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For my 25th birthday in 1974 I bought a 10 MHz BK Dynascan 1460 Oscilloscope for $450.00. It was my first scope and I was servicing Audio Electronics at the time with an occasional TV thrown in. My primary job was as an independent service tech for 20 Radio Shack stores in Wisconsin and Minnesota. I had hopes that the scope would help me to diagnose some of the tougher puzzles that came across my bench. Since that time I have had dozens of shops and the BK scope has always been there for me.
I like to take care of my things so I have always made sure it was handled carefully and stored properly when not in use. I have also kept track of the Owners and Service Manual which came with it.
I have not used it very often since I bought a modern digital scope a few years ago but I still like it. Recently I have noticed that it had gotten quite a bit out of calibration. When I would switch between the different vertical voltage settings the trace would not stay centered. When changing from 1 v/div to 2 v/div or 5 v/div it would be necessary to recenter the trace. The horizontal trace had also shrunk so that it only covered the left 3/4 of the screen. I was pretty sure that the vertical voltage and sweep times were also off. Finally I wanted to upgrade the input connector from the SO259 that it was supplied with to a female BNC so that a modern scope probe could be attached.
The first step was to break it open and clean some of the dust off the circuit boards.
This is state of the art for a low price scope in 1974. It is all transistors except for the CRT. The cabling to the boards is wire wrapped to pins. This is the underside of the Horizontal Control Board. I began my repair process by spraying and cleaning all the pots.
This is the Vertical control board. The service manual had a step by step procedure for calibrating the scope. Within an hour I had the vertical board adjusted so that there was no shifting of the trace as I switched between 1, 2, and 5 volts/div. I also had the trace set on zero when the vertical position knob on the front panel was centered. I had also used a reference voltage to calibrate the gain so that as accurately as possible the trace would indicate the proper voltage. Keep in mind this is nothing like the convenience we have with the present generation of digital scopes. Reading voltages and frequencies with this scope requires sharp eyes, taking measurements and doing the math to calculate frequency from how many divisions are crossed by a wave form.
The next step was to calibrate the Horizontal sweep. Once again the service manual had a step by step procedure to accomplish this. I can't over emphasize how important it is to keep track of manuals and support information. Without the manuals this scope would not have been able to be fixed. After all the trimmers were properly twisted into place here is the results.
The signal generator is set on 1 kHz and 4 volts peak to peak. The scope is set on vertical 1 volt/div and Horizontal 1 mS/ div.
Here we have the signal generator set on 1 MHz and 4 volts PP. The scope is set on 1 volt/div and Horizontal is 1 uS/div.
If you look carefully at the screen you can see me holding the camera. I was also holding a black screen as the problem with reflections in the pictures is always a concern.
The final thing I wanted to do was to get rid of the old clumsy original probe with its PL259 connector. My first thought was to remove the SO259 on the panel of the scope and use washers to position the much smaller female BNC jack.
However after studying the situation I decided instead to build a PL259 to BNC female adapter and leave the original SO259 in place. I did not feel that I could do a professional looking job. While the adapter would stick out, the position of the scope on my bench would not make this a problem. Here is the finished scope with its new adapter and probe.
When I consider what kind of scope can be purchased now days for $450 compared to this scope we have come a long ways in value for our money. Keep in mind that this was purchased with 1974 dollars. The one thing that I can say for this scope is that at 43 years old it is still working nearly as well as the day I bought it. I will not live to see the condition or functionality of my newer Rigol 40 years from now but I have my doubts that we will be able to say the same about it.
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发表于 2017-12-28 01:45:30
