Time Base Range for tektronix 40mhz oscilloscope is 5 ns to 50 sec/div is it will not show pulse up to 5ns??.
5ns/div means that a 50ns pulse will fill the screen, NOT that a 5ns pulse can be detected.

I recall (long ago, when a fast scope was but a dream) a very sharp engineer and yours truly were trying to find an intermittent for, if I can recall, a month, without success. Finally we put the scope aside and after a day or two of reasoning we decided that if a pulse slipped through to point x, the problem would show. we replaced a LS gate with a S and the problem disappeared.

THUS it is proven that a pulse was there and that the scope could not 'see' it.

We found out later that the reason was that a Signetics chip had been replaced by a TI (or vv) both within spec, one leaning towards max, the other leaning towards min. Of course the REAL reason was not the chips, but the designer, if your design can not work regardless of which side of the tolerance window a chip is at, the design is faulty.

I have had an episode of using the "DNA scope" once since. There is nothing more frustrating than finding out that the reason you can not find a problem is insufficient capabilities of your instrumentation.

Erik