How to upgrade an U1496E into U1496E+
=====================================

Yes!   after  one night of testing, I finally succeded into upgrading a
U1496E into a PLUS MODEL!!  I have no replaced the 68000-12 and I'm now
using  it  at  20mhz  since  3 days now and it works perfectly and it's
still  cold!  (the modem is powered on 24 hrs/days on the third line of
my BBS).
 
The  modem  now  flies  at  "CONNECT 19200/ARQ/V42b" with an average of
2300-2350 cps on compressed files!!

Here is the istruction for the upgrade, as you can see is very SIMPLE!
======================================================================

First  of  all,  you  can do the upgrade ONLY on motherboard with this
revision :

PN 45-000009-REV-B (or lower, but at least 0000009)

YOU  CANNOT  UPGRADE a PN 45-000009-REV-B2 (or higher I suppose), since
this  new  version  lacks of the sandwitch-motherboard mounted over the
crystal  oscillator.   If  you try to modify this review the modem will
get mad :-(.  This motherboard uses two new VLSI chips (dated 1992) and
I think they are different for the normal and plus models :(

BTW,  altough  I  have  tried  to modify only a PN 45-000009-REV-B, the
upgrade  should  be OK also for other lower REVs, but your modem should
have  the  sandwitch-motherboard over the crystal oscillator and should
have a jumper called (CK20M) on the left (or right) of the 68000.

What you need for the upgrade:
==============================

n.1 resistance of 10ohm
n.1 condenser of 20pF
n.1 chip 74F74 or 74AS74 (DO NOT USE 74LS74, since they are too slow for
    a 40mhz clock and they will not work!!! You are advised :)
n.1 14 pin socket
n.1 pair of 6.00 or higher EPROMs for U1496E+

Here is the scheme of the ZyXEL U1496E motherboard
==================================================


        +-------------+  J  +---------------+
        |     U23     |  P  |      U22      |
        +-------------+  1  +---------------+

      +---------------+   +---------------+
      | EPROM U25     |   | EPROM U24     |
      +---------------+   +---------------+

 JP2    +---------------------------------+
  |     |            68000-12             +
 C97    +---------------------------------+
  |
 L3
  |
 +-+
 | | U41
 | |
 +-+


 - Open the ZyXEL :)
 - Cut JP1 (it should be labeled CK13M)
 - Close JP2 (it should be labeled CK20M) This way the 68000 will get the 
   20mhz clock!
 - Insert the 20pF condenser in C97
 - Insert the 10ohm resistance in L3
 - Insert a socket in U41 and above it a 74F74 or 74AS74
 - Put away the old EPROMs from U22 and U23
 - Insert into U23 and U22 the new pair of EPROMs

 - CONGRATULATIONS!!! You now have a U1496E+ !!!

 - Close the ZyXEL
 - Power  it  on keeping pressed the DATA/VOICE botton, this way the modem
   will  reset  and  self-test.   If  you  hear the usual handshake noise,
   everything is OK!  Load you favorite terminal program and type "AT&T8",
   if  you  get  a  "CONNECT  19200/ARQ/V42b" and the alphabet chars, then
   EVERYTHING WORKS great!!

As  said  above, you don't need to replace the 68000-12 with a 68000-16
as  used  into the PLUS models, since it still works great and I really
think  that  the  price for the 68000's is so low that the manufactures
produce  only  a  single  68000  and then they labeled it as 68000-8 or
68000-12  or  68000-16, but the CHIP is the same!!  Infact my 68000-12,
now overclocked at 20mhz is cold as before!

OK... let do it and let me know if everything is OK!

I have already modified the 4 ZyXEL's and they run 19200bps without any
problems!!

Remember me when you will go at 19200bps :))

Ciao!
                                                   Sky Luke
                                          (skyluke@skylink.sublink.org)