This post is a collection of notes I made during the recap and repair of an Amiga 600 I bought on Swedish eBay. If nothing else, it contains a useful collection of links where I gained a lot of information on recapping and repairing the Amiga 600. The unit I bought looked to be in good condition, but suffered from a black screen according to the seller. It had not been recapped, and these units are infamous to have leaky capacitors. If these capacitors are not replaced, they will leak and corrode nearby components.
The disassembly of the machine is rather straightforward. Remove the screws from the bottom, open the case, and remove a couple of screws from the mainboard. Use a screwdriver to gently pry up the joystick ports from the case. Remove the screws next to the ports holding the machine to the RF shielding.
At first glance, my unit looked ok only with minor corrosion around the U12 Sony video encoder chip. I did a quick first recap just to see if there was some further issue with the machine. Then, I put it in the dishwasher to get rid of any corrosive fluids. The process went ok, but the video output lacked blue and green color (only red was presence) and RF + composite was not working. I learned a lot about the machine by reading on forums and checking schematics (see: http://amiga.serveftp.net/Schematics/A600_schematics/), and I spent a week or so to do continuity tests to see what could cause the missing blue and green colors. During this step it was also helpful to check Google images of certain parts of the board (examples: http://theamigamuseum.com/wp-content/uploads/2016/09/A600-mainboard.jpg, https://bigbookofamigahardware.com/bboah/media/download_photos/a600mb_rev15_6.jpg), or zoom in on images taken with my own phone.
However, I soon realized that a lot of components around U12 was somewhat corroded and the legs on this component were white-ish. This made it a bit difficult to use the multimeter for tracing as I did not know if the problem was a broken trace or the presence of corrosion on a component. So I did some more reading and decided to “rebuild” the area around U12, to further futureproof the machine.
Amiga 600 recap
During the change of capacitors I found a few useful links with capacitor maps of the different mainboards of the machine. My version was 1.5. Here you can find a useful map over capacitors:
My biggest problem during this process was pads that were lifted when I removed the capacitors. Luckily, I was always able to trace the lines from the pads and find nearby solder points to use instead. The Amiga 600 mostly uses SMD capacitors, in combination with a few through hole-caps. Sometimes the space you have to position your soldering iron is very limited. I used through-hole caps where appropriate to gain some space and wiggle room during this step. The two capacitors near the keyboard connector was one such example. Many people first remove the keyboard connector to be able to solder a couple of SMD:s here, but I did not have to perform this step since I used through hole caps here.
Amiga 600 video fix
As aforementioned, the area around the U12 encoder chip suffered from corrosion, including the Z221 and Z222 band pass filter and delay line. These components (shaped as silver squares) are difficult if not impossible to purchase today (read more here: https://www.lemonamiga.com/forum/viewtopic.php?t=17554). A remedy for this information is to replace the U12 encoder chip with a newer version, which enable you to bypass these components: the CXA2075M chip.
Essentially, you remove the old U12 (use a heatgun if you own one, I managed to do it with a lot of flux and a soldering iron). Then, you snip leg 8+9 on the new chip, bridge the connection beneath them, solder the new chip in place, and place a resistor between pin 12+17. The instructions on this page: (https://www.ikod.se/cxa2075m/) says to use a 2.61k ohm resistor for the Amiga 1200, but another advice is to use a 2.2k ohm resistor for the Amiga 600 (see, https://8bitshardway.blogspot.com/2020/08/fixing-video-on-my-amiga-600-after.html). I went with the 2.2k ohm resistor and it worked just fine.
During this step I also replaced the nearby transistors.
Overall I am quite happy with the results. I learned a lot during this process. If I would do something different next time, it would be to be more careful while removing the capacitors: I had a bit to many broken traces, but everything worked out fine in the end.
Additional images (non-recapped mainboard):
