"Chuck Olson" wrote in message
news:Tz5uc.14050$eY2.3710@attbi_s02...
My Metcal RFG-30 soldering system power supply quit on me a week or so
ago,
so yesterday I decided to look into
the problem. After removing 8 screws holding two bottom covers I was able
to slide out the front and back dress panels for very limited access to
fasteners. I couldn't find any way to unfasten the top cover which would
allow separating the two halves of the case, but that turned out to be
unnecessary. The single power transistor, an IRF130 TO-3 case FET was
mounted with nuts on studs that came up through the mounting holes. One
end
had a Nylon shoulder washer under the nut but the other end made
electrical
contact with the case and was found to be barely finger tight. Since that
had to be the drain connection to the device, I gently firmed up that
fastener and reattached the cables to test the unit - - back in operation.
I was particularly impressed with the toroidal power transformer in the
base - - that had to cost the manufacturer some serious cash. If anyone
knows how to remove the plastic top panel, that knowledge will help
improve
the serviceability of this excellent product.

Chuck W6PKP

Well the RFG-30 quit on me again, so this time I had to get into the package
to find out what was the matter. Pete, KE9OA, said something about removing
an overlay, which at the time went by me without even pausing at my brain.
But faced now with this puzzle, I looked and looked, and eventually I could
see where sheetmetal screws came down through the aluminum top panel, but
there were no screw heads visible above them. They had to be covered up
with something, so I started tapping on the flat surface around the on/off
switch, and sure enough in places it sounded thin and hollow. So I got a
sharp little screwdriver and found a corner that looked like there was space
around a thin covering and started to pry up on the corner of that covering,
and what do you know - - it was a thin "overlay" (now I know what an overlay
is) that was glued down to the plastic top panel with rubber cement, and it
came up fairly easily, exposing the four Philips-head sheetmetal screws that
needed to be removed to get down to the aluminum top panel holding the
on/off switch.

So there you have it. Now the halves of the case can be separated and
re-arranged to service the innards of the machine. One thing surprised me,
though. I found a whole lot of stored energy in the 1000 uf 50 volt filter
capacitor, and it stayed charged up to around 40 volts between the times the
unit was turned on. Now 40 volts is something to be a little concerned
about. I remember being zapped by a 45 volt "B" battery when I was a kid,
so this thing is not so different. If shorted, the sound of that arc is
sure to attract some attention from people nearby. Okay, it's not deadly,
but a little bleeder resistor across that 40 volt supply wouldn't hurt.

I found help servicing this unit from the 1986 Metcal patent 4,626,767 which
contains a pretty accurate circuit diagram of the RF and power supply
sections of the RFG-30, missing only the use of the SG3526. You can view
and print out this patent by using http://www.pat2pdf.com/ which will turn
the document into a PDF file you can download. I wasn't able to find out
much from their other patents about the use of the SG3526 where they (oddly
to me) ground the A and B outputs of the chip, but the OnSemi data sheet
from http://www.newrock.com.cn/pdf/igbtgo/SG3526.pdf shows an application in
figure 21 that looks like it's probably how they're using it. If anyone
knows of a source of more recent schematics on the RFG-30, the PS2 or MX-500
power supplies, this is a good place to let all the people that are
interested see them. I found a 1N4001 diode that passes rectified pulses to
the 470 uf 25 v filter capacitor on the 16 volt supply, I think it was D7,
bad, and replaced it, restoring operation.

Chuck W6PKP