Macintosh 512K

That screen looks like the entire bottom half is being shown in overlapped scan lines near the middle of the screen. Horizontal deflection is OK, but vertical is either all mashed up in the center (possibly adjustable) or the bottom half conked out.

Working inside the enclosure where the CRT is located is dangerous. Voltage of about 10,000 Volts (for monochrome) can be present months after the AC power is removed.

The good news is that the top half of the diskette shown says it passed its self-test, and is ready to boot.

The drive on the 512MB is very similar to the drive on the SE but only has heads on one side, so the diskettes (Diskette 2D) can hold only 400K instead of 800K. They are physically identical diskettes, so if it will not accept a diskette, it is jammed, and will have to be dis-assembled and cleaned.

Well as Grant mentions there are some lethal voltages inside these Macs so if you don't know what you are doing......

Plus it is quite easy to kill the tube by snapping off the tiny glass pin on it's end if you aren't careful....

Because it is intermittant it feels like a bad connection somewhere.

Compact Macs had a tendency to have problems where the 4 wire plug from the monitor enters the vertical board housing the flyback transformer. The typical repair was to resoldier all the connections and check the plug for signs of burning.

But did we mention the lethal voltages inside this Macs......

Kevin

pkmnct wrote:
Do you think there may be an easier way? (I've never soldiered before) If not then I have a dead Mac SE, would it be possible to switch the displays (I'm guessing not unless first discharging both displays [which I wouldn't do personally]). I also tried just jiggling all the connections around (except for the red one connected directly to the CRT). There was no difference. I also tried adjusting the brightness, max brightness, width, and height. Nothing has worked. It does make a semi-loud POP on occasion (without jiggling the connections) and changes viewable area back to seeing the full disk.

Easiest way would be to find an Apple service depot with an older tech who has worked on these Macs.....

Your problem if it's what you showed in the link is not the picture tube but most likely a connection or the analog board. The analog board contains the flyback transformer which is the area with the deadly voltages.

It's been a long time since I've repaired a 512k but it seems to me the analog boards are not interchangeable. I think it went something like this,

128k <-> 512K and maybe the Plus though I have a feeling no.
SE <-> SE/30
Classic <-> Classic II

Kevin

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Important Note: If you ever feel that this is beyond your knowledge, then STOP - don't attempt the repair yourself. Let a professional do it instead. Anyone even slightly experienced with working inside computers, and with exposed CRT tubes, and with some soldering experience, should be able to tackle a compact Macintosh. But if you don't have any experience of the aforementioned areas, then it is probably best left to a professional. As Larry Pina's book wisely says in its first Chapter: "Know your limits. If unsure of any procedure, stop! For your own safety, seek further information or defer to qualified personnel."

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Kevin is correct in that the parts between a 512K and SE are not interchangeable. The socket on the video board for the CRT are different and the analog boards also differ between these models. With the 512K, the power supply circuit is located on the analog board, exposed. On the SE, the PSU has its own enclosed unit, which is mounted at the bottom of the analog board. Apple made several different revisions of analog boards during the production of the compact Macs.

Before you start, you ideally need a PDF copy of Apple's official service manual for the Macintosh 512K, which can be obtained if you know where to look. A copy of Larry Pina's Macintosh Repair & Upgrade Secrets is also essential, in my opinion, because it is the only book to this day to detail the correct diagnostic and repair procedures for compact Macintoshes. Used copies of this book can be purchased from Amazon and other retailers online.

You will need to open the case, and you will need a T15 long torx screwdriver to do this. Once the cover is removed, you must discharge the CRT before you proceed any further. By searching on Google you can find sufficient guides on how to properly discharge a CRT. Unlike the SE and later compact Macs, the flyback transformer in the 512K does NOT have a built-in bleeder, which means most of the charge is still there after you power down. The CRT in a compact Mac holds about 9,000 volts. Avoid touching the anode cap, video board, CRT neck and yoke, and the analog board. In the Macintosh 512K, the power supply is exposed on the analog board. This also contains high voltage which is dangerous.

Here's a handy tip: To get rid of most of the charge initially, to turn the brightness knob to full while the machine is ON, and then flip the power switch at the back to the OFF position. This is a quick and relatively safe way of getting rid of most the charge. Do this, then let it sit for a week, then discharge using the correct procedure. Then you should be safe to proceed to the next stage.

According to Larry Pina's book, when the display collapses half-way to a horizontal line, it means you lost the vertical sweep. Check for a cracked solder joint on pin-5 of the J4 connector. - this is the easiest repair. If that's not the problem, it gets a little more tricky. I will explain if need be, but it's best to check the J4 connector's solder joints first.