Tek 2467B U800 - Page 1
Forum section: electronics / repair

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: December 23, 2020, 09:39:39 pm
content: For those that may have experienced something similar, does this look like a failed U800? I have not had the time to tear into this yet, but its clearly concerning. Upon power up the readout is shifted about 1 division left with the horizontal level cursors off center, but the trace is centered. After a couple minutes the entire display shifts completely off screen to the left. From that point it will come and go, but readout is never centered. In the video I am shifting between horizontal 1x and 10x during one of the periods that the display has returned from the left side.https://youtu.be/WddIKXFB8Cs

author: David Hess
author_rank: Super Contributor
timestamp: December 23, 2020, 11:48:51 pm
content: That is consistent with other U800 failures that I have heard reported.

author: Raindog
author_rank: Contributor
timestamp: December 26, 2020, 07:42:35 pm
content: I have a Tektronix 2465 that had this same issue. With my scope both the trace and readouts would start to shimmer and then shift so far to the left that everything would be completely off screen. Pressing the beam find button would restore it for a while but would happen again a few moments later. But since then I have used this scope very infrequently, and now the problem has seemed to have fixed itself. I have used this same scope to adjust the OCXO's in my T&M gear and it has been working fine, for now. There are however some light artifacts that are present during the first few minutes of operation but go away after that. My guess is it's either the U800 or some intermittent issue in the power supply.

author: Kwakerman
author_rank: Regular Contributor
timestamp: December 27, 2020, 04:44:52 pm
content: Different from the U800 failures I've seen but not saying it isn't a U800 failure. With the ones Ive seen a displayed sine wave starts to compress at one end (linearity, not amplitude) until it looks like a vertical line then the trace moves slowly off screen and the horizontal control can't move it back to centre. Normally a quick squirt of freezer on U800 fixes things for a few seconds.

author: bdunham7
author_rank: Super Contributor
timestamp: December 27, 2020, 05:07:54 pm
content: Any horizontal issues are likely to be the U800, although it is still probably wise to check the power supply and everything else involved just to make sure.There's a drop in replacement available, with limitations:https://www.ebay.com/itm/The-RU800-Ver-1-0-A-Drop-In-Replacement-for-the-Tektronix-U800-155-0241-XX/154246923795?hash=item23e9d54613:g:BDoAAOSwS9Jf2KzPOr, I might be persuaded to sell my spare that I've been hoarding if you want the original. It's looking less and less likely that I'll ever need it.

author: PaulAm
author_rank: Frequent Contributor
timestamp: December 29, 2020, 03:54:29 pm
content: I wish that guy had open sourced it. Getting a few more eyes on that could probably get it to match the original specs without limitations.

author: David Hess
author_rank: Super Contributor
timestamp: December 31, 2020, 04:15:45 pm
content: Quote from: PaulAm on December 29, 2020, 03:54:29 pmI thought he did; I have seen the schematic and it gave me the impression that it was a seat-of-the-pants design.

author: BravoV
author_rank: Super Contributor
timestamp: December 31, 2020, 04:57:12 pm
content: Quote from: David Hess on December 31, 2020, 04:15:45 pmHows that compared to Thomas Lafay's design ? ->Tektronix 2465/2467 series U800 IC replacement design

author: Dr_Ram
author_rank: Contributor
timestamp: January 01, 2021, 05:31:12 am
content: Quote from: BravoV on December 31, 2020, 04:57:12 pmCuriously enough @BravoV, you already asked that question earlier in another thread, and I answered it too:https://www.eevblog.com/forum/repair/tektronix-2467b-display-issues/msg3095894/#msg3095894

author: BravoV
author_rank: Super Contributor
timestamp: January 01, 2021, 06:03:05 am
content: Quote from: Dr_Ram on January 01, 2021, 05:31:12 amYep, I know, but that from the "seller" point of view, hope you get what I mean.David Hess is a well respected member here and very knowledgeable when it comes to Tektronix (especially analog products) and also imho, he is very experienced in analog stuffs.My interest is when he said "seat-of-the-pants design", just want to hear more about that.

author: Dr_Ram
author_rank: Contributor
timestamp: January 01, 2021, 03:19:13 pm
content: Quote from: BravoV on January 01, 2021, 06:03:05 amOK, let's see. The Cambridge dictionary says "...done using only your own experience and trusting your own judgment." By Jove no. As I have said elsewhere, I certainly used Thomas Lafay's design as a starting point. IIRC there's something someone said about standing on the shoulders of giants. That's probably more like it. And no, I have not open-sourced the design as of now.Best - Ram

author: bdunham7
author_rank: Super Contributor
timestamp: January 01, 2021, 05:30:00 pm
content: Quote from: Dr_Ram on January 01, 2021, 03:19:13 pmSince you haven't published the design, perhaps the comment refers to the previous design which was published.The advertised performance of your RU800 appears to be acceptable, but I'm wondering if running the whole calibration process might alleviate the range-to-range accuracy at high sweep rates? Or are you already doing that calibration step and this is as good as it gets?

author: Dr_Ram
author_rank: Contributor
timestamp: January 02, 2021, 03:49:40 am
content: Quote from: bdunham7 on January 01, 2021, 05:30:00 pmI believe it's the latter case. The accuracy of the top 3 speeds depends critically on the HF rolloff / compensation network of the output stage. You will see two trimmer caps on the top of the RU800. Despite being a measly 1-3 pF and they being in series with a tiny 0.5pF, a half-turn of these trimmers visibly affects these 3 ranges. Once I got to a point where I could get to within 1 minor division deviation across ranges, I decided to call it a success. From the discussion on the Tekscopes forum I believe it was indeed the shortcomings of the compensation network in Lafay's design that led to it being abandoned. With the RU800 I also ship instructions on adjusting this compensation for the best possible result.Best - Ram

author: David Hess
author_rank: Super Contributor
timestamp: January 03, 2021, 12:47:44 am
content: Quote from: BravoV on December 31, 2020, 04:57:12 pmOh, I did not realize that there was a second U800 replacement available. The design I was thinking of was probably that one so never mind.