Macintosh SE User Manual download pdf (Page 4)

Classic Mac Tech Docs, v1.1: No warranties expressed or implied. Use at your own risk!

The solder joints on the deﬂection yoke connector J1 are notoriously unreliable. These

should always be resoldered as a matter of course because a visual inspection does not

always reveal problems such as hairline cracks. Flakiness here results in symptoms that

include an intermittent raster, no raster, or a single vertical or horizontal line in the center

of the CRT. Without question, this is the most common problem with the analog board.

Many old Macs are tossed in the trash because of this; I know, because I’ve ﬁxed many

that were retrieved from dumpsters.

The horizontal windings of the yoke have a low DC resistance (~0.2 ohms). You should

measure an inﬁnite resistance between the horizontal and vertical windings.

The ﬂyback transformer T1 may be checked out with an ohmmeter for basic functionality.

Approximate interwinding resistances are listed on the schematic, and should be used only

as a rough guide. Suspect failure only if the values you measure are very different from the

ones in the schematic. (When testing, also verify the proper lack of continuity between

windings that should not be connected.)

Be sure to use a nonmagnetic, nonconductive hex tool to adjust L2’s core (you can get

these at places like Radio Shack, or make them yourself out of chopsticks, toothbrushes,

etc., if you’re really determined to do everything from scratch). Width increases as the

core is withdrawn from the windings, and is a minimum when the core is centered in the

windings.

There is no adjustment for horizontal linearity, but it is sensitive to L3 and R1, among

other things. Try ﬁddling with those if you are sufﬁciently unhappy with the linearity.

Capacitor C1, which does fail fairly often (usually in a visible way -- check for bulging

and cracking at its bottom, where it meets the circuit board), is 3.9µF in many versions.

Replace it only with a nonpolar, low loss (low ESR) unit rated at 50V or more. This

capacitor can be a little difﬁcult to locate on occasion, however, so if you are in a hurry,

I’ve had excellent success substituting a parallel combination of four 1.0µF ceramic disk

capacitors (there’s plenty of room; build it up as a module of four caps, and use two pieces

of bus wire to connect it to the pc board). These are readily available and inherently non-

polar, and the parallel combination reduces the overall ESR to lower values than the sug-

gested replacements.

4.0 Vertical Circuit

Compact models developed after the Plus use the ever-popular TDA1170 IC for the verti-

cal deﬂection circuitry, but the classic Macs use an equivalent circuit made out of standard

parts and a boxload of discretes:

1 2 3 4 5 6 7 8 9 ... 17 18

No comments

Macintosh SE User Manual Page 4