Paul -
OK. See below.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
Paul Gerhardt wrote:
OK still troubleshooting but found 2 more clues....
I pulled all the tubes and the AC4 power resistor R3 in the 250V line
is now cool to touch and V is 260V with NO tubes in.
When OA2 is in place (only OA2) R3 is too hot to touch and V drops
about 12V.
The 0A2 will glow blue when it is working, and will have +150V across
it. 12V drop across R3 is a little high, but is about 1.5W dissipation,
assuming it is 100 ohms.
2nd Clue I finally found what smoked in the chassis. It was hiding
under a switch shaft in the RF compartment. The 'smoker' was R30 the
68 ohm 1/2 watt resistor on V5 (final)
So I think maybe the tube had a grid to fil short and took out both
circuits.
I think that's where we started! :-)
I am still not getting a spot signal. R3 is still too hot when OA2 is
'IN'
SPOT will not be present with V8 out of the socket.
Again, 12 V drop across R3 is ok, only 1.5W, and if the 0A2 is blue,
it's regulating. The +150 bus drives the PTO, BAND OSC and the screen
of the PreMixer, along with V1, V2 Screen and V3 screen. The PTO supply
should have about 11 V on it, at the "low" end of R64, 6k @ 5W.
OA2 is blue not shure otherwise if it is good? Problem may be on the
150 V line as that powers the VFO (I think).
Still have the tubes out.
Paul K3PG in 'snowy' MD
pix on http://pgerhardt.blogspot.com <http://pgerhardt.blogspot.com/>
On Thu, Feb 4, 2010 at 11:31 AM, Paul Gerhardt <phgerha...@gmail.com
<mailto:phgerha...@gmail.com>> wrote:
Turned on my Working T4Xb and smoke came out the bottom of the rig
which I can't see for some reason. The filimant fuse (8A pigtail
lead fuse near the 3 big power resistors) is open so replaced
that, then no 250 V B+ and found R3 1K 5 watt resistor to be
open. Both of these were 'effect' and not cause (I suspect). I
changed R3 and got 150V and R3 is hot. Unhooked the yellow 250V
wire to the rig and V is good about 270V. Turned power OFF and
measured Resistance on yellow wire and it is low only about 150
ohms. Last thing is always suspect and for this the last thing I
did a few days ago was install some used FleaBay finals which
worked ok it seemed but were very weak only about 60-70 watts out
(maybe one was not working?) Put the bright light on the bottom
and compared to photo I took before and fail to 'see' any burned
parts on the bottom but there was smoke and I think it was from a
hot wire and not a componet. Will probably change the finals back
to the 'other' weak ones that were at least putting out 120W into
the Cantenna and see what is pulling the 250V B+ line down.
Any ideas on this one?
73
Paul
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