Tek 2445B - Dead display, but processor seems OK, Next Steps? - Page 1
Forum section: electronics / repair

author: davefr
author_rank: Contributor
timestamp: June 13, 2023, 02:54:51 pm
content: I have a Tek 2445B scope with a totally dead display but it seems to boot up OK. The front panel sequences thru most steps but gets hung up on "ADD" but I can continue on normally with most controls which appear to function normally. There is absolutely nothing from the CRT. (no beam find). I measured all voltages at J119 and they are all good and within spec so I conclude the PSU board is OK. (I already recapped the problematic RIFA caps).Any tips on common issues/troubleshooting next steps with this scope when there's no response from the CRT? This unit is in otherwise minty condition with minimal signs of use.TIA

author: tggzzz
author_rank: Super Contributor
timestamp: June 13, 2023, 03:38:21 pm
content: Measure the PSU voltages and ripple.RTFM to see what it means when the start sequence reaches there.Check the SMD electrolytics on the A5 side board to see if they have vomited across the DAC components.Readthe2465 thread; the 2445x and 2465x are very similar.

author: davefr
author_rank: Contributor
timestamp: June 13, 2023, 06:43:47 pm
content: Thanks, I did find that 4 of the 6 SMD caps on the A5 board were open circuit from leakage. I'll replace them. Would that prevent response from the CRT display?

author: tggzzz
author_rank: Super Contributor
timestamp: June 13, 2023, 07:22:32 pm
content: Quote from: davefr on June 13, 2023, 06:43:47 pmPotentially.The components around there form a "strange" DAC that is used to set various "trimpot" voltages around the place. Capacitor vomit can disturb the operation by changing the PCB properties and component values.There is a lot of information around; I'm not going to waste my time repeating it poorly.Start with the manual; it has a lot of useful information on faultfinding.

author: davefr
author_rank: Contributor
timestamp: June 14, 2023, 01:45:26 pm
content: So I replaced the SMD caps which didn't fix the problem. The manual says to try increasing grid bias to max which instantly brought my dead display back to life. However the display is showing odd lines and dots and the message "Test 5, Error 44" comes up. All the manual says for that message is "positive level too positive".There are others who've had the same problem and the culprit seems to be the area surrounding the A5 DAC.

author: tggzzz
author_rank: Super Contributor
timestamp: June 14, 2023, 03:26:39 pm
content: Quote from: davefr on June 14, 2023, 01:45:26 pm... just as I suggestedFFI, google for that error message. It is common.As for "strange dots", a photo would help. I sounds like the other common problem (NVRAM).

author: davefr
author_rank: Contributor
timestamp: June 14, 2023, 09:10:01 pm
content: This thread was worth it's weight in gold:https://www.eevblog.com/forum/testgear/2465bct-error-test-05-fail-44-(24)-trouble/I probed around the A5 DAC area and discovered R2013 was reading 23.7K vs 10K ohms. I picked out a 15K ohm resistor to touch in parallel with it to approximate 10K and the scope completed a successful bootup past the stuck ADD LED and with no error messages. I removed R2013 and replaced it with 10K and all seems pretty good. It functions like a scope but I do see one random dot show up on the screen but I'll worry about that later.