When an Amiga A570 Repair Took a Strange Turn

I recently bought a faulty Amiga A570 and intended to write a repair blog post about it eventually, but this adventure ended up in a completely different direction: a fault affecting many Amigas in the wild. There is a lot to cover, so, let’s get to it.

The Amiga A570

Put simply, the A570 is a single-speed CD drive for the Amiga 500. It has pretty much everything in it to convert the Amiga 500 into a CDTV, to the extent that it even boots the CDTV ROMs.

There are two variants of the A570, one called the A690 which is a prototype version that seems to have somehow ended up into retail. Estimates show that 500 units of the A690 were made. The final version is the A570 that is more commonly known and it is estimated that 20,000 units were made. More information on the CDTV Land page.

The A570 plugs into the side bus socket on the Amiga 500. You hook the audio from the Amiga into the back of the A570 for passthrough and you plug your speakers into the A570 instead for mixed audio. The Amiga 500 itself doesn’t provide a lot of power on the side slot, so it requires independent power via another Amiga 500 power supply.

Just like the CDTV, there is a slot in the back covered by a plate on the A570 to add SCSI support. I think the connector for this is the same as the CDTV one, but I haven’t really investigated this. There is also a connector inside to add a 2 MB Fast RAM memory module.

The drive itself is made by Matsushita and uses a non-standard interface. It uses caddies to load the CDs in, just like many single-speed drives of the era.

My A570

I bought mine relatively cheaply (for today’s prices) on eBay, the description claimed that nothing came up on video when discs were inserted. There is tape holding the logo badge on, at some point it needs re-gluing. There was no PSU or audio passthrough cable, but that is fine, as I had spares of both.

Testing

I knew that CDTV titles need 1 MB of Chip RAM, so I quickly modified my test motherboard so that expansion RAM is Chip RAM and added a 512 KB board to make 1 MB. I sprayed some contact cleaner on my Amiga’s edge connector and the A570 edge connector. Plugged everything in and the familiar CDTV screen showed up.

I popped in a copy of Xenon II for CDTV (I have an original disc, but it is worth a lot of money, so I’ll use a copy). It “just worked”. Well, that is the end of the repair blog post… Or is it?

Failure of Real Setup

Now that I knew everything worked, I tried to set it up with my Amiga 500 Plus, at the time, set up as a stock machine with 2.05 ROM (compatible with the A570). I wired it all up and just got a black screen. I disconnected the A570 to check, and the Amiga 500 Plus worked fine.

I tried several things to diagnose this, DiagROM (black screen / no boot), testing every pin of the edge connector to make sure there was no damage, etc. All I could determine was that something was causing a bus issue very early on. Then I noticed something.

There were two parts that seemed to have fresher solder than others on the motherboard. I looked back at my blog posts and in 2020 I added RP106 and RP107 to this board. At the time, this was for potential ROM compatibility that others online had mentioned years ago.

I should note that most of the rest of the upgrades on that post are undone now. It has a normal floppy drive, normal 68000 CPU, DF switch is gone and Kickstart 2.05 ROM.

Now, those are pull-ups on the address bus, specifically the lower 16 bits of the bus. My theory is that these were affecting timing or signal integrity. So, I desoldered them. I then set everything up again and the A570 immediately worked!

This explains a lot. I have a GVP A500-HD+ drive and this hasn’t been very stable when connected to this particular machine.

The Bigger Problem

After doing some searches, I found a couple of things:

1. People were quoting this part of my 2020 blog post.
2. Almost every photo I can find of reproduction Amiga 500 Plus boards had these populated.

This potentially means that people who assembled these boards at least second or third-hand got info from my blog post. It also means there are many reproduction boards out there that will likely not work well with devices plugged into the side expansion slot, especially the A570.

I’ll be updating my old blog post, but for now my recommendation is simple: do not install these resistor packs.