[aprssig] RC-D710 APRS display head on an old IC-2AT HT

Stephen H. Smith wa8lmf2 at aol.com
Wed Sep 24 18:58:24 CDT 2008

Robert Bruninga wrote:
> Hummh...
> It doesn't work.  The RC-D710 display head draws about 50 mA for
> about 1 sec and shuts down (running on a 1 amp bench supply).
> But it works fine when powered from the 10v in the PG-5J
> interface.  I have it apart and there is NOTHING in there, but a
> 10v 3 terminal regulator chip with only 47 uF on the output.
> Im stumped.  It must not like the power somehow.  It begins to
> pwer up and then decides not to complete the evolution...
> Bob

I just had this experience last night with a digital TV converter box.  
This box, an "AirLink 101" that was only $10.00 at Fry's Electronics 
after the Federal $40 converter box coupon, is powered an external 12 
VDC switch-mode wall wart instead of having the usual  built-in AC supply.

The box has exactly the same size coax power jack as a KPC3 tnc.    I 
thought, when I got the unit, "this is great -- I can run this box off 
my 12VDC hamshack battery plant and use my 19" Samsung monitor (wjhich 
can also run off 12 VDC) to have a complete digital TV that can run on 
emergency power".    

I was curious what the current draw was at 12 VDCso I connected the 
converter box to an old Heathkit regulated current-limited bench supply. 
The box would start to boot (These devices are essentially DSPs driven 
by dedicated computers and go through an involved boot sequence before 
the picture appears) and then shut down. 

It turned out the unit has an initial inrush current of  about 1.2 amps 
before dropping back to about 450mA.  Once I set the current limiting on 
the Heath supply to 1.5A, it booted and ran perfectly.   

I wonder if the Kenwood head has a similar startup inrush surge that is 
dumping your supply......


Stephen H. Smith    wa8lmf (at) aol.com
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