modessitt
Volunteer: Encyclopedia Submission Moderator
Otherwise known as a WGM2774.
Anyway, I'm trying to diagnose one that has raster but no picture. You can turnup each color until you get a full screen of that color, but no game picture. Since the signals basically go straight to the neckboard, I swapped the neckboard and got the same problem.
I'm thinking the issue lies with the L550, L551, and L552 that are the only part in each color path between the video input connector and the connector to the neckboard. On the 25", these are straight jumpers, but on the 27" they are populated. Now, the "L" designator would indicate an inductor, but there are 470uf 10v caps in these locations. WG's support site doesn't have a parts list for the 7400, nor show the differences between the 25" and 27" models. I've seen pics online that show these spots populated, but I need someone to look at one (preferably working) and tell me what part (and value) is there. Do you also have caps? Or do you have inductors?
BTW - these parts are right on the edge facing you if you have it mounted horizontally in a cabinet, just to the right of the connector to the neckboard. No need to pull it out of the chassis to check. Just get a flashlight...
Anyway, I'm trying to diagnose one that has raster but no picture. You can turnup each color until you get a full screen of that color, but no game picture. Since the signals basically go straight to the neckboard, I swapped the neckboard and got the same problem.
I'm thinking the issue lies with the L550, L551, and L552 that are the only part in each color path between the video input connector and the connector to the neckboard. On the 25", these are straight jumpers, but on the 27" they are populated. Now, the "L" designator would indicate an inductor, but there are 470uf 10v caps in these locations. WG's support site doesn't have a parts list for the 7400, nor show the differences between the 25" and 27" models. I've seen pics online that show these spots populated, but I need someone to look at one (preferably working) and tell me what part (and value) is there. Do you also have caps? Or do you have inductors?
BTW - these parts are right on the edge facing you if you have it mounted horizontally in a cabinet, just to the right of the connector to the neckboard. No need to pull it out of the chassis to check. Just get a flashlight...