rrw@naucse.UUCP (Robert Wier) (12/23/88)
From time to time I have noted discussions on the power supply
problems of the Mac+. Mine has now developed the symptoms
of an intermittant expansion/contraction along the horizontal
display axis. Occasionally the horizontal drive will collapse
completely and I'll just have a (bright) vertical line.
When I pound on the case, the video comes back, so it sure looks
like there is a bad solder joint somewhere. I looked at the
analog board closely, but couldn't spot any obvious problems,
nor were the electrolytic caps at the "top" of the board
obviously bad. So I just swabbed as many connections as I could
conveniently get to with tuner cleaner, reinstalled the board,
and powered up. It looked good for about a week, but things are
now deteriorating again. Could someone who has successfully treated
this tell me *where* your bad solder joint was? Is there a
particulary suspect connection somewhere? Also is it true that
authorized mac service shops will not exchange, but will only
replace, mac analog boards that have been obviously worked on,
regardless of how minor in nature ( a persistant rumor here ).
My mac+ is now about 4 years old, and I'm thinking I would like
to keep it going until I find out if there really is going to
be an SE/30 in 1st Q,89.
Any suggestions gratefully received...
-Bob Wier at Flagstaff, Arizona Northern Arizona University
College of Engineering *usual disclaimers*
NAU Box 15600 ...arizona!naucse!rrw
Flagstaff, Az. BITNET: WIER@NAUVAX
86011 602-523-2052
(note: Bitnet node NAUVAX may not be
known yet to all stations)
College Motto: "The highest level of engineering in the Southwest
(7,000 feet)"grg@berlin.acss.umn.edu (George Gonzalez) (12/28/88)
I've fixed a Mac that had this same problem. The basic problem is that the components, wires and connectors in the horizontal deflection circuit are a bit on the weak side. This circuit has to carry several amps of current, and some of the components break down under the strain. The one I saw failed in the yoke connector. This is a white plastic connector that connects the deflection yoke (around the neck of the CRT) to the top area of the analog board. Unplug this connector and inspect both halves closely. Is it deformed, brown or yellow colored in spots? Are the wires ok, or does the insulation look slightly melted near the connector? Do the flimsly metal connector pins look burnt or heavily tarnished? Is the connector very warm or even HOT to the touch? These are signs that the connector has been overheating. This causes the connector pins to tarnish even faster, leading to a poorer electrical connection, leading to more heat, ... and eventual failure. Also look at the connector half that is on the analog board. Excess heat on this half can cause the solder to remelt and form a bubble over the connector pin. The connection *looks* perfect from the outside. It fooled me for a few minutes. But if you check for continuity with an ohmmeter, you may find *no* continuity through this perfect looking solder joint. There are varying levels of solution to this problem: (1) Have the analog board replaced by a dealer. This will "fix" the problem, but cost you many $$$. I don't know for sure, but I assume that newer analog boards have sturdier connectors. Apple is surely smart enough to have discovered and fixed this problem themselves. (2) If you are handy, you can replace the connector yourself. Try using a sturdier connector. Most auto shops sell very hardy "trailer hitch" connectors for under $4. ---- Other things that can go wrong in this area include: Other solder joints in this circuit can go *bubble up*. Trace the printed circuit lines from the connector and try reheating the solder joints. A capacitor in this circuit can overheat from the strain and fail. These will often discolor as a clue. Replace these with a sturdier array, say 2 capacitors of 1/2 the value each in parallel. The flyback xformer may fail, especially in very old Macs. These are identifiable by a bad smell, a cracked case. If you are *very* handy at soldering, you can replace this too. Replacements are available from MCM Electronics (513) 434-6959 for $33 each. These weaknesses in the Mac are annoying, but at least their remedy is often inexpensive. --- Important Notes: Don't try any of these steps unless you know all the proper safety precautions. You can damage yourself and your Mac if you don't know how to protect each other. You *must* know how to safely discharge high voltage capacitors and CRT's. You *must* have a static-free environment, and a GROUNDED soldering iron. A $6 ungrounded iron from RS can easily and instantly blow your analog or Mac logic board. I destroyed a $500 car stereo this way.