6,400 CHANNELS FOR YOUR PRO-2004 SCANNER

                     by Bob Parnass, AJ9S

Chicagoan Denny Beringer sent in a few sheets he picked up at Dayton
describing a modification to expand the memory in the Radio Shack PRO-2004
scanner from 300 to 6,400 channels.

   The new circuitry adds 3 ICs, a 7 segment readout, a ribbon cable, a
pushbutton switch, and a few resistors and capacitors.

   First, diode D510 is added which expands the scanner from 300  to  400
channels. Then, IC504, the stock memory memory IC (a uPD446G), is removed and
replaced by a  ribbon cable leading to an added printed circuit board. The
additional board contains an HM62256 32Kx8 static RAM IC, which holds 16
groups of 400 channels each.  (note: if you don't do diode D510, I think
you'll get 4800 channels, though I haven't tried any of this. I heard that the
400 channel mod makes the markings on the 2004 keyboard incorrect.  WA2ISE)

   A pushbutton switch, attached to a 4060 CMOS 14 bit binary counter IC,
selects one of the 16 groups.  The 4 counter output leads are used to select
the high order 4 bits of the HM62256.  The new group select pushbutton switch
is mounted on the front panel, in place of the headphone jack.

   How can you tell which group you are in?  A specially programmed  EPROM
(type 2716, 2532, or 2732) is addressed by the ouput of the counter.  The
EPROM output is connected to a 7 segment LED readout, mounted in place of the
Sound Squelch pushbutton.  The readout indicates groups 0, 1, 2, 3, 4, 5, 6,
7, 8, 9, A, B, C, D, E, and F.

   [Note: If I were to expand the memory in my PRO-2004,  I would use just the
new HM62256 memory IC and a BCD switch instead of the pushbutton.  This would
eliminate two of the three ICs, and the 7 segment readout.  Sorry, I cannot
provide further information, nor a reference, as the sheets sent to me
contained no name or address. - Bob
   Parnass] Bob Parnass AJ9S