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434: Difference between revisions
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The original instrument design utilized an all-discrete switching power supply, making this an incredibly light portable scope. Unfortunately, this power supply was extremely difficult to troubleshoot when it went belly-up. At serial number B500000 and later, the design of the supply was simplified to use the same basic circuitry as found in the 7704A using a Tek-manufactured controller chip. | The original instrument design utilized an all-discrete switching power supply, making this an incredibly light portable scope. Unfortunately, this power supply was extremely difficult to troubleshoot when it went belly-up. At serial number B500000 and later, the design of the supply was simplified to use the same basic circuitry as found in the 7704A using a Tek-manufactured controller chip. | ||
In general, the 434 is a nice-looking, easy-to-use oscilloscope. However, the 434 was probably one of the worst MECHANICAL scope designs to come out of Beaverton engineering. This was the model that caused bench technicians to think that the factory should send all new mechanical engineers out into the field to work at a Service Center for a year to get an idea of good and bad mechanical designs. First of all, the 434 design departed from the proven 4-40 steel PCB mounting screws. Instead, it uses 3-48 brass screws in a design that requires a screw-holding driver to get the fasteners in place. Brass screws are non-magnetic and getting them started in some of the more obscure places on the vertical preamp board is extremely difficult. Since these scopes are of an age that one can make modifications without incurring the wrath of Tektronix technicians, it is suggested that these brass screws be replaced with steel 3-48 screws, preferably ones with captive washers like the original brass screws. Most dedicated Tektronix fans and ex-technicians do not like changing any circuit design from the original, but some mechanical changes such as this are for everyone's benefit and don't affect operation of the oscilloscope in the least. | In general, the 434 is a nice-looking, easy-to-use oscilloscope. However, the 434 was probably one of the worst MECHANICAL scope designs to come out of Beaverton engineering. This was the model that caused bench technicians to think that the factory should send all new mechanical engineers out into the field to work at a Service Center for a year to get an idea of good and bad mechanical designs. First of all, the 434 design departed from the proven 4-40 steel PCB mounting screws. Instead, it uses 3-48 brass screws in a design that requires a screw-holding driver to get the fasteners in place. Brass screws are non-magnetic and getting them started in some of the more obscure places on the vertical preamp board is extremely difficult. Since these scopes are of an age that one can make modifications without incurring the wrath of Tektronix technicians, it is suggested that these brass screws be replaced with steel 3-48 screws, preferably ones with captive washers like the original brass screws. Most dedicated Tektronix fans and ex-technicians do not like changing any circuit design from the original, but some mechanical changes such as this are for everyone's benefit and don't affect operation of the oscilloscope in the least. In fact, if the circuit boards are removed, the original 3-48 threaded holes in the castings can be drilled out and retapped for 4-40 screws. | ||
If the V/DIV knob skirt lamps go out, the vertical preamp board must be removed to replace them. This is a process involving the removal of a lot of the aforementioned brass 3-48 screws, the removal of some connectors, the unsoldering of a lot of wires and the removal of knobs and shafts all over that area of the front panel. Remember, it is always better to leave those red VAR V/DIV knobs on their shafts and instead remove knob and shaft as a unit by loosening it from the coupler on the potentiometer itself. Since these oscilloscopes are considered obsolete, the suggestion is to replace ALL of the vertical knob skirt lamps with light emitting diodes, choosing either white or yellow LEDs. These lamps already have small-value current limiting resistors on the circuit board that are in series, so replacing these resistors with the appropriate value to limit LED current is an easy process. Be careful that you select an appropriate power rating for the resistors. It is suggested that current be limited so that the panel lighting is sufficient for bright room lighting, but not so bright as to make it difficult to read the numbers on the knob skirts. | If the V/DIV knob skirt lamps go out, the vertical preamp board must be removed to replace them. This is a process involving the removal of a lot of the aforementioned brass 3-48 screws, the removal of some connectors, the unsoldering of a lot of wires and the removal of knobs and shafts all over that area of the front panel. Remember, it is always better to leave those red VAR V/DIV knobs on their shafts and instead remove knob and shaft as a unit by loosening it from the coupler on the potentiometer itself. Since these oscilloscopes are considered obsolete, the suggestion is to replace ALL of the vertical knob skirt lamps with light emitting diodes, choosing either white or yellow LEDs. These lamps already have small-value current limiting resistors on the circuit board that are in series, so replacing these resistors with the appropriate value to limit LED current is an easy process. Be careful that you select an appropriate power rating for the resistors. It is suggested that current be limited so that the panel lighting is sufficient for bright room lighting, but not so bright as to make it difficult to read the numbers on the knob skirts. | ||