[time-nuts] Austron/ Systrom Donner 8181 Time Code Reader
w4ej15 at gmail.com
Sun Apr 23 19:01:44 EDT 2017
Glenn, your calculator comes up with the value I first calculated, around
13k. However, I'm pretty sure the original value may have been 4 times
higher based on the partially visible bands on one of the resistors that
indicates it might have been a 56k. If I use the zener test current in the
data sheet and the max current of the load, I end up with about the same
value the calculator estimates. But if I use a lower value of zener
current and a lower drain from load I end up with a value pretty close to
what may have been in there originally. I was hoping someone on the list
had an 8181 and could look to see or have a diagram. If I use the lower
values then the dissipation of the resistor is within limits but at the
high end. Using 13k ups the power to a one watt device, which I realize
should have been the value in the first place. Worse case I start with 56k
and work down until the circuit is happy again. 73 and thanks!
On Sun, Apr 23, 2017 at 5:50 PM, Artek Manuals <Manuals at artekmanuals.com>
> If you know the Zener voltage and the supply voltage then calculating a
> reasonable value for the series resistor is pretty straight forward
> 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>
>> There is usually a power dissipation reason why a resistor becomes
>>> toast, and the reason is frequently a shorted bypass cap or a shorted
>>> 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
>>> 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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