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Q: Video flicker and vertical lines on mac 6400 ( Answered 3 out of 5 stars,   2 Comments )
Subject: Video flicker and vertical lines on mac 6400
Category: Computers > Hardware
Asked by: arclyte-ga
List Price: $5.00
Posted: 18 Jun 2002 10:24 PDT
Expires: 18 Jul 2002 10:24 PDT
Question ID: 28540
I have an old Powermac 6400 and I can't figure out where it has gone
wrong.  Recently I started getting video flicker and color distortion
(horizontal bars flicker up and down the screen, color is off) and
white vertical bars across the display.  at first i thought it was the
old monitor i had, which i replaced.  still had the problem. so then i
thought it was the video card, which i replaced. still had the
problem.  it's an old machine that's seen it's fair share of days but
i don't want to give up on it because other than this it still works
fine, but neither do i want to spend lots of cash on it or replace
every single part of it before figuring out what's wrong.  i've put in
my best effort to find an answer online. maybe you guys can find me
something (fingers crossed).  I'm looking for someone who's had
similar problems and how they solved it, or even just a hint as to
what else the problem could be.  I'm thinking maybe a cable is dying
or something, but like I said, I don't want to go replacing every
piece without any clue as to what's wrong...
Subject: Re: Video flicker and vertical lines on mac 6400
Answered By: fugitive-ga on 18 Jun 2002 14:00 PDT
Rated:3 out of 5 stars
My 11 year old son and I are long time Mac afficionados. Guy Kawasaki
(author of the Macintosh Way) actually once gave a friend of mine and
I a couple of state of the art (at the time) Performas for originally
introducing him to this new-fangled thing called "the World Wide Web."
I HAVE run across this problem on a vintage 6500 before. Yes, this
would be classified as a "vintage" computer as computer years are like
dog years, i.e., 1 computer year is 7 years of "real" time.

After verifying the monitor was fine, we replaced our monitor out card
and also had the same problem remain. Our conclusion was that either
we got another bad video card (we bought it second hand as a "pull" on
eBay with no guarantees) or there was a logic board problem. Though
we're still not absolutely, positively sure that the second card was
bad, we eventually (and sadly) set aside "the beast" for parts.

For more information, you may want to refer to the actual service
manual for this machine. The best site I know for service manuals for
Macs (personal knowledge) is at:

The specific Service Manual for PowerMac 6400, 6500, Performa 6400,
6410, 6420 is at:

This is the manual used by a Mac hardware specialist in order to solve
 problems, upgrade, etc. It has troubleshooting charts, exploded
views, guides on how to take apart things, etc. It is surprisingly
easy to use for the non-technically savvy, and it is awesome.

In the 6500 Service Manual see:

		Symptom Charts

There are several comments regarding video problems that refer to
problems with the logic board (ouch!). Also some of the
troubleshooting hints refer to zapping the PRAM (I can't remember how
to do it without consulting one of my old Mac Bibles or PowerMac
Secrets books - if you need that information just ask and I'll get it
for you if it exists in my print sources).

The general troubleshooting for NO video says:

1 Check monitor connection.
2 Try known-good monitor.
3 Replace monitor-out card.
4 Remove all DRAM DIMMs and try replacing them one at a time
to test. Replace any bad DIMMs.
5 Replace logic board. Retain customer’s DIMMs.
6 Replace power supply.

These would thus be all the places to look for fixes and indicates
that video problems can be affected by memory chip problems and the
logic board. I still can't figure out why "Retain customer's DIMMs" is
there as it is in almost all of these Mac service manuals. Tech

If you can locate a known working monitor-out card and swap it in to
your machine, that would definitively tell you if it's the logic board
or if the second card is bad also. If it's not the card, 90 percent
chance the logic board is hosed. I KNOW it's unlikely you can find
someone who just happens to have a 6500 who would lend you a good
video card, but that's the problem with "vintage" computers!

The 6500 service manual also refers to an additional section for video
problems you may want to check out:

	Additional Procedures
		6500 Distinguishing Video Jitter ...

Though excellent, such manuals can never detail every problem that
occurs, but this is the best approach I've found yet.

It would be nice to say something like "just turn the little screw
beneath the case 1/4 turn to the left and it'll work perfectly," but
that's unlikely. If you download the service manual (it's about 5 mb
of PDF file) you may find some other possibilities as well.

Good luck and Apple rules!

Clarification of Answer by fugitive-ga on 18 Jun 2002 14:06 PDT
I noticed I kept referring to the "6500" instead of your "6400."
That's a habit because I had a 6500 - however, nothing I said really
changes since the same service manual is used for both, and I would
approach the problem exactly the same way. If you feel the difference
matters, feel free to save your fee "guilt free." fugitive-ga and
Apple STILL rules!

Clarification of Answer by fugitive-ga on 18 Jun 2002 14:11 PDT
... and this is just sloppiness on my part (darn long url's). The
correct URL for the site pointing to ALL available Mac Service Manuals

and that's the LAST time I don't "copy and paste" my URLs. The URL I
posted was missing the final "l."

arclyte-ga rated this answer:3 out of 5 stars
I still haven't solved the problem, but I was certainly given a lot of
information to help me on my way.  I've tried going to different mac
specialist stores and all they give me are blank stares and indirect
answers, so I'm very glad to have an outlet like this to ask all my
dumb questions to :)

Subject: Re: Video flicker and vertical lines on mac 6400
From: chromedome-ga on 18 Jun 2002 12:10 PDT
Has any new equipment come into the immediate vicinity over the last
couple of months?  You may be picking up interference from other

If you haven't gotten anything new lately, and are on good terms with
your neighbors, you may want to check with them.

Good power bars have filtration, of course, and RF chokes can be
purchased from outlets like Radio Shack to go onto your monitor's
video cable, but in some cases physical shielding may be necessary.
Subject: Re: Video flicker and vertical lines on mac 6400
From: arclyte-ga on 23 Jul 2002 10:59 PDT
Any new equipment... Well, my roommate's cable wires for digital cable
run through my room and he just had someone come in to reinstall the
wires recently.  I don't know if it's possible that that's causing
interference. It hasn't caused trouble with any of my other monitors
or computers though. I guess it could be that, as I've tried mostly
everything else. I don't think it's the logic board because the
computer works great other than that, and if the logic board was going
I think I'd start to see other errors crop up as well.  Well, thanks
for all the good info...

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