Tektronix 465B: B sweep not working, strange square wave shape, shadow signal  - Page 1
Forum section: electronics / repair

author: robb.casanova
author_rank: Newbie
timestamp: May 09, 2020, 07:12:41 am
content: Hi everybody, I recently purchased a Tek 465B. I'm not an expert but I'm doing lot of work with MCUs so i decided to dive into electronics basics.The issues I'm trying to solve are these ones:- B sweep not working- Square wave from calibration is not square- There's a back shadow signal on displayCan somebody please help me? Thank you!

author: tggzzz
author_rank: Super Contributor
timestamp: May 09, 2020, 07:59:32 am
content: Quote from: robb.casanova on May 09, 2020, 07:12:41 amThat's as much information as "my computer's modem is not working"!Was it sold to you as a working scope? What makes you think it isn't working?QuoteYou need to calibrate the probe.QuoteTurn the brightness down.QuoteYou should read the 465's manuals (easily found on the web e.g.http://w140.com/tekwiki/wiki/Main_Page) and optionally some simple "introduction to an oscilloscope" texts.

author: robb.casanova
author_rank: Newbie
timestamp: May 09, 2020, 08:39:01 am
content: Thank you for your reply. I already downloaded the operation manual and I'm using it to test voltages touchpoints, i cannot test the "time shapes" because i don't have another oscilloscope.The issue with the shadow is not related to brightness because increasing brightness both the main trace and the shadow intensity increase.About the square wave, i will receive today new probes so I hope it will fix that issue. Thx.My main concern is related to the B trigger, i can see only the first vertical line of the trace as you can see on the image.

author: tggzzz
author_rank: Super Contributor
timestamp: May 09, 2020, 08:50:30 am
content: Your picture makes the trace seem very bright.Have you tried and failed to calibrate the existing probes? Be aware theonlypurpose of the cal out signal is to allow the edge to be flattened out when seen with a standard *10 probe. The amplitude and frequency are not well defined. The probe's "capacitance compensation range, e.g. 10-30pF, must encompass the scope's input capacitance, e.g. 20pF.For all we know, you may have the controls in the wrong position for the B channel to trigger.

author: robb.casanova
author_rank: Newbie
timestamp: May 09, 2020, 02:18:02 pm
content: Yep, i calibrated the probes but that distortion on square wave is not related to probe compensation.Btw i found the issue with B triggering, the knob that controls the time resolution of B trigger was mounted in the wrong position.

author: tggzzz
author_rank: Super Contributor
timestamp: May 09, 2020, 02:53:26 pm
content: Quote from: robb.casanova on May 09, 2020, 02:18:02 pmGlad you sorted the B timebase issue. It sounds as if somebody has already attempted repair.Presuming the overshoot is not probe related, and I remain to be convinced of that, there are three broad areas where it might arise: in a channel's input attenuators, in a channel's preamplifier, in the common amplifier.Defining the problem as a functon of the channels and vertical sensitivity settings will help you understand where the problem lies.