Archive for the ‘Mac128K’ Category

Macintosh 400K Floppy Rescue

Monday, December 29th, 2014

I’ve been on a lookout for a 400K external floppy since restoring the 128K Macintosh that I obtained a while back. Operating a 128K Macintosh without an external floppy is extremely painful. I did have an 800K external floppy, back in the day, but I sold it some time back.

Back in November, I picked up a couple of broken drives off of ebay for $70, shipped. I thought that this was a pretty good deal, as good drives often go for over $100.

Mac 400K Floppy Drives

Mac 400K Floppy Drives

From my experience resurrecting the internal 400K drive, I knew that these units were very well built. I was thinking that I could probably get one of the two working. Maybe if I was lucky I could get both going and sell one to pay for my purchase.

When I received the units, I opened the box, only to discover that the units had been taken apart, and weren’t even completely reassembled. This concerned me a great deal, as I expected that when I found time to dig into them, that I would find that some inexperienced hacker turned a broken unit, into a broken beyond repair unit. I didn’t have time, to do any further analysis and the units were stacked at the rear of my workbench until time allowed me to dig into them.

Well, yesterday, I found that time. First thing I noticed is that all the screws holding the chassis and enclosure in place were gone, except for one. I pulled the first mechanism out of the chassis and took a look. The auto-eject mechanism was completely bound up.

Mechanism Hang Up Point

Mechanism Hang Up Point

Some of the components were bent, apparently from someone trying to force the mechanism open. One lever was actually completely frozen on it’s pivot. I disassembled the components that could be removed and cleaned off as much gunk as possible. It took a bit to free up the frozen lever, but it soon was operating smoothly. I straightened the bent components and checked the mechanism out. I noticed that sometimes a roller bearing would hang up partly through it’s movement, locking up the mechanism. I took a small file and filed a bit off of where it was hanging up, and the mech started working almost like new. With that problem, this unit might might have been misbehaving from the day it was made.

Now I reassembled the drive and attached it to my 128K Macintosh. The computer recognized the drive and it appeared to operate normally. I was able to format floppies and exchange them with the internal drive, so alignment and operation was perfectly fine.

I thought, maybe I’d be that lucky with the second drive and I put the first drive aside. Before doing anything else, I figured I would clean the mechanism of the second drive. It seemed to have much less wear then the first drive. I closely examined it and the mechanical pieces seem to be in excellent shape. After cleaning, lubing and reassembling, I hooked it up.

After turning it on, the stepper motor moved the head to the inside track and continued turning. This one had some kind of problem with the control system. I tried a lot of things, including swapping controller boards with the other drive with same result as before. I decided that it was pretty likely that the sensor that indexes the heads to the outer track probably was not working.

Track Alignment Sensor

Track Alignment Sensor

After some more mucking around, I decided to do a search on the internet and came up with a “Click of Death” result that matched my problem. It seems that I was on the right track, and it was very likely that the head indexing sensor wasn’t working. I removed the mechanism again and used a sewing needle to try to clean the tiny slots in the sensor. The needle seemed to draw away some kind of oily residue from the slot. I kept at it until I didn’t see any more of the oily residue. I wonder if someone had sprayed something into the drive as part of a vain repair attempt.

I put the drive back together and I was in luck, as the “Click of Death” was gone and the drive seemed to boot normally. However I encountered a new problem. This drive’s alignment didn’t match my other drives or the old disks that I still had from back in the “old days”. This was clear, as floppies formatted and created on this drive would only boot and be read on this drive. Floppies created on other drives would not work in this drive.

This created a bit of a dilemma for me, as the factory seal on the alignment mechanism still was present. Either the factory alignment was off or somehow the problem with the sensor had affected alignment. I tried cleaning the sensor again to see if it would get better, but had no better luck. After much thought, I decided that I had no choice, but to muck with the factory alignment to try to make it better.

Normally you will align a floppy drive with special test software and a calibration disk and some test equipment. I have neither the software or a calibration disk, so I figured that I would just try to “wing it” by getting it to read disks made on my other drives. The alignment setup can be accessed with the unit completely assembled.

Floppy Alignment Points

Floppy Alignment Points

You loosen the hold down screw just a bit, so that the board holding the optical sensor can be moved back and forth, but not so much that it is completely free. On the side of the chassis is a groove that matches a groove in the board. Using those grooves, you can use a flat bladed tool to tweak the board in very small increments.

Tweaking Alignment

Tweaking Alignment

After a lot of tweaking and testing and re-tweaking and re-testing, I have the second drive working as well as the first one. I wonder if this drive had problems with alignment from the factory, which is why the mechanism seems to have had so little use. I also continue to wonder if the problem with the index sensor had affected alignment. In any case, the drive functions well now, and floppies can be freely interchanged with my other drives.

Once I pick up some M3-.50 by 8 MM screws with matching star washers, I’ll be able to put both drives back together. I’ll probably sell the extra drive, as I just don’t see the need to keep a back-up parts drive.

MAC 128K intermittent operation resolved.

Thursday, May 2nd, 2013

In this series of earlier posts and I had posted some notes on acquisition and repair of an all original MAC 128k. One thing I didn’t mention is that the video on the machine was a bit intermittent. This has bugged me a bit and yesterday, I decided to figure out what was going on. The symptoms were intermittent video, either working normally, or completely black. Taking the machine apart, I determined that wiggling or touching the connector that leads from the digital to analog board could cause the video to go on or off.

Some websites and an old book, “Macintosh Upgrade and Repair Secrets”, say that this sort of problem is often due to bad solder joints on the connectors on the analog board. Following those directions, I pealed off the plastic cover and resoldered the joints on the analog board. However, this did not affect operation. Figuring that I had nothing to lose, I then touched up the joints on the connector on the digital board. Wiggling this connecter seemed to affect the problem, so I was kind of hopeful that resoldering that connector would do the trick. Sure enough, the intermittent operation seems to have disappeared once I resoldered those joints. Now, I just need to find some foam with adhesive on both sides to use, to put the plastic panel back over the analog board and I think I’ll be back in business.

I hope I don’t have any further issues, at least for a while. By the way, my opinion is that those connectors could have used a bit more solder in the first place, and this probably contributed to the issues.

This experience with a MAC 128k shows how even a lightly used old computer that is in excellent cosmetic condition, may need some work in order to get it running like it was new. I had three problems with this machine that needed addressing.

  • two bad memory chips
  • floppy drive needed cleaning and lubrication
  • bad solder joint on motherboard connector
  • Note that there are high voltages in this system and it should only be operated by experienced technicians when the cover is removed.

    Mac 128K and Imagewriter Working Together Nicely

    Friday, February 24th, 2012
    MacWrite printout on Imagewriter

    MacWrite printout on Imagewriter

    Mac 128K up and running

    Tuesday, February 21st, 2012

    The memory chip replacement I mentioned in the previous post was routine and got the motherboard up and smiling.

    I figured that since I had the machine apart, I should clean and grease the floppy drive. This turned out to be an adventure that took a good part of three days.

    Since I had never successfully restored a floppy drive to working condition in a couple of previous attempts on more modern macs, I was a bit concerned. First I found a couple of web sites that described what to do, or so I thought. I followed the directions cleaning some of the gunk off of the worm gear and the mechanism and then lightly greased it. However when I tried to boot the machine, it barely worked. I was able to boot the machine only two times between countless failures. Once booted, it seemed stable, so I was fairly certain that the problem was in the drive, not the motherboard. At this point I disassembled and cleaned the drive, some more. This repeat effort also resulted in a drive that barely worked.

    At this point, I really studied the mechanism and determined that a clean worm gear is critical to proper head positioning. A dirty worm gear or worm gear follower could really mess positioning up. As it rotated, any grime or dried grease could shift the follower forward or backward a bit, ruining head positioning. I went back and cleaned more gunk out of the gear and removed piece of grime that had attached itself to the follower.

    I also examined the circuit board to see what kind of debugging or calibration was possible. The parts all seem to be off the shelf parts, that should still be attainable, and their data sheets are on line, so I felt comforted by that. There are only two two calibration points. One is the read amplifier gain, and the other is the differential input phase adjust. There is no adjustment for the motor speed control, which is somehow controlled by software, anyway. For now, I left both adjustments alone. I did measure resistance of the adjust pots, so I could put it back to factory settings, in case I decided to change either setting later on.

    I also partially disassembled the sliding mechanism and really cleaned it out, which you can’t do without disassembly. The red arrows in the image denote slip rings and a spring that need to be removed in order to do this. Don’t do this in a carpeted area, since you may never find a dropped slip ring in a carpet. At this point the mechanism worked as smooth as new and I thought I had a chance for success.

    floppy drive disassembly points

    floppy drive disassembly points

    This time, rather than reassembling into the carrier housing, I just attached via the ribbon cable and used some paper to insulate the drive from the chassis. Once again, the drive didn’t work. Somewhere around this time, I placed the drive upside down outside of the chassis in order to get a better view of things. Lo and behold, it booted several times in a row. I played with the machine for a while before going to bed.

    The next day, I moved the drive back into the chassis, just prior to reassembling and it started behaiving badly again. Moving it back out of the chassis, it started working again. Maybe it was sensitive to position, since it was on it’s back when outside the chassis and in it’s normal position when inside the chassis. Moving the drive right side up, and setting it carefully into the chassis, I immediately encountered more errors. Trying different positions only revealed that it didn’t work when in it’s normal position inside the chassis.

    I was stumped. This drive is very well built, I didn’t see anyway in which gravity could affect operation. In fact, it is so well built that I thought that it would be very unlikely that it could ever get out of mechanical adjustment. Do to this, I resisted the great temptation to fool with mechanical adjustments. I know there is a website that suggests raising the head could help things. Based on what I saw, I figured that that was unlikely to significantly help matters, especially when the problem for that person really could have been a dirty worm gear or follower throwing the head positioning out of kilter.

    I even got out my scope and checked the phase adjust test points. The phase relationship between the two signals was dead on. I thought it was unlikely that there was a problem with the circuit, though gain could still be off. I had no real way to know what gain should look like, so I left well enough alone.

    I put things back together and tried some more experiments with positioning the unit, only to find that putting it in the chassis brought bad performance.

    Finally, it struck me, the CRT was right next to the floppy when I had the floppy in the enclosure. In addition, I had removed the shielding/mounting bracket for my testing. EMI from the high voltage CRT was screwing up the drive read and write capability! Loosely putting the mounting bracket over the drive to shield it from the CRT, quickly changed performance from awful to normal! I had solved the issue.

    A couple of lessons learned about Mac 400K drives should be shared here.

  • Never muck with mechanical adjustments – these devices are very well built and never should need adjustment
  • You should not need to muck with gain or phase, if you do, make sure you record factory settings before you change anything
  • Never operate it loosely in the chassis without proper EMI shielding from the CRT
  • If you are mechanically skilled you should take the mechanism apart to really get it cleaned and lubed properly
  • The worm gear should be as clean as you can get it
  • Clean the follower arm where it follows the worm
  • The good news about this, is that I believe that these mechanisms are extremely well built and should last a long time with a bit of careful maintenance.

    new toy

    Saturday, February 18th, 2012

    I really don`t need another retro project, but I managed to pick up an all original 128K mac this weekend. I got it from a local source for a fair price. It does need a DRAM repair, but I have original mac 128K drams left over from a 512K upgrade that I did on my original unit back in 1984! I`ve really been wanting to get one of these computers. The original unit I bought back in 1984 was so upgraded, hacked on and otherwise beat on, it was beyond reasonable restoration. I had to turn it into a macquarium. On the other hand, the unit I just picked up, appears almost completely original and hardly used. I still have my original 1984 imagewriter, so this is going to be quite a retro trip. I already found a couple of books I have saved, including Doug Capp`s “Macintosh”