Wolfden Press Electronics

Electronics Projects from Wolfden Press

Page one contains Test and Measruement Instruments.
Page two contains Audio, Radio and Miscellaneous circuits
Page three contains Some Manufactured Instruments

The D32, Repairing an older oscilloscope

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Telequipment D32
This oscilloscope, made in England, dates back to about 1972. It has not worked since 1989 when it received water damage caused by rain after the Loma Prieta earthquake on the San Andreas fault in the Santa Cruz mountains of California. After opening it and drying it for two weeks it gave only a phoof and a puff of smoke. It was then considered only good for parts. I found a blown fuse and a burned off wire. After fixing these it powered up but would not focus the trace.
The scope has been in a box for more than 20 years. I thought I'd give it another try. After much internet searching, I was able to find schematics. This time, success. Here it shows a 500Hz square wave from my function generator.
The images below show the scope as I worked on it.

Click images below for a larger view.

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Out of focus trace

This is the best it would do to show a trace. After studying the schematics, I began measuring resistances, then voltages.

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Circuit board panels

Here the scope is wide open making it easy to test components, even while powered up. No ICs, just transistors.

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PCB moved for repair

Here is the underside of the CRT control circuit board. I was able to lift it enough to remove the bad resistor and solder in the new one.

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The new resistor

The new 5M6 ohm resistor can be seen at the forward edge of this picture just in front of the 1M8 1 watt resistor.

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A 5.76 mHz trace

The trace of a 5.76768 mHz crystal from my crystal tester. Measured at .5us and 5X. Considering the 10mHz limit of the scope, it looks okay.

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