TV-7 Tube Tester - Repair Notes:

Symptom 1 TV-7's meter does not move smoothly.
This is the very first problem that a beginning collector comes across from his onstart. You find a tremendously
attractive TV-7 tube tester sold at some auction site, and cannot resist purchasing it in spite of the description
saying," I used this tube tester a few years, and I am selling this as is now, because I don't know if this works okay now...,"
or "This used to be my dead father's tube tester, and as I don't know how to use this, I am selling this tester AS IS."
I have purchased this sort of TV-7 tube tester before, and some worked perfectly all right, and the seller, obviously a woman in
her forties, was telling me the truth, and her tube tester beautifully and very carefully packed, reached me in good shape,
and the tube tester itself had no problem at all, but oftentimes the descriptions given were not true
and found out to be total lies.
Yes, I purchased TV-7 tube testers whose meters do not move smoothly.Maybe that meter is bad, or broken,
but there are sometimes another cause that is existent.
A electrolytic capacitor connected in parallel with the meter is sometimes almost worn out and broken and preventing the smooth
movement of the meter indicator. You can test whether your meter is really bad or good just by disconnecting the meter
terminals from the tube tester circuit and let it work separately from the circuit. You can connect the meter
with a 1.5V flashlight battery with a 30 k ohm potentiometer in series connection. Also you had better connect a on-off switch in
series, too. The purpose of this potentiometer is of course to protect the meter from over-deflection when switched on.
1) First, turn the potentiometer counter-clockwise, and gradually and slowly turn it clockwise and then turn of the switch and
then turn it on. In this way you can learn the continuity and whether the meter itself is okay or not.
The electrolytic capacitor may not be totally broken but in most cases, the 100 micro Farad, 6WV capacitor is now worn out
and is very weaK and is about to be broken down. If you replace it by the same kind of brand-new capacitor the meter will restart
to move more vividly and normally and will work to your heart's satisfaction. The testimony I can give you is that
I experienced the same kind of trouble when I successfully repaired a TV-3 US Navy Tube Tester a couple of months ago.
You can tell the reason why this happens just by testing the electrolytic capacitor alone. A good-working electrolytic capacitor,
if you test by your circuit tester will let the indicator of your cicuit tester move very forcibly or vividly with a good speed while it
is charging. Also it moves quite rapidly when it is discharging, whereas inferior electrolytic capacitors charge or discharge very slowly,
and their movemnet is somewhat similar to the unsatisfactory movement of TV-7 meter itself. I believe the purpose and function
of this capacitor connected in parallel with the meter is for meter protection.and the worn-out capacitor is often impeding the
smooth movement of the meter, so why don't you give it a try and your meter will start to move more vividly and forcibly.

2) Symptom 2 The Meter Is Broken:
TV-7 or TV-2 tube tester's meters are of sealed type, and their enclosures say, "Do not open, SEALED."
Yes, sir. They are sealed very tightly and it seems that you can hardly repair such highly complicated, sealed meters.
I understand that some specially trained, experienced repair persons in the United States alone can reapir such stuff.
I firmly believed so. I myself tried to open the front portion of the meter and in the case of TV-7 /U or TV-7A/U meter,
it is accompanied with great difficulty because the meter glass is glued to the meter vessel. After removing the glass out of
the meter case, I tried to loosen the pivot bolt and succeeded in letting it move smoothly but perhaps this is a very dangerous
and adventurorous way of fixing the meter. Later I tried to open the TV-7B/U and TV-7D/U meters and as those meters' front
covers are made of plastic and the meter frames are fixedwith nine screw bolts, it is easy to open the front part of the meter by
removing those nine small screws. If the bad, sticking movement is caused by dirts or bad pivot supporter, one spray of CRC
lubricant may repair the meter once and for all(*), but there are other causes, which amateur repair persons cannot make head
or tail of it, then you can rely on my old ham radio friend whose callsign is JA3OEJ, Masami Hayashi, living in Wakayama
City Japan. He will be able to help you worldwide. His email address is cbt96560@pop06.odn.ne.jp . He does not reveal his technical
know-how of repairing the meters, so I can only guess this and that, but of course he will be willing to repair your broken meters
for nominal rewards, however he cannot repair those meters whose coils are open. Such are the dead meters.

(*) As regards, this method, I got the kindest advice from Mr. Daniel J Nelson, TV-7 Doc. of the United States:
I had a moment to read over your repair experiences with the TV-7. Your experiences are interesting and I
approve from a technical point of view. However, I do not think spraying anything into the meter is a good thing.
Perhaps, as a last chance for the meter, but I think it will cause the meter to stick later.

3) Symptom 3 No Plate Voltage at All:
I came across this kind of TV-7 tube tester the other day. The US military Maintenance and Repair Manual is of great help in
pin-pointing trouble spots, and oftentimes by through and through going the calibration procedure you can learn what part in the
circuit is wrong. The latest broken tube tester I came by through Ebay Auction in the United States was a non-working one. The
seller has mentioned that you can zero-adjust the tube tester, but you cannot test tubes because there is no signal voltage.

Well, the repair of this tube tester was the toughest job that I had ever done till today, and of course it took longer hours than
anything else I had ever attempted. I read and read the repair manual and had to learn the flow of test signal from the beginning
to the end. Bias voltage was okay, screen voltage was okay, and still there was no plate voltage. I checked the continuity of the
transformer, the function of rectifiertubes,5Y3 and 83, and their circuits. They were all okay!! And yet still no plate voltage was
detected at the Octal(GT) socket, as a result I had to restartchecking everything from the very beginning. I checked and thought
of every possible causes of this trouble every evening. Then one day, while I was looking at the plate voltage switch, I finally
found out the cause of all this trouble. There was a crack on one section of the ceramic rotary switch, and there was no connection
at the top wafer (section) of the rotary switch, so I was at a loss what to do. Again my old friend suggested to me that I should
replace it by taking one section from the broken rotary switch of another TV-7 tube tester and surely enough, I was able to succeed
in repairing the damaged rotary switch. It was so easy because all I had to do was to loosen the the nuts on the top section, and
remove the cracked ceramic wafer and replace it by a normal one and then resolder the wires on it again.
After that my TV-7D/U began to work perfectly fine.

4) Symptom 4/ bad Function of TV-7 after measuring Shortened Vacuum Tubes:
Mr. Daniel J Nelson says;
Also, you may wish to include the following note. If during testing of a tube, where the tube is shorted internally,
and this is not detected before pressing the test buttons, the grid and or screen supply may be connected to the
plate supply while the button is pressed. The fuse light will glow very brightly and the test button should be
released immediately. However, if this is done very
long or very many times, damage to the TV-7 may result. In most cases, the damage is to some 47 ohm resistors
which are located on the Grid/Plate/Screen rotary switches. You have to look for them as they are between
the switches or between the switches and the transformer. These resistors are carbon and if overheated, will
open circuit or cause erratic operation. Low power tubes may test fine, while power tubes will test odd or bad
due to the increased current, which heats up the resistor. When the resistors are already 'cooked' from previous
mistreatment, they can change resistance values a lot, sometimes 4 or 5 times. Inspect these and replace with
carbon film or metal oxide 1 watt resistors. Often resistors which are stressed, are fragile and pressing on them
with a screwdriver blade will break them. If you can break them in this way, they were bad.

5) Sympton 5/ No Plate, Screen, and Bias Voltages can be detected at HS5-3460 on TV-7C/U Tube Tester:
One of the Japanese hobbists purchased this broken tube tester from Canada, and the problem with his TV-7C/U was that he could not
test any vacuum tubes even though he could make zero-adjust without any trouble.
Yes, he was right. I checked and found exactly what he had mentioned.
I set this tube tester to the switch positions HS5-3460 just as I always do, and to my regret I was not able to detect any voltage between
6-3 pins, nor 6-4 pins, nor 6-5 pins of GT socket whatsoever. So I thought of every possibilities, I looked into the maintenance manual for
any possible causes of this kind of trouble; I checked the voltages at the terminals of the transformer, but nothing was wrong with the
transformer. I checked all the resistors, also the voltages on the resistor board, but nothing was wrong with any of them.
I was still not able to pinpoint what is wrong with this tube tester. Days passed, and every evening I looked into the Schematic of this
TV-7C/U ( whose circuit diagram is just the same as TV-7/U , remind you ). When I am at a loss what to do next day, I always sleep with
the schematic, and sometimes, while sleeping I can think of the possible causes of the trouble. However I was not successful this time!

One day, I hit upon a good idea; if I can not detect any voltages at the tube socket, why not try with the following method:
I connected one tester lead to No.19 terminal of the transformer and the other to GT socket pins.
Yes, sir! I was able to detect plate, screen, and bias voltages all right, so I was able to conclude that something was wrong with the
minus circuit of the tube tester, even though I could not tell where the trouble spot was, but at least I was at the door of the troubled
spot. I traced every wire connections in the minus circuit at HS5-3460. I was not able to spot where it was wrong yet. But accidentally
I turned the filament switch to GS5-3460, then I was amazed to find that all the normal voltages were detected on my TS-352 Multimeter!
Uhuum!, I realized that SW positon G and H are the most likely position where something is wrong.
I traced every possible mis-connection in the circuit, but there was nothing to be found! I used multimeter's ohm range, and checked
again and again, and finally, yes in the true sense of the word, FINALLY I have successfully found the cause of all these troubles.
The Nr. 6 contact point of the Cathod rotary switch was wrong, it was crooked and was not touching the Rotary portion of the switch,
so I have very carefully repaired the contact point of the switch, and gave some flash of contact point jeveniler, and then the tube
tester has started to work normally--
Plate volatge is 150.0V DC/ Screen voltage is 129.0V DC, and Bias voltage is 39.0V DC at the potentiometer scale of 100.
So the rest of my work is going to be very simple, I will calibrate this tube tester just as the US military maintence manual says, and
also just as Mr. Daniel Nelson, Tube Tester Doctor of the United States, guides us.
I have learned a lot from him, and also from the specialists on TV-7 tube testers thoughout the world. So I hope that this descriotion of
mine will help you to some extent, even in the smallest way when you come to your broken tube tester, or those of your friends.
Your knowledge of electricity will help but I have also experienced that more than knowledge, what matters is your patience, physical and
spiritual stamina, and willingness to fight the trouble until you finally find out the true causes of the tube tester troubles.
If you are repairing these tube testers for money, at first hours that are required for finding out the causes, seem to be ever-lasting,.
and never-ending, but it is not so.
You learn by experience, and little by little you learn to repair very quickly, and some guidance like mine will also helpful.
The trouble I have found on this TV-7C/U must have been deliberately created by somebody in the Canadian military authorities concerned,
when they cast away this tube tester. Japanese Defense Force cast away TV-7 tube testers by breaking the meter of the tube tester using
hammmers. US military forces stationed in Taiwan cast away their TV-7 tube testers by breaking all the ceramic rotary switches to pieces,
each used different methods to make tube testers non-usable. However, I believe this TV-7C/U, produced by Stark in Canada, and had been
used by the Canadian Military Forces in the past was fortunate in that they had not broken this tube tester to pieces!

( described by Philip Y. Shibuya on the evening of May 25th, Tuesday, 2004)

To be continued....
Philip/JA3KEV
January 14th, 2003