Colecovision PAL power supply fix

hino · April 4, 2021

I couldn't find enough information online about fixing a Colecovision PAL power supply so I decided to share my experience with it. Hope it will be useful to someone.

So my Colecovision wasn't working because it wasn't receiving sufficient power. The 12V and -5V power lines were ok but it only got 4V from the power supply instead of 5V. Most likely an exhausted capacitor. I had to open the power supply to fix it. As you know, the case is clipped and glued so it is not easy to open. I decided to go for the Dremel approach.

Next is the special feature of the PAL model. The whole block is filled with some sort of thermal resin. Probably because it was designed with a 110V power source in mind and they were afraid it would get too hot with a 220V transformer. I don't know.

Anyway the top is almost impossible to remove without destroying everything. Fortunately, with the time the resin became rock solid and all crackled. With some skill you may be able to access the back of the board. Use a hammer and your tiniest screw driver as a chisel to split and detach the resin small piece by small piece. Insert the chisel in the cracks alongside the board. Gently hit it with the hammer. Sometimes rotating the chisel inside the crack is enough to break another fragment. Once all the apparent cracks have been opened use the same method for the remains inserting the chisel between the board and the resin. Be careful and try to maintain the chisel as parallel as possible to avoid scratching the board.

There are two ceramic capacitors that may get damaged during the process. Those are 103z capacitors. The letter Z being the highest tolerance, any 10nF capacitor can be used as a replacement. In my case one was critically damaged. I replaced both of them and also noticed a weak solder joint I hardened.

Before going any further I tested the power supply...

Lucky! The capacitor or the solder joint was the cause of the issue. Maybe the damaged capacitor was already broken before removing the resin.
My initial plan was to follow the 5V power line, try to guess where are the dying capacitors on the other side and add new ones in parallel mode which would have been dodgy. Moreover there is not much space on the back of the board so I would have opted for cms capacitors. I really don't know how it would have ended up so I am very grateful the problem was on the actual backside of the board.

To compensate the resin loss, I added two spot of hot glue on the edges to balance the block so the capacitors don't get squished by the weight of the power supply.

Finally I used sanding sheet to smooth the Dremel cut and some tape to wrap it up.