Kikusui analog oscilloscope drifting problem - Page 1
Forum section: electronics / testgear

author: iloveelectronics
author_rank: Frequent Contributor
timestamp: June 01, 2013, 06:37:05 am
content: I recently got this what I believe to be a product from the mid 80's Kikusui COS5041 analog scope just because being a novice I thought I could learn a thing or 2 from using a less than modern device.The scope costs me only about 90 odd dollars delivered and appears to be in fair condition, with a sticker that indicates that it used to belong to some university in China.It seems to function correctly and shows rather accurate measurements when first switched on, as shown in the attached photo where it is showing a 6V p-p 10kHz sine wave on the 20us time base. However, having left it on for a few minutes I noticed that the waveform started to drift. It started to drift slowly lower vertically (Y axis), without noticeable change in amplitude, which I can live with. But the bigger issue is that it also drifts horizontally, at a faster rate as the machine gets warmer, and the measured wave length changes too. I left it on for maybe half an hour and the wave length has increased by more than a division!I don't have a service manual for this thing but I was wondering if anyone knows if this is a common problem with analog scopes and is it fixable? Any obvious (but safe) steps I can follow to try to diagnose it?Cheers,Franky

author: iloveelectronics
author_rank: Frequent Contributor
timestamp: June 01, 2013, 06:49:24 am
content: One other problem I forgot to mention - the intensity of the display also gets dimmer as the scope gets warmer.

author: KJDS
author_rank: Super Contributor
timestamp: June 01, 2013, 07:51:48 am
content: I'll take a random guess that one of the power supply rails is drifting with time causing the odd affects you are seeing.

author: qno
author_rank: Frequent Contributor
timestamp: June 01, 2013, 08:10:41 am
content: A little drift is normal after switching on for these kind of scopes.If you want to take measurements have it warm up 15 to 30 minutes.Before reading the value, first ground the input with the AC/DC/GND switch, adjust the vertical offset to a line on the screen and switch to AC or DC to read your signal.

author: iloveelectronics
author_rank: Frequent Contributor
timestamp: June 01, 2013, 08:18:48 am
content: Quote from: qno on June 01, 2013, 08:10:41 amI am aware of the grounding procedure, which is how I found out about the vertical drift.This particular scope seems to take the most accurate measurements when it's first switched on, when everything is cold. The longer I leave it on, the more drifted it gets, and the drifting doesn't seem to stop (I haven't tried leaving it on for more than an hour or so though).If I turn it off again and let it cool down a bit, the drift would reduce, but won't be the most accurate until it's completely cooled down.

author: Bored@Work
author_rank: Super Contributor
timestamp: June 01, 2013, 09:47:44 am
content: Service manuals seem to be rare, although a few companies seem to sell them.Anyhow, I would think checking the power supply is indeed a good idea. Take the usual precautions, like staying away from the high-voltage parts, using a safe meter, etc.