Mike,
Interesting. If the 544 schematic is correct, the Display Board has no common
+Vcc. +Vcc is supplied individually to each 7-segment LED module via Q14-Q19
(PNP) on the Logic Board. +Vcc on the Logic board is RF bypassed with a
0.047uF cap at C6. +Vcc on the Logic Board is also connected to IC-1 with
ample decoupling, consisting of a 22 ohm resistor and a 0.1 uF cap at C7. The
22 ohm resistor is mainly there to regulate current into a Zener diode that
feeds +Vcc to IC-1 but it also functions to decouple.
To me it looks like Ten Tec adequately decoupled one part of the Logic Board,
but not the other going into the display board. The only problem with
duplicating R/C de-coupling on the +Vcc bus feeding Q14-Q19 is that any series
resistance will make the display slightly dimmer -- and the green LED segments
are already way too dim due to green-wavelength filtering through the smoked
Plexiglass lens. So, that leaves adding an additional RF bypass across C6
(0.047 uF). Possibly something like a 4.7 uF 'lytic cap in parallel with a 0.22
uF film bypass will do the trick.
Paul, W9AC
-----Original Message-----
From: TenTec <tentec-bounces+w9ac=arrl.net@contesting.com> On Behalf Of Mike
Bryce
Sent: Friday, February 26, 2021 10:47 AM
To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Triton IV 544 Digital
When you first hear it, you’d bet money that the calibrator is running.
However, there isn’t one in the digital Triton 4.
Decoupling the power supply will reduce the signal level to a point you won’t
notice it with an antenna connected.
One of my Drake TR5s did the same thing. Its counter/display put a S-7 signal
right on the MIDCARS freq of 7.258. Recaping the display pcb eliminated 94% of
the problem
Mike, WB8VGE
SunLight Energy Systems
The Heathkit Shop
http://www.theheathkitshop.com/
J e e p
o|||||||o
> On Feb 26, 2021, at 8:10 AM, Paul Christensen <w9ac@arrl.net> wrote:
>
> Thanks, Mike. I'll look into it.
>
> Paul, W9AC
>
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