Hi again Jacques and the group..
I ran the tests with the Ant Trim assembly completely removed and
disconnected from the RF deck.
My best VTVM is a fully restored and calibrated Marconi TF 1041B and it was
used on the 500 Mohm scale and wouldn't even twitch during the
testing...Testing for capacitance and insulation resistance with my TO-6
also showed no problems during testing.
I think I'll go ahead and re-install the RF deck and see if I've solved the
problem..
P.S...Does anyone have some spare connectors which I could use to build an
extension cable for the PTO...? I might give adjusting a pair of Cosmos
PTOs for linearity a try. They are fine across the 1Mc coverage, but are
1khz or so out at some points along the way...
73...Jordan VE6ZT
----- Original Message -----
From: "Jacques Fortin" <[email protected]>
To: "'Jordan Arndt'" <[email protected]>; "'Collins R-390 HF Receiver
List'" <[email protected]>
Sent: Monday, September 30, 2024 3:04 PM
Subject: RE: [R-390] Antenna Trim trouble
Hello Jordan,
You should have figured it already, but...
It will be impossible to diagnose temporary shorts between the plates of
C225 A+B as long as all the antenna coils are left in place, because they
have a so low resistance value on their secondaries that this will mask
any
leakage coming from the variable capacitor sections.
Check the schematic, you will see it.
What I believe can be done by leaving C225A+B in place is:
1_ Tune MHz knob to 00.
2_ Locate T201 and remove the related slugs rack. Take care to not loose
the
springs in the RF deck...
3_ Remove T201: with the MHz tune in 00 position, the A+B sections of C225
are connected in parallel between pins 3 and 6 of the T201 socket.
4_ Using a sensitive ohmmeter connected between those pins, any (even
temporary) leakage of the capacitors can be measured, and with a
capacitance
meter connected to the same pins, the total value of the variable sections
can be checked for any rotation angle of the control shaft.
Let us know...
73, Jacques, VE2JFE in Montreal
Hi again group...
I'm ready to re-mount the RF deck temporarily in the radio, but before I
do
that, I'd like to know if there is a test technique or method I haven't
tried yet.
I was getting some scratching noises and "dead spots" at some positions
of
the Ant Trim control.
After an attempt at repair, without being able to pull the variable cap
out
of the can, I've used a 50 Mohm impedance VTVM with a 500 Mohm scale as
well
as the Insulation test of my Sprague TO-6 and checked between every line
and
each line to ground and I can't provoke even the slighest twitch of the
metering when rotating the cap
Is there anything else I should try..?
73...Jordan VE6ZT
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