[time-nuts] HP58504A antenna
bruce.griffiths at xtra.co.nz
Mon Jul 21 20:46:03 EDT 2008
Jose Manuel wrote:
> Hello all,
> I´d like to repair a HP58504A antenna that don´t deliver any output signal. The current is about 30 mA ( I think too high), and the transistor (unknown type) and the MMIC (uPC2749TB), seems to be with correct voltage.
The resistive voltage divider feeding (from the +5V supply) the Vcc pin
on the MMIC will draw about 15mA by itself plus 6mA for the MMIC is a
total of 21 mA.
The input stage has a total dc resistance of around 421 ohms to the
drain, with 90.5 ohms from the source to ground, should the input
transistor have a drain to source short the input stage current would be
about 9.7mA giving a total of about 30.7mA.
To eliminate the possibility of a drain to source short, the drain to
source voltage of the input device needs to be measured (or inferred
from resistor measurements with the circuit unpowered and by measuring
the voltage drop across the 100 ohm resistor in series with the drain
with the circuit powered - this is unlikely to cause parasitic
oscillations) without causing it to oscillate.
> Does anyone have any experience or data about this antenna?
> I took an inside photo: http://www.ea1px.es/HP58504A.jpg Can the transistor be identified by the color code?
> Thanks in advance, José, EA1PX
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