reaction that caused the foil to deteriorate 
over time. The pre-RoHS caps did not have the problem but could no 
longer be built/sold due to RoHS requirements. The manufacturer was 
forced to redesign the supply to accomodate oversized capacitors 
over-rated by nearly 3 times in operating voltage in order to 
withstand their rated voltage for the warranty period.

Just another sad story of unintended consequences of RoHS.

Steve, K0XP 



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