My Amiga Build Notes

Welcome

These are notes on how I set up my Amigas, written from my own experience rather than as a step-by-step guide. I am not an expert. I am relying on memories of what I did, so some details may be off, and I note what went wrong as well as what worked. I worked by trial and error without keeping a journal, so the order of events is hard to recreate. I follow the procedure I have always used for AmigaOS 3.1, minus the development tools such as AmiBlitz.

Partially modernizing an old computer that has been in storage takes patience, and it is not a cheap hobby. Between replacement ROMs, memory, accelerator cards, repairs and video equipment, the costs add up.

By "custom chips" I mean the original chips made by MOS for Commodore, as opposed to commercially available parts.

My machines

Amiga 1200

This machine has its original Commodore custom chips, except for the Lisa, which I replaced and, as it turned out, did not need to. It has a GVP 1230 Turbo+ 68030 accelerator running at 40 MHz with 32 MB of RAM, a Netgear FA410TX PCMCIA network card, and AmigaOS 3.2.

Amiga 500

This is the machine I have modified myself:

• Individual Computers ACE2B, with an NTSC Agnus (8375) that raises Chip RAM to 2 MB.
• IDE68K and GottaGoFastRAM, which add 8 MB of Autoconfig Fast RAM and an autoboot IDE controller.
• A replacement Denise, because the original was simply a bad chip. It cost me £86, according to my receipt.

Startup tweaks

Put your own additions in S:User-Startup rather than editing S:Startup-Sequence. That keeps the system file clean and makes upgrades easier. Always keep a backup first:

Copy S:User-Startup S:User-Startup.bak

Anything with an icon placed in SYS:WBStartup is launched automatically when Workbench loads.

After installing AmigaOS 3.2, the first job is to copy the LHA utility into the C: drawer. LHA unpacks .lha archives, which is how most Amiga software is distributed. If you run AmigaOS 3.2 under UAE, the easiest way to get LHA (and other files) onto the Amiga is to share a folder from your workstation with UAE. Once shared, the folder appears as a drive in the Amiga, and you can copy files across in either direction.

Networking

I try to support the developers who keep the classic scene alive by buying commercial software, so I use a paid copy of Roadshow with AmigaOS 3.2 and have had no problems with it. Roadshow provides the standard bsdsocket.library interface, so software written for it works as expected. My existing licence carried over from my 3.1 setup.

My Amiga A1200 uses a Netgear FA410TX PCMCIA network card. Alongside Roadshow I installed two archives from Aminet:

• cnetdevice.lha - contains the SANA-II network driver. The Netgear FA410TX (its dongle is marked 100M) is NE2000-compatible, and in my experience it works with this driver.
• CardPatch.lha - fixes memory mapping and interrupt timing bugs that affect PCMCIA cards on the A1200.

Both are .lha archives, so you will need LHA installed first (see Startup tweaks).

Installation steps

1. Copy cnet.device into DEVS:Networks.
2. Copy the CNET interface file into DEVS:NetInterfaces and edit it to contain the line configure=dhcp, so the Amiga gets its address automatically.
3. Copy the CardPatch binary into C:, in the same drawer as AddNetInterface.

Memory and speed

A stock 68020 with 2 MB of Chip RAM was very sluggish for browsing, first with AmiWeb and then with IBrowse. I added a DKB 1202 with 8 MB of memory. With the PCMCIA network card I had to limit it to 4 MB, because of a bug as I recall. I later bought a Great Valley (GVP) 1230 Turbo+ card, a 68030 at 40 MHz, and upgraded it to 32 MB of RAM. That RAM is no longer available.

For a faster A1200 I would suggest looking at the Terriblefire TF1230, a 68030 accelerator with 64 MB of fast RAM and an IDE port. I have not tested it with my PCMCIA network card. Availability varies, so check the maker's site for current stock, and note that a motherboard timing fix is recommended before fitting it.

Replacing ROMs

I bought AmigaOS 3.2 ROM replacements for both machines. The A1200 takes a pair, a HI and a LO chip, and the A500 takes a single ROM. For my NTSC A500 I asked the seller to write its ROM with a force PAL flag, so the machine starts up in PAL mode.

Tools: I use a plastic spudger rather than a ROM puller. I tried a puller once on an EPROM, the kind with a clear window covered by a white sticker, and broke off the pin at the top left on the notch side. I had to solder it back on, and I was lucky that the break was not flush with the chip, so there was enough pin left to work with. The spudger has never damaged a pin for me. I leave the sticker in place, since it covers the window and stops light from erasing the chip.

Video output

I started with an A520 modulator and its RCA output, which I have since put into storage where it belongs. I replaced it with an RGB cable: I bought a cable with solder-tipped ends at a swap meet and fitted a 23-pin connector and a 9-pin RGB connector myself. I used it with an older ViewSonic VS17623, which handles 15 kHz natively and which I still like very much. With that cable the monitor could not change mode. I also had ghosting, which I was told came from the signal not being buffered on my home-made cable.

I then bought a GBS-8200, a cheap board, and gave each machine its own, both version 4. The 8200 came with a cable in the box, so I bought a 23-pin connector and soldered it onto that cable to feed it. It fixed all of those problems. I still use ViewSonic monitors, and I see no screen tearing. My guess, which I have not tested, is that the 8200 does the work of holding sync, so the monitor does not have to.

Cable wiring for a 15 kHz monitor

This is how I wired a cable from the Amiga 23-pin video port (the cable end is a female DB23) to a VGA-style connector. It only works with a monitor that accepts a 15 kHz signal. An ordinary VGA monitor will not show a picture. The Amiga pin numbers match the listing on AllPinouts, which is the reference I started from. This is the wiring that worked for me, so please check it yourself before building your own.

The Amiga DB23F video connector I used.

Grounds matter. Solder wires to Amiga pins 16, 17, 18, 19 and 20, and to VGA pins 5, 6, 7, 8 and 10. Do not connect Amiga pin 13 to them: it is a separate digital ground. Keep stray strands well away from the power pins (21 to 23). To join the grounds you can either:

• twist each set of five together and join them with one solder joint, or
• use a small perfboard as a shared ground rail: pass all ten ground wires through holes in a plastic box (mine was a playing-card box), put them into one row of holes on the perfboard, solder each one into its copper ring, and bridge all ten rings with one line of solder.

Capacitors

The capacitors in my A1200 dated from the 1990s, and I knew it was time to replace them. I had been pushing my luck for some time. One of them had started to leak. It was a small leak, on one of three capacitors near the video DAC and the Lisa chip, and I think it was the one closest to the video DAC. The technician told me that the leaky capacitor was likely causing my video problems because of where it sits. That capacitor was replaced and the trace under it was cleaned.

While chasing those video problems I also replaced the Lisa chip. It turned out to be perfectly fine, and I regret the money I spent on it. I noticed the video trouble as changes in the frequency of the video output, and the picture from my A520 modulator was always poor on my old TV.

My A500 still has its original 1980s capacitors, and they all look good. I do not know why the two machines differ. It may just be luck, or the different parts used in each.

I had some success recapping x86 motherboards myself, where the capacitor legs go through the board. The A1200 uses surface-mount capacitors, which are much harder to do by hand, so I paid someone to replace them.

Links

• Back to top
• Amiga.org
• Aminet
• Retro Rewind (Canada)