July 1972 Popular Electronics
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
This 1970s-era Mac's Service
Shop story made me think about all the cellphones today being dunked in toilets, swimming
pools, lakes, and washing machines. Of course back in Mac's day not everyone was
walking around with an electronic device tucked into his or her pocket waiting for
its absentminded owner to bend over or drop his/her drawers. At the time, far more wallets made
the dive than transistor radios. I won't bother linking to any articles about how to
best dry your dunked phone because there are hundreds - nay, thousands - of them out
there. They contradict each other about which absorbent materials to use or not use.
Nearly identical tests with a wide variety of phones show completely opposite
results. Nearly everything is anecdotal, with no truly scientific method applied. One
thing most people agree on is that plunging your wet phone into a bowl of rice will
only get you a dry outside with sticky rice residue all over it. If the phone manages
to work afterward, it likely would have done so without the rice. Note, as mentioned
before, that the seasonal setting of the story coincides with the edition's publish
Mac's Service Shop: Salvaging Dunked Radios
By John T. Frye, W9EGV, KHD4167
Summer had finally come with a vengeance. After a hot and humid night, the morning
sun blazed from a cloudless sky and was already pushing up the mercury when Barney stepped
gratefully into the air conditioned coolness of Mac's Service Shop.
"Man, it's going to be another scorcher," he said to his employer busy training a
heat lamp and a small fan on an uncased transistorized radio lying on the end of the
service bench. "Oh, oh!"he broke off. "I see the dunking season is upon us."
"Right on both counts: it is going to be hot and humid, and people have started dropping
their radios into oceans, lakes, ponds, rivers, creeks, swimming pools, bilge water,
"I'm always a little astonished at how many of these victims you're able to resuscitate,"
Barney admitted, "especially since I know what an enemy of electronic components moisture
"In the beginning, I was pretty pessimistic myself," Mac said. "It all started years
ago when a customer brought in a big console Philco radio with the first remote control
system I ever saw. This system used a low-frequency r-f control signal and a complete
control receiver, together with thyratrons, a stepping relay, and electric motors to
tune the receiver and control the volume.
"It had a very impressive chassis, and it was a real mess. The river had come up suddenly
in the night while the owner was away from home, and when he waded out to his house an
the following day he found the receiver floating speaker-down in three feet of muddy
water. He simply loaded it into his trunk and brought it right in here to the shop.
"Everything, including the tube-type battery-operated remote control unit that was
about the size of a football, was caked with a thin coating of mud. The veneered cabinet
was already starting to split and break. I took one look and advised him to forget about
it, but he was stubborn. He said he liked the way that radio operated and sounded, and
he was not concerned with the looks of the cabinet. He wanted it repaired, no matter
what it cost. He was willing to pay me for my time if I would just try to make it work.
Money was of no concern at that point."
"Must have been a well-heeled bank robber," Barney observed.
"No, just a well-heeled bachelor brick layer," Mac answered. "Anyway, I took on the
"First I washed off all of that mud I could with the garden hose and then wiped off
the rest. Then I used a couple of heat lamps and a big fan to dry off the moisture as
fast as I could before I started checking. The tubes, of course, were unaffected. I checked
out all the paper capacitors and replaced a half dozen or so that showed leakage.
"The electrolytics were OK; and resistance checks looked all right; so, with considerable
misgiving, I turned it on. It began to play at once. For three days I kept it going continuously
with the fan blowing on it; then I shut it off and completely realigned all tuned circuits,
including those of the remote control receiver. After it ran for three more days without
the least trouble, I gave it back to the owner with a request to let me know how it worked
out. I did not see him again for over a year, and then the trouble was simply a burned
out tube. The set, he reported, had been working perfectly all the while. And fortunately,
there had been no more floods."
What About PC Boards? "That was a hand-wired job," Barney pointed out. "I imagine
things may be a little different with a printed circuit board where short leakage paths
can really foul things up."
"That seems reasonable," Mac agreed; 'but, as you yourself pointed out, we've had
very good luck reviving transistorized receivers that have even been dropped into salt
water - if they have not been in the water too long and if we get them reasonably quickly
after their baptism. If the receiver is dropped into salt water, the best thing the owner
can do is to rinse it thoroughly in fresh water just as soon as he can. The idea is to
wash away, or at least dilute, the corrosive salts before they have time to eat into
metal parts and to attach themselves to the circuit board. If these salts are allowed
to dry on the board, they can still continue their dirty work because of their hygroscopic
nature. They can readily absorb moisture from the atmosphere and continue to cause their
chemically corrosive action."
"One thing that helps protect these radios from moisture damage," Barney suggested,
"is the coating over the circuit board and the wax impregnation of the coils. Transistors,
of course, are hermetically sealed, and electrolytic capacitors that have been sealed
to keep the electrolyte moist are also protected against the entry of water. One item,
though, that has no protection is the paper cone of the speaker. I notice that quite
often you replace the speaker.
"That's right. Oddly enough sometimes the cone suffers no warping at all after being
soaked, while again it may come out looking like a washboard. This probably has something
to do with the nature of the cone material or possibly with the synchronization of the
drying action of the different areas. At any rate, I replace the speaker if there is
any rattle or distortion in the sound or if the cone is visibly warped. Since the owner
is usually convinced his favorite radio - quite often one with a deep sentimental value
- is hopelessly ruined, he is very glad to pay for a new speaker.
"Incidentally, a final critical check of a dunked radio is a comparison of the measured
current drawn by the receiver with the manufacturer's specification. Any appreciable
increase in this current indicates leakage that will impair performance, shorten battery
life, or both. The current must be brought down to normal before the receiver is returned
to the owner."
"Summer vacation time is pretty hard on electronic equipment that is not dropped into
the drink," Barney observed. "Radios and tape recorders are left in the boat, on the
dock, or by the swimming pool all night. A thundershower soaks a portable TV or hi-fi
left on the screened-in porch. Night-flying bugs and even mice crawl into portable TV
sets operated out-of-doors or in cottages and are electrocuted."
"Yes," Mac agreed, "and while most people have learned you shouldn't leave your loaded
camera on the back ledge of a shut-up car on a hat summer day, they still leave their
radios and tape recorders there. Sun shining on such an item through the rear window
can raise the temperature inside the case to 140 degrees or higher - hot enough to melt
the wax of capacitors, dry out the electrolytics, and shorten the battery life. The radio
or recorder is much better off under the seat where it is safe from both the sun and
the eyes of a possible thief."
"Hey!" Barney interrupted, "when our basement was flooded by a cloudburst a couple
of years ago, the gas company men came out and shot carbon tetrachloride into the various
furnace controls to take the moisture out of them. Why don't we use carbon tet[rachloride]
to dry out radios?"
"For the same reason we don't use it as a degreaser," Mac answered promptly. "It is
too dangerous to use except under carefully controlled conditions by carefully trained
technicians. However, there are several aerosol chemical products on the market, such
as General Cement's Dri-Spray and their Formula 70 Moisture Remover that will do the
same job safely. You'll find both up there in the cabinet."
Effects of Air Conditioners. "I'd think the widespread use of air conditioning would
make things a lot easier on electronic equipment in the home during the summer time,"
Barney remarked. "Not only does it keep the temperature down, it also takes the harmful
moisture out of the air."
"Again you make sense," Mac replied, "but I can recall at least one instance in which
things did not work out that way. This was the case of a roll-around color TV set that
seemed to have more than its share of summer breakdowns. After the third call to replace
components in the high voltage system, I checked that set out very carefully and was
puzzled to discover the chassis was actually rusting in several places; yet the owner
assured me the receiver was never used outside the house or in the basement. Persistent
quizzing, though, revealed the source of the trouble:
"The set was ordinarily used in the living room right next to a window air conditioner.
The owner noticed the cabinet became quite warm during operation - it was a tube type
receiver - so he was accustomed to pulling the receiver away from the wall and directing
the cold air stream from the window unit directly into the back of the cabinet. This
kept the chassis cool all right, but it ,also kept it yo-yoing up and down through the
condensation point as both the receiver and the air conditioner went on and off. Moisture
condensed on the metal chassis and the metallic leads of the printed circuit boards.
High voltage arced across various points and either burned out components directly or
formed carbon paths that did the job more slowly. I suggested he discontinue his practice
of 'cooling it,' and that was the end of the summer complaint with that set."
"Just goes to show you can get too much of even a good thing," Barney said. "But it's
still a good idea to protect electronic equipment from heat and humidity. The two in
combination are particularly harmful. That's why it is murder to install such equipment
in a warm, moist basement. Many a ham has learned to his sorrow that a snug basement
ham shack is not a good idea at all unless the humidity can be carefully measured and
controlled continuously. Persistent moisture is especially rough on high-voltage transformers.
I had one ham friend who blew three of these before he finally got the message and moved
"I know, I know," Mac said. "That is one of the chief reasons I put air conditioning
in here. Before I did, I was having a lot more trouble keeping the instruments in calibration
and in good operating condition during the summer season."
"Did you have to go and say that?" Barney asked plaintively. "Here all this time I
thought you put the air conditioning in to provide for Matilda's and my comfort! Can't
you leave a guy a single illusion? I certainly hate to realize I've been playing second
fiddle to a VTVM!"
Posted January 30, 2019
Mac's Radio Service Shop Episodes on RF Cafe
This series of instructive 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
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.