[TenTec] Triton IV 544 Digital

Bob McGraw rmcgraw at blomand.net
Fri Feb 26 19:02:39 EST 2021

It is not at all unusual for electrolytic capacitors to decrease in 
value as they age.  Thus an original 10mfd, after a few, years may 
effectively be a 1mfd capacitor.  Although I don't care for the 
"shotgun" approach, this usually saves time and money.

Keeps life simple and less frustrating.


Bob, K4TAX

On 2/26/2021 10:33 AM, Mike Bryce wrote:
> I’ve never done a shotgun approach when it comes to replacing electrolytic capacitors, but in the case of this particular display unit, that was alway the first thing I did.
> Then, and it’s been  years ago, some smaller electrolytic caps (1mf) and .001 disc took care of it. Nothing I did eliminated it 100%
> Mike Bryce
> prosolar at sssnet.com
> "The eye is always caught by the light, but shadows have more to say"
>> On Feb 26, 2021, at 11:20 AM, Paul Christensen <w9ac at arrl.net> wrote:
>> 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.
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