Tektronix 2465B Readout Intensity weak but Trace is plenty bright - Page 1
Forum section: electronics / repair

author: W3KW
author_rank: Contributor
timestamp: August 24, 2025, 02:14:25 pm
content: I am fortunate to own two very nice 2465B’s. One is perfect. The other, which I bought fully calibrated, was well, less than calibrated. I had to adjust the X1 Gain to align the spread and the Y axis was off a hair. But, the main issue is that the Readout Intensity is weak at full intensity, yet the Trace is more than bright enough even at 50% of the brightness setting. Focus is fine. Readout placement on the display is right where it should be. Just dim. (My other 2465B has to be set at a much lower intensity for comfort)Does anyone have a solution? Maybe the adjustment pot is failing? Maybe the jitter cal is off? Does the readout display jitter cal effect brightness of the readout?Thanks in advance.WesW3KWPS: I searched for a while and I’m pretty sure this isn’t a repeat post. Sorry if I missed this topic elsewhere.

author: Testtech
author_rank: Regular Contributor
timestamp: August 24, 2025, 08:53:56 pm
content: If the readout characters bloom and get fuzzy with increasing brightness, you have a weak CRT. Yes, the main trace intensity may seem OK, but you will find that at higher sweep speeds it too has weak intensity.How many hours does the instrument show? Of course the hour meter may have been altered in the apst.

author: tggzzz
author_rank: Super Contributor
timestamp: August 24, 2025, 08:56:43 pm
content: Have you had a look at the infamous SMD electrolytics on the A5 board, to see whether they have spewed bile and changed nearby resistance values?

author: W3KW
author_rank: Contributor
timestamp: August 25, 2025, 11:16:32 pm
content: Yup. It sure did. Three SMD capacitors leaked. No corrosion or damage to the board however. I cleaned up the spew (which appeared to be clear and shinny like simple syrup) with alcohol and measured the caps and surrounding SMD’s and all seemed ok. Just the same, I will replace the three suspect SMD’s (along with other recommended SMD’s when I research the usual suspect list).The hours in the suspect unit are lower than my other 2465B, and as stated, the signal trace has tons of brightness to spare. I’m pretty busy and this is a hobby so it might be some time before I replace the SMD’s. I also ordered new DS1225AD chips from mouser and an eprom programmer. That should be a new and fun experience. The DUT already has a socket installed and a date of June 1994 on it. 31 year battery. Not bad work, Dallas. I haven’t torn into my other 2465B but I’m looking forward to it. At first, it’s very intimidating. Once you spend some time in there, it starts to make sense. Gotta love the Tek manuals!I will be re-capping the power supply boards in both units also. If I’m in there already, why not? Fun.I will report back any findings on the readout intensity front when I know more. Thanks for the help.

author: tggzzz
author_rank: Super Contributor
timestamp: August 25, 2025, 11:33:46 pm
content: Glad to nudge you in a suitable direction.As a belt-and-braces backup, use the test routines to step through the 256 values in the Dallas chip, while videoing the values on the CRT. Hopefully you won't have to look at the video, but if something goes wrong there is an escape route.Watch out for any discrepancy between the PSU capacitor reference/value shown on the PCB and manual. Prudent to replace one capacitor at a time.There's a condoraudio PDF on recapping 2465s, the author is on this forum, and he sells capacitor kits.

author: W3KW
author_rank: Contributor
timestamp: August 26, 2025, 02:27:10 pm
content: Grok (AI help I use) insists that there is a potentiometer, R878, on the CRT Control Board that controls readout intensity. (not Grid Bias). Grok insists that the answer was found on EEVBLOG forum. Hmm. I can't find R-878 anywhere in the 2465B manual. Grok and other resources insist this mystery potentiometer is on the CRT control Board.Any ideas? I searched the forum for it and found nil.UPDATE: I spoke with Alex, the gentleman that calibrated my 2465B. He said I merely need to increase the grid bias a hair on the CRT Control Board. Done. I still have no clue what Grok was referring too.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 26, 2025, 03:34:03 pm
content: Yes! ChatGPT knows it better:Quote

author: W3KW
author_rank: Contributor
timestamp: August 26, 2025, 04:00:06 pm
content: Hmmm. R356 doesn't exist either!

author: tggzzz
author_rank: Super Contributor
timestamp: August 26, 2025, 08:02:02 pm
content: Quote from: W3KW on August 26, 2025, 02:27:10 pmLLMs assemble pretty paragraphs of words that statistically go together in their training set, without comprehending the meaning. When humans do something similar proficiently, they are called bullshitters.Seehttps://www.eevblog.com/forum/chatgptai/the-incredible-shrinking-resistor/msg5996641/#msg5996641for a typical example involving resistors.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 28, 2025, 02:24:02 am
content: found it! – the volume-knob for on-screen charactersrelated pages:procedure 218,in schematics 433& board location 432https://download.tek.com/manual/070686301web.pdf

author: Kwakerman
author_rank: Regular Contributor
timestamp: August 28, 2025, 07:35:08 am
content: Cal 8 doesn't change the brightness of the readout.All it does is:1. Change ithe readout overall vertical position on the CRT.2. Set the distance between the top and bottom rows of the text (that is the 'gain' bit).

author: W3KW
author_rank: Contributor
timestamp: August 29, 2025, 02:35:43 pm
content: Correct. Gain is how far apart they are and the other pot is for centering as you stated. so far, it's still a mystery. They is gobs of extra intensity available. I maxed out the grid bias to just below the level that shows spots on the screen. So odd.When I go in again to swap the Dallas chip out, recap the PS board, and replace a few suspect SMD's, I'll check all the SMD's in the readout chain that I can find. It's such a nice 2465B otherwise.My second 2465B, which is even nicer, will get the same treatment but that unit has a probe-coding issue on Channel 1.Thanks for the replies, all.

author: Kwakerman
author_rank: Regular Contributor
timestamp: August 29, 2025, 04:52:27 pm
content: Do both scopes use the same style A5 pcb (DALLAS)? If so, you can swap them between scopes to help fault diagnosis (on both scopes). You won't lose any Cal settings by swapping them around. Just don't place them on any conductive surfaces in case shorting the Dallas pins affects the battery (I'm pretty sure it won't but I don't take the chance).