tek 2445 horizontal time base does not change - Page 1
Forum section: electronics / repair

author: scottie4442
author_rank: Unknown
timestamp: August 22, 2016, 02:19:55 pm
content: I just acquired a tek 2445 that the person I got it from said the fan is not working, opened it up and ther was no fan. I got a refurbished power supply with fan and the scope comes up fine now. The problem I have is when I put a signal on it, I get a trace but the horizontal time base rotary switch doesn't do anything, no change in the time base. Another friend who is a retired electronic engineer said I might try to clean the switch (he did was not able to look at the unit itself just an idea he had). I was wondering if this is the probable cause or if someone has another suggestion. If I need to clean the switch what cleaner do you suggest and where to get it, no radio shack anymore, so thought digikey or mouser something like that. Thanks for any help.

author: singapol
author_rank: Frequent Contributor
timestamp: August 23, 2016, 06:13:23 am
content: To be frank it's not trivial but you may get lucky as something simple. Hope you have electronics knowledge and experience.Please be careful as there are dangerous high voltages inside. At least read the tektronix scope troubleshooting guide below to have an idea. Do a diagnostic test of the scope to see what's wrong, refer to user's manual or the page below (cromwell_intl).Is scope model A or B?Read this first.www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf85Mb file:330pg.Wait till "Processing" turns to "Download manual".http://elektrotanya.com/tektronix_2445a_2455a_sm.pdf/download.html20Mb file:http://elektrotanya.com/tektronix_2445b_2455b_sm.pdf/download.htmlA repair 2445 page:http://cromwell-intl.com/radio/tek2445a.htmlRelated 2445:https://www.eevblog.com/forum/testgear/new-member-in-need-of-a-little-help-with-a-tek-2445b-oscope/https://www.eevblog.com/forum/testgear/tektronix-2445-teardown-pictures/

author: scottie4442
author_rank: Unknown
timestamp: August 23, 2016, 09:42:06 pm
content: it is a 2445 no A or B. I checked and when I have the probe on the calibration point on either channel 1 or 2 the time base readout changes but the trace does not get any wider, it does tend to slope the tops and bottoms of the wave when I change the time base to a faster time (way over to the right), still trying to figure this scope out. I have a rigol ds1054Z hacked to 100mhz and all options and use it to do most of my raspberry pi/arduno stuff, I was told that for tube audio an analog scope is better and I had this one given to me so wanted to try it out on some of my headphone amps, I have 3 of them and I am in the process of finishing the build on two more. Thanks for all the info so far, just checking if this scope is working correctly.

author: singapol
author_rank: Frequent Contributor
timestamp: August 24, 2016, 05:02:39 am
content: As said it's not trivial looking inside it's very tight but you may get lucky if it's just a contact problem.Disassemle scope like this person below.Unseat connectors and reinsert ,clean them withalcohol or IPA if you have it but just "scratching" connector by unpluging and reinserting will also do.http://www.kerrywong.com/2013/04/25/tektronix-2445-teardown/

author: siggi
author_rank: Regular Contributor
timestamp: August 24, 2016, 10:26:37 am
content: Quote from: scottie4442 on August 23, 2016, 09:42:06 pmHey Scottie,The calibrator signal on the 2445 changes with the time base to keep a steady 5 periods on the CRT. You're not the first person to be confused by this. As far as we reasoned on the TekScopes group, this was done to allow checking the horizontal calibration of the scope against the built in crystal oscillator.Enjoy your beautiful old scope. The 2445/2465 have the nice quiet impeller fan. You can hardly hear it running in a quiet room.SiggiSent from my iPad using Tapatalk