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Re: [TenTec] Troubleshooting Century 21 Power Issue

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>, Johnathon Allread <john.allread@gmail.com>
Subject: Re: [TenTec] Troubleshooting Century 21 Power Issue
From: "Ken, W8EK" <kenw8ek@gmail.com>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Mon, 7 Oct 2019 08:03:40 -0400
List-post: <mailto:tentec@contesting.com>

Hi John,

I am parting out a Century 21, and have all of the power supply parts available.

Please let me know exactly what you would like, and we can go from there.

Century 21, Model 570 Parts For Sale:
I have parts from a Century 21, model 570, available.
Most of these parts should also fit the Model 574
digital version.
Hopefully these parts will let several rigs live again.
Most cabinet parts are presently available.
Many internal PC boards are available.
Power transformer is available.
The 271, 15 meter crystal, and the 272, ten
meter crystal are both available.
Please let me know what you need, and we can go from there.


Ken, W8EK

Ken Simpson
E-mail to W8EK@FLHam.net or W8EK@arrl.net
Voice Phone  (352) 732-8400

Johnathon Allread wrote on 10/6/2019 9:57 PM:

It appears that the transformer is bad.  There may be more bad components,
I am not sure.  While taking meter readings, my main fuse blew.  I changed
it and it blew again.

I desoldered the 2 output connections to the power supply circuit and was
only getting 2VAC from the output of the transformer.

So it appears I need a power supply.  If you have one, please let me know
what you want for it shipped to 75077.  Thanks!


John - NE5J

Johnathon B. Allread

On Sun, Oct 6, 2019 at 9:19 AM Mike Bryce <prosolar@sssnet.com> wrote:


that supply is very simple.

if you have 25 V AC from the secondary of the transformer yet no dc on the
cap, check the bridge rectifier. They have been known to go bad in that
radio. Most likely one or more of the diodes inside have opened.
Replacement is the best way to check, they’re not expensive or hard to

the over trip circuit uses the voltage drop across a low value resistor
that when it drops an excessive amount, trips a scr that shuts the PS down.
It only controls the DC side of the power supply.

when it trips, you would still see both ac from the transformer and dc
across the filter cap.

Mike, WB8VGE

> On Oct 6, 2019, at 1:01 AM, Gary Follett <dukeshifi@comcast.net> wrote:
> Well I have a transformer for the C21 sitting right behind me if you
find that you need it.
> With the power switch on, you should see voltage across C1 regardless of
trip condition, as long as the power switch is OK.
> You should also see voltage across C2.
> If not, use an ohmmeter to measure transformer windings and power
switch. It is not unheard of for that switch to be bad. I may have one of
those too.
> Since it is ,not blowing the fuse, likely the diodes in the bridge are
OK but it would to hurt to test them for open. I doubt you sill find any
open though. Diodes usually fail shorted.
> Gary
>> On Oct 5, 2019, at 10:15 PM, Johnathon Allread <john.allread@gmail.com>
>> Hello everyone,
>> I recently purchased a digital version of a Century 21.  Unfortunately,
>> when I received it, It will not power on.  When I turn it off, it very
>> briefly powers on then off.  I have verified 120VAC going to the
>> transformer from the switch and tried to verify 25VDC from the
>> but I am not seeing a DC output across the capacitor C1.  I did this
>> quickly, so I will recheck tomorrow.  My question is, if there is an
>> with the excess current trip shut down circuit, would it have any
impact on
>> the unregulated output of the transformer or just affect the regulated
>> of IC1?  I am trying to understand the circuit, but my electronics
>> knowledge is limited when it comes to ICs and transistors.  By the way,
>> this unit is spotless inside and does not look like it has been worked
>> Lastly, If there was an issue with the transformer, where could I
>> a replacement?  Thank you!
>> 73's
>> Johnathon - NE5J
>> Johnathon B. Allread
>> john.allread@gmail.com
>> 469-336-7763
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