New member in need of a little help with a Tek 2445B Oscope - Page 1
Forum section: electronics / testgear

author: mskobier
author_rank: Regular Contributor
timestamp: February 27, 2015, 02:34:47 am
content: Hello All,I apologize in advance for the long post. Now, a little history about me. I went to tech school for electronics in 1979. However, I have not been in the electronics field since then. I am an Extra Class amateur radio operator, so I am still somewhat familiar with modern electronics. I do a little hobby electronics, but nothing serious.I found this group while looking for documentation on a newly acquired Tek 2445B. Specifically, I am looking for a copy of the service manual and a full set of schematics. I have found the manuals for the 2465B, and that is what I am currently using to troubleshoot the scope. I have spent several hours searching the net with no luck. I did order a set of manuals on CD off of -bay, but they will not be here until late next week. I would like to be a bit more certain of the documentation I am using to sort out this scopes problem.Now, a little info on the scope. I came in to possession of this scope last Saturday. While roaming around the local metal salvage looking for "treasures" I stumbled upon this Tek 2445B scope along with a HP 54601A 4 channel 100mhz scope, a BK Precision 1856C 2.4ghz frequency counter, and a Fluke 7220A 1.3ghz frequency counter. Needless to say quite the find! I was able to purchase them for way less than pennies on the dollar. Anyway, I brought them home, wiped them down and checked them out. I could not believe that they all work!. The frequency counters need calibration, The HP works good, but the trace is a little weak, and the 2445B has one issue.Now on to the issue with the 2445B. It powers on fine, and goes through all of the software diagnostics with no issues. No error messages of any kind. Everything seemed to be working fine. Upon further examination, I discovered that channel 1 does not have a trace. I can push the beam find switch and all four traces show up. With the beam finder pushed, I can change the position of all of the traces except channel 1. Channel 1 does not respond to the position control. The mode light shows channel 1 is active, but still no joy. It appears that whatever is wrong with channel 1 is confined to only channel 1. The other three channels work fine and display a signal when connected to the calibration point on the front. In studying the service manual for the 2465B, it appears that the problem is associated with the channel 1 preamp U100, or supporting components. The way I see this, the trigger circuit gets the trigger pickoff from the U100 preamp, and if it was the trigger circuit, it should affect all channels, not just one. So I'm thinking that something between the preamp and the trigger circuit is faulty.So I'm asking for the groups help in getting me pointed in the right direction to resurrect this beautiful piece of test equipment. One other thing, I ran the exer 05 test and it showed the scope only has 5118 hrs with 865 power cycles on it. This thing must have sat on the shelf most of its life. Anyway, any and all help will be greatly appreciated.ThanksMitch

author: c4757p
author_rank: Super Contributor
timestamp: February 27, 2015, 02:46:51 am
content: Hrm,thisseems to be missing the schematics.I've got them, here you go:https://db.tt/RTWJGsQ7Pretty good quality. I've got the rest of it too, if there's anything else you can't find.Edit:oh shit, you said 2445BOh well, have some 2445A schematics...(AFAIK, the analog section is similar enough. There were never significant architectural changes that might get in the way of your debugging.)

author: gfiber
author_rank: Contributor
timestamp: February 27, 2015, 03:04:41 am
content: http://www.ko4bb.com/manuals/index.php?dir=Tektronix/Tektronix_-_2445B_OscilloscopeFollow this link the KO4BB's pages it appears he has the service manual here. I did not download it however to check it for completeness.Gary K8IZ

author: mskobier
author_rank: Regular Contributor
timestamp: February 27, 2015, 03:24:37 am
content: All, thanks for the replies.c4757p,Thanks for the link to the 2445. I'll download it and take a look.gfiber,I had found the KO4BB page and downloaded what was there. That manual is not complete, and does not contain the schematic.Again, my thanks for your responses. Hopefully I can get this thing back working properly.Mitch

author: miguelvp
author_rank: Super Contributor
timestamp: February 27, 2015, 05:32:10 am
content: Checkhttp://bama.edebris.com/manuals/tek/2445/Edit: seems to have the schematics but in two pages per page with overlaps.Edit2: also if you want the original one, I recall someone was selling it in the buy/sell/trade part of the blog, but I think it was for the 2445AFound Link:https://www.eevblog.com/forum/buysellwanted/for-sale-genuine-pristine-tek-2445a2455a-bound-service-manual/

author: mskobier
author_rank: Regular Contributor
timestamp: March 02, 2015, 01:02:59 am
content: All,A bit of an update on the scope project. The CD version of the manual arrived yesterday. Finally, I have a manual that matches my scope. I know the 2465 and 2465 are very similar, but the capacitor values on my A5 board are different that what the other scopes manual say they should be. The capacitors that are currently mounted on my A5 board, C2113 and C2131 are 33uf 35v, and C2011, and C2965 are 10uf 35v. The manuals call for 47uf 25v and 15uf 25v. It appears the capacitors may have already been change out on mine, however, they re-installed the little electrolytic cans that can leak and cause problems. Anyway, they will be getting replaced with tantalum surface mount caps.I also made a video of the values stored in NVRAM using the EXER 02 diagnostic to step the programmed values. At least if I loose the programming while replacing the Dallas chip, I can use one of the BINs available on the net and change the appropriate values and reload it that way. At least I do not have to start over from scratch.Another thing I noted while examining/troubleshooting the scope is that the rear computer grade fan has been replaced. Its date code is from 2008. The scope was manufactured in 1990, according to all of the various items with dates on them in the scope. I do know where the scope originally came from, and I am certain that it had regular calibration and maintenance. I have contacted a friend who works where it came from, and they are going to see if they can locate the maintenance history on the scope. Probably too old to still have those records around, but one can hope.Hopefully in the next couple of weeks, I will be able to sort out the channel one issue and start on the preventative maintenance.Mitch