After reading these posts, checked my 544. No such pulses anywhere. If they
only appeared at 14.0, I wouldn’t care. I never operate on band edges.
-de K4CWQ
Sent from my iPhone
> On Feb 26, 2021, at 7:03 PM, Bob McGraw <rmcgraw@blomand.net> wrote:
>
> 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.
>
> 73
>
> 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@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@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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