Tektronix 475 Not sweeping - Page 1
Forum section: electronics / repair

author: Quiz
author_rank: Newbie
timestamp: December 26, 2024, 10:47:44 pm
content: I and my father was "gifted" a Tektronix 475 (Serial no. B289252) on the condition that we fix it and return it. As such we have no knowledge of prior owners or repair work that was either attempted or completed.When hooking the scope up to it's own test post, two dots are seen and can be moved both vertically and horizontally with each respective position knob. When nothing is connected, there's a single dot.We believe the problem lies with a sweep generator, but this scope is more complicated than others that we've repaired in the past. The 475 manual we have does not have waveforms or voltages indicated, so we've been using the 475A manual and hoping that the two are similar enough. This is not helped by the fact that in some cases the 475 manual appears to not exactly match our scope; incorrect part numbers or components in different spots on the PCB than is indicated.Does anyone know where we:Can find a 100% accurate (to our scope model) manual featuring waveforms and voltages?This is the 475 manual we've been usinghttps://download.tek.com/manual/070133200web.pdf.This is the 475A manual we've been usinghttps://w140.com/tekwiki/images/6/62/070-2162-00.pdfEven begin to diagnose this issue? Probing without understanding the circuit has us narrowed down tosomething, but we don't know what we're looking for.We're pretty sure the problem lies just after U720, as we stop seeing waveforms. However, we're using other scopes that we repaired ourselves to diagnose the issue, which does not fill us with confidence.New to the forums, we did search before posting but other 475 issues seemed unrelated or unanswered. Thanks for y'all's patience with us!

author: Testtech
author_rank: Regular Contributor
timestamp: December 26, 2024, 11:39:04 pm
content: A few tips here;Match the serial number of your scope to the serial number range of manual if possible. There were changes made during the life of the instrument.I suspect that the 475A may be different enough to cause confusion.Check the power supply and the voltages at the trigger board and around the sweep circuits first!Suspect any and all tantalum caps, especially those connected to the voltage source rails! These can be replaced by radial aluminum caps of similar value.Suspect dirty erratic switches and trigger pots. The trigger source push button switches may need to be cleaned. Some of these are not readily accessible.Exercise and watch for a flash of a trace.Is the "Triggered" indicator illuminated? Try adjusting the trigger controls to light it, or make it flash.These are great scopes, but can be a challenge to diagnose and adjust.Good Luck!

author: Quiz
author_rank: Newbie
timestamp: December 26, 2024, 11:45:54 pm
content: Quote from: Testtech on December 26, 2024, 11:39:04 pmThanks for the tips! Where in a manual would a serial number range be listed? I would've expected it to be in the very front or very rear of the manual, but no dice. As fun as it sounds, I'd also rather not read every page if possible.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: December 27, 2024, 03:22:18 am
content: HiTry asking here.https://groups.io/g/TekScopesTek serial numbers are on the fist page of the manual.G Edmonds

author: Analog Kid
author_rank: Super Contributor
timestamp: December 27, 2024, 03:36:56 am
content: I have a Tek 475, fully functional.I also have the user manual in PDF. It lists changes according to serial numbers, including revised schematics.That info is at thebackof the manual.I'd post the manual but it's huuuuge (65 MB). Pretty sure I got it somewhere online for free.I'll look around and post the link if I find it.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: December 27, 2024, 03:52:14 am
content: HiThe start serial numbers the manual covers are on the front/title page only.This maybe a link to the relevant manualhttps://w140.com/tekwiki/images/2/2f/070-1862-00.pdfTek Wiki is also a good starting pointG Edmonds

author: Analog Kid
author_rank: Super Contributor
timestamp: December 29, 2024, 08:46:41 am
content: Quote from: George Edmonds on December 27, 2024, 03:52:14 amNot all of the manuals; here's the title page from the PDF I have:The manual you linked to says it covers models from serial # B250000 and up, and it only has a few pages of "manual change information" at the back.The manual I have says nothing about serial #s on the front cover. However, it has almost 40 pages of change info, including revised schematics, at the back.I'll try to find this manual online. I don't think I found it at the Tekwiki site, but who knows?

author: Analog Kid
author_rank: Super Contributor
timestamp: January 01, 2025, 02:32:36 am
content: The 475 manual I downloaded came from Tektronix's site:https://download.tek.com/manual/475Service.pdfHope this helps.