Tek 465 vertical deflection woes  - Page 1
Forum section: electronics / testgear

author: Filter_head
author_rank: Contributor
timestamp: October 25, 2013, 01:59:07 am
content: I have a 465 that recently developed a vertical deflection "symptom". The vertical position knob, both CH1 and CH2, has limited amount of vertical adjustment. For example, turning from hard left to hard right will deflect the rastering beam about 1.8 vertical div max. out of the 8 vertical div total on the screen.Looking at the trigger view using the line as source shows a "clipped" sinewave (top and bottom flattened). I can't recall what line source trigger view should look like but if it is supposed to be 60Hz sinewave, it's a clipped 60Hz sinewave (time base looks good however).Can't center the rastering beam on the center of the display either. Horizontal display, time/div appears fine.I have another 465 I can scavenge for parts and though about swapping the vertical deflection board as a brute force approach.Any suggestions?

author: Filter_head
author_rank: Contributor
timestamp: October 27, 2013, 07:36:52 pm
content: Spent some time with the manual and measured the voltages at the vertical deflection plates. Spec shows 34V in both top and bottom plate, measured is 34.1V on top and 32.7V on bottom.

author: oldway
author_rank: Super Contributor
timestamp: October 28, 2013, 04:27:54 pm
content: First check the power supply:+55V+15V+5V- 8V+110VLook for bad contacts off transistors and trimpots of the vertical output amplifier . The are all mounted on sockets. Move them a little in their sockets.

author: Filter_head
author_rank: Contributor
timestamp: October 28, 2013, 08:23:07 pm
content: Oldway-First off, thank you for responding.The low voltage supply rails show good nominal values, all within specification tolerances. The ripple is excessive however, 4-5X the values listed in the manual with the 110V showing close to 80mV p-p on the scope.Also pulled and reset the transistors I could find (both plastic and metal can types). I still need to check all the wave forms at the TPs identified on the board.The "constrained" vertical deflection is observed in both channels (almost identical) suggesting that the fault lies with a board or component that shared between the two.

author: oldway
author_rank: Super Contributor
timestamp: October 29, 2013, 09:12:18 am
content: Ok, very good, for instance, do'nt worry with excessive ripple, first try to repair the vertical deflection issue.QuoteThat's right but it kan also be a CRT issue (broken internal conection of one of de two vertical deflection plates)To be shure that's not the problem, measure the deflection voltages of both vertical deflection plates directly on the CRT pins for max up and max down positions of the vertical position knob.If the voltage difference is large (more than 20v), it is a bad CRT issue.If not, that's a fault in the vertical output amplifier or in delay line driver.

author: Filter_head
author_rank: Contributor
timestamp: November 02, 2013, 03:50:16 pm
content: Vertical deflection plate voltages are near 34V, each.All voltages on, and feeding the vertical amplifier board are close to nominal.The probe cal signal from the sick 465 is good.With 10x probe on calibrator and plugged into Ch1, waveforms at test points 27 and 28 are consistent with manual rqmnts.Waveforms at 29 and 30 are not however, almost flat-line on a 20mV/div scale on the test scope.So the fault lines somewhere on this board!

author: Filter_head
author_rank: Contributor
timestamp: November 02, 2013, 07:35:55 pm
content: Well, I cheated.Instead of trying to "fix" the problem I pulled the vertical amplifier board from a clunker 465 and that did the trick. I can now be calibrated, no vertical deflection problems.Now with the faulty amplifier board out of the unit, I can try to determine what is wrong with it.

author: Filter_head
author_rank: Contributor
timestamp: November 03, 2013, 11:11:16 am
content: I've posted the full parts schematic for the 465 here:http://www.northreadingeng.com/tek_465/465.pdfI've created a forum dedicated to discussing vintage Tek scopes too.http://www.northreadingeng.com/Forums/index.php

author: grumpydoc
author_rank: Super Contributor
timestamp: November 03, 2013, 12:33:12 pm
content: QuoteThere's already a pretty active one on Yahoo

author: Filter_head
author_rank: Contributor
timestamp: November 03, 2013, 01:03:04 pm
content: Quote from: grumpydoc on November 03, 2013, 12:33:12 pmAgreed, but the formatting is sort of "Usenet"-ish.I can also enabled webpages for schematics, photos and whatever else will be required by folks that join and do it directly off my servers.I keep it up for a few months. If no interest, no big deal.

author: Filter_head
author_rank: Contributor
timestamp: November 11, 2013, 02:19:57 am
content: Quote from: Filter_head on November 02, 2013, 07:35:55 pmDone, faulty film resistor.Board now functional.http://www.northreadingeng.com/Forums/index.php?topic=7.msg16#msg16