ian@inmet (01/31/89)
Two flickering horizontal lines recently appeared on my Mac 512KE's screen about an inch from the top and bottom. The move up and down slightly and sometimes even go away. Is my power supply going bad? Help?! ================================================================================ Ian Dowell ian@inmet.inmet.com Intermetrics, Inc. uunet!inmet!ian
mattp@oakhill.UUCP (Matt Pressly) (02/02/89)
In article <127200056@inmet> ian@inmet writes: > >Two flickering horizontal lines recently appeared on my Mac 512KE's >screen about an inch from the top and bottom. The move up and down >slightly and sometimes even go away. Is my power supply going >bad? Help?! I had a similar problem for about 4 months until my screen finally collapsed one day to a thin vertical line. The technicians said that the flickering on the edges is due to the power supply getting ready to fail. I read in some back issues of MacTutor (unfortunately after I had already had the power supply board replaced) that there are several solder joints on the power supply board which tend to heat up enough to cause the solder to melt and freeze back later, leaving bad solder joints. The primary ones which are to be suspect are the ones to which the wires feeding the CRT are attached -- should be a white/clear plastic connector either soldered to the PS board or wires feeding that connector soldered to the PS board. Examine these joints carefully to see if they look bad. Even if they look okay, it's a good idea to touch them with a soldering iron and maybe add a little solder to ensure a good connection. In order to get at the board, you will need to remove a thin cardboard backing which is on the back of the power supply board. Be careful not to touch the CRT while you are inside the Mac. It would be a good idea to do this as soon as possible, because if you continue to use the Mac in this state, you may end up blowing some components later, but since it is still working now, you can probably prevent that from happening. If you don't feel confident about doing this yourself, find a technician at school or work that'll do it for you. It'll only take about 10 minutes, and it can save you roughly $130 or more for a new PS board, since Apple technicians in general refuse to do any trouble shooting and just swap boards instead. The reason the joints get so hot during operation of the Mac is that a very high voltage is required for the CRT. The connector between the CRT and the power supply board has enough resistance, because of the relatively poor contact within the connector, to cause a tremendous amount of power dissipation in the connector. The heat conducts down the wire to the solder joints holding the wires to the PS boards. Some people have said that inside their Macs the plastic housing on the connector has been totally melted. As the Mac is used more and more, the solder joint gets hotter and hotter because of the additional resistance which results from the joint getting a little bad in the first place, so the problem escalates itself. For more information on this, look in some old issues of MacTutor (around 1986 or earlier, I think) in the section at the front where people write in with problems/solutions. There are several issues which contain a discussion of this problem. One person who was a technician said, if I remember correctly, that out of 10 PS boards he had examined, all of them had crystalline (i.e. bad) solder joints at that connector. I tried this on a friend's Mac that had similar symptoms to mine, it it fixed it. I hope it works for you. One more suggestion is that after you get this problem eradicated, put a fan in your Macintosh. You can get a small piezoelectric fan for ~$40, and it will greatly prolong the life of your computer. According to some stuff I learned in a Fault Tolerant Computing class, for every 10 degrees centigrade rise in temperature, the mean time between failure for a computer doubles. I would imagine that a fan would reduce the temperature by more than 10 deg centigrade. I hope this helps and saves you some money, but be careful soldering, and be careful around the CRT. You can get a tremendous shock from the CRT, and it is easy to poke a hole in it with the case open. As long as you are careful, however, you should have no problems. Also, don't heat up the solder joints too much or to long (only a few seconds) or you can cause the trace to be lifted from the board. If you don't have a long handled Torx screwdriver, you can get one from Snap-On Tools, or you can use a hex allen wrench to get the easily accessible screws on the Mac case and you can file down one of those 8" long thin pieces of metal that you can find in the gutters on the sides of streets (they are blades that fall off of street sweepers, and you can find one about every 30' on the roadside) to get at the screws inside the handle. There are also one or two screws hidden inside the battery holder on the back of the Mac, so you'll need to pop out the battery to get to those. Good luck, Matthew Pressly -- address: oakhill!godiva!mattp@cs.utexas.edu