whistling mac plus

From: jpero_at_pop.cgocable.net <(jpero_at_pop.cgocable.net)>
Date: Tue Oct 20 20:57:23 1998

> Date: 20 Oct 98 23:07:41 EDT
> Reply-to: classiccmp_at_u.washington.edu
> From: Marion.Bates_at_Dartmouth.EDU (Marion Bates)
> To: "Discussion re-collecting of classic computers" <classiccmp_at_u.washington.edu>
> Subject: Re: whistling mac plus

> --- SUPRDAVE_at_aol.com wrote:
> i fear it's probably that infamous cold solder joint issue. i'm
> looking at a spare mac power supply board; does anyone know any exact
> locations of common solder joint failures? finally, if i do touch up some
> contacts with a soldering iron, MUST the high voltage lead be discharged? i'm
> hoping i can just remove the protective cardboard cover, reheat the solder
> joints and not even go near the HT lead or tube at all.
> --- end of quote ---
>
> In my experience, the C-shaped ring of joints corresponding to the flyback transformer go bad pretty often. Also, I've re-soldered them before without discharging the high voltage lead, and everythin>
> Good luck!

Not needed to discharge that tube but if that gives you shivers when
coming close to guts of that mac, build youself a discharging tool
for that:

Take a old red wire off a duff flyback snip it in half/half
length terminate one in clip on terminal and a probe on other end
then connecto all in series to that pack made of one or 2 10W 1meg
ohms power resistors all covered up in epoxy and in tube because
epoxy alone is too brittle.

Discharging process: clip that to the tube grounding strap that go
across from two corners and carefully slip under that rubber
cup to touch that metallic spring hook that is stuck into the lipped
metal cup on that tube surface. Discharge is very quick and less
scary this way than a blue arc with a loud snap!

Do by soldering and add a bit of new solder wire to all the connector
pins, flyback pins and heavy component leads and any thing that are
hot looking. Don't bother the logic board it's better designed
anyway.

This does usually doesn't address the shortcomings of this analog
boards in all of common compact Macs; those damnable 3.9uF bipolar
capacitor going bad, burning the pin 1 on yoke connector and cook the
inductor L1 coil if not caught early. Again, the shortcomings in the
PSU and in video circuit on that board.
That, can be addressed all the potiential problem by getting a
rebuild kit from CSS or Data Display Ltd (Canadian version of CSS.

Not more than $30 in needed rebuild kit.

The whistle noise is from either PSU components vibrating or the
horizontal section components vibrating. Touch each components with
plastic or wooden stick until that noise stops or change in pitch and
you catch the baddie. :-) Oh, don't foget those ferrie cores on that
flyback and anything like that on coils and transformers.

Oh, Whistling could be sign of a bad flyback arcing internally or
along the high voltage wire.

Jason D.

>
> -- MB
 
email: jpero_at_cgocable.net
Pero, Jason D.
Received on Tue Oct 20 1998 - 20:57:23 BST