Changing TOS v1.2 to 1.4 on a Mega ST.

[+DarkLord]

Hey gang. I know that somewhere out there is information on changing

a Mega ST with TOS 1.2 and the 2 chip set to TOS 1.4 and the 6 chip

set. Google is being decidely unfriendly and uncooperative about revealing

such info...

 

Anyone have a link with English instructions and pictures? I know you have

to change some jumpers (W3 and W2 seem to come to mind) but I need

to know which ones for sure.

 

Thanks.

[+poobah]

ROM    W2     W3    W4      U12
----   ---    ---   ---     ---
256k   1-2    1-2   jumper  no use
1Mx2   2-3    2-3   open    use
1Mx6   2-3    2-3   jumper  no use

U12 is a 74LS11

W3 is A15, W2 is A16, 1-2 is pulled hi, 2-3 is connect to bus
W4 bypasses U12 when not installed

[+DarkLord]

ROM    W2     W3    W4      U12
----   ---    ---   ---     ---
256k   1-2    1-2   jumper  no use
1Mx2   2-3    2-3   open    use
1Mx6   2-3    2-3   jumper  no use

U12 is a 74LS11

W3 is A15, W2 is A16, 1-2 is pulled hi, 2-3 is connect to bus
W4 bypasses U12 when not installed

 

Okay, thanks for that. Any chance you have a link to the page that used to walk through it

with pictures? I seem to recall some website like that.

[+poobah]

ROM    W2     W3    W4      U12
----   ---    ---   ---     ---
256k   1-2    1-2   jumper  no use
1Mx2   2-3    2-3   open    use
1Mx6   2-3    2-3   jumper  no use

U12 is a 74LS11

W3 is A15, W2 is A16, 1-2 is pulled hi, 2-3 is connect to bus
W4 bypasses U12 when not installed

 

Okay, thanks for that. Any chance you have a link to the page that used to walk through it

with pictures? I seem to recall some website like that.

 

Alas no, I took that info off my schematics and out of my head.

[krupkaj]

Okay, thanks for that. Any chance you have a link to the page that used to walk through it

with pictures? I seem to recall some website like that.

I think it was on the DoItST and DoItFacon. Unfortunately these pages are offline for some time...

[+Guitarman]

Here's what the jumpers look like on a 1040ST. They look the same on the Mega. I have done 2-3 Mega rom switches and it's very easy.

 

[+DarkLord]

Okay, thanks everyone - I'll prob take the info given and try it

tomorrow before work.

[+poobah]

This is a picture of the jumpers in my Mega 2.

 

View is from the right front of the motherboard looking at the left front corner.

 

It currently has Rainbow TOS, 6 Chip version.

 

[+DarkLord]

Thank you!

[tjlazer]

[+DarkLord]

Sweeeeet! Thank you all again.

[+DarkLord]

Okay, I gave this a shot and it looks like I've done something wrong...

 

When booting up, it gets as far as when the floppy drive access light

first comes on...as soon as the disk is read, it 2 bombs.

 

A couple of things - there were resistors (1 black band) at W2 and W3.

I replaced these with straight wire (both of the resistors were mounted

right down to the body and I had to cut them to remove them). Could

that be the problem? I also put a straight wire at W4. U12 looked to

be already open - there was no 74LS11 that I could see - wasn't that

supposed to be there for the 2 chip version?

 

Thanks.

[+poobah]

Okay, I gave this a shot and it looks like I've done something wrong...

 

When booting up, it gets as far as when the floppy drive access light

first comes on...as soon as the disk is read, it 2 bombs.

 

A couple of things - there were resistors (1 black band) at W2 and W3.

I replaced these with straight wire (both of the resistors were mounted

right down to the body and I had to cut them to remove them). Could

that be the problem? I also put a straight wire at W4. U12 looked to

be already open - there was no 74LS11 that I could see - wasn't that

supposed to be there for the 2 chip version?

 

Thanks.

those are the famous "0 ohm resistors". straight wire is fine

there should have been a 74LS11.

 

if the floppy lights up, your roms are working. (they told the floppy to do so!)

something else might be amiss.

[+DarkLord]

those are the famous "0 ohm resistors". straight wire is fine

there should have been a 74LS11.

if the floppy lights up, your roms are working. (they told the floppy to do so!)

something else might be amiss.

 

Okay, pic is still blurry, but I'm gonna try to show what I did by drawing on it.

 

 

Perhaps you can show me where the 74LS11 is supposed to be? Thanks.

 

Also, the 6 TOS 1.4 ROMS read:

 

RAINBOW (TOS 1.4) RAINBOW (TOS 1.4)

C300790-002 L2 C300787-002 H2

© ATARI CORP. © ATARI CORP.

 

RAINBOW (TOS 1.4) RAINBOW (TOS 1.4)

C300791-002 L1 C300788-002 H1

© ATARI CORP. © ATARI CORP.

 

RAINBOW (TOS 1.4) RAINBOW (TOS 1.4)

C300792-002 L0 C300789-002 H0

© ATARI CORP. © ATARI CORP.

 

How can I tell if they are 256k or the 1mb variety?

 

Thanks much.

[+poobah]

The 74LS11 is immediately to the right of the circle you have labeled "W4".

It needs to be disabled.

 

Snip the power pin (yellow arrow in the pic).

If you ever want to un-do it, solder a wire from the snipped pin to the bypass cap (blue arrows in pic)

 

See closeup (looking from the TOS roms towards the front of the board.)

 

Looks much more barbaric than I remember

 

[+DarkLord]

Okay, got it - thanks to all who contributed to this thread.

 

I finally found the 74LS11 - doh, was right under my eyes.

Admittedly, I've got a very bad habit of overlooking the obvious

and overthinking things.

 

After cutting the power pin to the74LS11, all is well, the machine

is booting up with TOS 1.4, and we're good to go.

 

Thanks to everyone again!