Thread
Mac Classic Screen 'Wobble' (Caps?)
I turned on my Macintosh Classic after not using it for a few months and I noticed that the screen had some interference lines going through it and now and then appeared to 'wobble' a bit. I'm thinking that the capacitors are starting to go bad, but I wanted to get a second opinion since I'm not particularly knowledgeable about these things. The system still appears to work just fine, but I didn't test it very long as I didn't want to cause any damage (fired up Shufflepuck Cafe for a few min).
If it is the caps, does anyone here offer repair services? I'm in the SE Michigan area. I'm a little gunshy about sending the board out after phreakout disappeared with my SE/30 board, but it would appear I don't have much of a choice.
If it is the caps, does anyone here offer repair services? I'm in the SE Michigan area. I'm a little gunshy about sending the board out after phreakout disappeared with my SE/30 board, but it would appear I don't have much of a choice.
Uniserver is in SE Michigan, and offers re-cap services: http://68kmla.org/forums/viewtopic.php?f=4&t=20193
I suggest you contact him! He has worked wonders on my various logic boards.
I suggest you contact him! He has worked wonders on my various logic boards.
Thanks. Am I right in assuming it's the caps?
Seems that the analog board in the Classic in particular is vulnerable to capacitor issues... This thread documents it somewhat: http://68kmla.org/forums/viewtopic.php?f=7&t=21471
I haven't seen the exact issue you're describing on a Classic though, myself - I do have an SE I'm trying to figure out that has a fuzzy CRT, and when I changed the analog board it started wobbling. From what I've read so far, it could be a power supply issue (caps in there of course), flyback transformer, or analog board caps.
Correct me if I'm wrong, the Classic has the power supply built onto the analog board, right? So the caps there are for the video circuitry and power for the whole machine?
I haven't seen the exact issue you're describing on a Classic though, myself - I do have an SE I'm trying to figure out that has a fuzzy CRT, and when I changed the analog board it started wobbling. From what I've read so far, it could be a power supply issue (caps in there of course), flyback transformer, or analog board caps.
Correct me if I'm wrong, the Classic has the power supply built onto the analog board, right? So the caps there are for the video circuitry and power for the whole machine?
Dumb question. Can I put the Classic motherboard into a SE/30 case (missing its motherboard) or are they completely different connections? That might tell me if it's the motherboard caps or the analog board or power supply.
Unfortunately, they changed the pinout of that connector between the SE/SE30, and the Classic / Classic II. The only functional difference is that sound in the Classics goes through the main connector instead of its own lead, but they changed everything else as well.
I seem to keep referring you to existing threads, I guess that shows the tremendous value this forum represents! Have a look here, the last post in this thread sums it up: http://68kmla.org/forums/viewtopic.php?f=7&t=22306#p217909
I seem to keep referring you to existing threads, I guess that shows the tremendous value this forum represents! Have a look here, the last post in this thread sums it up: http://68kmla.org/forums/viewtopic.php?f=7&t=22306#p217909
Oh well, I thought I could do that as a simple test. I'd hate to send my board out for capping only to find out it's the analog board or the power supply. I guess I'll need to find someone local that I can take the whole thing over to for testing.
If you want it to work your going to want to recapp both. Not much testing can be done with caps, and even if you find one the others will be close to done. It's age and/or use.
Would leaving it on for awhile help the problem or just make it worse?
My Classic had this issue. Uni recapping it fixed the problem. So, it's def. a cap issue.
Was it the caps on the motherboard or on the analog board (or both)?
Uniserver will recap the analog board, too. I think he will need to charge a bit more, but he'll definitely do it.
He redid mine (which was experiencing power issues). Unfortunately, I think there is something else wrong (still having power problems; I think it's a bad potentiometer or transistor in the regulator circuit), but at least the capacitors are good now!
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He redid mine (which was experiencing power issues). Unfortunately, I think there is something else wrong (still having power problems; I think it's a bad potentiometer or transistor in the regulator circuit), but at least the capacitors are good now!
c
I had both done at once, so I couldn't say with any certainty.
I fired it up again and got some more info. In addition to the occasional 'wobble' (which seems to happen when there's a lot of hard drive activity or when windows or apps are opened) there are two very distinct 'interference lines' go across the top (right above the HD icon) and bottom (through the trash can) of the screen. There are other bits of interference, but these two lines are the biggest and are permanent. You can see them in this picture (sorry for the crappy shot):
Does this sound like a cap issue or something else that's going wrong. I'm 99% sure it's the caps, but I want to make sure before I spend money to have it fixed.
Does this sound like a cap issue or something else that's going wrong. I'm 99% sure it's the caps, but I want to make sure before I spend money to have it fixed.
Work all the pots on the back left and right then return them to Orginal spot. See if that clears up your oddity.
Ok I can try that tonight. It's been a while since I've opened up the old Mac, are the pot locations obvious or is there a picture I can look at? What are those pots for?
BTW here's a bigger version of that picture: http://www.atariprotos.com/temp/Mac.jpg
All the important adjustments are behind a snap-off panel on the back. No need to open up the whole machine.
c
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I would say this indicates a power supply issue where the psu is not able to supply enough current and the voltage drops.
Also is there any source of interference / magnetic field near the machine (e.g. large speakers, transmnitter etc)?
Just a thought...
Ok that seems to have fixed it. Can you tell me why that worked? What do those pots control?
Just about everything deflection related...
what happens is humidity/dust, Over the years can cause a potentiometer's internal mechanical connection to lose or interfere with its electrical connection, moving it back and forth mechanically restores a better electrical connection, and in the Classic and Classic II's fixes oddness, (sometimes) 
Also what might be happening, Dust/humidity (COULD be) creating kind of a short, allowing abnormal RF into that specific circuit.
Showing abnormalities on the screen
Also what might be happening, Dust/humidity (COULD be) creating kind of a short, allowing abnormal RF into that specific circuit.
Showing abnormalities on the screen
Anything else I can do to clean it out so this doesn't happen again? Shoot an air duster into the back of it?what happens is humidity/dust, Over the years can cause a potentiometer's internal mechanical connection to lose or interfere with its electrical connection, moving it back and forth mechanically restores a better electrical connection, and in the Classic and Classic II's fixes oddness, (sometimes)
Also what might be happening, Dust/humidity (COULD be) creating kind of a short, allowing abnormal RF into that specific circuit.
Showing abnormalities on the screen
i would use your air compressor and blast the whole thing out.
And then once you've cleaned out the dust and grime, you should probably apply some sort of contact cleaner or lubricant to each of the controls (except maybe the width coil) to help prevent the problem(s) from reoccurring.
Also, if you haven't yet, you should recap it. That will spare you a lot of troubleshooting grief later on (and, given the age of those things, it's inevitable that something will fail.)
I'm glad it's working for now, though.
c
Also, if you haven't yet, you should recap it. That will spare you a lot of troubleshooting grief later on (and, given the age of those things, it's inevitable that something will fail.)
I'm glad it's working for now, though.
c
Are Classics noted for having cap issues? Were they part of the capacitor plague or were they before that?
Well, I don't really know for sure. It just seems like a good idea since many computers of that period are probably going to start showing signs of "capacitor plague" as time moves forward.
c
If you're thinking of the era of electronics that had faulty caps when new, failing at staggering rates (early to mid 2000's), I'd say no - however the vast majority of Macs built in the early 1990s have caps that are failing now.
Plague? I suppose in a way, but these machines have all outlived their planned useful life. Component failure is unfortunate, but not necessarily a sign of faulty design.
Plague? I suppose in a way, but these machines have all outlived their planned useful life. Component failure is unfortunate, but not necessarily a sign of faulty design.
Yeah I was talking about those batches of bad capacitors that found there way into a lot of different computers. I think that started in the mid-late 90's though.
I should get these caps replaced eventually though.
I could have sworn that Cap Epidemic was in the early/mid-2000's. I remember because I have seen some computers from that era (non-Apples) with cap bursting and leak problems.
Dang it, it's still doing it. Looks like I need to get it recapped after all.