[Yaesu] FP-1025 Power Supply, Schematic?

[Dr. Gerald N. Johnson]

The built in switcher in the FT-736r has a reputation for failure. When 
I dug into mine (no schematic in the technical supplement) I found two 
or three capacitors in the control circuit open. All aluminum 
electrolytics. I replaced them with the highest temperature and lowest 
ESR capacitors I could buy from Mouser and its worked a long time now. 
Miniature electrolytics are not the world's highest quality products, 
some have arrived from China bad on the first application of voltage, as 
if the manufacturing formula didn't include the forming process, only 
the mechanical assembly.

There is a need in a switching supply to minimize the high current high 
frequency loop area to cut down on radiated RF noise, so the board lay 
outs around the control and primary switch transistor will tend to be 
very similar.

73, Jerry, K0CQ

On 3/7/2013 10:44 PM, KBØNLY wrote:
> 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
>
>
>