How to Repair Century Electronics FC-1 & FC-2 Fast Check Tube Testers: Century Electronics FC-1 and FC-2 Fast Check Tube Testers are among my most favorite Emission Measuring tube testers manufactured in 1960 - 1970's in the United States of America. Century Electronics Co.,Inc. 111 Roosevelt Ave, Mineola, N.Y. is the manufacturer of these tube testers. Their characteristics and merits as compared with other vacuum tube testers manufactured by other companies are: 1) Various tube sockets are prepared for fast-checking purposes. As a result, you don't have to move a large number of levers up and down on the operation panel as seen in the case of EMC, Heathkit, Knight and many other tube testers. 2) You just look up the set up data in the Tube Data Sheet for a particular vacuum tube you are going to test. All you find in the data sheet is the following: Suppose you are going to test an EL34 power tube; EL34 D 32 3 The first alphabet letter D means that EL34's filament voltage is 6.3 V.and the numbers that follow are the value on the scale for the adjustment of plate and screen load. You can simply turn the knob of load control potentiometer to the value designated for your particular tube. The number that comes at the tail is the name of the socket into which you are supposed to insert your tube. 3) The next thing you are supposed to do is to push the test button and watch the reading the needle pointer of the quality meter shows. The schematic diagrams of FC-1 and FC-2 are below, and you can easily download them if you need any of them. Schematic of Century FC-1 Fast-Check Tube Tester schematic1/schematic2(Download PDF Files) Schematic of Century FC-2 Fast-Check Tube Tester (Download PDF File) I) Case Study - Repair 1: Simple Is This Cure! I have repaired and/or calibrated over twenty FC-2 tube testers and a couple of FC-1 tube testers so far. The trouble spots of each tube tester are different, so finding out where the trouble lies is an interesting challenge for my head, and the pleasure and satisfaction after I have successfully repaired the broken tube testers is very great!! Now the Easiest Repair!/Is this called a repair job???? Most often this happens -- I had been waiting for the coming of a tube tester from the United States. And it came to my house and with a pounding heart I switched on the stuff, and waited for something to happen. But nothing happens at all. Well I was just going to regard this tube tester as a completely broken one, and was about to remove the screw bolts out of the panel, and then all of a sudden, the meter's indicator needle starts to move very very slowly and like a man who had woken up from a long sleep, this tube tester,slowly but steadily, starts to work properly. I believe the reason for this kind of phenonmenon is that some part of this tube tester's touch points, like those of switches had been oxidated, but just by turning on the power switch, the tube tester's whole system comes back to its normal condition, after an hour or so, nothing abnormal in its functions are found out, I can call this a perfectly working tube tester! II) Case Study - Repair 2: A Little More Difficult Repair! Of course this kind of tube tester works in accordance with a simple principle of OHM's LAW, so you can understand various portions of the tube tester from the famous equation E= IxR, R=E/I, or I=E/R. However, you need some skills or experiences in repairing these sorts of broken tube testers if you are going to repair them at all. 1) You also need some basic knowledge about the qualities of resistors, capacitors, electrolytic capacitors, transformers, DC ampere meters, rotary switches, etc. 2) You also need to know how to use a multimeter ( a circuit tester, we call it in Japan), but as an amateur hobbist, you will know how to use your multimeter as a matter of course! Now let's start to find where this non-working tube tester is wrong. A) Check whether the quality meter is okay: The First Check Item is the Quality Meter!!! I always try to check the quality meter of this tube tester -- Unlike the quality meter of TV-7 tube testers which are 200uA DC meter, the meter for this tube tester is 5mA DC meter, so you need a larger current to let it deflect.---Just a 1.5 volt flashlight battery, a couple of cords, and a 10k ohm potentiometer are the stuff with which to test its meter in my case. Whatever tube tester I try to repair, I start with a quality meter, wishing to know whether it is okay or open, and if there is continuity, whether it deflects normally or not. If there is no continuity in its meter coil, there is no need to check the tube tester further, because the tube tester is dead! This tube tester I came across did have continuity, so I checked all the resistors and capacitors inside -- there are ten resistors including two potentiometers, and four capacitors, and the rest are three neon lamps, three switches,a transformer, a rectifier diode. If you are just a beginner in repairing this tube tester, it is not a waste of time to check all the qualities of all the parts inside. 1) Continuity of transformer's coils 2) Resistor Values 3) Capacitor Values 4) Rectifier Quality 5) Or any visible changes or transformation of circuit constructions -- Often this inspection by your eyes will solve all the trouble problems once and for all, because some amateur hobbists seem to have tried to repair the tube testers without knowing how to repair, and seem to have replaced some radio parts without sufficient knowledge of electricity! This kind of repair is the most difficult of all, do not believe that all the parts inside the tube tester are of the correct resistors and capacitors -- they are often replaced by wrong ones by ignorant repairmen who know nothing about the circuit or do not have any schematic of this tube tester. 6) If you do not have the schematic of this tube tester, please do not attempt to repair the tube tester too much, you may complicate the trouble to the degree in which you can no longer repair it and make it unrepairable!! First obtain the schematic of this tube tester, it is like a map for treasure hunting! The tube tester I was going to repair had a meter continuity, but it did not work, even though the pilot lamp lightened up, but nothing further happened. I have discovered the following faulty part; A meter shunt was open,and this was all the cause of the non-working circuit. However, the next problem is how to get a part necessary to replace this shunt, a 1k ohm semi-variable wire-wound resistor of the same value, and the same qualtiy. The counter-measure I took was to replace it by the same wattage resistor I picked up out of my junk box, and to find the appropriate value for its proper reading of the quality meter, I checked the value of the same model FC-2 that I happened to possess, and have found it is about 620 ohm. So I soldered a resistor of that value, and the repair of this tube tester was successfully finished! III) Case Study - Repair 3: Multiple Parts Are Broken: If one part is broken, your trouble-shooting is not too difficult. However, if more than one part is broken it takes time to spot the wrong parts! You have got to find out one wrong part after another. As I have mentioned above, this tube tester is very simple in schematic structure, you can learn a lot out of this repair. The second tube tester I tried to repair had more than one broken parts. 1) The shunt resistor was open, and I coped with this trouble by connecting wires reversely because one direction of the potentiometer was broken but the opposite direction had a continuity. 2) The Load Control rheostat had been replaced by 20 ohm potentiometer. I don't know the reason why this kind of big mistake had been made but really such a replacement had been made, and I wondered how this kind of wrong repair had been made. Probably an amateur repairman tried to repair this tube tester misread the reading of his multimeter, and replaced a faulty part by a wrong part. I took a replacement part out of my FC-1 tube tester with a frozen rotary switch and seemed impossible to repair, and then the above tube tester came back to life again. III) Case Study --- Repair 4: Rectifier Diode Was Broken; This repair was just simple. I checked up all the parts used in the circuit, and found the only diode in the circuit was short-circuited, and no DC current had been produced The rectifier diode used in this tube tester is 1N48, I don't have any rate table about this American diode,but my rough conjecture about this diode is VRM 170V VR 150V IF 150mA Io 60mA So I picked out a diode a bit larger in its rating and my repair was over. IV) Case Study --- Repair 5: Strangest Troubles; Last but not least, I am going to refer to the strangest troubles you may really laugh it away! (^.^)!!! Just as somebody was mentioning on his web page, we should not purchase such tube testers as have no screws for fitting their panels to the enclosures. What he says is completely true and does make sense; and the reason is self-evident. Such tube testers have been attempted to repair by amateur repairmen in various ways, and oftentimes some of the resistors or capacitors are replaced by wrong value resistors or capacitors, say, at random. And these repairmen may not have had a schematic and may have tried to repair his tube tester in terms of his own experiences, skills and his sixth sense, and as a result he may have complicated the troubles three- folds and after giving up his own repair, he may have put it to sale on the auction. I believe this kind of tube tester is the most difficult to repir and even if you may succeed in your repair, it takes more time than you have expected. In some cases, it may seem to you that you are trying to newly produce a new kind of tube tester from the very beginning. Philip Y. Shibuya February 22nd, 2003 To be continued: