Tek 465M Screen Off - Page 1
Forum section: electronics / repair

author: coldfiremc
author_rank: Regular Contributor
timestamp: July 13, 2019, 05:09:44 pm
content: Hi guysI have a Tek 465M scope. Until yesterday worked OK. but today in the morning, after working good some minutes, suddenly, just the screen turn off. Trigger and channels still work (signals are triggering in the same point). The last I was doing was using the delayed timebase mixed with normal, using the intensity option.these the last images I have of it, prior to death (I see it working properly, but I can be wrong). (Don't worry about the quasi-sine waveform, is correct, is being formed from PWM)in this, mixed timebase(I see it working properly, but I can be wrong) (the quasi-sine waveform is correct, is being formed from PWM)Something I noted: yesterday I smell "old capacitor". This guy always smell like that because was stored in a place with tons of old equipment, with old capacitors. Is possible that I mistaken this smell with a cap failure. No smoky smell, no strange behaviour of buttons, no whines, nor buzzes, no hot spots. Anything apparently works Except Screen. The last time I opened it was to fix the horizontal position shaft, anything looked ok and worked ok 3 years from that.I suspect that one of the high voltage CRT power sources "died".Thanks for any help :-

author: tautech
author_rank: Super Contributor
timestamp: July 13, 2019, 09:31:23 pm
content: Looks more like PSU and timebase problems IMO and nothing to do with the EHT supply.This post has plenty of links to resources for Teks:https://www.eevblog.com/forum/repair/repair-documents-and-links-sticky-me-please-mods/You could also consider moving this thread to the Repair board by using the Move Topic feature at the bottom of the page that can be seen only in your posts.So first, check the PSU meets Service manual specification.

author: med6753
author_rank: Super Contributor
timestamp: July 13, 2019, 11:47:40 pm
content: Agreed, check the PSU...especially the +55V reference. If it's not present your entire PSU will be dead.

author: David Hess
author_rank: Super Contributor
timestamp: July 14, 2019, 04:37:21 pm
content: The old capacitor smell is ethylene glycol leaking from big capacitors. Old big can capacitors usually fail through oxidation of the internal aluminum leads before running out of electrolyte after they start leaking. This is a sudden failure so might explain what happened to your 465M.Start by checking the low voltage power supply outputs. There are also some internal fuses; especially check the +32 volt unregulated fuse which feeds the high voltage inverter.If you lack a 465M service manual, use the service manual for the 455 which is practically identical.Quote from: med6753 on July 13, 2019, 11:47:40 pmThe 465M is only nominally part of the 465 series and has considerable differences. It uses a +32 volt reference instead of +55 volts.

author: coldfiremc
author_rank: Regular Contributor
timestamp: August 15, 2022, 11:44:33 pm
content: Finally after years, this scope was fixed. Was the B+ cap for the tube, inside the high voltage cage. The +95v DC testpont was way under, and with the replacement and some tuning, now runs fine. Also, the fuse needed replacement, and there was some cold joints hanging around making the vertical position to behave strange. Everything ok now.Thanks

author: andy3055
author_rank: Super Contributor
timestamp: August 16, 2022, 05:10:07 am
content: Parts for the 465M is very, very difficult to find. Especially the EHT block. It has many things packed in that little block other than the high voltage components for the anode. Heat will kill that very easily.