You are probably doing more soldering than I do, and I would not want to
be without my
solder station.
I had the nice Weller one...with digital readout of tip temperature. But
as slick as it was, it just
one day crapped out.
Replaced it with a Hakko station. Still using it.
The trick is not on the wattage of the iron, but in the tip being used.
I have several tips that go from what you are talking about...down to
SMD stuff.
If I have to solder a wire to a chassis...or heavy boat anchor
transformer wires, I break out
the old Weller gun.
Not a new Weller gun...with the set screws holding the tip. They are junk.
The old ones with a nut holding down the tip are the ones to have.
Plenty found at garage sales,
flea markets, and tons on ebay....but of course, you pay premium there!!
....Dave
On 10/15/2013 3:08 PM, Paul Harker wrote:
Before I go at it, any tips on desoldering the power transistors? My 35W
iron is not up to the task unless I cut the foil leads beforehand. A bigger
iron might be in my future.
On Tue, Oct 15, 2013 at 1:03 PM, Mike Bryce <prosolar@sssnet.com> wrote:
excellent troubleshooting
although the diodes on the swr board don't control the PA in anyway.
but it could be that a spike came down the coax and took a few things out.
It's possible.
if you can get to the base of the transistors in the PA, in the lock
posistion position and the drive all the way down, you should see supply
voltage on the collectors, zero on the emitter and .7 on the bases.
since the base resistors are toasty, be sure you replace them with like
units, carbon flim or metal film and not wirewound.
call RF parts and see what they have in stock. I'm not much for matched
pair in simple PA designs like the ones in the Omni, so save some money
mike
Mike, WB8VGE
SunLight Energy Systems
The Heathkit Shop
http://www.theheathkitshop.com/
J e e p
o|||||||o
A man with one clock knows what time it is. A man with two clocks is never
sure.
On Oct 15, 2013, at 12:23 PM, Paul Harker wrote:
Well... here is where I'm at:
Checked the 914 diodes on the SWR board and sensing diode (D1) was bad
(leaky reverse biased). A big smile.
I replaced the offending diode, put everything back together, attached a
dummy load to the output and turned up drive to see how much current was
drawn. I noted a 3 amps input power increase, and smoke. Smile goes away.
Tearing it back down I discover 3.3 ohm R5 and R8 have acquired deep
tans.
These couple the impedance matching transformer to the bases of the power
transistors. A subsequent check verifies proper bias voltage to the final
stage.
Though toasty brown, and slated for replacement, R5 and R8 are still
correct values.
Unless I'm missing something major (always a possibility) I'm thinking
that
this kinda seals the deal on the power transistors being bad.
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