Strange Classic II CRT Problem

[shifuimam]

Back story:

Classic II I found in a dumpster a few years ago. Recently thought I was going to gut it and use the case for a separate project, so I cannibalized the four power supply wires between the CRT and the analog board for a much-needed SE/30 repair. The same weekend, my boyfriend decided he wanted the Classic II to play around with, so we soldered on new power supply wires with a molex connector in between.

Now:

The machine boots and chimes. However, the display is messed up in a way I haven't seen before:



The image does not flicker or move. It's just a static image that looks like that. There's a little fraying of the copper mess around the end of the tube, but that's about it. No caps or resistors on the analog board and CRT board look visibly damaged, leaking, burnt, or otherwise malfunctioning. That being said, it's entirely possible (and likely, even) that something needs to be replaced.

Has anyone seen this before?

[techknight]

it looks as if the tank circuit capacitor, C16 i think? cant recall.... had failed on the analog board, its in the same circuit as the horizontal peaking coil. Regardless, i would resolder the yoke connector, and other various points on the analog board, and double-check your rewiring job.

[shifuimam]

Thanks for the tips! We will try this and report back...

[PowerPup]

When you sit and look at it, that picture actually looks pretty cool. Like some form of wavy energy beam, folding and bending and stuff.
I'm going to (at least temporarily) make it my desktop pic. See if I like it there.

Anyway, good luck on the repairs!

[tomlee59]

You seem to have sufficient horizontal deflection, but vertical deflection is wonky. I'm not sure I fully understand the history you provided -- are all the components from the Classic II, or is there now a hybrid of SE/30 and Classic II bits? The reason I ask is that the deflection yoke (the assembly that sits around the neck of the CRT), to which the four "power supply" wires (they're actually the horizontal and vertical deflection signals), is a very different beast in the Classic II, from what is in the SE/30. Mixing-and-matching can result in a variety of pathological behaviors.

[shifuimam]

Well, the only part we butchered and replaced were those four wires (they were four different colors; I remember that much). We took the four off the Classic II and used them on the SE/30's power (P1) connection. When we decided to reassemble the Classic II, we used four wires from a standard power cable (like one of the molex cables to attach to hardware) off an ATX power supply, putting a male molex connection on one set and a female on the other so we could connect the analog board to the yoke assembly.

The wires we replaced are the four on the top left corner of the analog board in this photo:

http://www.flickr.com/photos/damianward ... 4625062466

[PackingTape]

Agree with powerpup: the picture is really cool.

[techknight]

Ah ok, so you just butchered/re-spliced the yoke wires. You might want to ohm/ring check your yoke, you could have shorted turns and it will produce an awkward picture exactly like this.

[shifuimam]

Ok so boyfriend did some testing and discovered that the deflection yoke coil is bad - he measured 20+ ohms across the vertical and 300+ ohms between the vertical and horizontal deflection coil.

Unless we are mistaken, there should not be measurable resistance here, correct?

[techknight]

You need to measure this against a known good one in order to find out.

[shifuimam]

Is the SE/30 similar enough to use as a test? It's the only other compact Mac I own.

[tomlee59]

Ok so boyfriend did some testing and discovered that the deflection yoke coil is bad - he measured 20+ ohms across the vertical and 300+ ohms between the vertical and horizontal deflection coil.

Unless we are mistaken, there should not be measurable resistance here, correct?

To the best of my knowledge, the two sets of coils should indeed show no continuity with each other, so it does sound as if there's a short somewhere. Yours would be the first shorted classic Mac deflection coil I can recall, so, um, congratulations.

(I'm assuming that the resistance measurements were made with the yoke disconnected from everything.)

[shifuimam]

Sorry to necro a thread and all but I wanted to post back on this since we JUST fixed this problem tonight, and someone might find this thread via Google.

One of the vertical deflection yoke wires was broken. No idea how it happened, I'm guessing it was just from age. We resoldered that single wire back together very carefully, and it worked perfectly.

We used a technical reference for the Classic II's CRT to figure out that it was the broken wire in the yoke winding.

Reference here: ftp://ftp.apple.asimov.net/pub/apple_II ... tes%20.pdf

[uniserver]

strange, also yes the picture was pretty cool!


can you take a picture of the fix please?

[shifuimam]

Got a few things, actually.

Here's the fix:



Click here to go to the flickr page, where you can see a full-res version.

Incidentally, we have a new problem. The machine has stopped booting reliably. Seems like just jostling it causes it to either start or stop working. This is what we see, along with the sad mac tune, or whatever it's called.



The pages I've found on various on-screen indicators of different problems don't have any info on THIS particular problem. We think it may be related to a manually-soldered blue wire that looks like it's for the clock speed between the CPU and the GPU, but we're not certain.

ETA: So dropping the machine from a very small distance onto the workbench it's on makes it boot up. There's definitely a bad solder joint somewhere. We checked the RAM and the four removable ICs on the board, so I think it might be something soldered directly to the board. What would be the most likely suspects that we should check first?

[Macdrone]

Caps ? Caps? and did someone say caps ? The classics both I and II have had the worst leaky caps I have ever seen. I wonder its from years of use or sitting I am not sure but every classic I have seen now the motherboard looks like a jelly sandwhich. My color classics are bad but the tighter space with more directed airflow leads me to believe they had possibly better cooling in comparison.

Good Luck on getting it fixed straight away.

[uniserver]

yeah you have to watch out for those jelly sandwitches, the classic is pretty easy to recap, the Classic II not as easy.

Caps! -- Macintosh Classic II
http://68kmla.org/forums/viewtopic.php?f=7&t=19785

Caps! -- Macintosh Classic II Rev. 2 (Enhanced Sound)
http://68kmla.org/forums/viewtopic.php?f=7&t=19815&p=188654&hilit=ClassicII#p188654




The more I think about it, with that tube issue you had, I am wondering if this was someone's mad science project?

[uniserver]

By the way , I thought that image of the funky crt was so cool I had to save it.

[shifuimam]

I'm glad people like the image of a messed up CRT, at least!

So does it seem likely that our current symptoms are related to bad caps? We can recap that board; that's no big deal.

[8bitbubsy]

Check for corroded pins on any removable IC (and the RAM too). The leaky SMD cap phenomena can corrode pins even at a long distance from the actual leaking cap!
And yeah, replace those surface mounted electrolytic caps while you two are at it. I wouldn't care too much about the through-hole capacitors in the first place.