Tek 465 XY mode - Page 1
Forum section: electronics / repair

author: Simon Spiers
author_rank: Regular Contributor
timestamp: July 06, 2022, 07:44:46 am
content: Hi all. Just picked up a partly working 465 that after a full switch clean mostly works.When I say mostly the XY mode produces an extremely bright moving beam somewhere off screen. I can not move it to the crt screen and would not dare as I'm sure it would burt the screen. Also even at minimum intensity it is too bright. I know this as the beam can be seen reflecting off the side of the CRT.Is this a knows fault? Any pointers?Thank you in advance.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: July 06, 2022, 08:42:37 am
content: HiDoes the beam finder bring the beam on screen?G Edmonds

author: tggzzz
author_rank: Super Contributor
timestamp: July 06, 2022, 08:56:47 am
content: Quote from: Simon Spiers on July 06, 2022, 07:44:46 amThose are two independent faults.Always start by checking the various power supply rails for voltage and ripple.If you apply a large input signal, does the trace partially come onto the screen. If so, the problem lies in the amplifiers, possibly correctable by following the service manual maintenance procedures. If not, additionally suspect the connections to the tube or tube itself.The intensity problem indicates a problem in the blanking circuits. Quite possibly there is a failure in the high voltage diodes or capacitors in that translate the 75-150V blanking waveform up to -2500V. I've also seen a detached grid connectioninsidethe CRT, which would be game over.Caution: in extreme cases an excessive grid current can damage the mesh or CRT envelope.

author: bd139
author_rank: Super Contributor
timestamp: July 06, 2022, 09:49:47 am
content: Quote from: Simon Spiers on July 06, 2022, 07:44:46 amDo both channels work independently in normal mode i.e. can you get a trace?When it's off screen does it move at all when you change the X or Y axis position?

author: Simon Spiers
author_rank: Regular Contributor
timestamp: July 06, 2022, 10:40:09 am
content: Thanks for your replies. The scope off XY mode works perfectly so I assume amps are working correctly. All rails in spec.

author: bd139
author_rank: Super Contributor
timestamp: July 06, 2022, 11:00:07 am
content: Ok firstly set the controls to the default position specified in the service manual. I would then refer to the A&B TIMING SWITCH schematic (sheet 7). Look at the switch positions for X-Y mode and make sure that the relevant switches are closed and actually contacting. I had something similar a few years back with one and it was an infernal leaf switch in the timebase that needed cleaning. There are numerous functional changes that it makes to various bits of the scope to get X-Y mode so it's probably easier to start at the switch and work from there.

author: Simon Spiers
author_rank: Regular Contributor
timestamp: July 06, 2022, 01:55:44 pm
content: Will try that tonight thanks.

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 06, 2022, 02:52:16 pm
content: Hope you find it. I have the 466 which does not have XY mode.Older scope here has XY but no ability to adjust X level.

author: Simon Spiers
author_rank: Regular Contributor
timestamp: July 06, 2022, 06:47:47 pm
content: Right ?I have set it up ias the manual and after cleaning the time base switch again I now have XY input. But if I have Auto or Norm pressed in the Trig mode selection I get a extremely over intense slow sweeping Lissajous waveform on the display. So at least it now appears to work, but is that normal?

author: bd139
author_rank: Super Contributor
timestamp: July 06, 2022, 07:11:17 pm
content: That’s definitely not normal. Think it usually ignores those. Sounds like the mode switching isn’t working quite right. Not sure how to proceed on that one.If it’s any consolation I’ve got a broken B model I’m waiting for a new mode selection PROM for. At least yours doesn’t have a £23 bill lurking in it