432
The Tektronix 432 is a 25 MHz dual-trace portable solid-state oscilloscope.
There is also a rack-mount version, the R432.
Each 432 vertical signal path starts with the coupling switch, then a rotary cam attenuator, then a dual-JFET source-follower buffer amp, then a 155-0050-00 differential amplifier (switched to 155-0050-01 after serial number B239999).
The vertical and horizontal output amplifiers are fully discrete, using silicon bipolar transistors.
Triggering is done by a 4.7 mA tunnel diode that is fed by a discrete trigger amplifier.
The 432 consumes 55 watts maximum and weighs 20 pounds.
P31 phosphor was standard. P7 was also available.
Key Specifications
- please add
Links
- Ken Matheson, Servicing the 432/434 Oscilloscopes. In Tekscope Vol. 4 No. 5, 1972
- Handle Replacement Modification Kit
Pictures
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This shows the area around the BNC input connectors for channels 1 and 2. This photo was taken when the owner was cleaning the vertical gain rotary switches which had become flaky after 45 years.
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View from the rear. The vertical gain attenuator switches are under the metal covers.
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When the metal covers are removed, one can see the shaping/compensation capacitors. These can be unplugged, each one has 6 legs.
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Another view of the shaping capacitors. Work on one channel at a time to avoid mixing these up. Carefully clean the legs with isopropal alcohol and paper towels.
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In order to access the rotary gain switch fingers, one must first remove these BNC connectors, which means unsoldering the central wire (connects to a resistor/inductor feed-through) plus a debouce capacitor and lead going to the x1 x10 indicator lights.
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Close up view of BNCs
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Close up view of BNCs
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Close up view of BNCs. These need to be unsoldered for removal, but nothing else must be unsoldered to access/clean the vertical gain rotary switch.
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View of the input preamp. This board needs to be unplugged only, but not removed or unsoldered. It has four 2-pin connectors. Then it can be removed, still attached to the compensation capacitor carriers.
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Lifting off the assembly consisting of the 2 compensation capacitor carrier plus the vertical preamp board plus the push-button switch board for CH1/CHOP/ALTERNATE/CH2. The switch board has two plug connectors below that must be removed. It helps to have long fingers or a good pair of needle nose pliers.
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Second view under the assembly being removed.
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The rotary switches exposed. Each one has four contact fingers underneath. They are cleaned using small (5mm) wide strips of paper soaked in isopropanol alcohol (2-propanol).
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One can just see the four contact fingers peeking out. You can get paper under them using small tweezers. Patience and calm are required.
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A view of the variable-gain potentiometers. Note that the bodies are both cracked in the same place. Both had been noisy, but the noise was largely eliminated by sweeping them back and forth a dozen times. That may have scrubbed off the oxide.
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A view of the contact fingers underneath the capacitor shaping blocks. Each channel has 8 NC and 8 NO fingers (the other half are on the bottom). These are easy to reach and clean as described. So each channel has a total of 20 contact fingers to clean.
