GW Instek GOS-6112 - intermittent trace display - Page 1
Forum section: electronics / repair

author: draker
author_rank: Newbie
timestamp: December 25, 2024, 03:59:45 am
content: Hi, there. New user here with a troubleshooting question. I bought a used GW Instek GOS-6112 from someone on Craigslist, took it home and found that it is unfortunately in need of repair. I found the user manual online and set the oscilloscope up to do a function check using the calibration test point. The readout on the display works fine, but the trace display is not solid. The test waveform briefly flashes on the display every second or so instead of displaying continuously. This is the case for both inputs. A video is worth 1000 words:Time/div = 0.5ms, probe attached to test point:https://youtu.be/-cDWGR3lHbkTime/div = 20ms, probe grounded:https://youtu.be/XcU20RCF30II found the scope's schematic online and looked at it, but it's not very helpful until I have a rough idea of what part might be failing. Any tips on where to start diagnosing this problem? I don't want to just start randomly replacing capacitors. Would be nice to isolate this to a specific failing board or area. And of course, this is a complicated scope, so it may just be operator error. That would be nice.Any tips or suggestions welcome! Thank you very much anyone who can help.

author: MathWizard
author_rank: Super Contributor
timestamp: December 25, 2024, 05:31:24 am
content: I've barely worked on scopes so I'm just guessing.Would it be some HV problem, where it takes a while to build up enough voltage, maybe on some cap, or to tun on some BJT, and then gets drained away and repeats ? I'd check all the voltage rails too, maybe the supply can't keep up with the HV for some reason.Or maybe it's a sweep problem ? I can't remember the sweep's on very long time bases on my Tektronix CRT scope, but it looks more like your 20ms trace, which should be sweeping way more often.Here's some schematic's, for fun I'm looking at some of it, but yeah there's plenty of cool circuits that I'm not that familiar with, when you tie them all together.

author: Kurets
author_rank: Regular Contributor
timestamp: December 25, 2024, 08:08:49 am
content: From your videos it looks like the sweep time and vertical amplifiers are ok. The problem seems to be infrequent trigger.Your videos show that you are using AC coupled input and trigger when measuring the probe comp. square wave (typically 0-1V 1kHz). If you have followed instructions from the manual I guess you have set the scope to auto trigger, which will result in self triggering if your trigger setup is bad. I don't know how frequent auto trigger is for this scope. When you are measuring with grounded inputs there is nothing to trigger on, so you will only see the auto trigger sweeps.I don't have experience with this scope, but I expect that your problem is related to setup rather than faulty equipment. Set the scope to normal trigger, DC coupled inputs, DC 0.5 trigger, 10x probe should be used, to ensure a reliable configuration for the test waveform.

author: draker
author_rank: Newbie
timestamp: December 25, 2024, 07:15:27 pm
content: Thanks, Kurets. I could have sworn I went through every configuration, mode, coupling combination possible with no luck. But I sat down and tried again, and after a while, one of the combinations seemed to reset the device such that every mode works now. I don't remember what combination did it, but now cycling through all the modes, time bases, triggering modes etc. all work as I'd expect. Very strange--I hate it when things fix themselves, but I'll accept it! Scope is working correctly now, and all the functions that I can test with the calibration square wave seem to work except the ch2 "invert" function which isn't doing exactly what I'd expect (it's inverting but with some kind of offset. I'll need to study the user manual more carefully.Thanks for the advice--it got me looking in the right place and I didn't have to replace any components.

author: inse
author_rank: Super Contributor
timestamp: December 25, 2024, 07:22:20 pm
content: Was the horizontal x10 button pressed, probably?