Tektronix 466 problems - Page 1
Forum section: electronics / testgear

author: mirokamh
author_rank: Newbie
timestamp: March 01, 2017, 12:03:27 pm
content: Hello,recently, I bought a Tek 466 which was dirty and didn't work propperly. One of the timebase golden switches was stuck, so timebase acted weird, and couple of knobs were broken/missing. Also some pixels of channel 1 were "jumping" around 1mm up and down sometimes, like it was picking some noise. Anyway, I managed to repair everything expect that channel 1 problems. It happens randomly, sometimes after some time, sometimes right after power-up. Changing V/div or Time/div doesn't have any effect. I cleaned ch1 V/div golden contacts with paper strips and rubbing alcohol, but it didn't help. Does anyone know where the problem should be? Maybe i can record it on video.Also, there is unusual dark green filter on screen, but it's all scratched and hard to see through. I assume that it's because of the storage crt. I'm affraid that it's impossible to get this green filter in good shape nowdays. Do you know if I can change it to transparent plexiglass or something? Or is there any way to restore original screen filter, maybe with abrasive polishing paste?There are some photos of how I bought it, and how it looks now, after some cleaning

author: David Hess
author_rank: Super Contributor
timestamp: March 01, 2017, 12:47:27 pm
content: Quote from: mirokamh on March 01, 2017, 12:03:27 pmI might be able to identify the noise from a video with the oscilloscope set to 20 MHz bandwidth and a sweep speed of 1ms/div or slower. Does the noise look anything like the examples below with constant amplitude and varying timing?The source is certainly between the attenuators and channel switch. I would try swapping U3290 and U3790 to start off with and see if the noise moves to the other channel.QuoteStorage CRTs are significantly dimmer than non-storage CRTs so do not expect the brightness and sharpness of a common analog oscilloscope.There is nothing wrong with removing or changing the green filter; it is there to improve contrast. The CRT implosion shield is clear and should be left in place.Plastic polish will not help much with scratches which are too deep but will improve the clarity significantly where the filter is damaged. After polishing, I might try using something like an automobile wax to help with the scratches.

author: mirokamh
author_rank: Newbie
timestamp: March 01, 2017, 02:10:57 pm
content: Thanks for response. I managed to get it on camera, first I tried variable persistance mode with slow sweep speed, but it isn't looking good on video. It's better later in non storage mode. Noise and "trace jumping" is clearly visible. Changing v/div or sweep speed doesn't affect the noise at all. Bandwidth was restricted to 20MHz. I will try swapping U3290 and U3790 as you suggested.Video:https://youtu.be/KxltT5Ci38Q(sorry for my shaking hands, maybe I should have used some stativ)Also, can you please tell me where can I find those U3290 and U3790? I can't find them in my manual

author: David Hess
author_rank: Super Contributor
timestamp: March 01, 2017, 04:41:15 pm
content: It was not the noise I was thinking of.Mechanical problems are most likely so I would start by resocketing all of the ICs and transistors on the A2 preamplifier board which constains all of the electronics for both channels up to the vertical channel switch. Then I would go through and operate all of the trimmer potentiometers which affect the channel 1 preamplifier circuits.If that does not solve the problem, then I would probe along the channel 1 vertical signal path to see if the noise starts at any part.You will need the466 service manualto see what is involved.