[Yaesu] FP-1025 Power Supply, Schematic?

[KBØNLY]

Yep, as always with these switchers it was bad caps.  This FP-1025A has some 
of those brown Elite brand caps around the voltage set trimmer.  In 
particular a 10uf 50v and a 47uf 50v.  I have been replacing the Elite brand 
caps in LCD tv power supplies for years, first radio power supply I have had 
to do the same in but its still just a switcher.  Pretty basic little power 
supply, basically just the same looking board as you find in a ATX power 
supply with a little added circuitry to make the voltage adjustable and also 
an added thermostat on the heatsinks, one is a normally open that runs the 
fan, the other is a normally closed that opens the AC supply voltage feeding 
the power switch to shut it off if it overheats.

Figured I would need a schematic until I just decided to open it up and poke 
around, as soon as I saw those bulged Elite caps I knew what I was up 
against.  Took longer to tear the power supply apart to get the board out 
and replace the caps the actual repair.  Replaced the caps, adjusted the 
voltage and put my load tester on it set for 20a for five minutes.  If they 
are going to explode I want it to happen here on my bench!  No smoke and 
purrring like a happy kitten now.

73,

Scott KBØNLY

-----Original Message----- 
From: Steve
Sent: Thursday, March 07, 2013 9:08 PM
To: KBØNLY ; Yaesu Reflector
Subject: Re: [Yaesu] FP-1025 Power Supply, Schematic?

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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