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Mad With Macintosh


Vertical Line On A Mac Plus Screen



Date: Fri, 27 Nov 1998 11:17:14 +0000
To: Classic Posts <classic-post@hitznet.com>
From: Rebecca and Rowland <rebecca@astrid.u-net.com>
Subject: Re: MacPlus: Vertical white line inc 128/512/Plus upgrade info

>From: EDRIZER@aol.com
>Date: Thu, 19 Nov 1998 17:01:09 EST
>To: classic-post@hitznet.com
>Subject: MacPlus: Vertical white line
>I remember this topic from several months back, but I wasn't paying attention.
>My Mac Plus suddenly lost its picture.  I now have only a vertical line
>running down the middle of the screen.  What's the solution?

I'm not *certain*, but Larry Pina's `Macintosh repair and upgrade secrets',
Hayden Books, ISBN 0-672-48452-8 says that the cause is most likely a fault
with L2, C1, and/or J1 - these are the reference numbers on the PCB.

(L2 = inductor, C1 = capacitor, J1 = connector)

Likely faults are component failure (in the case of C1), or cracked solder

If you replace C1, you need to get a 3.9 micro farad *unpolarised* *high
frequency* capacitor, with a 100V rating.  Make utterly certain that the
replacement part is suitable for high frequency use - most electrolytic
capacitors aren't.  Get this bit wrong and you might well end up looking at
the wreckage of an exploded capacitor in the near future.

I've also heard that the flyback transformer has been known to fail and
produce this symptom.

If you're going to be doing component-level repairs, it's as well to
replace as many electrolytic capacitors as possible, because they'll all be
near or past the end of their lives by now.  In particular, replace the
following parts, using capacitors rated for at least 105 degree C and high
frequency operation.

The rest of this email applies to the original 128K thin Mac, the 512K and
Ke, and the Mac Plus.

In the follow parts lists, do check the values I've written down against
what's on the PCB.  If the capacitance value on your PCB differs from what
I've typed here, assume I've made a mistake.  The voltage and temperature
ratings are supposed to be higher than what's fitted - they make for longer

I am at the moment half-way through this upgrade procedure myself - I've
got to get a few more bits before I can switch on and re-adjust everything

I've supplied part numbers for suitable parts (where I could find them)
from RS,a global industrial electronics supplier

(uF = micro farad, or x 10^-6 F)

Part numbers for US Mac Plus/512K/128K:

C1   3.9 uF 100V
C3   220 uF 35V     RS 394-872
C24 2200 uF 25V     RS 394-844
C25 1000 uF 25V     RS 394-838
C26 1000 uF 25V     RS 394-838
C29 2200 uF 25V     RS 394-844
C30  220 uF 35V     RS 394-872
C31 1000 uF 25V     RS 394-838

Part numbers for international Mac Plus/512K/128K:

C1   3.9 uF 100V
C3   220 uF 35V     RS 394-872
C24 2200 uF 25V     RS 394-844
C27 2200 uF 25V     RS 394-844
C28 1000 uF 35V     RS 394-917
C30 2200 uF 25V     RS 394-844
C31 1000 uF 25V     RS 394-838
C32 2200 uF 25V     RS 394-844

have a look at C33 and C36 (int. board) or C33 and C37 (US board).  These
are a pair of 250V 470pF suppressor capacitors which suffer abuse from
mains spikes - mine were cracked so I replaced them - this got rid of some
nasty arcing in my Plus's mains switch that used to occur each time I
switched off.  You *must* use 250V Class Y capacitors for this job, such as
a Rifa PME 217 Y, RS 210 594.  If in doubt, assume the capacitors you have
are unsuitable.

It's also worth replacing (US and international board refs):

CR20 and CR21 with 45V-100V 10A Schottky barrier diodes
              suitable part: MBR1045 10A 45V RS 642-250

CR1 and CR5 with 400-600V 5A fast rectifiers (150ns or less if possible)
            suitable part: STTB506D 600V 5A 95ns RS 217-8420

and finally...  `Mac repair and upgrade secrets' says that the zener diodes
on the analogue board are inclined to drop out of spec.  It's worth
replacing them:

International board:

CR15   6.2V 500mW zener BZX79 series suitable RS 283-671
CR17   6.2V 500mW zener BZX79 series suitable RS 283-671
CR18   6.2V 500mW zener BZX79 series suitable RS 283-671

US board:

CR15   6.2V 500mW zener BZX79 series suitable RS 283-671
CR18   12V  5W    zener 1N5349B      suitable RS 850-338
CR19   6.2V 500mW zener BZX79 series suitable RS 283-671

If you do replace all these parts, you'll need to adjust the power supply
voltage and re-align the video circuitry - I've not got this far yet, so I
can't be much use.

Spec for the PS voltages is:

 +5V      +4.85V to  +5.15V
+12V     +11.90V to +12.80V
 -5V      -5.25V to  -4.75V
-12V     -13.00V to -11.30V

All the adjustment knobs are marked on the cover for the analogue board, so
it shouldn't be impossible to work things out.  Getting access to the
various PS voltages is tricker - the connector on the logic board (from the
analogue board) has three of them:

Pin number

1           White (video)
2           Empty (key)
3           Orange (hor sync)
4           Yellow (speaker)
5           Green (vert sync)
6           Blue +5V
7           Violet (ground)
8           Red -12V
9           Orange (ground)
10          Yellow +12V
11          Green +4.5V battery

Now then...  I've done an honest job with the stuff above, but mistakes do
happen - if anyone who reads this is in the slightest doubt about
*anything*, don't do it, and ask me about it.

<insert standard disclaimer>


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