A2000 Rev 6 motherboard differences

[Robbie]

Hi there,
I've got a couple of Revision 6 A2000 motherboards and while looking at them earlier I noticed a significant difference, and I was wondering if the experts here could explain it; just because it intrigued me really.

It's the section just to the right of the ROM, on one board there appears to be some kind of hack maybe? Seems strange to me but both boards work normally and have the same specifications afaik...

Let me know if you have any ideas

[Oldsmobile_Mike]

Hi, your picture links aren't working.  If you click on the "Manage attachments" button under "Additional Options" when making your post, it will allow you to attach pictures directly to your post.  Might want to try that!  

[giZmo350]

Pics load OK here Mike....  Hmmmm.
Anyways, what is that little board stuck on there with... gum?
That's weird... I can't imagine what that is. Are there some components on the underside of that? How is it electrically connected? That's a stumper!

[zipper]

As there were about 6 different versions no wonder - the latter is v6.2 AFAIK. Former 6.0 (ROM Tower)?

[mechy]

As there were about 6 different versions no wonder - the latter is v6.2 AFAIK. Former 6.0 (ROM Tower)?

latest board was 6.4. thats definately not a rom tower. Does it have some pals on it or 74ls components?
never seen a tower on the 2000 like that,especially 6x board.

[QuikSanz]

There must be a way to read whats happening there when it boots, it must add something.

Chris

[magnetic]

Rev 6 a2000 boards dont have "Rom towers"

[Oldsmobile_Mike]

Ah, now the pictures are loading for me.  I have seen that exact same thing before, in another A2000.  And I asked the exact same question.  And damned if I can't remember what the answer was.    But if it helps any, it's not unique to just your A2000!

[danbeaver]

When the pictures loaded for me, this was at the bottom:

http://imgg.mgid.com/1284/1284790_vb.jpg

Is that a Fat vs Skinny Agnus?

I also used to own an A2000 with that modification and it worked fine.

[guest11527]

It's the section just to the right of the ROM, on one board there appears to be some kind of hack maybe?

That's a factory-installed hardware hack. For one batch of A2000 boards, CBM ordered the wrong memory type and had to come up with an additional fix to make this memory usable for the machine. If you desolder the RAMs (chip RAM) and replace it by the proper type, this tower can go and can be replaced by the simple bus drivers that are usually in its place. It was CBM with all its glory...

[Robbie]

Ah, should have known it was a commodore goof.

Thanks for solving that mystery

[tommywiz]

I realize this is an old post.  I thought I was very familiar with A2000 motherboards, until now. This description appears to describe a motherboard I recently received. A strange looking upside down circuit board to the right of the kickstart rom, socket labelled  HN62402.  If you are looking at the board with the battery at the bottom.

Did you ever figure this out for sure? I did read the previous post.

[Castellen]

Yes, see my response in this separate thread:
https://forum.amiga.org/index.php?topic=75191.0

I doubt if it was actually a case of "CBM ordering the wrong memory type" as suggested in this thread; more likely there was a supply or cost issue with the usual DRAMs qualified for the design, and this was a short term solution to allow use of an alternative DRAM part.