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INSTALLING THE K0BGH PCB IN THE SWAN 117XC POWER SUPPLY
Some time ago I acquired a Swan 700XC transceiver along with a Swan 117-XC power supply. These components had been stored in the cellar of the home of KA3AWN and W3VEG for the past 20 some odd years.
After spending several hours cleaning up the interior and exterior of the radio I slowly powered the radio back to life over a few hour period of time using a Variac (tm) variable line transformer to control the input line voltage to the power supply.The only failure encountered during this procedure was the capacitor in the 12 Vdc relay line was failed to ground and the circuit diode and dropping resistor to fail. After replacing these 3 components I was able to successfully key both relays and put the rig back on the air.
However the possibility of one of the aging electrolytic capacitors in the power supply failing and causing additional damage was a omnipresent worry. When I heard of Bob's ( K0BGH ) newly introduced power supply up grade for the Swan 117XC power supply I contacted Bob and purchased the new PCB for my ageing 117XC. This board comes prewired and tested and includes the addition of HV bleeder resistors and inrush current protection that is not present in the original power supply.
Not being an expert at this type of modification what follows is how I successfully installed the new PCB. The PCB Bob provides is a high quality two sided board with through plated holes for ease of soldering. The board itself is clearly marked with all the connections you will have to make. With the exception of the filter choke (L1) and the capacitors for the pilot lamp plus the power transformer this board replaces all of the original power supply components.
Tools required to complete the installation are common tools found around most ham shacks. A mulitmeter. My digital
multimeter only reads as high a 600VDC a slight disadvantage when trying to confirm the unloaded high
voltages of 600VDC and 800VDC lines present in the power supply. A VOM reading up tp 1000VDC would be a better choice. A soldering iron, solder,
wire strippers, screwdriver, both straight and phillips. Long nose pliers, diagonal cutters and a soldering aid round out
the minimum tools needed. A few small wire ties will aid in cleaning up the finial dressing of the wires.
The first step I took was insure that the 117XC was unplugged from the ac line. I then removed the outer and inner protective covers. Using a voltmeter I checked the DC lines to confirm the power supply caps were fully discharged.(0 VDC on the DC lines ) Placing the power suppy, the new PCB and the instructions side by side. I read the instructions comparing them to the new PCB and the existing wireing in the PS. Once I was familiar with present and and planned layout after the modification I made a diagram of the existing terminal connections of the old printed cicuit board noteing in particular the color code of the wires at each connection. This proved to be helpfull as one of my wires to the terminal block was not the same color as the original specified color.
Just a word to the wise: After removing my old aluminum electorlytics I noticed that one of the cans was developing a bluge on one side. This was in
an area the could not be seen until the caps were removed.
In a recent email Bob indicated that a revision to the above board is already in the works. A new design eliminating the terminal strip
and mounting all the components below the board (single sided) will allow a cost savings which will be passed on to the Swan user. Bob
said that the board pictured here will for a limited time continue to be sold on the internet. The latest iteration of the PCB
when ready will be most likely be avaible directly from Bob. More information and photos when it becomes avaible.
Old PCB removed from PS
One problem I encountered was with my twenty watt soldering iron. I had difficulty tinning the old wires. I
switched to a 40 watt iron and had good success from that point on. I guess the plating on the old wiring
had oxidized to some extent and resisted tinning. Another small glitch was one wire had to be spliced to lengthen
it in order to reach it's solder tab on the new PCB. I found that after tinning my filament lead
from the transformer it was slightly larger than the solder tab hole in the new PCB. I enlarged this hole ever so
slightly using a soldering aid and then soldered the wire on both sides of the PCB to ensure a good connection. An easy fix to that situation.
After finial assembly was complete I reviewed the instructions and re-checked all the wiring once again with an ohm
meter to be sure I hadn't fallen asleep at the wheel during the installation.
Satisfied that I had it "right" I connected the rig and the power supply to a Variac (tm)and slowly
brought up the line voltage checking all voltages as I went. Satisfied that everything went well I let the
power supply burn in for about an hour before putting the 700CX back on the air. A half a dozen contacts later
I was satisfied that all was well and allowed that smile of satisfaction to spread across my face.
With my limited expierence the conversion of the power supply took me almost two and a half hours. Not having tackled a project
of this type in the past I moved very cautiously consuming more time than an expierenced technician would take. I would estimate
the skill level to complete the project as basic. Overall, the PCB, the components and the instruction set are first rate. It's obvious that
Bob put a lot of time and effort into the design and ease of installation of this PCB.
If you skipped reading the safety tips page please go back and read it at this time.
Prepared by Ralph M. Ferrara WA2NTK
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last updated 04.30.05