Star Tech Journal

STAR*TECH
Journal
Enzo
June 1996
CD
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"Hey Enzo, I can't find the self-test button on this Captain Fantastic!,,
Douglas 'Enzo' Mccallum • Shiawassee Technical Services • Lansing, Ml
PARTS SUBSTITUTION AND USING STANDARD PARTS
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The best substitute for a part is no substitute at all. Use the real parts as often as possible.
Call your distributor, call the catalog parts houses, call the manufacturer of the game,
call the manufacturer of the sub-assembly, call others in the business.
Not everybody in this industry thinks of competitors as enemies.
Sometimes we have no
choice, and we must
replace a component
with something else.
BE INFORMED
You can't make subs unless you
know what you need and what
you have. Buy a Japanese tran-
sistor manual, and find domestic
semiconductor
guides.
Motorola's data books cover their
line, which is the most extensive.
Texas Instrument and others are
useful. For domestic IC suppliers,
get the National Semiconductor
books to start. These manuals
and guides will tell you the speci-
fications of the parts you are try-
ing to replace. These data books
are available through some of the
catalog parts houses like MCM,
DigiKey,Jameco, etc. Electronics
Now is a good magazine (for-
merly Radio-Electronics) for sup-
plier advertisements. All of these
companies and more can be
found near the back of the maga-
zine.
Go beyond symptom-response
servicing and really learn how
things work. Read, read, read.
Subscribe to Electronics Now and
other publications of the sort. You
will learn a lot there. A good un-
derstanding of circuits will al-
low you to make reasonable sub-
stitution decisions.
For example: the capacitors used
in filtering, decoupling and the
like are fairly insensitive to value
and will be OK with any more-
is- better sub. (CSl 1 in the
Electrohome G07, the power
supply filter, or C407 in the
Sanyo, the sweep foldover cap
are typical.) Their job is simply
to smooth out the DC and re-
move any traces of signal. On the
other hand, caps used in the sig-
nal path or in timing applications
are much more critical, and off-
value subs can cause loss of sync
in your video, wrong picture size,
hot flyback transformers, funny
color, and so on. For these the
value of the sub should be pretty
close. You can always use higher
voltage caps than the originals.
You should at least teach your-
self enough electronics to be able
to recognize filter applications in
the various circuits.
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Transistors have similar story -
subs in the power regulation cir-
cuitry are fairly forgiving, so long
as voltage and current minimums
are met. After all, frequency re-
sponse and switching time are
not too important in DC circuits.
On the other hand, a horizontal
output transistor needs to be re-
placed with a transistor designed
for such use. As an example the
2SD870 will replace the 2SD869
because they are essentially the
same except for the 870's larger
current rating. We can look this
up in our Japanese transistor
manual.
When you look past all the cur-
rent and voltage ratings, all the
sizes and all the shapes, there are
two kinds of horizontal output
... continued on next page.
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