Oscilloscope won't adjust under 10ms - Page 1
Forum section: electronics / beginners

author: nixcamic
author_rank: Newbie
timestamp: March 14, 2024, 05:01:11 am
content: I have an old Tektronix 314 I inherited from my dad, been using it to probe a couple of issues with my solar inverter, however it's giving me a weird issue. It seems to work fine on most settings however if I set the Time/Div dial to anything over 10ms it just goes blank. All lower (higher? not sure correct nomenclature, smaller time, higher frequency works, larger time, lower frequency no work) settings work fine. I'm wondering if the issue is eitherA: I'm an idiot and missed something obvious about how oscilloscopes work and this in entirely user error, in which case, what the heck am I doing wrong?or B: If something is wrong with the scope itself, in which case how would I go about troubleshooting the issue?Video for clarification:https://youtu.be/gQcGha1_x9g

author: xavier60
author_rank: Super Contributor
timestamp: March 14, 2024, 11:53:40 am
content: The Chop/Alternate setting maybe. Chop for slow time-base and Alternate for fast.

author: Zenith
author_rank: Frequent Contributor
timestamp: March 14, 2024, 12:54:59 pm
content: If you are not used to using oscilloscopes it can be hard to make them produce anything, or they can produce confusing results. This is a storage scope, which adds to the complexity.If you set the channels to GND and triggering to Auto, you should see a straight line at high timebase speeds, (that is fewer ms per division), and as you decrease the timebase speed, (more ms and then seconds per division) you should see a spot starting from the left and moving across the screen slowly and then repeating.If it's a fault, I'd guess it's either a triggering problem, or the timebase doesn't work at the lower speeds. To fix it you need the manual, which for most Tek scopes can be found on line, and work through it systematically. It helps if you have another scope, which need not be a very high performance one. A lot of faults in old scopes turn out to be soldered joints which have become bad, or switches in need of cleaning.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: March 14, 2024, 12:55:35 pm
content: It looks like that whenever a timebase slower then 5ms per division is selected the trace just disappears. And this is not normal. To me it looks like the scope is broken. I assume it's a small thing such as a faulty solder connection somewhere in the timebase generator.The timebase generator is on page 129 of this document:https://w140.com/tekwiki/images/7/78/070-1824-00.pdf

author: CaptDon
author_rank: Super Contributor
timestamp: March 14, 2024, 01:29:44 pm
content: The timebase switch is multi-ganged and may simply have dirty contacts. Also, look closely around the timebase switch for cracks in the solder connections. Those older 3" Tek scopes with the 3WP1A C.R.T. or the later Tek made tube with deflection leads through the neck were very nice scopes and still sell for $50.00 at the hamfests. They are too slow for modern digital work but excellent for sub 30MHz radio work. The timebase uses combinations of resistors and capacitors switched in different ways to achieve the sweep rates. Smaller values of resistors and capacitors equal faster sweep speeds. Be aware that the very same capacitors used for 10, 20 and 50ms could also be used for the 1, 2 and 5ms range simply by using a resistor of 1/10th the resistance of the slower range. Tek timebase and vertical volts/div switches can be frustrating and the calibration of the ranges very time consuming especially at the higher frequencies.

author: David Hess
author_rank: Super Contributor
timestamp: March 14, 2024, 01:44:46 pm
content: Nothing special happens at sweep speeds slower than 10mS/div, so my guess is a mechanical problem with the cam switch.As I recall, the Sony/Tektronix oscilloscopes had all kinds of reliability problems. Manuals can be found here:https://w140.com/tekwiki/wiki/314