20MHz analog scope troubleshooting  - Page 1
Forum section: electronics / testgear

author: Vancata
author_rank: Contributor
timestamp: May 09, 2014, 12:26:17 pm
content: Hey there again folks.Finally i got some decent scope, analog one to help me troubleshooting my projects but first i need to troubleshoot the scope. The actual model is TRIO (old kenwood brand name) 20mhz CS-1820Will go on the short version. I bought the scope from Austria and received the scope by a courier company using trucks for transport way (~1 000km of travel).Before i bought it a friend of mine that lives there took a look on the scope for me, (we used video phone call because he don't know a lot from electronics at all). So it was working fine there, placed jumper wire, showed the 1kHz 0.5Vp-p calibration freq and so on. He bought the scope for me and send it via courier but we forgot to arrange the package on the thing. Anyway I received the unit, read the manual (got nice schematic on the lastpage with all the components there) and placed all the knobs as sayd in the manual, turned the sucker on, but no trace at all. Either both channels.. So something happened in the transport, unplugged it, opened it (ofc shorted the HV tube end to ground, wont be nice to have direct hit with 1.5kV). Inspected the boards, really looked fine, no major issue or anything.Found one metalic part like pin from knob at the bottom of the scope so i guess i might have broken know pin or something (have added photo of it). My suggestion is something have slammed the knobs few times and they are causing the problem.Hit me with some more suggestions to go for, will check the knobs operation later today!Also included video with the scope and some more explanations.Here is a link with the video of the scope:Anyway I'm pretty sure the problem is in some swtich/knob will inspect them all, but i guess will focus on the Sweep time/dev switch, something tells me there is the problem, because i don't have either on both channels trace, but still don't know how i can see for short period of time like mS the traces when I'm switching the MODE switch..

author: Andy Watson
author_rank: Super Contributor
timestamp: May 09, 2014, 01:14:53 pm
content: There were traces there! Looks like it is not triggering. Any chance of a (steady) picture of the front panel so that we can see where the knobs are.

author: w2aew
author_rank: Super Contributor
timestamp: May 09, 2014, 01:38:39 pm
content: Quote from: Andy Watson on May 09, 2014, 01:14:53 pmAgreed - looks like a triggering issue. Either there's nothing wrong except some trigger controls in the wrong positions, or a problem with the trigger circuits. Try setting the trigger to internal / line, which should give you a stable trigger source at least to see a trace, etc.

author: Vancata
author_rank: Contributor
timestamp: May 09, 2014, 02:01:40 pm
content: Yeah something wrong with the triggering circuit. On Line (internal one) I see the two traces, but no trace on ch1, ch 2 or ALT Source. Hmmm now I'm kinda confused. Seems there is something with the triggering circuit as you guys told me

author: Andy Watson
author_rank: Super Contributor
timestamp: May 09, 2014, 02:06:17 pm
content: Quote from: Vancata on May 09, 2014, 02:01:40 pmHave you put a signal on ch1 or ch2? I am not familiar with the Trio, but unless the scope has an "auto" mode it will not trigger without a signal.

author: Vancata
author_rank: Contributor
timestamp: May 09, 2014, 02:17:16 pm
content: Quote from: Andy Watson on May 09, 2014, 02:06:17 pmIf I could i would hug you right now! You are totally right (kinda new in analog scopes, worked only with some pc-usb hantek one). It don't have auto mode so yes It triggers only with input signal is connected.Thanks for the help again folks! Seems some one didn't read his manual to the end...

author: w2aew
author_rank: Super Contributor
timestamp: May 09, 2014, 03:16:40 pm
content: Quote from: Vancata on May 09, 2014, 02:17:16 pmWithout an auto mode, it makes it a little inconvenient to not have a trace when you're poking around in a circuit. If you want to have a "free-running" trace before you find what you're looking for, you can use Line trigger. Then, once you see the voltage levels of the signal you want to see, and setup the vertical controls, then you can switch from Line to Ch1/2/alt as required to trigger on your signal of interest.

author: Stonent
author_rank: Super Contributor
timestamp: May 09, 2014, 06:42:09 pm
content: Very similar to what I dealt with on my first scope. Like you I could get a blip of the signal on the screen when flipping some switches. In the end, it was just a combination of coupling, trigger, and operating mode.

author: sarahMCML
author_rank: Regular Contributor
timestamp: May 10, 2014, 02:29:48 am
content: Hi,I'm sure that when I watched the video I noticed that it said "Pull Auto" on the triggering knob above the set of three vertically arranged lever switched in the timebase section of the scope. Might be worth giving that a try?

author: Vancata
author_rank: Contributor
timestamp: May 10, 2014, 08:40:00 am
content: Thanks for the information guys. I have already get in use to with the oldy scope. You need probe connected or some noise, something to trigger the trace. Anyway played a bit with it, checking the triggering options. Ofc took me 1hour to see that i need to calibrate the volt/div and time dev with the red top knob.. because i wasn't getting the 1kHz 0.5vp-p calibration signalSeems they placed this knobs so you can see some more signals by stretching it et.c only for visual purpose. Some cool things there but I'm waiting one dds signal generator from ebay so i can play moreFor now I'm using one 555 as signal generator.