|
Content created by Sandy. Edited by Major Tom.
Overclocking is, err... bad, especially for PS/2 and PS/55 machines. What we
expect from them is stable operation and reliability. So, it is not recommended
to replace the CPU clock oscillator with a faster one. IBM really didn't not
account for clock modifications. Therefore it's probably better to keep your
MCA box "stock". But I was MAD, so here we go...
Japanese Type 1 "J" with 25 MHz oscillator for 61-W0 will take a 30 MHz one
without any trouble. But all other complexes will not work with faster
oscillator in place of the originally equipped one (to be more precise, it is
possible to use 35 MHz oscillator in place of the 33 MHz one for some
complexes). If you change the base clock, you need to modify the BIOS as well,
in most cases. Without BIOS modification, system will hung up during POST with
error code 102.
I didn't (well actually I still don't) have any knowledge of how to read or
write BIOS. Mr. Sugiura, one of my friends, who knows about BIOS
reading/writing, examined BIOS of the 5561-W1x complex and he modified the BIOS so that the 61-W could boot without the
102 error. According to him, there are several lines
indicating jump to the 102 error section during the POST routine. He couldn't
determine which line exactly was triggering the error with the modified system
clock. So he rewrote all lines that were jumping to the 102 error section. I
don't know if his modification includes any bugs or not. But, so far, BIOS ROM
with his modification works fine. At least in my systems. He kindly examined
another models' BIOS ROM and burnt new EPROMs for me, and for other members of
the forum.
List of models and complexes modified by Mr. Sugiura:
| Model |
Original Oscillator |
Replacement Oscillator |
CPU Clock (before/after) |
BIOS ROM Type |
| 5551-N |
66.66 MHz |
84 MHz |
33 to 42 MHz |
PROM (write once) |
| 5551-W0 |
40.00 MHz |
60 MHz |
20 to 30 MHz |
PROM (write once) |
| 5561-W1/W2 |
50.00 MHz |
62 MHz |
25 to 32 MHz |
EPROM |
| 5580-Y |
33.33 MHz |
40 MHz |
33 to 40 MHz |
EPROM |
| Type-A Upgrade |
66.66 MHz |
80 MHz |
33 to 40 MHz |
EPROM |
| Type-B Upgrade |
66.66 MHz |
80 MHz |
33 to 40 MHz |
EPROM |
More of this story is available HERE.
|