Heathkit IT-3117, test no longer works. - Page 1
Forum section: electronics / repair

author: gtr
author_rank: Contributor
timestamp: July 20, 2025, 03:40:21 pm
content: Hello everyone,I replaced the 1N191 diode with a 1N34A on my Heathkit IT-3117 tube tester. Then I tested the Filament button voltages by connecting the probes of a multimeter to pins 1 and 5 of the octal socket, as indicated in the manual. I switched all positions from 0.63V to 110V. Everything is fine. However, I didn't test it with tubes, and the next day I ran the air compressor inside. Then I tested it with a tube like the 6BE6 and other tubes that are good.The problem starts there. I center the galvanometer needle by turning the Set Line knob, and everything lights up, even the tube. After heating the tube, I lowered the ADJ-LINE SHORT knob to TEST. The galvanometer needle dropped to zero (BAD) and didn't rise until the ADJ-LINE knob was in its SHORT position, even though the needle should go to the right (GOOD). The other tests, like the filament or neon, should light up; this one didn't.I replaced the original 1N191 diode, and the problem is still there. I tried it with a 1N60 Schottky diode, and the problem still persists. So I don't know if the problem is due to the air compressor cleaning since I hadn't tested a tube before.I replaced this diode to improve the Filament knob readings so they were as close as possible to the indicated values. I examined the solder joints, which are very solid, but I can't see what could have happened. I only changed one diode without spilling any solder, and it was still pretty clean inside. But while I was cleaning my other purchases, I took the opportunity to do this one too. I placed the diode the right way around and checked with a multimeter, and everything was fine.I tried another neon lamp, and it didn't light up during testing, and this neon lamp is in good condition (tested beforehand).It was working fine before the diode change.I tested all the transformer secondary voltages, and everything was fine.I tested the voltages across the terminals (the component legs) of the resistor, diode, capacitor, and neon lamp with a 6BE6 vacuum tube, in Short mode of the "ADJ-LINE SHORT" switch, and in TEST mode of the same switch.Here are the results in Short mode and Test mode:**********************************************************Capacitor = 0.072VTest = 0.054R1(100K) = 0.072VTest = 0.074VR2(270K) = 0.879VTest = 0.658VR3(2.2M) (Switch Short-Leakage)Short = 1.67VLeakage = 5.68VTest Short = 1.71VTest Leakage=4.15vR4(2.5K-7W)=1.3vTest=2.05vR5(1.5K)=0vTest=0vR6(360Ω)=0vTest=0vR7(820Ω)=0vTest=0vR8(3.6K)=0vTest=0vR9(1K)=1vTest=1.53vR10(75K-1W)=0.567vTest=0.435vDiode=Black Probe on Cathode=0.959vTest=0.035vRed Probe Diode on Cathode=0.954Test=0.077vTest diode without voltage:******************************Black probe on Cathode = 0.249VRed probe on Cathode = 0.564VClearly, there's no voltage reaching the neon.Does this give anyone any insight into the problem?Thanks in advance!The manual is here and the diagram is on page 11 of the PDF, the last two pages, but the front is in the correct position.https://www.rsp-italy.it/Electronics/Kits/_contents/Heathkit/Kits/Heathkit%20IT-3117%20tube%20checker.pdf