new scope, strange behaviors?! - Page 1
Forum section: electronics / repair

author: raphrath
author_rank: Newbie
timestamp: March 21, 2020, 09:00:15 am
content: I recently got a new digital oscilloscope , a KIKUSUI COR 5501U. I have been experimenting all day and the graph is offset to the right significantly to the point it doesn't even reach the middle of the display, this is with the horizontal offset fully to the left. x-y mode works fine and so do all the other storage, cursors etc only the offset problem.I would preferably not have to tear down the scopeThanks in advancePS i know my probes aren't compensated properly

author: benj38
author_rank: Frequent Contributor
timestamp: March 22, 2020, 03:54:57 pm
content: This is not "strange behavior". This is a malfunction.Do the "coarse" and "fine" horizontal position knobs move the trace smoothly as expected (only not far enough to the left)?If not, it may indicate that one of these pots is bad.In any case, you will have to open the scope to troubleshoot this.I suspect that the problem is in these pots or very close to them, so there is a good chance this will not be too hard to fix.

author: Caliaxy
author_rank: Frequent Contributor
timestamp: March 22, 2020, 04:16:27 pm
content: Not familiar with this scope, but most (if not all) the other digital scopes I’ve seen so far have a “Default setup” (or similar) button that lets you go back to the factory settings. If you can locate such an option on yours, it worths trying it. Sometimes, settings changed somewhere deep in the menus (and not obvious by just looking at the front panel) can result in behaviors hard to understand.

author: benj38
author_rank: Frequent Contributor
timestamp: March 22, 2020, 05:06:43 pm
content: @Caliaxy, this instrument is much better described as an analog scope (notice for example the "alt" and "chop" dual trace modes), with a digital storage mode. One usually operates it in analog mode since it has a bandwidth of 100MHz, but only 20MS/s. Thus, in digital storage mode, it is usable only to 5MHz or so for non-repetitive signals.Also, it's mainly controlled like an analog scope, and its menu system is far from the ones normally found in digital scopes. I doubt if there is a "default setup" option anywhere.@raphrath, did you try the scope in storage mode? do the position knobs control the trace correctly in this mode?Does the trace extend from left to right in storage mode + roll mode (timebase settings <= 0.2s/DIV)?

author: raphrath
author_rank: Newbie
timestamp: March 23, 2020, 04:15:47 am
content: @benj38 the knobs do move the traces smoothly but not far enough to the left, as you said i have also tried it in storage mode and the problem is exactly the sameI have also had a good sniff around and cant find schematics or a service manual (that i dont have to pay for).i have begun to tear down the front panel and the coarse knob seems easier to turn than the rest wondering if this is a symptom of a bad pot?

author: benj38
author_rank: Frequent Contributor
timestamp: March 23, 2020, 01:37:05 pm
content: Quote from: raphrath on March 23, 2020, 04:15:47 amMaybe opening a new thread asking if anybody has a schematic they can share is not a bad idea...Quote from: raphrath on March 23, 2020, 04:15:47 amA significantly friction-less movement may indicate a bad pot. In any case, once you get to the pot an ohmmeter will quickly show if it matches the value stamped on the pot, and if the center tap resistance ranges from zero to the full value.

author: benj38
author_rank: Frequent Contributor
timestamp: March 23, 2020, 02:09:17 pm
content: Quote from: raphrath on March 23, 2020, 04:15:47 amForgot to say that this indeed sounds like you have a hardware fault in the trace positioning circuit.