(Continued from Part 3) As I have found, solder connections can be the main culprit, if the tuner doesn’t operate like it should. The next thing to check is the switch bank (mode selection push buttons or the rotary switch) that sets the unit up for the desiered operation. With older equipment, these switches can become oxidized or just dirty. These assemblies can be cleaned with a spray contact cleaner. Be careful what contact cleaner you use, as some cleaners can deform (and / or discolor) plastic. Read the product label very carefully, as this will inform you on how to use the product effectively and what you can use it on without worrying about incurring damage upon the use of same. Volume, Balance and Tone Controls can be cleaned with contact cleaner, too. This may require a lot of disassembly to get at these controls, as most of the time, these controls are soldered directly to the printed circuit board. A quick burst in a switch and operate it several times will do the trick. Spraying a few quick bursts in the knob control(s) and turning them back and forth will clean them up good. If your volume control makes popping noises when you turn the knob, it needs to be cleaned. Most volume / loudness controls will have 2 (two) resistive elements (called ‘potentiometers’). Both of these must be cleaned to insure that both channels will operate correctly. This is known as a 2 gang potentiometer, or, as us technicians say, a 2 gang pot.
There are some Multiplex Receivers out there that have Electron Tubes still in use today. These can be serviced as above, but I must warn you that these units operate at high voltages and could cause harm to persons and / or property, if not handled properly. Electron (Vacuume) Tubes operate at high voltages because it takes a high potential to move electrons through them. Tubes are not very easy to get these days, but can be found, if one knows where to look. In Russia, a company called ‘Sovtek’ manufactures Electron Tubes for customers such as ‘Marshall’ Amplification and Military applications. (I’m not sure where these tubes can be ordered from. I’m working diligently on this, as I’m awaiting on e-mail responses from Sovtek, Allied and a few more leads. I’ll let you know what I find out later in this series. MCM Electronics doesn’t carry common Electron Tubes anymore. If you need a hard to find Electron Tube for an old Radio, Amplifier or even a Juke Box, feel free to e-me, as I can help.
Troubleshooting equipment that operates on tubes requires skill in the knowledge of what your working on. Be aware of high voltages, as the filter capacitor(s) can store up these without you knowing it. Make shure that the unit is unplugged and discharge the capacitors with a screwdriver referenced to ground. Expect to hear a loud POP when you do this. This includes Computer CRT Monitors, as well: for the second anode voltage of this tube can exceed 25,000 (25K) Volts! I’ll continue the servicing of this ‘dated’ equipment in Part 5.
As usual, feel free to e-me if you have any questions, comments or concerns on this (or any other) article that I’ve published to: firstname.lastname@example.org