Challenges installing 3.1 rom in A500 rev6A

[james666]

I've spent a frustrating couple of hours trying to install a 3.1 rom in an A500. After swapping out the old (working) 1.3 rom, I got a black screen and flashing power LED. I messed around taking it in and out, checking the contacts etc, but no joy. It's a rev 6A board so it shouldn't need any pins wired together etc.

I then tried the rom in another A500 and it worked fine. This second machine was also a rev 6A, albeit an older one shipped with OCS Agnus. I wanted KS 3.1 for the first machine because I'd just fixed the jumpers to enable 1 meg of chip ram and I planned to install this internal IDE adaptor / fast ram card so I could run WHDLoad.

I remembered reading somewhere that A500 EPROMs are very sensitive to resistances on the CPU address and data lines and that it may be necessary to install additional resistor packs. It occurred to me that the IDE adaptor might be enough to swing the balance. I put the KS3.1 back into the first machine, plugged the IDE / ram into the CPU socket and, lo, it works perfectly! Has anyone else seen this issue? Seems the tolerances are very fine on these old machines, even with nominally identical board revisions.

[PascalDe73]

Hi,

Strange... I have 6 Time Amiga500 Rev.6A ECS AGNUS 8372A (PAL) with a standard CPU 68000 (7Mhz).

All of my A500 have a dual Kickstart ROM 1.3/3.1 from Sordan.

All worked like a charm... directly after the Kickstart ROM SWAP.

[r.cade]

I have a very finicky Rev5. I even have the adapter board with added resistor packs and even that doesn't always work. It's really odd. It may just be a dodgy ROM (original 1.3 masked ROM, even).

[james666]

Interesting. I would have guessed that the rev 5 boards would be a bit more particular but didn't expect any problems with 6A. Based on Pascal's experience I might just have been unlucky.

[PascalDe73]

Hi,
Here is The Link for The dual Kickstart Rom

https://sordan.ie/product/550/dual-d...2000-switcher/

[SkulleateR]

Kick 3.1 works out of the box with Rev6A ... I would suspect the kickstart socket to be the culprit

[james666]

Originally Posted by SkulleateR

Kick 3.1 works out of the box with Rev6A ... I would suspect the kickstart socket to be the culprit

That was my guess too, but it worked fine when I replaced the original 1.3 rom.

[Elmo Putney]

Kickstart 1.3 is 256KB vs 512KB for 3.1, so you might be missing the higher address line signal to switch to the upper 256KB : A17 pin1 (I think).

[dag]

You need adapter like this

[SkulleateR]

Originally Posted by dag

You need adapter like this

He´s got a Rev 6A so no need for an adapter ...

[Elmo Putney]

Originally Posted by Elmo Putney

Kickstart 1.3 is 256KB vs 512KB for 3.1, so you might be missing the higher address line signal to switch to the upper 256KB : A17 pin1 (I think).

For clarity I was not suggesting the machine does not have the circuitry to address A17, just that a fault somewhere on the A17 address line could cause this behaviour.

So if I was checking continuity/solderjoints/socket....thats as good as any place to check first.

[james666]

Thanks, I'll look at that next time I take it apart. It's working OK now - but only when the CDTV-RAM-IDE board is plugged in. I've just read that this board actually supports autobooting from an unmodified KS1.3 rom, so I'll have to check that out at some point.