Scope unable to trace time axis? - Page 1
Forum section: electronics / testgear

author: CatsLoveJazz
author_rank: Newbie
timestamp: October 14, 2013, 07:04:59 pm
content: Hello,I have a Hitachi V223 scope that seems to have a problem with tracing in time correctly. I only see one point on the x-axis at a time so I end up with a dot/line that moves across the screen (eg When the probe is connected to the cal pin you would obviously expect to see a square wave, however, I see with a vertical line that moves across the screen over time.)I am familiar with using scopes and have checked the time base and trigger settings although I do not know how to troubleshoot any further.Any help would be much appreciated.Thanks

author: w2aew
author_rank: Super Contributor
timestamp: October 15, 2013, 03:14:27 am
content: Quote from: CatsLoveJazz on October 14, 2013, 07:04:59 pmAnalog scopes like this really only have a single point that moves across the screen. It is the persistence in the phosphor that makes it look like a line. It sounds like on your scope the sweep speed is very slow, so you're seeing the dot. In the case of the cal signal, the dot is moving up and down quickly in response to the cal signal, that's why you see a vertical line.Have you tried adjusting the time/div setting to a faster value, like 1ms/div, 200us/div, 10us/div, etc? If that makes no difference, then you may have a fault in the horizontal timebase circuitry.

author: CatsLoveJazz
author_rank: Newbie
timestamp: October 15, 2013, 09:23:37 am
content: Yes I have tried all the timebase settings and they do not appear to make any difference to the scan rate so I supsect this is the problem.Now the more tricky question...Is this a common fault found in oscilloscopes (eg. could I just switch out a cap or blown resistor) or is this problem likely to be more difficult to fix.Thanks for the help.

author: Rerouter
author_rank: Super Contributor
timestamp: October 15, 2013, 09:42:07 am
content: i'm going to assume you only recently acquired this scope, and it didn't just fail this way yesterday, if so while i have not seen this kind of scope before, make sure your channel mode is only 1 channel and not X/Y mode, and that triggering is set to auto,to be even more certain snap a picture with all the knobs and switches of how you have it now, we may spot a setting that might not seem relevant to yourself,

author: CatsLoveJazz
author_rank: Newbie
timestamp: October 16, 2013, 06:39:22 pm
content: Yes I recently acquired the scope. I have it set to auto trigger, channel 1 and have tried all the time base settings so I suspect there's a fault.Here's photo of the settings and problem. Apologies for the poor quality, it's the best I could get in the light.

author: Neilm
author_rank: Super Contributor
timestamp: October 16, 2013, 07:26:26 pm
content: Can you adjust the horizontal position? If you can then it is not a fault with the CRT, but must be on the signals to it.

author: edavid
author_rank: Super Contributor
timestamp: October 16, 2013, 07:29:57 pm
content: What's up with the display mode buttons? It looks like all 3 of them are pushed in.

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 16, 2013, 07:58:31 pm
content: Quote from: edavid on October 16, 2013, 07:29:57 pm+1 on this one. That looks like it could create the problem you're having.

author: CatsLoveJazz
author_rank: Newbie
timestamp: October 16, 2013, 08:17:24 pm
content: I thought that looking at the picture myself but I can assure you that only Norm is depressed.Yes I can adjust the horizontal position left and right but this just offsets the dot/line that as it scans across the x-axis.

author: w2aew
author_rank: Super Contributor
timestamp: October 17, 2013, 02:58:19 am
content: Sounds like a fault in the horizontal sweep, since the time/div control has no effect. The good news is that the sweep is working - it just isn't adjustable. I've seen a couple of similar failures in the past, and it was a simple fractured solder joint on the rotary timebase (time/div) switch-gang. In two cases, it was a fractured solder joint where one of the switch contacts was soldered to the PCB, and another was a failed joint with a wire connection to the switch. These switches often are composed of a gang of many rotary stages, and are subject to shock/vibration every time you rotate it to a new position. This vibration can sometimes lead to fractured/stressed solder joints. Check them out first.

author: CatsLoveJazz
author_rank: Newbie
timestamp: October 17, 2013, 08:16:30 am
content: Thanks that's great information. I'll crack it open and get my meter out. Hopefully it's as simple as resoldering a broken joint.

author: GreyWoolfe
author_rank: Unknown
timestamp: October 19, 2013, 09:01:59 pm
content: W2AEW, thanks for putting me on the right track. I picked up a TEK 2235 100 MHz scope at the Melbourne, FL hamfest for $40 and had the same problem with the traces not moving across the screen. Instead of starting with looking for fractured solder joints, I removed the horizontal and vertical control knobs and shot everything inside and out with contact cleaner. Lo and behold, I have a working scope again. I am planning to use this with my octopus component tester that your video convinced me to build. I can go back to using my BK 5100 combiscope for other things. Boy, the bench is getting crowded. I also picked up a Heathkit IG-72 audio generator with a bad meter but works fine and a Fluke 1952A counter/timer that I hope that either someone has the user manual for or can tell me that the 1952 and 1953 are close enough that I can use the 1953 manual as I can find that one. Allen, keep up with the great videos, you rank right up there with Dave.73, Tom, NW0LF