Mac Plus screen flicker

[danielb]

Hi all,

When I first got my Mac Plus, it had no video at all. The video came back after I hit it vigorously on the left hand side. Since then it has got more and more stable, seemingly on its own.

The only video problem that it still has is that the screen flickers for a few minutes when you turn it on. After a few minutes the flickering goes away and the screen is completely stable.

I have resoldered the two plugs on the analog board, and this didn't seem to make much difference.

Today I opened the machine up and turned it on in a dark room. I couldn't see any obvious arcing. There is however a ticking sound, which seems to come from very low down; possibly from the motherboard.

There has already been a long thread about this on another forum, and I thought I'd bring it here to see if anyone has any ideas.

Here is a video of the flickering:

Note that when the screen appears to go completely black, that is the fault of the camera, not the Mac. This did not happen. It is only the lines at the top of the screen that I am asking about.

Since the screen stabilizes after a few minutes, I would be happy to ignore the problem if I thought it would stay like this, and not get any worse . . .

Thanks,

Daniel

 

[bibilit]

probably a solder gone bad on the analog board.

Look here for something similar:

viewtopic.php?f=7&t=18065

 

[danielb]

All the signs pointed to a bad solder, but I have already done all of the usual suspects, and it doesn't seem to have helped.

One thing is a bit weird - immediately after I did the soldering, the picture was perfect. A couple of days later, it was flickering again.

Of course it is possible that my soldering was not good enough, but I am also wondering whether the culprit may be the power plug on the motherboard, rather than on the analogue board, or whether it might be a grounding problem. Has anyone ever seen this happen?

Thanks,

Daniel

 

[RS232]

I followed the thread that Bibilit quoted and it worked for me. I had the jitters or blank screen on boot up... I had to hit the poor Mac a few times (Someone may report me for Mac abuse here!). Eventually it would be stable after 8 minutes.

I mentioned in that thread I was lazy just reheating the old solder joints which actually made the jittering worse - slamming the side of the Mac Plus no longer worked because of this. Anyway, some fresh solder and soldering joints that would have made my Science teacher proud, my Mac Plus has been 100% fine since! :beige:

 

[danielb]

Thanks for your reply.

I have already resoldered the connectors on the analogue board (J1 and J4?).

It is of course possible that I didn't do it properly. Basically the symptoms before and after were identical.

I NEVER get the blank screen anymore. At first I had to hit it to get a picture. After that it would be very unstable when it stood on top of its external hard disk (an SC 20).

Now however, I always get a screen, but it is unstable (as shown in the video) for the first 5 or 6 minutes. After that it is perfect. Tapping it, operating the floppy drive etc. have no effect on the screen.

These are pictures of my soldering for your amusement:

 

[CC_333]

Hi,

It could be the flyback, because my Mac Plus had an unstable screen (jittering), that would come and go every so often (it was worse when it was cold). Anyway, I left the room for a bit, and when I came back, the place smelled of burnt electronics and the Plus's screen was blank. I sniffed around for the source of the smoke, and it was the poor Plus. I opened it up, and discovered that the flyback had blown, taking with it a transistor. I replaced both, and it works fine now, but it was kind of scary since I thought it was ruined.

Anyway, this story isn't meant to scare anyone; I was just trying to relay some anecdotal information which someone will hopefully find useful.

c

 

[Trash80toHP_Mini]

I've been waiting for this info to re-surface, thanks! I've had one of my three ABs sitting on my bench waiting for these fixes. :approve:

 

[danielb]

Is it worth redoing the flyback solders? Do they ever go bad?

 

[FlyingToaster]

Is this information relevant to the SE's, Classic's? Cold solder flyback? My Classic is messed up with this problem, well I think it is the same kind of issue. I re-soldered the pins for the display plug on the analog board (whole thing was loose) but this didn't change the vibrating screen. I think my SE is starting to do this too..

 

[danielb]

To be honest, I am reluctant to mess with it any more, since it's working perfectly, aside from the unstable screen for the first 5 minutes until it warms up.

For now, I think I will just regard this as a symptom of old age.

It will probably get worse in the future. When that happens I'll attempt to fix it.

Thanks,

Daniel

 

[techknight]

So it gets better when it warms up? Definitely caps. they are gone.

 

[8bitbubsy]

Caps indeed.

Check the DC filtering caps (the big one(s)), also measure the PSU startup-resistors (if any) while you're at it.

 

[FlyingToaster]

I attempted to reflow new solder on my $20 Classic (which I neglected up to this point because it was "broke")

I'm happy to say that the flicker is gone! It looks like a new screen.

Good info here, thanks!

 

[techknight]

My classic starts up out of focus with poor range until it warms up. So i know its time to recap mine, symptom of low HV, caused by low B+

 

[danielb]

Hi all,

I was reading this post :

http://68kmla.org/forums/viewtopic.php?f=9&t=18421&p=175550#p175550

where Dennis suggests that someone's Macintosh TV is not working because the power cord is not properly plugged in.

Since i have long suspected this might be the case with my Mac Plus, and since I knew that the screen flickering was somewhat intermittent, I used as much force as I dared to really mash the plug into the socket.

It has not flickered since.

Is this even remotely possible?

D.

 

[zuiko21]

As far as I know, the Plus' PSU is integrated into the analog board. By inserting the plug real hard, you might have moved and/or flexed the board a bit, probably helping some bad connection. This is compatible with the fact that you had to slap the machine in order to get any video the first time.

 

[danielb]

This is true. I was actually wondering whether there might be a bad connection behind the power socket itself.

But doesn't it also mean that my problem is most likely not a dying capacitor?

 

[sirwiggum]

Sounds like a solder bad connection issue.

But regarding plugs, I once had a desktop PC that was flaky to get up and running. Sometimes it would boot, sometimes it wouldn't.

I changed the lead and it worked perfectly.

So I am not sure if some "kettle" style leads change resistance over their lifetime?

 

[Trash80toHP_Mini]

I've had problems with "Power Cords" as well, it's usually the cord in my experience. I assume you tried several cords before the brute force insertion method? I received a faulty Power Cord for a small AC Adapter in an IDE <-> USB-2 Bridge kit recently and I've had others fail in the past.

ADB Cables with badly shaped or oversize surrounds can be problematic as well, sometimes it's the cable, other times it's poor PCB/Case alignment for recessed connector sockets.

Like the iMacs Dennis mentioned, some other Macs, especially the B&W 17" CRT Studio Display's recessed Power Cord socket, have had power cord/socket alignment problems. Switching cords a/o using the brute force insertion method have always been the answer for me.