Here's the step by step procedure to speedup Jr to 8mhz:
.
1) Remove the soldered in 8284 and install an 18 pin socket. It is
located just behind the diskette drive next to the crystal. I used
a solder removal tool bought from Radio Shack for $6.95. It is a
modified soldering iron with hollow tip and a bulb for easy removal
of the solder.
.
2) I inserted a new 8284 and made sure that everything worked okay.
.
3) I then built my speed-up: a piggy-backed pair of 8284s in a socket:
.
           LOWER 8284         UPPER 8284
           ----------         ----------
           Pin Number         Pin Number
.
               1 ----------------- 1
               2                   2 NC
               3 ----------------- 3
               4 ----------------- 4
               5 NC                5 TO SOCKET connection for Pin 5
               6 ----------------- 6
               7 ----------------- 7
               8 NC                8 TO SOCKET connection for Pin 8
               9 ----------------- 9
              10 ----------------- 10
              11 ----------------- 11
(Lower 12     12 -----,            12 NOT CONNECTED
 to upper 14) 13      |            13---\/1Kohm/\/--- (to common pin
              14      `----------- 14                  on toggle
              15 ----------------- 15                  switch)
              16                   16---------||-\/500ohm\/-Pin 9
              17                   17-,       XTL           (GRD)
              18 ----------------- 18 |--5pf-||
                                      |
                                      +-\/500ohm\/--Pin 9 (GRD)
Except for pins 5 and 8, lower 8284 was connected to board.
.
Pins 2, 5, 8, 12, 13, 14, 16 and 17 of upper 8284 were bent out.
.
4) Connect the toggle switch as follows:
.
          stacked
          8384's & SOCKET
           +--------+             +---+
    grd    | pin 9  |-----------o-|---|
           |        | 1K ohm      |   |           toggle
   spd swch| pin 13 |/\/\/\/\---o-|   |=======    switch
           |        |             |   |
     +5v   | pin 6  |-----------o-|   |
           +--------+             +---+
.
5) I then plugged the MOD into the socket on the system board and
mounted the toggle switch in a convenient place.
.
Norton Utility SI gave 3.1 with 24 mhz crystal and a V20 processor
running in upper 512k memory of PCjr. SI reports .8 for stock
12 (????) in the PCjr isn't rated at 8mhz. Thats why I switched
(????) note: the 8088 is NOT rated at 8mhz so thats why I switched
to the V20. Be sure and specify an 8mhz V20 when ordering.
.
Suggestions to others:
1. Order 24, 22 and 20 mhz crystals; use fastest one which works
in your machine.
.
2. My memory is all 150ns. 200 ns may be ok too but that as
slow as I would risk it.
.
3. I used wire wrap to connect upper pins 5 and 8 to the socket
pins and clipped lower pins 5 and 8. I then attached this (2 8284'
& SOCKET) to the socket I soldered in the motherboard.
.
Caveats
.
Please note that on some undetermined number of jrs, a beep may
periodically occur when entering data in high speed mode only.
The severity of the problem differs with each machine. I have 3
jrs - 1 no problems, the other 2 have periodic beeps - maybe 3
times per typed page.
.
Also you may not switch speeds while running. Lockup may occur.
It is best to switch then reboot the system in the higher/slower
speed. This is due to bouncing of the switch contacts and may be
corrected with the use of a flip-flop type of circuit to toggle
the speeds. I found the added complexity not worth the effort.
Have fun JRing...  (Special Thax to Tony Copper)
                                            .
                              - Erik Jantzen.

