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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