What A2000 MoBo can have 1MB chip RAM ?

I just put an 8372A in my good old 2000 and it still works fine but AVAIL says I still have 512k of chip ram...

If there is a jumper to switch around, now is the time to tell me which one it is.

Remember I have MoBo ver 4.4/4.5.

Thank you all!

[Lokki]

This is taken from one of the miscellaneous docs I've been reading, not sure where it's from or who originally wrote it:


Find Jumper J101 located on the lower right side of the power connector CN400, and consists of 3 posts - 2 of the posts are shorted together using a shorting block. Remove the shorting block and move it to the left, towards the power connector. For further info, see Page 13 of the A2000 system schematics - this jumper will enable address line 19 from the 68000 which controls the 1 meg address range.

Locate and cut Jumper pad J500 (to the lower left of the 8520 at U301). This is a 2-pad jumper with a trace connecting the two pads. See Page 9 of the A2000 system schematics - cutting this trace keeps the _EXRAM signal from being tied to ground.

To enable PAL rather than NTSC - locate and cut J102, NOT J201 as suggested in some docs. This is the equivalent of bending pin 41 of Agnes in the A500 mod.

Lokki wrote:
This is taken from one of the miscellaneous docs I've been reading, not sure where it's from or who originally wrote it:


Find Jumper J101 located on the lower right side of the power connector CN400, and consists of 3 posts - 2 of the posts are shorted together using a shorting block. Remove the shorting block and move it to the left, towards the power connector. For further info, see Page 13 of the A2000 system schematics - this jumper will enable address line 19 from the 68000 which controls the 1 meg address range.

Locate and cut Jumper pad J500 (to the lower left of the 8520 at U301). This is a 2-pad jumper with a trace connecting the two pads. See Page 9 of the A2000 system schematics - cutting this trace keeps the _EXRAM signal from being tied to ground.

To enable PAL rather than NTSC - locate and cut J102, NOT J201 as suggested in some docs. This is the equivalent of bending pin 41 of Agnes in the A500 mod.

Lokki you are a savior!

[rkauer]

J101 !?!?!?!?

Is not the J500 (RAM adress)) ?!?!?

[Lokki]

That's what the agnus substitution doc said... I'm not saying it's gospel, it's been too long since I saw inside an A2000. That and I can't find my A2000 schematics, I seem to have misplaced them.
It sounds about right though.

Lokki wrote:
That's what the agnus substitution doc said... I'm not saying it's gospel, it's been too long since I saw inside an A2000. That and I can't find my A2000 schematics, I seem to have misplaced them.
It sounds about right though.

J101 and J500 did it! I have 1MB chip!

Thanx again Lokki!

[Lokki]

No worries mate, good to have confirmation of it too!  :-)

Lokki wrote:
This is taken from one of the miscellaneous docs I've been reading, not sure where it's from or who originally wrote it:


Find Jumper J101 located on the lower right side of the power connector CN400, and consists of 3 posts - 2 of the posts are shorted together using a shorting block. Remove the shorting block and move it to the left, towards the power connector. For further info, see Page 13 of the A2000 system schematics - this jumper will enable address line 19 from the 68000 which controls the 1 meg address range.

Locate and cut Jumper pad J500 (to the lower left of the 8520 at U301). This is a 2-pad jumper with a trace connecting the two pads. See Page 9 of the A2000 system schematics - cutting this trace keeps the _EXRAM signal from being tied to ground.

To enable PAL rather than NTSC - locate and cut J102, NOT J201 as suggested in some docs. This is the equivalent of bending pin 41 of Agnes in the A500 mod.

Just a small update on this old but quite useful post.

On the Rev 6.2 MoBos, the jumper J101 is vertical rather than horizontal on the board. To get 1MB of chip, you have to move the jumper to the higher position that is still towards connector CN400.

[murple]

All but the very first A2000(A) mobos can run 1 MB chip. The old mobos are easily recognized by their DIP (long) Agnus, all newer ones have a PLCC (square) one.

On the off chance any unlucky person has a revision A motherboard A2000, I have one of the 1MB RAM cards that go in the MMU slot (what looks like the CPU slot in real Amiga 2000s). This is of no use in later Amiga 2000s, and was sold to me by a vendor who didnt know that it was only useful in the crappy A2000s.

I'm prepared to give this to anyone in the US for free. I'll send it overseas too, for the cost of shipping.

murple wrote:
... in the crappy A2000s.

I don't share your point of view concerning the A2000.

True enough the Zorro II slots aren't exactly top performance but this machine seems to be built around the legend concerning russian made combat helicopters...

This legend says "first they made bulldozers then they strapped a rotor to it..."

Just like these helicopeters, the A2000 is an incredibly rugged and long lasting workhorse. I like the incredibly tough casing and the totally overscaled power supply.

[Lemmink]

I guess there is a little misunderstanding. The very first versions of the A2000 that were designed in germany are often refered to as well A2000 while the later revisions designed in the US are refered to B2000. The A one are more like a collectable today as there are a lot of compatibility issues plus you only can have 512k ChipRAM unless you put the mentioned card into the MMU-slot. So either 512k chip or no accelerator (thare is a lot of compatibility problems there too)

[murple]

From what I recall (haven't read the info in a while) the A2000 Rev. A is essentially just an A500 motherboard that some German engineers added some Zorro slots to. It may look like an Amiga 2000. It may say Amiga 2000 on the label. It isn't an Amiga 2000 though, but rather is the result of some German engineers who were idiots.

[murple]

Well, guess its more like a 1000 than 500. Quoth David Haynie:

Yes. The original A2000 was designed in Germany. It was based on an integration of the A1000 motherboard design and the example Zorro II backplane from "Schematics and Expansion Specifications", the A1000 hardware manual. It used the thin Agnus, which handled only 512K of DRAM. They added a "Genlock" slot, which was essentially just the 23-bit video signals on an internal connector, and the "MMU" slot, which was essentially just the A1000 external edge connector on an internal slot. The machine shipped with 512K of Fast RAM in this slot, though the case was slow and had some reliability problems. About 60,000 of these machines were made, so I've heard.

[Zac67]

Yes. Since the A2000 - or A2000A - officially: Rev 4.0 - was built based on the A1000 OCS, there's no way to expand it to 1 or even 2 MB chip - other than swapping the board with a later rev.

The A model was designed in Germany and was basically an A1000 plus the Zorro backplane base design. When the better Fat Agnus for the A500 was designed, the guys in West Chester designed a new & improved B2000 (Rev 4.1+) that also featured the Buster (the German A2000 had lots of discreet logic there).

[Kronos]

@Lemmink

I think you got some things wrong here.

The A2000A is pretty much an A1000+Z2-slots, so it allways has only 512K Chip, since thats the maximum the "thin" Agnus can handle.

The RAM in the MMU-Slot is REAL Fast-Mem, not just Slow-Mem as in the later A2000s.

[TjLaZer]

I might have a related problem.  I have a early 2000B machine Rev 4.4.  When I got it, it had Kickstart 1.2 in it and already had 1MB Chip enabled.  Problem is when I try to do PAL screen goes black and video is jumpy.  Switch back to NTSC and it works ok.  So PAL does not work.  What could cause this?  It has a 8372 Agnus.