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I’m trying to resurrect a Craigslist Amiga A1000. After replacing Paula it now boots. Several basics still missing (RF shields, screws, port covers, etc.) but essential electronics are okay.

However, I would like to add the 256 KB RAM expansion but I haven't been able to locate one. I have been able to recreate much of the schematic for much of the A1050 (thanks to Raffzahn for excellent information), but not sure of 2 things - 1) capacitors, and 2) the black blob:

  1. My guess is 8 the capacitors are 220 nF but don't know about the other one (c9?). I think they are connected between 5 V and GND?
  2. The blob maybe a 39 Ω resistor pack to buffer the address lines? Or?

Any insights/thoughts/facts appreciated.

Front of board: Front of board

Back of board: Back of board Source: http://amiga.resource.cx/exp/a1050

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  • Have you measured it?
    – Omar and Lorraine
    May 19, 2021 at 8:58
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    The capacitors are probably decoupling capacitors, right? So do you really need to replace them like for like?
    – Omar and Lorraine
    May 19, 2021 at 9:00
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    Can you post the schematics that you've created?
    – Alex Hajnal
    May 19, 2021 at 10:36
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    Based on the photos I've seen I'd concur with your take on things. The caps all appear the same and wired the same (VCC to GND). One photo I saw had the label 224 on one of them, i.e. 220nF. The "black blob" is probably 8×39Ω 5% resistors wired straight across (pin 1-16, 2-15, 3-14, 4-13, 5-12, 6-11, 7-10, 8-9).
    – Alex Hajnal
    May 19, 2021 at 12:23
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    @OmarL I think TOD is trying to recreate the board without having physical access to an original board.
    – Alex Hajnal
    May 19, 2021 at 12:32

1 Answer 1

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Finally designed and built an Amiga A1050 knockoff. Seems to work well on my Amiga 1000.

Schematic, PCB and BOM is posted on github https://github.com/TheOrangeStrain/Amiga-A1050-RAM-Expansion

The answers to my question are:

  • The black blob is indeed a 39 ohm resistor pack
  • C1-C8 are 0.22 uf capacitors
  • C9 is a 10 uf capacitor

Thank you to those who gave me feedback and input here. It is truly appreciated.

Enjoy, TOD

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    The linked project is excellent and I'm sure anyone wanting to know this will end up going there. It's the norm here for answers to be able to stand alone, so I took the liberty of editing in the answers to the question.
    – Wayne Conrad
    Jul 29, 2021 at 15:25

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