Signal input for B&K 1476 precision oscilloscope

Thread Starter

hoader

Joined Mar 27, 2015
29
Hi there: I bought this used scope 30 years ago. Soon after channel B quit working. The pots and switches got less and less dependable wit dirt. I cleaned it out last week. The switches and pots are working now but I broke a yellow cylindrical component right after the BNC connector for channel A. I touched a wire from the square wave generator post to the other side of the component and channel A worked. I did the same test on channel B and it also works. What is this yellow component? Should I replace it or bypass it? What do I risk if I bypass the component? My guess is it serves as a form of protection for other components in the Oscope.
Thanks George
 

Yaakov

Joined Jan 27, 2019
3,737
Hi there: I bought this used scope 30 years ago. Soon after channel B quit working. The pots and switches got less and less dependable wit dirt. I cleaned it out last week. The switches and pots are working now but I broke a yellow cylindrical component right after the BNC connector for channel A. I touched a wire from the square wave generator post to the other side of the component and channel A worked. I did the same test on channel B and it also works. What is this yellow component? Should I replace it or bypass it? What do I risk if I bypass the component? My guess is it serves as a form of protection for other components in the Oscope.
Thanks George
According to the service manual (https://elektrotanya.com/cgi-bin/download2.cgi?fid=299&file=bk-precision_1472b_oscilloscope.pdf) it is a .1 600V cap for AC coupling. If that’s the component then, as @dl324 suggested by his question, switching to AC coupled will show that it is not working. (NOTE: this is the B, 15MHz version. They also have the non-B version manual but it doesn’t have schematics and almost certainly the differences are not in the input section.)

53778E1A-2EE5-4F6D-BFE0-62705911849A.jpeg
 

dl324

Joined Mar 30, 2015
13,505
Some good news for people with old B&K Precision equipment. The person who sent me the manual said they plan to create an on-line library of manuals for their discontinued equipment.
 

Thread Starter

hoader

Joined Mar 27, 2015
29
Crutchow, I took some pictures and put some circles and arrows with descriptions and proved Yaakov correct and dl324's point. I didn’t try the ac switch now that I saw that picture. We are looking at C101 and C121 on dl324's schematic. Problem; did not see C101 or C121 on the parts list. The C301 cap is electrolytic. That yellow thing feels like ceramic. Below the C1xx number is Q1 600V. The parts list calls it an FET. An FET with only 1 input and 1 output, no gate? Bottom line, is it as simple as 0.1mF @ 600V as in the picture?
Thanks George
 

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