My Tektronix 2465 shows no trace during *warm up* - Page 1
Forum section: electronics / testgear

author: yugu
author_rank: Contributor
timestamp: December 27, 2014, 04:30:23 am
content: Hi guys. When I turn my 2465 off for a long time (more than 1 hour) and then turn in on, the screen shows a few dots instead of traces (see picture 1). it responded to the vertical position adjustment. And I could also make cursor measurements. After a few minutes, it showed normal traces and everything seemed to be working fine (see picture 2).If I turn it off for just a few minutes and turn it back on while it's still *hot*, it shows normal traces.It seemed to me that something on this scope needs some time to warm up before normal operation. Is this normal or does it indicates something is failing?Thanks!

author: c4757p
author_rank: Super Contributor
timestamp: December 27, 2014, 04:34:51 am
content: Definitely not normal, but a somewhat usual sign of failing capacitors in the power supply. Check the power supply rails while it's warming up!

author: yugu
author_rank: Contributor
timestamp: December 27, 2014, 04:55:24 am
content: Thanks. Sounds like another fun project!

author: AMR Labs
author_rank: Frequent Contributor
timestamp: December 27, 2014, 05:09:43 am
content: Nice scope, but it uses a bunch of custom Tek hybrid ICs that are very hard to get, including the deflection ckts. The problem might be related to one of them. Hopefully not, and its just a leaky cap, tests should tell.

author: edavid
author_rank: Super Contributor
timestamp: December 27, 2014, 08:06:21 pm
content: Quote from: AMR Labs on December 27, 2014, 05:09:43 amAbsolutely not. If you have a nice readout like in the photo, there is nothing seriously wrong.ETA: Lots of misinformation here. They are not hybrids, they are custom ICs. They don't run especially hot. They don't have a high failure rate. It is perfectly fine to run the scope with the case off and no extra cooling... that's what they did at the Tektronix service centers.

author: AMR Labs
author_rank: Frequent Contributor
timestamp: December 28, 2014, 12:19:52 am
content: Well as said before, I hope its not the case. But the hybrid might still be flaky, just my 2 cents. They get quite hot during operation, and your fault seems to be thermally related, so its still a possibility. They been known to sometimes develop reliability issues and to get intermittent, over the years this topic has been discussed extensively at the Tek Yahoo group.

author: Wim_L
author_rank: Regular Contributor
timestamp: December 28, 2014, 12:25:42 am
content: So, about those hot running parts: it's best to get extra airflow on the boards if you run it out of the case to probe the supply, or you might kill them faster.

author: yugu
author_rank: Contributor
timestamp: December 28, 2014, 07:30:35 am
content: Thanks fellows. It was really a time consuming process to track down the problem, since I only had a 2-minute time window per hour to measure stuff. Beyond that time window, everything was normal and I couldn't do much.Long story short, it turned out that the pin 1 of U650 (display sequencer module) was broken and had a flaky contact. As a result, the selector signals sent to U800 was incorrect. It forced U800 to only output the readout signal, instead of switching between readout and sweeps.As for why the scope functioned normally after a few minutes, my guess is that the broken pin expanded with accumulated heat, and the flaky contact became "solid" when the scoped was warmed up.With the broken pin fixed, I tried a couple of cool-off-and-then-power-on testings. The scope no longer showed the symptoms described in my original post. Problem fixed!!A few notes about U800:I heard a lot about how easily it could be fried when running with an open case. So I checked its temperature with my finger tip frequently when poking around (I don't have a service fan). Interestingly, the U800 in my scope did not heat up quickly. It only felt warm after running 10 minutes without the case.YMMV, though. It's hard and expensive to get a replacement. Be careful and play safe!

author: tautech
author_rank: Super Contributor
timestamp: December 28, 2014, 07:46:56 am
content: Quote from: yugu on December 28, 2014, 07:30:35 amIs U650 a thru-hole IC?Do you mean Pin 1 solder joint was broken or the pin itself?Good find and fix BTW.Thanks for sharing.

author: yugu
author_rank: Contributor
timestamp: December 28, 2014, 08:33:40 am
content: Quote from: tautech on December 28, 2014, 07:46:56 amThere is an IC socket for U650. The socket has no problem. Pin 1 of the IC was broken into two pieces.

author: tautech
author_rank: Super Contributor
timestamp: December 28, 2014, 09:02:59 am
content: Quote from: yugu on December 28, 2014, 08:33:40 amInteresting.I wonder if this is at all common in these Teks?Fatigue from thermal cycling do you think or corrosion?

author: rf-loop
author_rank: Super Contributor
timestamp: December 28, 2014, 02:57:11 pm
content: Quote from: yugu on December 28, 2014, 07:30:35 amAnd scope settings was so that horizontal amp was running maximum power dissipation? May I quess - not.Also if we look Tek specifications.This model max operating temperature is -15 to+55Celsius! (and it is real deeply tested specification, not just printed on paper without enough knowledge as today some manufacturers do.)When it is used in +55C and 24/7 and with settings where hybrids power dissipation is maximal... it can say itishard.And Tek engineers have designed it without extra heat sink and they have not been noobs without enough experience what to do. Then some peoples think they need redesign it without any real knowledge and experience why.I have seen lot of 2465's what have been in "good hands" and there have not visited any "adjust and repair hero" and surprice or not but I have never seen real U800 damage if users have not been stupidos. (also perhaps just partially good luck of course because fraction from total is really minimal)It is possible there have been weak chips and some time after product launch they have failed.. this is other case and perhaps partial explanation for this "urban legend" about lot of U800 fails.(but if "service man" is not careful, it can destroy very easy... one mistake with test lead (inside of course) and thats it - chip internal smoke has escaped.... Then explain to lab boss that this is just this famous U800 fail what everybody know... I have not done anything..

author: yugu
author_rank: Contributor
timestamp: December 28, 2014, 08:18:41 pm
content: Quote from: tautech on December 28, 2014, 09:02:59 amI didn't inspect the broken pin thoroughly before trimming and soldering. All I have are a couple of photos now. For those who are interestedpic 1: the broken point looks corroded. (not 100% sure. the photo was not taken under sufficient lighting)pic 2: some dude had used the IC socket as a home.Quote from: rf-loop on December 28, 2014, 02:57:11 pmDefinitely not. I don't want to test how U800 could failSec/Div was set to 1ms through out the job, it that's related.Quote from: rf-loop on December 28, 2014, 02:57:11 pmThanks for sharing!

author: edavid
author_rank: Super Contributor
timestamp: December 28, 2014, 08:20:57 pm
content: Quote from: tautech on December 28, 2014, 09:02:59 amNo, it's not common.

author: edavid
author_rank: Super Contributor
timestamp: December 28, 2014, 08:24:56 pm
content: Quote from: rf-loop on December 28, 2014, 02:57:11 pmIt's not quite an urban legend, since there were definitely excess U800 failures. It seems to have been a die attach problem, since people have been able to repair some of the broken parts by baking them. However, a lot of semi-related legends have sprung up, like this idea of needing a service fan.

author: tautech
author_rank: Super Contributor
timestamp: December 28, 2014, 08:34:53 pm
content: Quote from: edavid on December 28, 2014, 08:20:57 pmOK not common, I guess like any ageing equipment, shit happens.I have seen corroded pins/leads in socketed components in our humid climate in NZ, but as U650 is such a large package, I'd be inclined to suspect thermal cycling was the main cause of breakage, or a combination of both. I see some marks in the gold plating on other pins that might support this view.Anywayyuguthanks for sharing.

author: miguelvp
author_rank: Super Contributor
timestamp: December 29, 2014, 01:22:55 am
content: Quote from: yugu on December 28, 2014, 08:18:41 pmI guess that dude couldn't read English or not enough lighting to see the 100 V present warning next to his/her home.