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Only John T. Frye can turn an episode of an electronics technician / tinkerer
attempting to devise a method of blowing up mosquitoes with sonic waves into a lesson
in solving television and radio servicing issues by listening to the audio and interpreting
CRT test patterns, as applicable. Mac's young apprentice is introduced to the recently
released troubleshooting volumes - called "Pict-O-Guides" - published by RCA which
presents a set of uniquely distorted television test patterns (recall the
Indian
head test pattern) with an explanation of which circuit likely cased the problem(s).
I note that Barney was told to take the Pict-O-Guides home to study them on his
own time rather than while on the clock.
Mac's Radio Service Shop: Skeeter G's and Test Patterns
 By John T. Frye
Mac jokingly expressed it, it was "two l-o-o-n-g
years" now that the unpredictable Barney had been working for him; so when the former
came into the radio shop that fine June morning and found his red-headed assistant
prodding a small cylinder of screen wire resting on the service bench and savagely
muttering, "Come on, cuss you; fly! I double-dog-dare you to get off the bottom
of that cage," Mac did not turn a hair. Instead he merely leaned against the door
jamb and casually remarked:
"Excuse me for mentioning it, Buster, but aren't you slipping your clutch again?
Talking to yourself makes you live bait for the boys with the butterfly nets, you
know."
"I'm not talking to myself," Barney protested. "I'm talking to that blood-sucking
mosquito in the wire cage."
"Well, then; that's different!" Mac said with exaggerated relief. "All of us
like to have a little chat with a mosquito now and then. Will the two of you excuse
me for interrupting?"
"You quit trying to make it sound like I was losing my marbles," Barney shouted.
"Outside of being crazy enough to work on radios, I'm as hep as the next guy and
maybe a little hepper.
"The whole thing started last night after I walked Margie home from the show,"
he went on. "It was the first really warm night we have had; the moon was as big
and bright as a twenty-inch tube; and her old man had just put up the porch swing
that afternoon. In short, things were perfect for a little front porch woo-pitching-or
'sparking' I believe they called it in your day."
"Thankee kindly fur the translation, young feller," Mac piped in the cracked,
falsetto voice of age.
"Well, we had no more than snuggled down in the porch swing than a squadron of
mosquitoes started dive-bombing us. You probably are too old to remember, but smooching
takes a certain amount of concentration. You can't get very far whispering sweet
nothings into one shell-like ear while a mosquito is making like a miniature fire
siren in the other. After I had intercepted a couple of wild swats Margie was making
at the pests - at least I think that is what she was doing - I gave up and went
home and to bed; but I didn't go right to sleep. Instead, I lay awake and thought
up a fiendishly clever way of clobbering mosquitoes.
"And there it is!" he said waving dramatically at the service bench. "A captured
mosquito is in that little screen cage. Directly in front of the cage and pointed
at it is a tweeter speaker that is being driven by the output of that hi-fi amplifier.
Our audio frequency generator is going into the amplifier."
"I get it!" Mac interrupted. "You're going to drive the insects mad by out-singing
them."
"Worse than that," Barney said darkly. "I intend to tune the oscillator to the
natural vibration frequency of either the mosquito's body or his wings - it makes
no difference which - and then I'll simply shake one loose from the other with the
compression and rarefaction waves from the speaker. Because of the small masses
involved, I figure the frequency will be too high to be heard. This arrangement
will be set up on my porch with the speaker pointed toward Margie's. Boy! I can
hardly wait until tonight to see those de-winged mosquito fuselages ploughing into
the porch paint around that swing!"
"Hm-m-m-m,' Mac said a little dazedly, "And how is your experiment panning out?"
"Aw, Old Buzzo there won't cooperate," Barney said disgustedly. "I've got to
catch him on the wing to try out the gadget, but all he does is sit there with his
toenails dug into the bottom of the cage."
"We-l-l-l, let's not fret our little pointed head about it now," Mac said soothingly.
"After awhile I'll hunt up a graph that Sylvania put out a few years back for estimating
forces due to vibrational motion, and then you can really 'engineer' this project
by figuring just how many 'G's' a mosquito's wings will stand. Right now, though,
I want to talk to you about something else."
He opened a cupboard and took out two small album-shaped books bound in imitation
red leather and another black book with a spiral wire binder.
"Here," he said, holding out the red books, "are Volumes 1 and 2 of RCA's 'Pict-O-Guides.'
I want you to take them home and study the diagrams, the text, and, above all, the
pictures until they are literally sticking out of your big freckled ears."
"Why?"
"So you can learn TV servicing easier and better than I learned radio servicing.
In the beginning my radio knowledge, like that of most of us who grew up with the
business, consisted entirely of scraps of unrelated information picked up haphazardly
from experience, from reading, and from what other technicians told me. I wasted
ten years before realizing that some way had to be found to tie all of this knowledge
together into a compact whole if I was to keep it and get the most out of it.
"That is when I hit on the idea of servicing radios as much as possible 'by ear.'
Circuits were analyzed in terms of what they contributed to the receiver in the
way of sensitivity, selectivity, noise-suppression, and fidelity. Component failures
and misadjustments were studied for the effects they had on these qualities in the
receiver's output. In other words, all of the information I had collected was rearranged
and revised in terms of how it made a set sound."
"A system that really works!" Barney exclaimed. "It still seems uncanny to me
how you can always tell what's wrong with a set by just listening to it."
"Not always," Mac disclaimed; "but by concentrating on this approach both of
us keep our batting average pretty good. The funny thing is, though, that I forgot
all about this when I started studying television and began to make the same mistake
all over again. I studied r.f. tuners, sweep circuits, i.f. systems, flyback power
supplies, and so on, as individual units; and I was having one heck of a time trying
to keep all of this mass of new information in my head. Then suddenly I wised up:
what I needed to do was to apply the same technique to TV sets that I had been using
in radio servicing. Each circuit was studied for just what contribution it made
to the picture on the screen or the sound from the speaker. Every possible component
failure was projected as a defect in the picture or the sound.
"That system made all the difference in the world. Once I got it through my thick
head exactly how a picture on the screen was put together, precisely what contribution
each circuit and component made to the composition of that picture, the whole thing
suddenly came into sharp and clear focus" What is better, just as soon as I understood
how a good picture was made, I was able to work backward from the picture to the
cause of any defects in that picture.
"What burns me, though, is that this 'discovery' of mine was old stuff to many
people. John Meagher of RCA had been harping on this method of attack for months,
and he had been photographing distorted test patterns and explaining what circuit
defects caused these patterns. Other companies, too, were and are using test pattern
pictures liberally in their service information to illustrate various forms of trouble
and misadjustment.
"But these two books represent the largest number of clear pictures arranged
in a logical order that I have been able to find. I don't want you just to look
at them or even to memorize them. I want you to study them. Beneath each picture
is an explanation of likely 'causes of the picture distortion in terms of a particular
part failure in a typical circuit; but I want you to go beyond that: I want you
to give me, in each case, a clear and logical explanation of just why the failure
of that component resulted in precisely the pattern disruption shown.
"For example, a pattern with reduced height and poor vertical linearity is attributed
to the change in capacity of a condenser in the plate circuit of the vertical discharge
tube. I want you to explain how an increase in that capacity changes the waveform
presented to the grid of the vertical output tube (being able to draw the correct
and distorted waveforms) and then go ahead and actually show how this incorrect
waveform causes the picture to be stretched 'here' and crowded 'there.' You grab
me?"
"Yeah, I grab you," Barney said dubiously, "but I'll have to do a heck of a lot
of brushing up on my TV theory. You want me to use that group of test pattern pictures
as a kind of framework on which to hang all the knowledge of TV theory I have or
can get hold of. It would be a lot simpler just to use them as a kind of 'rogue's
gallery' for identifying an electronic 'criminal' when I meet up with one, but you
aren't satisfied with just catching the crook and clapping him into jail. You want
me to psychoanalyze him yet!"
Mac chuckled at this complaint and then went on: "After you think you are pretty
hot as a pattern-puzzler, I'll use this book of pictures put out by Sylvania as
a sort of final examination. There are nearly fifty pictures in here that will be
strange to you. When you can just glance at them and tell me the probable cause
of trouble in nine out of ten cases, I'll give you your diploma!"
It could be worse," Barney said philosophically. "I was afraid you might try
taking pictures of tough cases yourself for me to analyze."
"We are going to do that, too," Mac promptly countered. "I wrote RCA for how-to-do
information on this subject, and John Meagher, with the kind of cooperation those
fellows over in Harrison, New Jersey, always show technicians, promptly sent this
information:
"Those figures are for a perfectly stationary, fairly-bright pattern. If some
part of the pattern is moving, shutter speeds of 1/50 or 1/25 must be used. I'm
going to use a close-up lens on my camera and make it a practice to take a picture
of every puzzling form of distortion I meet in servicing and which I cannot find
duplicated in either the RCA or Sylvania books. These prints will be mounted on
4" x 6" file cards, together with data on the discovered cause of trouble, and then
filed in a box or punched and inserted in the "Pict-O-Graph' books."
Barney heaved a big sigh. "There goes another of my simple pleasures," he mourned.
"Up until now I have always associated a camera with pictures of beautiful babes,
but from now on every time I see a Kodak I'll think of a test pattern!"
Posted August 17, 2023
(updated from original
post on 7/12/2017)
Mac's Radio Service Shop Episodes on RF Cafe
This series of instructive
technodrama™
stories was the brainchild of none other than John T. Frye, creator of the
Carl and Jerry series that ran in
Popular Electronics for many years. "Mac's Radio Service Shop" began life
in April 1948 in Radio News
magazine (which later became Radio & Television News, then
Electronics
World), and changed its name to simply "Mac's Service Shop" until the final
episode was published in a 1977
Popular Electronics magazine. "Mac" is electronics repair shop owner Mac
McGregor, and Barney Jameson his his eager, if not somewhat naive, technician assistant.
"Lessons" are taught in story format with dialogs between Mac and Barney.
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