Need help fixing Amiga 2000 - San Diego

[Tavis]

Hey all,

I think I either fried my mega chip 2000 or my angus chip and I have no way of finding out without a spare angus to put on the main board to test.

Anyone in San Diego area who can help me look at this or support me in some other way?

I logic probed the board and tested traces etc a couple years ago extensively and then just shelved it but I’d like to pull it back out and try to fix it. Pretty sure I had a clock and I also remember testing the crystal. I think I got it all the way down to the culprit being either the megachip (bummer) or the angus. Problem is the angus in the megachip is 2MB version so I can’t just pull it out and put it on the main board. I do have an original Amiga as well but I don’t think I can put that angus in the 2000 either if my memory is correct.

Hope someone can help out.

Thanks

-Tavis

[Vypr]

What board version do you have?
You should be able to use the Agnus chip from your 500 as they used the same ones. Your MegaChip probably has an 8375 which is not pin compatible with the 8372 the A500 and A2000 used.
If you use an 8372 from a 500 you should at least get 1Mb Chip RAM.
Note that earleir model A2000s used the 8371, same as early A500 models but again, ti is pin compatible but it will show 512Kb Chip RAM and 512Kb Fast RAM

[Tavis]

Originally Posted by Vypr

What board version do you have?
You should be able to use the Agnus chip from your 500 as they used the same ones. Your MegaChip probably has an 8375 which is not pin compatible with the 8372 the A500 and A2000 used.
If you use an 8372 from a 500 you should at least get 1Mb Chip RAM.
Note that earleir model A2000s used the 8371, same as early A500 models but again, ti is pin compatible but it will show 512Kb Chip RAM and 512Kb Fast RAM

I will get them out and check the board versions.
The MegaChip has an 8375 (318069-11) i thought it won't work in the main logic board because it is the 2MB one. Or something like that.

my notes from 2019 say:

"Screen goes from dark gray to light gray but does not display
Workbench prompt. Most probable causes are:

• 8520 U7 Odd CIA (U300 A-2000)

• 8364 U3 Paula (U200 A-2000)

• EM1 1301 1 ohm resistor (R 309 Rev. 6A/7 boards: R200 A-2000)

• 8370 - 8372/8375 U2 Fat Agnus (U101 A-2000)

• 74LS32 U37 (chip select) U302 A-2000)

• U2 socket "

I remember going over the whole board with a logic probe and scope and i think i found a clock on a bunch of chips and narrowed it down to it must be the megachip of agnus.

[Zippy Zapp]

I had a similar problem but for me it turned out to be the socket pins on the MegaChip that connected to the A2000. Those things are very easy to break and it seems sitting in storage and getting moved around a lot for mine was all it took.

I had a spare A500 board so I just took the Agnus from that (8372 in mine) and plugged it into the A2000 and problem solved except for losing the 2MB Chip. I saved the 8375 just in case I ever decided to put it in a different MegaChip or a clone.

So if you have an A500 remove the Agnus and plug it in to your A2000 to rule that out...

[Tavis]

Thank you guys so much for the info. I am just now revisiting this page. Life keeps getting in the way. I am hoping to drag my A500 and 2000 out and put on the workbench and see if I can make some headway ASAP. Hopefully this week.

[Tavis]

Hey guys,

so my other amiga must be a 1000. It does not have a square type agnus chip It has a DIP 8361R3

the amiga 2000 has a 318069-11 that was plugged into the megachip ram expansion. i put it directly on the main logic board and not luck. but i figured its not compatible. What chip can I get top bring this back to stock and put in the FAT LADY socket?

[Jope]

The Agnus from the megachip is not compatible with your machine directly, the megachip is needed. The pinout is subtly different, hope the Agnus survived.

Your motherboard is directly compatible with a 8370 (NTSC), 8371 (PAL) or 8372A (switchable) Agnus.

[Tavis]

Originally Posted by Jope

The Agnus from the megachip is not compatible with your machine directly, the megachip is needed. The pinout is subtly different, hope the Agnus survived.

Your motherboard is directly compatible with a 8370 (NTSC), 8371 (PAL) or 8372A (switchable) Agnus.

Yes, i know. I need to rule out the megachip so i need an Agnus for a USA NTSC amiga 2000.

There's several versions. Do you know which one I should hunt down?

[Tavis]

Originally Posted by Tavis

Yes, i know. I need to rule out the megachip so i need an Agnus for a USA NTSC amiga 2000.

There's several versions. Do you know which one I should hunt down?

OK 8370(a) thanks. I need to find one.

[Tavis]

Your motherboard is directly compatible with a 8370 (NTSC), 8371 (PAL) or 8372A (switchable) Agnus.[/QUOTE]

Will this work? https://www.ebay.com/itm/28465571317...3ABFBMirbsxutf

[Jope]

Yes, it will work. That is a PAL Agnus though and will be locked into 50Hz mode, so your display must be able to sync down that low. I hear this is not always the case in USA.

[Tavis]

Originally Posted by Jope

Yes, it will work. That is a PAL Agnus though and will be locked into 50Hz mode, so your display must be able to sync down that low. I hear this is not always the case in USA.

Oh shoot. Ya I need ntsc