Mac Classic Screen 'Wobble' (Caps?)

[Tempest]

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.

 

[Blinkenlightz]

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.

 

[Tempest]

Thanks. Am I right in assuming it's the caps?

 

[Blinkenlightz]

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?

 

[Tempest]

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.

 

[Blinkenlightz]

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

 

[Tempest]

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.

 

[Macdrone]

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.

 

[Tempest]

Would leaving it on for awhile help the problem or just make it worse?

 

[Paralel]

My Classic had this issue. Uni recapping it fixed the problem. So, it's def. a cap issue.

 

[Tempest]

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)?

 

[CC_333]

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!

c

 

[Paralel]

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)?

I had both done at once, so I couldn't say with any certainty.

 

[Tempest]

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.

 

[uniserver]

Work all the pots on the back left and right then return them to Orginal spot. See if that clears up your oddity.

 

[Tempest]

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

 

[CC_333]

All the important adjustments are behind a snap-off panel on the back. No need to open up the whole machine.

c

 

[genie_mac]

which seems to happen when there's a lot of hard drive activity

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...

 

[Tempest]

Work all the pots on the back left and right then return them to Orginal spot. See if that clears up your oddity.

Ok that seems to have fixed it. Can you tell me why that worked? What do those pots control?