Monday, July 19, 2010

SuperSprint Repair - Pt 5 - Flyback replacement

Yea!! The replacement flyback for my K4900 monitor arrived from ArcadeCup today, and tonight I may get to see my SuperSprint's face for the first time in almost 10 years! First, I begin by getting all my tools and parts together.

Fig 1 - Chassis and new flyback.

Desoldering the old flyback is a tedious process involving lots of time, patience, and soldering wick. The posts are fairly large solder joints, so braid was a little slow. Here is where I really wish I had a solder sucker.

Fig 2 & 3 - Old flyback removed from chassis.

Taking the old flyback out took forever, but installing the new one took just a few minutes. The trickiest part is holding it still until you can get a few colder connections in place. To simplify that, I press the flyback into position and use a pair of hemostats to grip the legs and hold it tight to the circuit board. One connect on each side, and you can remove the hemostats. Since the legs are all in a circle, and the flyback is large, the next 8 connections are quick and easy.

Fig 4 - Brand new flyback in place

With everything in place, it's time to give her a test run. At first, she displays a very nice playfield, a little out of focus, small, and washed out but otherwise colored correctly. A few degrees on the focus pot, and she looks better. Suddenly, the screen goes pure bright green with horizontal lines every 1" or so. I shut her down and check all connections but find nothing amiss.

Second try is a repeat of the first. Starts out normal, goes green, and then after awhile, the screen goes dark for about 60 seconds and comes back with a definite blue tint.

Fig 5 & 6 - Blue shrunken screen
Note: Circular "waves" are a camera artifact.

Checking B+ at TP91 reveals it's only 100VDC and Fromm's points to the voltage regulator. This is a new regulator, but it's a slightly different part number (STR381 vs STR380). Not having another STR380, I decide to try the original. Bad move. She blew the main fuse immediately on power up. After replacing the main fuse and STR381, she no longer has a picture or heater glow. To make matters worse, while testing various voltages I see a ribbon of smoke and smell R503 overheating. I shut her down, and find the HOT is shorted. Man I hope it's just the HOT and VR IC.

Tomorrow I'll call Zannen again and order another VR and HOT...