128 won't go to 64 mode.

[128user]

I have a 128 that recently developed a problem.  When I try to get into 64 mode it won,t.  When I type GO64 and it asks do I want to  I type yes but it won't.  Also when I hold the Commodore key down at start it will not go into 64 mode..  Anyone have any idea what is wrong?  Thanks.

128user

[RobertB]

When I type GO64 and it asks do I want to  I type yes but it won't.

You're supposed to type Y (for yes).

Also when I hold the Commodore key down at start it will not go into 64 mode..  Anyone have any idea what is wrong?

Sounds like kernal problems to me.

             Back from Las Vegas,
             Robert Bernardo
             Fresno Commodore User Group
             http://videocam.net.au/fcug
             The Other Group of Amigoids
             http://www.calweb.com/~rabel1/
             Southern California Commodore & Amiga Network
             http://www.sccaners.org

[Hydrophilic]

It sounds like something is wrong with your equipment.  It is a very simple software procedure to switch to C64 mode... because you are having problems, I can only guess you have defective hardware... MMU or PLA problems seem most likely to me...

[128user]

When it asked if I wanted to go to 64 mode I do type Y.  Thanks for your reply.

Tom B.

[LokalHorst]

I already gave the tip to re-seat the ROM-chip U32 in your first thread with the same question:
http://www.commodore128.org/index.php?topic=3481.0

I doubt that the MMU is faulty because it would affect the native mode also.
For anyone being able to give further tips, we need more info regarding what happens after the go64 or reset with CBM-key held down. 'Doesn't work' leaves us guessing.

[128user]

When I try to go to 64 mode by typing Go64 and I answer "Y" the screen freezes and the keyboard does not respond.  When I hold the Commodore key down at power up
I get a blank screen and again the keyboard does not respond.  This all done in 40 column screen

128User

[Hydrophilic]

That is bad!  It sounds like the PLA, MMU or maybe C64 ROM is defective.  None of these are standard parts, but ROM is not to hard to aquire...

Anyway, here is a quick test.  In C128 mode, enter the following...

Code Select Expand


MONITOR
(you get CPU info... just ignore... continue to enter...)
.1300 SEI
.1301 LDA #00
.1303 STA $FF00
.1306 LDA #$F7
.1308 STA $D505
.130B LDA #$E7
.130D STA $01
.130F INC $D020
.1312 JMP $130F
.1315

G 1300

The first part is a BASIC command (MONITOR) which drops you into the Machine Language Monitor.  The next 9 lines are a tiny machine language program.  The last line executes the ML program you just typed.  This works in VICE and on a real C128.

On a good machine, the main (40-column) screen will be unchanged but the border should start flashing colors in a regular pattern.

If the border starts flashing colors, then it seems the MMU and PLA are okay, and maybe only ROM is defective (also be sure you have no cartridge attached).  But if border does not flash with consistant pattern, then MMU or PLA is not correctly setting C64 mode.

[128user]

Thanks for the tip.  I tried the program  and the border flashed horizontal lines of color.
So I have a bad rom.  I have to find  the bad rom.  Thanks again for the tip.

Tom B.

[128user]

There is joy in Erieville.  The problem was in the ROM in U32.  I forgot to say that I had
Jiffydos installed.  I swaped it out for the old ROM and it works like a charm.  Thanks for all the help.  Much appreciated.

Tom B.