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SE/30 CRT issues


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  • 68kMLA Supporter

Hi all,

 

I received a dead SE/30 that I’m trying to bring back to live. When I first switched it on it started without a chime and on screen was just a vertical line.

 

To fix the audio I did a manual cleaning and re-cap of the logic board. For the vertical line I read that it’s probably C15, however after changing that out I ran a smoke test and I heard a loud-ish squealing sound and I switched off the power supply.

 

To test the logic board I figured I’d try a known good AB/power supply and it booted into the flashing question mark (yay), but after 10 or so seconds the screen started to flicker, show static, then the squealing sound happened on the new AB as well and I quickly switched off the machine. I then started smelling burning (boo).

 

On the original AB there’s a brown spot on yoke connector at the green wire, and also at the CR2 diode.

 

Is there anyone here that can think of a clear cause of this? I thought about it being the fly back, but why would that happen immediately to a working AB? 

Another possibility would be the yoke connection in the CRT side, which looks a bit messy and I haven’t looked into schematics for that thing yet. Or something else on the yoke itself because that along with the LB were the same in both cases.

 

Mingo.

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  • 2 weeks later...
  • 68kMLA Supporter

Just now realized I read your reply wrong @just.in.time :) But no, I don't have another logic board (well, a classic, but that's not P4 compatible right?)

 

Anyway, I've measured the flyback connections according to the diagram on Figure 2. in the Classic Mac Tech Docs, v1.1 PDF and they're spot on.

 

I've pried open the yoke connector at the deflector yoke side to see if I could find anything responsible for an overheating green cable and it looks like this:

IMG_2699.thumb.jpg.d3202be448c9f46cc5daf2dd86906dd4.jpg

 

Both resistors measure correct values 2.2KΩ and 220Ω. I think the cap and diode are ok, though I'm not entirely sure how to measure that.

Any point in re-flowing/re-soldering the points on here? I see a slight crack on the yellow wire's connection. Also I measured continuity between yellow and green, is that OK?

 

Any help is greatly appreciated,

Mingo.

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Update: it seems to be stable now. I re-soldered above connector and replaced the ceramic disc capacitors on the CRT neck board as well as re-flowed some more solder joints on there. No idea if anything I did fixed it or that it's some other factor, but I'll leave this as it is now.

 

A new problem reared its head though, and that is that I now hear a continues crackling/static over the loud speaker. So, back to the logic board I go :)

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Well the crackling is a bad ground. Shouldn't be too hard to solve. Solder joints do break over time when exposed to high amounts of vibration, perhaps even the minute movements in a crt due to its high khz feedback were enough to move it lose over time.
A generous reflow of all joints with a touch of leaded solder should remove any doubt of bad connections before you troubleshoot other issues. 8-)

 

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  • 68kMLA Supporter

My problem came back, I had it running for maybe 10 minutes now (booted into the OS and was browsing around the folders) and then the display started to twitch and I started to smell the electric burning odor (is that ozone?). So I switched it back off, will troubleshoot again coming weekend maybe.

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  • 2 weeks later...
  • 68kMLA Supporter

Also, the sound issue went away after putting a thermal pad on UA9, but returned after I had it running with the case closed for a few minutes.

I decided to test the thermal pad option because UA9 gets very hot, anyone know if that's normal?

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Thanks techknight, I’ll add it to my list! Straying even more off topic, do you (or anyone else here) happen to know the value of C62 on the back of the board, near the floppy connector? It broke off and shattered in a million pieces when I touched up the solder on it.

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  • 2 weeks later...
  • 68kMLA Supporter

So, I replaced UA9 which now doesn't get hot anymore, but the video chips (the U*6 ones and especially UG7) do still get quite hot. I don't know how normal this is, but I don't think it is. Also I've still not been able to track down the static sound over the speaker problem. A clue to me that these seem to be related to each other is that the crackling/static noise increases with time. After being off for a while it starts with a nice clean chime and when the chips mentioned above start to heat up the crackling comes in until it's almost constant.

 

Another thing, in the time between my last post here and now I've also had a single-bright-horizontal-line issue that resolved itself after the computer being off for 24 hours.

 

Could this be something to do with improper cleaning of flux or something? I feel increasingly out of my depth with this, but I'm still enjoying trying to track down the issue(s) :)

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