Be sure to discharge the old capacitors before working on the power
supply. Here is a link to some good information on the AC-3 and AC-4
power supplies.
http://www.wb4hfn.com/DRAKE/DrakeArticles/TechTips/
PowerSupplyTroubleshooting.htm
Al, n7ioh
On Jan 27, 2010, at 9:18 PM, Garey Barrell wrote:
Frank -
The 200V caps would be ok. Later versions of the AC-4 used 40 uF
capacitors for C5, so if you can find bigger ones it would be better.
You must disconnect ALL wiring from the old can type capacitor.
Best is to mount an insulated terminal (tag) strip near the can,
soldered to the chassis, and move all the wiring there. You can
leave the old can in place for appearance, but NO connections to
its terminals.
NO, the two Negative (-) leads are connected internally and to the
outer can. This is why the can has a cardboard tube over it to
insulate the -100 VDC on it. The two terminals "big" in the
"center" are the Positive (+) leads of C5 A and B. Both (-) leads
of the new caps, the "free" end of R5, one "blue" transformer lead
are all connected together with a "green" wire going to Pin 9 of
the connector.
Once your repair is completed, I would strongly suggest testing the
supply without connecting to the transmitter. This can be done by
unplugging the supply, inserting a piece of bus wire to connect
Pins 1 and 2 of the connector together. Put a piece of tape or
other insulation over the bare wire to prevent accidental contact.
When the supply is plugged back in, it will be _ON_ so beware of
exposed HIGH voltage under the chassis and on the connector pins.
You should see the following voltages, referenced to the chassis.
Pin 10 (orange wire) should be 740 VDC. CAREFUL !!
Pin 11 (yellow) should be 300 VDC. CAREFUL !!
Pin 9 (green) should be adjustable with the BIAS control from about
-50 to -100 VDC CAREFUL !!
These voltages are with the supply wired for 120 VAC. Yours is
probably wired (or switched) for 240 VAC and these voltages may
vary roughly +/- 10%.
Be SURE and check the fuse. It should be a 5 Amp Slow Blow for 120
VAC and 3 Amp Slow Blow for 240 VAC.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
iz oos wrote:
Hi Folks,
I have 2 spare 400V 22microF and 2 spare 200V 22microF. The former
are
quite bigger than the latter ones but both types could be soldered
underneath the old big can as there is enough space. I would like to
make things as simple as possible and mechanically durable. How would
you suggest to place these newer capacitors exactly? Would you clip
off all the three leads of the old can? Pictures would be greatly
appreciated!!!
The old can as far as I see contains both caps inside; viewing from
the bottom one lead is the positive side of C5a, the lead in the
center of the can is the ground and the third lead is the negative
side C5b, thus, the connection between the negative sides of C5a and
C5b cannot be seen as they are connected inside the can, am I wrong?
TU and 73,
Frank IZ2OOS
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