Mac SE Video

[Dennis Nedry]

The video works on my Mac SE, but shadows are cast to the right of objects on the screen and the whole right side of the screen is bowed out a little. Also the screen is still slightly dark even on it's brightest setting.

There are so many people here with so much experience with compact Macs. Has anybody fixed this specific problem before and could give me a clue?

 

[porter]

but shadows are cast to the right of objects on the screen

Drop shadows to bottom and right are part of the Human Interface Guidelines.

Seriously, yes I have seen the problem before. Have you done a cursory examination of the analog board to confirm if there are any components that have burnt out? Also, look for bulging or leaking capacitors.

 

[tomlee59]

Without a photo, it's a bit hard to troubleshoot, so here are some very general steps:

1) Verify that the supply voltages are correct. In this instance, +5 and +12 are the important ones. They should measure within 5% of nominal.

2) Inspect all connectors for signs of oxidation and/or outright burning/melting. Sometimes the mere act of disconnecting/reconnecting scrapes the contacts clean enough to restore normal operation (at least for a time). Resolder the 4-pin yoke connector, even if there's no obvious sign of a problem. Leave the connector in place while soldering, to avoid deformation that would make reassembly difficult or impossible. Use fresh solder; don't simply reheat what's there.

3) Resolder the connections on the flyback transformer (again, even if there's no obvious sign of a problem).

4) Inspect the connections to the base of the crt; clean as necessary. Take care not to snap off the vacuum-sealing nipple. If you break it, the crt will be irreparably damaged.

5) Adjust the brightness "cutoff" control (it's one of the adjustments indicated by the cardboard cover on the analog board). With the front-panel brightness knob turned to maximum brightness, adjust the cutoff control until the black areas are fully extinguished. If brightness is still insufficient, that generally indicates a problem with the crt (or its bias circuitry).

6) If after 1) - 5) you still observe ghosting, post back for more troubleshooting hints. It will also help to indicate how much equipment/experience you have, so that we can tailor the advice accordingly.

Good luck!

 

[skeletor]

Without a photo, it's a bit hard to troubleshoot, so here are some very general steps:
1) Verify that the supply voltages are correct. In this instance, +5 and +12 are the important ones. They should measure within 5% of nominal.

2) Inspect all connectors for signs of oxidation and/or outright burning/melting. Sometimes the mere act of disconnecting/reconnecting scrapes the contacts clean enough to restore normal operation (at least for a time). Resolder the 4-pin yoke connector, even if there's no obvious sign of a problem. Leave the connector in place while soldering, to avoid deformation that would make reassembly difficult or impossible. Use fresh solder; don't simply reheat what's there.

3) Resolder the connections on the flyback transformer (again, even if there's no obvious sign of a problem).

4) Inspect the connections to the base of the crt; clean as necessary. Take care not to snap off the vacuum-sealing nipple. If you break it, the crt will be irreparably damaged.

5) Adjust the brightness "cutoff" control (it's one of the adjustments indicated by the cardboard cover on the analog board). With the front-panel brightness knob turned to maximum brightness, adjust the cutoff control until the black areas are fully extinguished. If brightness is still insufficient, that generally indicates a problem with the crt (or its bias circuitry).

6) If after 1) - 5) you still observe ghosting, post back for more troubleshooting hints. It will also help to indicate how much equipment/experience you have, so that we can tailor the advice accordingly.

Good luck!

Good advice.....have worked on many SE's, and that's exactly how I would chase that dog down..and yeah, I once ended up breaking the glass nipple on the back of the CRT...listening to it, lose vacuum , sucked!

I had to replace the tube.......but it was a learning experience.

the Pina book on SE's etc, is a great teaching tool...locate one

if you can..

I might have some extra SE analog and MB's lying around..if the need

is there....

keep us posted on yer progress

 

[Dennis Nedry]

Drop shadows to bottom and right are part of the Human Interface Guidelines.

lol

Seriously, yes I have seen the problem before. Have you done a cursory examination of the analog board to confirm if there are any components that have burnt out? Also, look for bulging or leaking capacitors.

Nothing "looks" wrong with the analog board. It's actually fairly clean and no caps show any signs of bulging. No components appear darkened and the board itself doesn't appear to have any dark spots.

Without a photo, it's a bit hard to troubleshoot, so here are some very general steps:

Let's take care of that:

http://benboldt.spymac.com/mac_se.jpg

You can't really see the edge of the screen to gauge the bulging, but I think you can tell that it isn't too severe. The lighter line going through the trash is an artifact of the camera and is not actually there.

1) Verify that the supply voltages are correct. In this instance, +5 and +12 are the important ones. They should measure within 5% of nominal.

I measure 12.57V and 5.03V, which both are within 5%.

2) Inspect all connectors for signs of oxidation and/or outright burning/melting. Sometimes the mere act of disconnecting/reconnecting scrapes the contacts clean enough to restore normal operation (at least for a time). Resolder the 4-pin yoke connector, even if there's no obvious sign of a problem. Leave the connector in place while soldering, to avoid deformation that would make reassembly difficult or impossible. Use fresh solder; don't simply reheat what's there.

All connectors appear fine with no oxidation whatsoever. I suppose a problem with the yoke connections could be causing the slight bulging, but I don't think the yoke can be responsible for the shadow. I will look into this, though.

(To do #1)

3) Resolder the connections on the flyback transformer (again, even if there's no obvious sign of a problem).

(To do #2)

4) Inspect the connections to the base of the crt; clean as necessary. Take care not to snap off the vacuum-sealing nipple. If you break it, the crt will be irreparably damaged.

This appears to be just fine. No oxidation on the pins.

5) Adjust the brightness "cutoff" control (it's one of the adjustments indicated by the cardboard cover on the analog board). With the front-panel brightness knob turned to maximum brightness, adjust the cutoff control until the black areas are fully extinguished. If brightness is still insufficient, that generally indicates a problem with the crt (or its bias circuitry).

I adjusted the cutoff, and actually it was pretty accurate where it was. Brightness is sufficient, but only with the knob on the front turned all the way to the maximum. I have noticed that the shadows reduce and even go away after a certain point when brightness is reduced. The bulging is not affected by this. Please note that the bulging is fairly subtle, and would be acceptable if not repaired. It seems a little beyond normal tolerance levels, but maybe not, maybe I am being too picky.

I believe this Mac has had some physical trauma; there are some deep dents and scrapes on the front of the case as if it had been dropped.

6) If after 1) - 5) you still observe ghosting, post back for more troubleshooting hints. It will also help to indicate how much equipment/experience you have, so that we can tailor the advice accordingly.
Good luck!

I still have to try soldering some connections that you had recommended (no time at the moment). Thank you for your help!

Also: I have a digital multimeter and even a scope. The scope can display up to +/- 20 V.

 

[Dennis Nedry]

New discovery:

I removed the plastic sheet from the outside of the analog board. The circuit board near the top pin of the yoke connector (green wire) is darkened on the outside of the board. I have resoldered this connection, including removing the old solder first, and it made no difference whatsoever when I turned it on again.

I still have to resolder each connection on the flyback transformer. I have visually verified each connection, but that doesn't mean much.

 

[tomlee59]

The photo unfortunately doesn't show the shadowing effect you refer to, but your verbal description offers a valuable clue. If you set the cutoff with the brightness turned up to maximum, and the brightness was still insufficient after the adjustment, then it is quite likely that the crt itself is the trouble. I've seen very few truly worn-out Mac CRTs (screen burn is much more common), but I have encountered a couple.

If it bothers you enough that you don't mind a small risk of killing this CRT, here's a final test: Disassemble the unit and remove the connector from the base of the tube. Connect a 15V DC regulated supply across pins 3 and 4 (the filament), and let that overvoltage cook the CRT for a good 5-15 minutes. In many cases, this will recondition the surface of the cathode (at least temporarily) and restore emission. Reassemble and test. If the ghosting goes away (or at least goes down signficantly), and brightness increases, then that pretty much seals the diagnosis.

 

[Dennis Nedry]

I'm sorry I've been away from my SE for a while and not been able to work on it anymore. If you look very closely at the picture (which I admit is NOT a very good picture), you can see a slightly dark area cast off to the right of the window that extends all the way to the right side of the screen. This is what I'm referring to.

It's not horrible, so I might shy away from cooking the CRT, but I will try the things suggested earlier in a week or two and let you know how it goes. Too bad I don't have another SE that I could exchange parts from - then I could more easily narrow it down between the CRT and the analog board.

 

[tomlee59]

...you can see a slightly dark area cast off to the right of the window that extends all the way to the right side of the screen. This is what I'm referring to.

Ah, now I see what you mean. Do these "ghosts" also show up to the right of all other objects (e.g., the trash can icon)?

 

[wally]

Verify that there is a good solid ground path from the crt safety band mount to the analog board ground, close to zero ohms. Viewed from the rear, the ONLY path is from the upper left band mounting screw thru the terminal lugged black/white wire to the B/W pad on the upper left corner of the CRT neck video board next to C2, then out the black wire of the ferrite sleeved harness to pin 3 of the analog board video board connector P2.

The aquadag is grounded to the mounting band by a conductive coating, and should measure in the low to mid hundred ohms probe tip to ground. If it floats the internal CRT anode capacitor (approximately 700 pF) is compromised (to about 150 pF), and the HV could vary more during each scan line as the video presents a varying load. If someone did a CRT swap and the replacement lacks continuity from the graphite coating to the safety band zone, you should improvise a contact with a spring and some bare wire.

That black/white ground wire crosses the extremely well insulated red wire of death [] ]'> and it would be best if the b/w wire hugs the aquadag and the red wire floats above it as not to concentrate voltage stress at an insulation point of contact.

 

[JDW]

http://benboldt.spymac.com/mac_se.jpg

Ah, now I see what you mean.

Wish I could, Tom. But that photo not only suffers from being way to small and way too distorted, it's also not very crisp. Some photo op advice:

1) Mount your camera on a good tripod. (Don't have one? Buy one. I did, and I don't sell on EBAY or use it daily either.)

2) Reduce your camera ISO to the lowest setting to ensure a noise-free shot.

3) Frame up the CRT screen straight-on. (Don't shoot it at an angle.)

4) Ensure your camera is set on a 2sec timer so your pressing of the shuter button doesn't blur the shot.

5) Shoot.

6) Optional: Color correct and sharpen in an app like Photoshop.

If you do this, you will shoot lovable photos of your classic Mac's CRT, similar to this.

(Sorry to hassle you about this. But I just love big, crisp, non-distorted photos! I also really want to see what your eyes are seeing, which I cannot now with your current photo.)

 

[Dennis Nedry]

UPDATE

I have gotten ahold of a working Mac SE that I can exchange parts with and I have gotten some new clues:

The shadowing and slight bulging problem is somewhere on the analog board. Swapping only that board and keeping the old power supply and video board that mounts on the back of the CRT, the shadow problem disappears.

The screen still has low brightness with the known-good analog board. I also tried swapping in a known-good power supply and that made no difference. I have yet to swap the video board that attaches to the back of the CRT, but I will do that soon to rule that out. As suggested earlier, the CRT may just be old and tired, and not as bright as it used to be. This really is OK at maximum brightness, though.

So I guess at this point, it's a matter of troubleshooting the analog board. I have noticed that the hot glue on the width adjustment (a variable inductor) has gotten hot and curled away from it due to the heat. Also the board has some dark spots on it nearby. Also, C12 has a big long, clear, waxy drip running down the board from it, but this isn't an electrolytic cap, so I don't know what to make of that. Other than this, the board and components are remarkably clean. If I didn't know better, I'd say the board is almost brand new just by looking at it.

It seems to me that a good thing to try first would be to replace the variable inductor just because of the visual clue. This is component L2. I don't really want to take the one off of my good board, so is there anyone that knows the specs for it so I could just get a new one?

 

[porter]

Also, C12 has a big long, clear, waxy drip running down the board from it, but this isn't an electrolytic cap, so I don't know what to make of that.

Is it easily replaceable?

 

[tomlee59]

Although inductors certainly do fail from time to time, that particular one is extremely robust, relative to what it's called upon to do. If it has failed, it is a victim of something else (e.g., a leaky capacitor in series with it -- it's C1 on a Plus/512/128; look for a 3.9uF or 4.7uF nonpolar electrolytic). Even if it's overheating, it may be fine.

Given the frequency with which the nonpolar cap fails, I would just replace it as a matter of course.

It's also a good idea to verify the supply voltages at various locations around the system. For example, see that +12 and +5 are within spec at the floppy drive, hard drive, and at the analog-to-logic board connections.

 

[JDW]

In terms of replacing C1, metallized polypropylene are the way to go if you never, and I mean never, wish to replace that cap ever again (unless you intentionally blow it somehow). More details on this in my Analog Replacement Parts listing.

 

[Dennis Nedry]

The big caps in the SEs are C9, C14, and C15. I was attempting to remove C12 because of the strange drip, and as I was doing it, more liquid came out of it. I will be replacing this first as soon as I can find a new one. I will also need a hotter soldering iron in order to adequately install the replacement. I'll let you know what all happens.

I also swapped video boards and that is now also ruled out. The CRT is simply old and tired, that's why it's dim, but that's OK.

 

[wally]

Yet another area to check...The video from the logic board passes thru a single 74LS38 buffer, U1, on the analog board (and pullup R1 and series terminator R30) before being passed on to the CRT mounted video board. U1 also buffers the vertical and horizontal drive into the analog board. R28 and C22 decouple the +5V power to U1. A bad U1 or bad decoupling could cause some video artifacts as well as weird interactions between video, vertical and horizontal drive signals. Even if the +5 looks good on the power supply connector, it could be less good at U1 pin 14 either in DC value or noise contamination.