dave@VAX1.CC.UAKRON.EDU (David Stoutamire) (01/13/89)
I have in the past noticed quite a few postings concerned
with video and power supply problems on the Mac. I
have a friend with an original (!) (being upgraded)
128K Mac on which I saw the screen slowly fade, shrink and
die. It seems restricted to the video --- the machine
boots and will read disks etc. but just no video. I have
enough experience to replace a component, use a volt meter
and so forth and would dearly love to save my friend some
$$$ here. My questions are:
1) What are the most likely suspects? I have seen
references to bad caps and flyback transformers.
If any articles have been published I would appreciate
being pointed in the right direction.
2) Where can one get schematics for an original Mac?
3) In upgrading (512K, new ROMs, double sided disk)
can a new full capacity drive be added to the external
drive port, ignoring the old internal one? Can
the new ROMs just be placed in the sockets of the old
64K ones? There would seem to be another address pin
needed for 128K.
Responses to any of the above will be appreciated. I have
seem many requests for these questions in the past, so I can
forward answers to anyone else with similar questions.
-= David Stoutamire =-granteri@pnet51.orb.mn.org (Grant Erickson) (10/15/89)
I have a 3 year old Mac Plus which has been having a wavering line problem on the screen for a little over a year now. It has been explained as a bad solder joint. However in the past week another problem has arisen. Every now and again, a loud popping sound is heard from the left side of the Mac (the analog board) and at the same time a BRIGHT white line flashes at a random spot on the screen. This line does not just appear in the Mac video threshhold but spans the entire CRT, including the black area that is always black. Does anyone have an idea what this may be? Please respond E-Mail. I will post it to the net upon request. Grant Erickson ._________________________________________________________. | UUCP: {rosevax, crash, orator}!orbit!pnet51!granteri | | ARPA: crash!orbit!pnet51!granteri@nosc.mil | | INET: granteri@pnet51.cts.com | |---------------------------------------------------------| | The right half of the brain controls the left half | | of the body. This means that only left-handed people | | are in their right mind. | !_________________________________________________________!
des7f@uvacs.cs.Virginia.EDU (David Sappington) (10/17/89)
I have a Mac 512 upgraded to a Plus at home that had a similar problem. First the screen had the "shimmies" a.k.a. waviness that came and went at random intervals. Later the screen degraded to a single bright vertical line running the full height of the screen and blackness elsewhere. Fortunately, there were several messages on the net which described the problem and offered potential fixes. It turned out that a solder joint on the Molex-type plastic contector that connects the analog (vertical) board to the CRT yoke had failed. Reheating the joint solved the problem completely (not even any shimmies!) but I had a relapse about a month later. The same joint was at fault and so a quick fix got me back on my feet. Recently the screen sometimes momentarily displays a bright horizontal line that is often associated with an audible pop. I think that the Molex connector itself is failing but I haven't gotten around to replacing it yet. Hope this helps. Caveat: I'm mostly a software person ... definitely not an EE! Dave Sappington Inst. for Parallel Computation U. of Virginia des7f@virginia.edu