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

 

Can you post a clear picture of the component and its connections to the BNC?

 

Did you try both AC and DC coupling from the BNC connector?

 

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.)

 

I couldn't find a schematic on the WEB, so I contacted B&K Precision to get the schematic.

 

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.

 

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

 

Bottom line, is it as simple as 0.1mF @ 600V as in the picture?

0.1uF 600V metalized polystyrene (from post #5).

We don't use mF to mean uF any more; it means milli Farads

 

dl324, been a long day

 

dl324, been a long day

Don't worry. Someday you'll be retired and it will be an endless vacation...