I have a Mac SE FDHD that has the screen a bit too wide. I opened it to adjust things and see the variable inductor (L2) is a bit messed up. The hollow core (that a non-conductive hex tool goes inside) has been chipped on the ends and I cannot rotate it to adjust it. I would replace the variable inductor with something new (Digikey or Mouser) but do not know the component values (uH, etc...).

I found the schematics online for the SE, but still cannot find info on this inductor to find a suitable replacement.

Does anyone have any info/guidance on this? Thanks, in advance.

-- Jason

 

It may help to post a picture of the inductor.

 

If they look like these, then you may have to go looking in old TVs or monitors as they tend to be custom made. I tend to go the salvage way & keep a few for repairs.

 

Here are a few pics I took of it. The internal core is hollow and chipped off on the end. As I stated, I tried using a non-conductive hex tool to rotate it, but it won't budge. Also tried a squirt of De-Oxit FaderLube - no dice.

The screen on the Mac SE is too wide (meaning, the mouse goes off the screen on both the left and right sides when booted). My thoughts were to replace the inductor. My problem is I cannot identify the specs of this inductor anywhere and don't know what a "suitable replacement" would be.

Again, thanks in advance for any help.

 

Un fortunately these are not a part normaly stocked by electronic retailers, as its rare to have to replace them. My sugestion is start looking scrap monitors & TVs as there should be plenty thrown out these days, as CRT type equipment is generaly thrown out (atleast here in Australia usualy find plenty on sidewalk rubish pickup days)

 

Find an SE someone is throwing away.

 

Here is the schematic of the SE analog board.
http://etech.dyndns.org/FDHD/SE-Analogb1.gif
http://etech.dyndns.org/FDHD/SE-Analogb2.gif
The width adjustment is on the right side SE-(Analogb2.gif). Unfortunately, the value is not listed. It is in series with the horizontal deflection coil (80uH), so it is basically a trimmer. I'm guessing it might be around 10uH. In your photos, it looks like it's wound with Litz wire.

 

Is the inductor L2 on the SE the same as on the original Mac?
I will have a look in the morning if I remember.

 

Here is the schematic of the SE analog board.
http://etech.dyndns.org/FDHD/SE-Analogb1.gif
http://etech.dyndns.org/FDHD/SE-Analogb2.gif
The width adjustment is on the right side SE-(Analogb2.gif). Unfortunately, the value is not listed. It is in series with the horizontal deflection coil (80uH), so it is basically a trimmer. I'm guessing it might be around 10uH. In your photos, it looks like it's wound with Litz wire.

Yes, I found the schematics also and yes they do not show the value of L2.

 

I have thought about cannibalizing the part (or similar) from a junked older Mac or a monitor or whatever, but thought the best approach would be to find out the component values (uH) and get a modern replacement to install in it's place.

How much tolerance would my Mac SE FDHD have if I replace my L2 with another inductor cannibalized from something else and the values are not EXACTLY the same (since, at best, I am GUESSING at the current L2 value)?

 

Solong as it looks simmilar it should do the job, its not a critical component.

 

I looked at the inductor on a Mac Classic and it looks like the same.
The inductance measured in-circuit is 2mH. Note that the wire is very course and is meant to handle a lot of current.

I have yet to check an original Mac.

 

Thanks for the replies - I'll mess with it this weekend.

 

OK, so tonight I went ahead and cut away the outer plastic tube around the ferrite core and the core just basically crumbled. So the inductor has no core at all. I've read about using a substitute core (like a regular screw) so decided to go that route for an experiment.

Once the crumbled ferrite core was removed I inserted a regular iron screw and powered it up - the display is still "too wide" so I went to adjust the screw and it was hot as hell so I powered off immediately. No harm done to my SE, but seems that inserting a solid metal screw will cause a fire hazard due to the heating up. The SE powers up fine and all, it's just I have no ability to adjust the horizontal width of the display, which is now maxed out on width (since there is NO ferrite core anymore in the variable inductor).

Any suggestions on my next move?

 

Hunt around for a core out of something else & try it, you have nothing to loose.

 

As you quickly found out, you cannot use a metal screw. It must be a ferrite core.