Kenwood CS-5135 Oscilloscope Horizontal CRT Problem - Page 1
Forum section: electronics / repair

author: Mikek400
author_rank: Regular Contributor
timestamp: November 13, 2014, 05:34:01 am
content: I have a Kenwood CS-5135 Oscilloscope which has some kind of horizontal problem in the CRT.Here is what the display is doing when adjust the trace up and down.https://www.youtube.com/edit?o=U&video_id=sXClXqIABcMAny tips where to start troubleshooting it?This is a copy of the service manual.https://drive.google.com/file/d/0B7ll7KI4S3PNaklpRkRYU3ZFa1JNVVVCNkg1QWVtaEZLc1dB/view?usp=sharing

author: tautech
author_rank: Super Contributor
timestamp: November 13, 2014, 06:15:50 am
content: Welcome to the forum Mikek400Get the link in the first post in the Repair board for assistance.

author: David Hess
author_rank: Super Contributor
timestamp: November 13, 2014, 08:01:56 am
content: It is not repairable unless you want to install a replacement CRT. The unit was dropped and internal elements of the CRT were bent and misaligned.

author: Mikek400
author_rank: Regular Contributor
timestamp: November 13, 2014, 08:29:39 am
content: Hey thanks for the reply.Well the strange thing is it worked ok when I first plugged it in and tried it.I pulled it apart to see if the scope had any bugs or whatnot inside it. It was a bit dirty with some kind of dust /dirt that was all over the horizontal board.I will give the aperture grill on the CRT a close look to check if I can see any distortion.

author: David Hess
author_rank: Super Contributor
timestamp: November 13, 2014, 03:06:18 pm
content: Quote from: Mikek400 on November 13, 2014, 08:29:39 amMonochrome CRTs have no aperture grill.Your video seems to show that the distortion is invariant with sweep speed and triggering and only depends onhorizontalvertical positioning which makes other possible causes unlikely. If you want to double check, make measurements of the ripple on the various power supply outputs.Another good test would be to short the vertical deflection plates together which should produce a straight sweep under all conditions.

author: anachrocomputer
author_rank: Regular Contributor
timestamp: November 13, 2014, 04:39:33 pm
content: It looks to me as though something has become magnetised, near the CRT. Magnetic fields will deflect the CRT beam. When you took it apart and reassembled it, could something magnetic have got near it? A magnetic pick-up tool? Has a bolt or nut or something become magnetised, and then been reassembled near the CRT? But the problem is, how to de-magnetise it.

author: Mikek400
author_rank: Regular Contributor
timestamp: November 16, 2014, 10:08:20 am
content: I thought the same thing. I first suspected something getting magnetized but I found the +18v is at +15. Anyhow going to see if I can track down the problem.

author: TheBay
author_rank: Unknown
timestamp: November 17, 2014, 12:24:46 pm
content: Haven't watched the video but, Check any transistors in the horizontal circuit, also capacitors and check nothing has fallen off the CRT Yoke or been disturbed.

author: David Hess
author_rank: Super Contributor
timestamp: November 17, 2014, 02:12:18 pm
content: Quote from: Mikek400 on November 16, 2014, 10:08:20 amMost oscilloscope vertical amplifiers have transconductance outputs so you can safely short the vertical output signals at the CRT together. This should prevent any vertical movement leaving a straight trace. Or you could carefully disconnect them from the CRT and then short the CRT pins together.