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Re: [TenTec] Troubleshooting Century 21 Power Issue

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Troubleshooting Century 21 Power Issue
From: Bob McGraw K4TAX <rmcgraw@blomand.net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sun, 6 Oct 2019 21:12:08 -0500
List-post: <mailto:tentec@contesting.com>
Sorry to learn the news.  Unless you want a matching Tentec supply, I'd opt for 
an inexpensive 12 volt supply. 

I purchased a new switching supply which I found to be astonishing clean 
radiation wise from Amazon for $20.  It is a LED lighting supply rated at 12 
volts @ 20 amps.  I tweaked the voltage pot so I have 14.0 volts. 

Bob, K4TAX


Sent from my iPhone

> On Oct 6, 2019, at 8:57 PM, Johnathon Allread <john.allread@gmail.com> wrote:
> 
> Gents,
> 
> 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!
> 
> 73's
> 
> John - NE5J
> 
> 
> Johnathon B. Allread
> john.allread@gmail.com
> 469-336-7763
> 
> "The Road to Success is Always Under Construction" - Lily Tomlin
> 
> 
>> On Sun, Oct 6, 2019 at 9:19 AM Mike Bryce <prosolar@sssnet.com> wrote:
>> 
>> gary,
>> 
>> 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
>> obtain
>> 
>> 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
>> www.theheathkitshop.com
>> 
>> 
>> 
>>> 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
>>> 
>>> W0DVN
>>> 
>>>> On Oct 5, 2019, at 10:15 PM, Johnathon Allread <john.allread@gmail.com>
>> wrote:
>>>> 
>>>> 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
>> transformer,
>>>> 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
>> issue
>>>> 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
>> side
>>>> 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
>> on.
>>>> Lastly, If there was an issue with the transformer, where could I
>> purchase
>>>> a replacement?  Thank you!
>>>> 
>>>> 73's
>>>> 
>>>> Johnathon - NE5J
>>>> 
>>>> Johnathon B. Allread
>>>> john.allread@gmail.com
>>>> 469-336-7763
>>>> 
>>>> "The Road to Success is Always Under Construction" - Lily Tomlin
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>>> 
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