Task: Create a Diagnostic ROM Chip for Your Amiga Computer Using a 27C400 EPROM and a TL866 Programmer with Adapter
Needed: 27C400 EPROM, TL866 Programmer, EPROM adapter, Diagnostic ROM file
Time: 30-60 minutes
Introduction
I have previously posted about building a diagnostic cartridge for diagnosing problematic Commodore 64s. A similar solution is available for the Amiga computers in the form of a Diagnostic ROM chip that replaces the Kickstart ROM. Developed by John Hertell (aka Chucky), this is a hardware solution that makes available a battery of diagnostic tests including audio, memory, IRQ/CIA, graphics, ports, drives, and keyboard. If your Amiga will boot with video, you can select these tests from a menu (shown below). If it won’t produce video, you can connect it to your PC using a serial connection and get the same info via a terminal program. I show here how to create your own DiagROM chip using an EPROM.
Instructions
First, you will need the DiagROM file(s) for the EPROM. These are available from the DiagROM download page. I grabbed the 16-bit ROM to burn a single chip for my Amiga 500. You will need two for the 32-bit Amiga 1200 that has two Kickstart ROMs. Also note that you need a special EPROM adapter like this to use in the Kickstart socket for Amiga 500s with Revision 3 and 5 motherboards.
Second, you will need a TL866 programmer. I have previously posted about these devices.
Third, you will need a 27C322/160/800/400 EPROM adapter. I previously posted about this important device.
Fourth, you will need an EPROM. I went with the 27C400 that is commonly used for the 16-bit Amigas. I purchased a set of 5 of these from a Chinese seller on eBay for $50 including taxes and shipping. You can also get these from AliExpress.
Fifth, optionally, you might need a UV light EPROM eraser if your chips come with data on them which is possible. I ordered a cheap Chinese-made EPROM eraser off of Amazon for about $30. However, I did not need it for this project.
Sixth, it is time to assemble the TL866 with the adapter seated to the right toward the lights and the EPROM on top also to the right as shown below. Note the DIP switches are all in the up position as indicated on the GitHub page for the 27C400 EPROMs. Note the position and orientation of the EPROM with the notch facing the lever.
Seventh, it is time to program the EPROM. Note that the TL866 does not natively support these EPROMs which is why the adapter is needed. Instead, we choose the AM27C4096 from the list. Turn off the PIN DETECT and CHECK ID options as the chip we are using will not match what the programmer is looking for. You can check BLANK CHECK if you want to be sure the chip is indeed blank. Now it is time to load the DiagROM file using the FILE menu and then select PROGRAM under the DEVICE menu option at the top. Click PROGRAM to begin. Writing the 512K files takes just a few minutes.
Eighth, replace your Kickstart ROM with your new EPROM. Mine is shown below in my Amiga 500.
Ninth, it is time to boot your Amiga! The screen will flash and, if all goes well, you will arrive at the menu shown above. Below is a successful test of the 1MB of Chip RAM on my Amiga 500.
Comments
The ability to burn ROM chips is a great skill to have. I plan to also create some Kickstart ROMs in a future project. I have an Amiga 500 with a Revision 5 motherboard, and a Kickstart 1.3 ROM I want to upgrade. I have the special adapter on order for that upgrade as it is needed for EPROMs to work on that revision.
As I mentioned above, there is a way to connect the Amiga to your PC using a serial connection to get the same info via a terminal program such as PuTTY. This helps do the diagnosis if your Amiga is not able to output video. I have not tried this as it required a special cable for the serial to USB connection.