A1200 + ACA1230 + Timing fix = blinking red screen

leonk · May 22nd 2019

I recently acquired an Amiga A1200. It was given to me with a (what the seller told me) brand new, never used, still sealed in the box, ACA1230 accelerator. I don't doubt that given how new it looks.

The Accelerator has an amigakit sticker on it with quality control passed from 7/1/11. The CPU is an MC68EC030RP25B There is 1 socket missing a chip, and the battery holder is missing a battery. I Can provide pictures. There is a Kick3.0 jumper spot, but the jumper is not set. The amiga 1200 is a rev 2B and has official kickstart 3.1

I am proficient at populating PCBs (including SMD, FPGA, etc. type of solder work under my microscope) so I decided to follow instructions I found online to try and see what timing fixes I can do to resolve this issue.

Attempt 1) Remove E123C and then E125C - no change (E121C and E122C were missing)

Attempt 2) Follow instructions found here (ianstedman.co.uk):

- populated E121C and E122C with 27pf

- replace E121R and E122R with the recommended ferrite beads

- E123R/E125R no change - 27R already fitted from factory

- E125C add 22pF cap - no change - RED blinking

- E123C add 22pF cap - no change - still blinking RED

At this point I don't know what else to try? Is it possible this ACA1230 accelerator is damaged?? Suggestions?

Jens · May 22nd 2019

First of all, make sure that the A1200 works without the accelerator. "red screen" and blinking LED means that "something" works (=CPU executes code and can talk to the main board), but there may be a contact problem between the board and the accelerator, or between the CPU and the socket (the old ACA1230 does use sockets).

Given that the accelerator is populated with an 68EC030-25 CPU, It is most likely that it was shipped with it, and that the logic clocks it at 28MHz synchronous to the A1200 main board. However, many people tried to clock it to 56MHz, which was also available, but at twice the price back then. You may just be looking at a failed attempt to re-install the CPU; if you remove it from the socket, are all pins in perfect order? If you look into the pins of the socket, does each and every contact have the golden spring-insert? This should be easily visible under a microscope if you have access to such equipment.

The easier inspection is of course to take a look into the 150-pin connector

leonk · May 22nd 2019

Jens .. thanks for your prompt reply. The A1200 works great without the accelerator. I've verified it using a test program running on the Gotek.

UPDATE: I purchased AmigaOS 3.1.4 for the 1200, burned the 2 EPROMs, and now it boots perfectly fine!! SysInfo, Workbench, and bunch of games and demos.. everything just works like a dream!!!

The 3.1.0 chips I have seem to have Amiga official stickers on them. Any reason why an ACA1230 not work with 3.1.0 but fine with 3.1.4?? Also, do I need to install any software for this accelerator? There's a 3.5" floppy in the box. Or should I just leave it be and enjoy as is?

Jens · May 23rd 2019

The ACA1230 has quite a few options that you can switch on/off with the ACAtune tool:

http://wiki.icomp.de/wiki/ACAtune

We dropped most of them for the later accelerators, because you can break more than you can gain. The one thing you should do is to activate MapROM, as that will speed up operation considerably.