Repair C128D
22 June 2021
Vectrex white dot fix and no buzz mod
3 September 2021
This console occasionally started to show blue tinted screens but with a little flick or moving the cable (where connected to the console) it returned to normal.
Well, the cable was immediately blamed, but with both RGB and composite cables the result was the same, so the problem didn't seem like the cable.
Then, when the console only showed the screen on this tone, the problem was examined.
From the symptom found, the red color seems to be missing and once I opened the console I cleaned and checked the connector and its soldering, but nothing to do and since the signal is missing both on the composite and on the RGB the problem must get upstream.
First I started to check the capacitors affected by the video circuit, but they were all good, going up we find IC21 which is the RGB encoder and for safety I add a little tin on the pins so as to avoid that they were false contacts, but the problem was not there.
Going even further back we find IC14 which produces the video signal ..
On this chip we find all the RGB signals and I start to check them all, and look in the photo below what I find ..
From the photo we see little but pin 82 is slightly raised and does not make good contact with the pad and if we check the diagram we see that this pin is the Red of the video signal !.
At this point, off with the soldering iron and add a bit of solder on the pins that seem only to be supported.
At the end of the rewelding here is the result!
Fortunately, the problem with the console was just that, but sometimes you get discouraged when you start looking for the fault and find nothing. The problem was not clearly visible because the pins are very small (even if in the enlarged photo it seems evident) and to check it I had to move the pins with tweezers to check if they were soldered or not.
