Troubleshooting The EICO 666/667 Tube Tester Meter Mike at MDBVentures.com 25 July 2017 (updated 31 Mar 2019) Mike at MDBVentures.com http://www.MDBVentures.com - Great prices on great tubes! So, you just bought an EICO 666 or 667 tester and it doesn't seem to work, here is a quick run down of the things to check. Note: This article assumes you have already performed the checks noted in the restr666.txt file, so if you haven't down-loaded and read the http://www.fourwater.com/files/restr666.txt file yet, do so before you continue on with this information. Also note that the test description below assumes you are doing the tests in the order written. If you do them out of order, the resulting problem description may not be correct for the test results seen. ***WARNING*** Caution! Be careful, there are lethal voltages present and exposed with the tester out of it's case. If you don't know what you are doing or feel uncomfortable doing the work, get a qualified technician to do it for you. ***WARNING*** Before you start, consider this: Sometimes a switch can go bad over a long time of sitting, especially in a damp location. So first, try moving the associated switches for the meter test a bunch of times to see if it will fix the problem. The switches involved are: 1. "Transistor Test" switch 2. "Line" calibration button 3. "Merit" switch 4. "C" button (only used for the Leakage cal). Before you remove the tester from it's case, do the following checks. Remember to properly set all the switches to the proper settings to check the meter. 1. Set the Transistor test switch to "Tube". 2. Press the "Reset" button so that all the latching push buttons are released. 3. Set all the levers to the "1" position. 4. Set the Line Adj control to 115. The other controls don't matter, although if you want, set the Grid and Plate controls to the center postion and the Filament switch to 6.3V. Plug the tester's power cord into a power source. Press the Line adjust control. The meter needle should move. If it doesn't, then the internal tests will have to be done to find out the cause. Note: There are four common causes. 1. The meter is broken (most likely cause). 2. There is a bad connection or part someplace internally (less likely cause). 3. The fuse is blown (rarely happens). 4. The tester is a parts unit that has had some internal parts cannibalized. Another consideration if the above test fails: Sometimes a switch can go bad over a long time of sitting, especially in a damp location. Try moving the switches multiple times to see if you can work the contacts to be free of oxidation or grime that might be the source of the problem, then try the above test again. Check the fuse: If you have a 667 tester, check the fuse before opening the tester. The fuse almost never blows, but it is an easy check since it is right there on the front panel. On the 666 tester, you will need to open the tester to check the fuse (we'll check that later). Internal tests of the meter circuits: (without removing the tester from it's case yet) You will need a Digital Voltage Meter for this test. Do not use an analog meter (one with a moving needle) as they will load down the circuit too much. (The exception is that a VTVM would be ok.) The easy quick check without removing the tester from it's case is to set the Transistor test switch to "Tube". Press the "Reset" button so that all the latching push buttons are released. Set all the levers to the "1" position. Set the Line Adj control to 115. The other controls don't matter, although if you want, set the Grid and Plate controls to the center postion and the Filament switch to 6.3V. Set the meter to measure DC voltage on a scale that will be able to read around 100 Volts. Press the "C" button until it latches. Connect the negative lead of the meter to the cap connection of the Cap test lead (the lead that connects to the cap connection on a tube that has one). Connect the positive meter lead to the tester's faceplate (it is a ground connection). (The tester uses a positive ground system.) You should see around -66 Volts DC on the meter (between -40V and -90V is ok at this point). If there is no voltage, then either the tube tester's meter is bad, or one of the switches is bad (an open circuit someplace is the most likely cause, although a short circuit someplace is also possible). This test goes through the Transistor Test switch, Merit switch, Line Cal switch and the "C" switch. This is the shortest path without opening the tester. If you don't see the voltage, try moving the switches a bunch to see if you can get them to make a proper connection in case they are the problem. If you see any voltage at all with this test, then it may be possible to fix it. If you don't see any voltage, then it is less likely that it can be fixed (but all hope is not yet lost, so read on). Removing the tester from it's case: The next test requires pulling the tester from the case. First unplug the tester. Then undo the screws around the edge of the tester faceplate (14 screws along the black line that marks the outside of the faceplate. (Do NOT remove the four screws next to the roll paper knobs, they hold the roll paper assembly in place). ***WARNING*** Caution! Be very careful at this point as there will be lethal voltages present which can kill you. If you are not comfortable doing the next series of tests, then get a qualified technitian to do it for you. ***WARNING*** With all the controls set as before, but with the "C" button NOT latched (ie press the Reset button to make sure all the buttons are released), Connect the negative meter lead to the center connection of the R7 Leakage Cal control. This is the internal control located next to the filament switch. Connect the positive meter lead to the tester's faceplate. Now plug in the tester power cord. You should see around -66 Volts DC on the meter. If you do NOT see the voltage, that is good news because it means you might be able to fix the tester. If you DO see the voltage, then the news is not as good as it means the meter test power is ok, so it may be a bad meter. It still might be a switch or bad wiring though, so all hope is not yet lost. Note: the exact voltage will depend on the line voltage and the position of the Line Adj control. A reading between -40 Volts and -90 Volts DC is ok at this point (with the Line Adj control at 115). The -66 Volt DC (+-5 Volts) reading will be more accurate once the tester has been fully calibrated. --- Test A: If you did NOT see the voltage on R7, then there is a limited number of things that can be wrong. Next to the R7 control is a black cube (it is a selenium rectifier). Note: on the 667, the selenium rectifier was moved to the transformer mount bracket where the fuse was located on the 666 tester. There is a resistor that goes between R7 and a lead on the black cube (the cube might be another color than black depending on the age of the tester). It may also have been replaced with a modern silicon diode which would be connected between a terminal strip next to R7 and the 50V connection on the filament switch. Which is ok as long as it is installed properly. Connect the negative lead of the meter to the connection to the rectifier where the resistor goes and check if you have the -66 Volts DC (+-20 Volts) there. If you do, then the rectifier circuit is ok and the fault is either the 270K resistor is open, or the R7 control is bad, or possibly something farther down the chain is shorting out the circuit. If you see less than -50 Volts DC (but more than zero), then the most likely problem is that the C1 connection is bad. This is usually caused by a bad solder connection to the tab on the R7 mount bracket. Alternately it is possible that the C1 capacitor has failed and no longer has any capacitance. If you see between -25 Volts and -50 Volts DC, then that indicates that the C1 capacitor is bad and is not providing adequate capacitance to perform proper peak filtering of the power. Replace the C1 capacitor with a 10uF electrolytic 150 Volt to 400 Volt rating. Preferably use a general purpose electrolytic. It is actually better to have a higher ESR (Equivalent Series Resistance) in this circuit so as to not strain the rectifier during power turn on. If you don't see any voltage, check the power to the rectifier circuit. Set the meter to measure AC Volts (we will be looking for a voltage in the range of 40V to 70V AC). With the positive meter lead still connected to the tester's faceplate, connect the negative meter lead to the ear on the black cube (or diode if the selenium rectifier was replaced) where the wire from the filament switch is attached (the cathode connection). You should see between 45 Volts and 65 Volts AC. If you don't, then there is a problem with the power coming from the filament transformer. If the measurement is zero volts, then the wire may be broken or have a bad solder joint. Check where it connects to the filament switch. If you do see the voltage, then the problem is probably the CR1 rectifier and it needs to be replaced. Note: It is rare for CR1 to fail. The usual cause is a fumble fingered technician accidently shorting it to the chassis, which will destroy the rectifier. Another possibility is that C1 shorting out can cause the same problem. I've also seen a case where C1 was installed backwards which destroyed both C1 and CR1. Just to be safe, if you are replacing the CR1 rectifier, you should also replace the C1 capacitor. (Be sure to get the polarities correct when you install them!) Since the selenium rectifiers are not made anymore, you can replace it with a silicon diode such as a 1N4004. This is a perfectly acceptable replacement and will work just as well as the original selenium rectifier in this circuit. It is recommended that you use a terminal strip (use the mounting hole where the selenium rectifier was mounted) to install the new silicon diode and C1 capacitor. A two or three ear terminal strip will work fine. If the problem is not the CR1 rectifier or C1 capacitor we will need to to do more tests. To see if it is something farther down the chain, unsolder the wire that connects to the R7 control (ear tab closest to the top edge of the tester) and check the voltage at the center connection of the R7 control. If you see the voltage now, then something is shorted out. This is likely to be either a pinched wire some place, or a broken switch. If you don't see the voltage, then either the resistor is open, or the R7 control is shorted. Check the resistor (with the previously mentioned wire unsoldered) you should see 270K resistance for the resistor. If you see the correct resistance, then the R7 control is bad and needs to be replaced. (A bad R7 control is the most common cause of this problem.) --- Test B: If you DID see the -66 Volts DC (+-20V) voltage on R7 (then ignore "Test A" section above), the most likely cause is the meter is bad or there is a broken wire someplace. At this point things get more difficult. You will need to remove the meter to check it. To remove the meter, there are four nuts on some screw posts that extend through the face plate of the meter and through the tester faceplate. Carefully remove the four nuts on the inside of the tester faceplate (these are located near the four corners of the transformer mount bracket. Be very careful as the screw posts are only held in place in the meter by the fragile plastic of the meter case and it is easy to break the plastic. (Warning! Do not try to remove the transformer.) Note: If you would prefer not to remove the meter, you can test it by setting the transistor test switch to the Tube position and press the reset button to release all the latching push buttons. However if there is a switch problem or a wiring problem, that can interfer with the meter test. The meter will come out through the front of the faceplate. Carefully remove the two nuts that connect the leads to the meter. As before, be very careful. Do _NOT_ remove the nuts closest to the meter body. They hold the internal connections of the meter and it is very difficult to "fix" that if they come loose. Alternately, if you are handy with a soldering iron, you can just unsolder the wires to the meter. Be very careful though as it is easy to damage the meter plastic with the iron. You should now be able to remove the meter. To check the meter, connect one lead of a 10,000 ohm resistor to the positive end of a 1.5 volt battery. Connect the other lead of the resistor to the positive terminal of the meter and the negative lead of the battery to the negative terminal of the meter. (WARNING!!! DO _NOT_ connect the battery directly to the meter without the resistor. DO NOT use a higher voltage battery - ie DO NOT use a 9 Volt battery. DO _NOT_ use a smaller resistor. Make ABSOLUTELY sure it is 10,000 ohms. Otherwise you can destroy the meter (if it isn't already). (Use the resistance setting of the digital meter to verify the resistance of the resistor.) Now look at the Eico tester meter needle. It should have moved to be between 1/2 to full scale deflection. If it moved as noted, then the meter is probably ok, if it did not move, then the meter is broken and it is time for a new one (good luck finding one). Note: If you decided to not remove the meter, you can connect the resistor and battery leads to the Transistor test switch ears where the Eico tester's meter is connected. The positive meter lead connects to the ear next to the one that the 1N34 diode is connected to. The negative lead connects to the switch ear by the R18 mount bracket. It is also possible to check the meter without removing the tester from it's case. To do this test Set the Transistor test switch to NPN2 position. That will connect the Eico's meter positive terminal to the "E" pin of the transistor socket. The meter's negative terminal will be connected to the tester's faceplate ground. Although keep in mind that this test relies on the transistor test switch being properly wired and functioning correctly. Meter test results: If the Eico meter needle moved as indicated, then the problem is somewhere in the connections between the meter and the meter test power supply circuits. Either a bad switch, or a broken or pinched wire. Check that the switches look ok and that there are no pinched or broken wires. There is also the possibility of a bad solder joint, so make sure all the connections are properly soldered. If the meter didn't move, then you can use the following test to determine if it is fixable. Checking the meter's resistance: First measure the 10K ohm resistor with a digital ohm meter. That will be your reference. using the same setup as with the battery noted above, replace the battery with the digital ohm meter. Using a digital ohm meter (do not use an analog meter as it might damage the tester's meter), check the resistance of the tester's meter by connecting the ohm meter positive lead to the 10K ohm resistor the other end of the resistor goes to the Eico meter's positive terminal. The negative ohm meter lead goes to the Eico meter's negative terminal. Check the resistance reading on the ohm meter. subtract the reading you got with the reference resistor. You should get 1000 ohms resistance +- 200 ohms). If it is "open" (infinite resistance), then the meter is bad and that is the end of it, you need a new meter. If it is zero ohms, then the meter is shorted. This may actually be fixable, but you should find someone who has the skill to repair a meter. It requires very special skills to do so without destroying the meter. Note: we use the 10K resistor to protect the meter. Many ohm meters put out enough current to potentially damage the Eico's meter. The 10K resistor limits the current to a safe level. If the Eico meter needle didn't move in the ohm meter test, it may be because the ohm meter uses a negative current to check resistance. You can check this by reversing the ohm meter leads. Alternately, the meter may simply use a very low current to measure the resistance, in which case you may see little or no meter movement. Regardless, for this test, the meter needle movement is not important. It is the resistance of the Eico meter that we are checking not the neddle movement. Protecting the meter: If the meter works, then you can use the opportunity of having the meter out of the tester to add the protection circuit to the meter (two 1N4148 diodes across the meter terminals). Although you can alternatly put the diodes over on the transistor test switch where the meter leads are attached. (Which would be a better option if you decided not to remove the Eico meter for the test.) See the 666/667 restoration file (restr666.txt) and the eico666-667-repair.txt file for more information on restoring and repairing the Eico 666/667 tube testers and how to install the meter protection didoes. If you have managed to fix the tester, then you can move on to the restr666.txt instructions to calibrate your tester. If it is not yet fixed, then you may want to download the eico666-667-repair.txt file to see if you still can fix your tester. Note: The Eico Tube Tester meters are sensitive to static build up. Touching the meter face can inject a static charge into the plastic which will disrupt the meter reading. Some meters have a black conductive paint along the lower edge of the meter to try to combat the static build up. Unfortuntely, it doesn't really work. If the meter needle doesn't return all the way to zero, it may be that the plastic meter face has a static charge on it. The best defense is to keep a small spray bottle of anti static cleaner handy (such as you sometimes get with a new pair of eye glasses), and spray the meter face with a small amount. Warning! Don't saturate the meter face, or it will seep inside the meter through the mechanical needle adjustment. You only need to spray a very small amount, and wipe it off with a cloth. More is not better. If the meter face is cracked, it would be better to lightly dampen a cloth and wipe the meter face with the cloth instead of spraying it so that the spray doesn't get into the meter through the crack. Again; Do NOT use an excessive amount. More is NOT better. You only need a small amount to bleed off the charge. If you see the needle drop back to zero when you spray the meter face, that is an indication that is was being affected by a static charge buildup on the plastic. Also see the companion files: http://www.fourwater.com/files/restr666.txt http://www.fourwater.com/files/666-667-mod.png http://www.fourwater.com/files/eicotesting.txt http://www.fourwater.com/files/eico666-667-repair.txt http://www.fourwater.com/files/mutualconductance.txt http://www.fourwater.com/files/eico666meter-power-notes.txt http://www.fourwater.com/files/eico666tester-meter-check.txt http://www.fourwater.com/files/how-eico666-works.txt http://www.fourwater.com/files/eico666parasitics.txt http://www.fourwater.com/files/testertypes.txt http://www.fourwater.com/tubeinfo.htm Visit us at http://www.MDBVentures.com - Great prices on great tubes!