[TenTec] Troubleshooting Century 21 Power Issue

[Johnathon Allread]

Hi Bob,

The Century 21 has a built in supply circuit.  I am not sure if I could
connect 12VDC to the unit without a bit of modification.  It has a over
current circuit protection.

John - NE5J


Johnathon B. Allread
john.allread at gmail.com
469-336-7763

"The Road to Success is Always Under Construction" - Lily Tomlin


On Sun, Oct 6, 2019 at 9:12 PM Bob McGraw K4TAX <rmcgraw at blomand.net> wrote:

> 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 at 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 at 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 at 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 at 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 at 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 at gmail.com
> >>>> 469-336-7763
> >>>>
> >>>> "The Road to Success is Always Under Construction" - Lily Tomlin
> >>>> _______________________________________________
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