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[bbond007]

Originally Posted by CodeHunter

How hard is it? I just got 4 A500s (one of them in great condition, but with 1.2 and the rest in really bad shape, but working and on Kickstart 1.3)
http://www.freemansgarage.com/stuff/P1010006.JPG

You could just swap the motherboard

The tin cover is not for dissipation of heat from what I recall. I believe its purpose is to block the RF noise the motherboard produces which can interfere with old school TV reception. With digital TV and cable, I doubt running without the RF shield will pose any problems.

I'm not an electrical engineer (I don't even play one on TV) and could be wrong, so if an airplane lands on your house, your wife can't watch Oprah or the FCC shows up at your door...

[ognix]

Originally Posted by tone007

I think that's only for 2.0 or higher ROMs.

Hello!
I investigated...

At the moment I didn't test what I'm going to say "for real" but the in theory this is what should be done to use K1.2 on 1.3 motherboards (rev.6a/7) or 2.04 motherboards (rev.8 - A500+) and vice versa (KS 1.3/2.04/3.1 on old rev.5 motherboards).

First of all one clarification (implicit above):
- A500 motherboard rev.5 (mounted KS 1.2 - OCS)
- A500 motherboard rev.6a/7 (mounted KS 1.3 - OCS/ECS 1MB Agnus)
- A500+ motherboard rev.8 (mounted KS 2.04 - ECS 2MB Agnus)

These are what I found here in Italy/Europe, in my personal experience (and not only).

By seeing the schematics (ROM related part can be seen below), in the rev.5 motherboards pin 31 of Kickstart ROM 1.2 is A17 (address 17), while on rev.6/7a ones pin 31 is connected to Vcc, while A17 is located on pin 1.
The same applies to rev.8 motherboards if you pay attention that these motherboards were designed with 1MB Kickstart in mind, so the ROM socket is not 40 pin (for "normal" 256kB/512K ROM) but 42 pin.
In fact numeration reported is referred to a 42 pin socket, but if you place the ROM from the 2nd pin (as printed on the motherboard), pin 2 becomes pin 1 of the ROM, so is the same numeration as rev.6/7a motherboards.
Hope I did not create confusion... re-read carefully with image...

So at the end:
- if you want to use KS 1.3/2.04/3.1 on old rev.5 motherboards you have to rewire pin 1 of the ROM to pin 31 of the socket, and put Vcc (5V) on pin 31 of the ROM (maybe some kohm resistor is not a bad idea, to limit current).

- if you want to use KS 1.2 on rev.6a/7/8 motherboards you have to rewire pin 31 of the ROM to pin 1.

Both modifications could be done with some wires and by bending pins (maybe better if you bend pins from a further socket in between) or creating a proper simple PCB (more work, of course).
In the past (I don't know now) Kickstart switchers provided jumpers for this purpose (but I don't know if they were done for working in all motherboard revisions with ALL Kickstarts, specifically 1.2).

Hope I clarified the thing completely.
If there are mistakes or imperfections let me know, but with precise references (eg. schematics).
I'm especially waiting comments from alexh and Cosmos, who are very competent on this arguments, from what I've read in their posts.

BTW, I'm NOT responsible for any damages to your motherboard, ok?!
Bear in mind that for doing this you need to have at least some basic skills of electronics.

Little tech note for novices:
A0-A17 address bus: addresses 2^18 (0-17) locations = 262144 = 256kB
A0-A18 address bus: addresses 2^19 (0-18) locations = 524288 = 512kB
A0-A19 address bus: addresses 2^20 (0-19) locations = 1048576 = 1MB

BY!

P.S. The schematics are available at the end of A500 user manuals (here pics are small, sorry - I don't know how to place bigger images; maybe a better account...)

[ognix]

Originally Posted by CodeHunter

Hello all,
I am tempted to open one of those bad shaped ones (well I already did!) and remove its 1.3 Kickstart ROM and replace it with my good A500's 1.2.

Follow my tech advices in the previous post: I think that just swapping KS won't work (depending on motherboard revision).
But nothing bad should happen, just black screen.
Ask for someone techy to help.

Originally Posted by CodeHunter

The thing is, I am not sure which chip is the real kickstart on A500. do you have a picture of motherboard which clearly shows it?

UPDATE 1: OK I found this image. Which one is the Kickstart ROM chip?
http://www.freemansgarage.com/stuff/P1010006.JPG

As other people stated, in this Amiga you have a Kickstart switcher: to change Kickstart keep pressed left (or right) mouse button at switch on.

The Kickstart ROM itself is normally located in the left part of the motherboard more or less centrally, right to big microprocessor MC68000 (where the flat cable of switcher starts from, in you picture).

Apparently the motherboard pictured is an old rev.5 (since the number of chips for 512kB of RAM).

Don't worry about the metallic shield: it's "just" for FCC RF noise (you should place some very electrically noisy stuff to get real problems).

Originally Posted by CodeHunter

Oh, and is 1.3 THE most compatible Kickstart, or should I stay with my 1.2 on my A500?

KS 1.2 is the way to go if you want to play many pre-1989 games.

BY!

[psxphill]

Originally Posted by ognix

So at the end:
- if you want to use KS 1.3/2.04/3.1 on old rev.5 motherboards you have to rewire pin 1 of the ROM to pin 31 of the socket, and put Vcc (5V) on pin 31 of the ROM (maybe some kohm resistor is not a bad idea, to limit current).

- if you want to use KS 1.2 on rev.6a/7/8 motherboards you have to rewire pin 31 of the ROM to pin 1.

Kickstart 1.3 is 256k, the same as kickstart 1.2. So you don't have to do anything special to upgrade. You should also be able to put a kickstart 1.2 chip straight onto a rev 6/7/8 motherboard without doing anything.

The problem was caused by commodore receiving incorrect information when designing the motherboards for 512k rom chips, which meant one of the address lines was wired to the wrong pin. You can fix it either on the motherboard or the rom. The official kickstart chips came with a wire connecting pin 1 to 31.


My revision 5 a500 shipped with kickstart 1.3 and it requires the pin 1 to 31 mod to work with 2.04 or 3.1