[time-nuts] Austron/ Systrom Donner 8181 Time Code Reader

[Glenn Little WB4UIV]

Here is a calculator to determine the resistor value.

<http://www.calculatoredge.com/electronics/zener.htm>

You will probably have to provide an external supply, at the zener 
voltage, to know what the current draw is for the calculator.

You might find that the original resistor value was too low or the zener 
wattage was too low for the circuit draw.

You might also find a leaky filter capacitor down stream causing the 
current to be too high.
There may be a leaky filter capacitor up stream causing the zener to 
draw too much current as the peak voltage may have exceeded the original 
calculations.

73
Glenn


On 4/23/2017 2:31 PM, Dave Wood wrote:
> Bill, actually what happened is the zener diode that the resistor fed
> shorted and that's the reason it burned up.  I have two units with this
> issue and I cannot read the resistor value since it burned up.  What I
> would love to know is what the original value of the dropping resistor
> was?  73  Dave
>
> On Sat, Apr 22, 2017 at 11:39 PM, Bill Hawkins <bill.iaxs at pobox.com> wrote:
>
>> There is usually a power dissipation reason why a resistor becomes
>> toast, and the reason is frequently a shorted bypass cap or a shorted
>> device.
>>
>> Have you measured the resistance to ground of the end of the resistor
>> opposite the power supply?
>>
>> Sometimes inputs get high voltages and short the amplifying device.
>>
>> Sometimes that is reason the units were for sale.
>>
>> Hope I'm wrong.
>>
>> Bill Hawkins
>>
>>
>> -----Original Message-----
>> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Dave
>> Wood
>> Sent: Saturday, April 22, 2017 8:43 PM
>>
>> Anyone on the list own the above Time Code Readesr.  I have one of each,
>> they are identical with the same issue.  I need to identify the correct
>> value of a resistor in the power supply that provides 27 volts to the
>> input amp.  They are both toast in my units and I do not have a manual.
>> Thanks in advance!  Dave _______________________________________________
>>
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-- 
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Glenn Little                ARRL Technical Specialist   QCWA  LM 28417
Amateur Callsign:  WB4UIV            wb4uiv at arrl.net    AMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)  USSVI LM   NRA LM   SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
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