[Solved/kind of] How long can I keep my tektronix 2235 oscilloscope on? - Page 1
Forum section: electronics / beginners

author: solder_boy132
author_rank: Contributor
timestamp: December 26, 2020, 03:30:00 am
content: I have a tektronix 2235. Got it of of ebay for $160. The scope works best if left alone to warm up for 4 hour. So instead of waiting, I thought, "can i keep it on for 2 or more work days?" So what is the longest time i can keep it on. Apart from the CRT burning, because I turn the crt off when unattended. If needed i can add cooling using a self cooling fan.

author: george.b
author_rank: Frequent Contributor
timestamp: December 26, 2020, 03:42:05 am
content: There isn't a hard limit on how long you can leave it on, but keep in mind it's already old, and everything has a finite lifetime.Unless you're doing critical measurements - in which case I don't believe you'd be using a Tek 2235 - I don't think there's much of a point in letting it warm up, let alone for 4 hours, especially considering that its characteristics, as stated in the manual, are valid for a warm-up time of at least 20 minutes.

author: bob91343
author_rank: Super Contributor
timestamp: December 26, 2020, 04:46:50 am
content: While there is seldom a need to leave stuff running all the time, sometimes I forget to switch off this or that unit and it stays on for a day or two. No ill effects. Keeping it warm is good in some respects but not others. It's a puzzle which is best. So I try to remember to switch off my units when I close up for the night but if I don't, no big deal.

author: andy3055
author_rank: Super Contributor
timestamp: December 26, 2020, 05:24:41 am
content: A lot depends on the age of the equipment. Once I left my old 465 M ON overnight on a worm day and it ended up with a busted EHT unit. Even if that does not happen in your case, leaving it on for days at end is not a good thing. To begin with, unless you turn down the brightness control, you will end up burning off a line on your CRT face.Most scopes will be stable in about 20 minutes or so. Basically, it is the time taken for components to warm up and become stable in their response/performance etc. without drift over temperature changes. There is no reason for a scope not to perform unless you have it on for 4 hours. There must be already some issue with it. You may have to check as to what is causing that.

author: TERRA Operative
author_rank: Super Contributor
timestamp: December 26, 2020, 06:23:30 am
content: The warmup time is a lot less than 4 hours, but if you want to keep it on, I'd be first replacing the Rifa caps inside (actually, do this anyway, they are guaranteed to fail at some point), and maybe checking the power supply output filter caps are in good condition and also check if the service upgrades are done, to ensure a long lifetime.Also a fan can be retrofitted to these scopes relatively easily to keep things cool and lasting longer.Also also, if you do leave it turned on, be sure to turn the CRT intensity dial right down when not in use so you don't burn the phosphors in your screen.I have a youtube video on restoring one of these scopes which has a bunch of information on modifications and stuff that you might find interesting. Follow the link in my signature below.

author: bdunham7
author_rank: Super Contributor
timestamp: December 26, 2020, 06:31:59 am
content: You don't need a cooling fan, but I typically don't leave these running unattended just because once in a while something burns up or explodes. I certainly wouldn't leave a recently acquired one on even leaving the room. My overhauled ones get tested for at least 8 hours, but by then they've earned my trust! Does your horizontal displacement issue go away after being on for 4 hours???

author: vk6zgo
author_rank: Super Contributor
timestamp: December 26, 2020, 08:05:54 am
content: Turning down the intensity to avoid burning a line on the screen is a good tip, but another, & perhaps more important reason why leavingany'scope using a Cathode ray tube on for very long periods is not a good idea, is that CRTs rely upon the thermal emission capabilities of their cathodes, just like any other vacuum tube.Loss of emission happens whenever the heaters are energised, even if the CRT beam is cut off, so beam current when itisin use will drop over time, & you may struggle to obtain a bright enough trace.Eventually, it will become too dim to discern.When such 'scopes were current, this could be discounted to a large extent by the major enterprises that might use them continuously, as being "a long way down the track", & even if expensive, replacement CRTs were available.The average crazed sufferer from TEA will inevitably be using a device which has already had an honourable career, so, if it still has a nice, bright display, it is wise to "husband this resource", as your chances of getting a good replacement CRT are fairly low.

author: TERRA Operative
author_rank: Super Contributor
timestamp: December 26, 2020, 10:54:24 am
content: In the note of thermal emmission, make sure that the transformer mod is completed on any 2213/2215 and 2235/2236 scope.On early inots, the voltage to the filament was set too high, leading to greatly reduced CRT lifetime.It's a relatively straightforward procedure to perform the mod, as detailed in this document:https://www.hakanh.com/dl/docs/hardtofind/SUP3010.pdf

author: bd139
author_rank: Super Contributor
timestamp: December 26, 2020, 11:34:48 am
content: Do not leave it unattended. It has RIFA capacitors in it and a Schaffner filter and is likely to burn your house to the ground. Also the power supply and EHT is fragile so it’ll probably just eat up what remaining life it has or explode anyway. I speak from experience from owning two of them. You don’t want to have to fix the power supply side of things. Thread herehttps://www.eevblog.com/forum/testgear/tektronix-2235-repair-thread/I never leave anything over about 5 years old plugged in even if I’m in the house.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: December 26, 2020, 12:01:42 pm
content: Quote from: solder_boy132 on December 26, 2020, 03:30:00 amWhat are the symptoms if it "does not work so good"?I may be a sign of some part almost failing.And indeed, replace those mains filters before they fail, there is a lot smoke in them.

author: solder_boy132
author_rank: Contributor
timestamp: December 26, 2020, 06:49:32 pm
content: The oscilloscope is in its pre tektronix condition. No non tektronix stuff in there. I think. Anyways. This scope has been serviced one time. And that was at the Service factory in Beaverton Oregon. So replacing the caps seem like a good idea. I checked all the caps and most of them are tektronix branded caps. But all the parts are around the same time. The seller said this scope was rarely used since it was in the back of a lab.

author: solder_boy132
author_rank: Contributor
timestamp: December 26, 2020, 07:10:50 pm
content: So if i replace them, do I replace them with another rifa brand cap? or just the same type cap?

author: george.b
author_rank: Frequent Contributor
timestamp: December 26, 2020, 07:33:56 pm
content: Quote from: solder_boy132 on December 26, 2020, 06:49:32 pmOther than the RIFA caps, if it ain't broke, don't fix it.Quote from: solder_boy132 on December 26, 2020, 07:10:50 pmSame type.

author: bd139
author_rank: Super Contributor
timestamp: December 26, 2020, 08:27:00 pm
content: Yes same type. Replace the mains filter as well. That’s basically a bunch of RIFAs put inside a pipe bomb

author: David Hess
author_rank: Super Contributor
timestamp: December 26, 2020, 08:50:17 pm
content: If you are leaving it on, then it is best to leave the CRT on dim and unfocused rather than off to prevent the formation of interface resistance in the cathode.My 7603 was in storage for a long time and might have displayed the same symptoms of improved CRT performance after warming up. I suspect this comes from contamination in the CRT which gets swept away and embedded in the aluminized anode during operation. I left it on accidentally for several days and the CRT performance improved considerably. So you might try this however only do so where you can keep it under supervision. Do this with the CRT beam unfocused as outlined above.

author: solder_boy132
author_rank: Contributor
timestamp: December 28, 2020, 06:05:36 am
content: Yea kinda. It starts centering, but its still there. I contacted a friend who is smarter than me, (yes I'm stupid some times) and he said " If you can't fix it, send it to Norway Labs. They may be able to fix it, that is only if they accept the oscilloscope for repair". So is it a good idea?

author: solder_boy132
author_rank: Contributor
timestamp: December 29, 2020, 06:55:31 am
content: Y E A P! I HAVE BLOWN MY OSCILLOSCOPE. $160=shipping down the drain.

author: george.b
author_rank: Frequent Contributor
timestamp: December 29, 2020, 07:44:47 am
content: Quote from: solder_boy132 on December 29, 2020, 06:55:31 amWhat? How?

author: solder_boy132
author_rank: Contributor
timestamp: December 29, 2020, 07:46:15 am
content: Dropped it while going down the stairs. Glass everywhere. Started smoking for some reason.

author: george.b
author_rank: Frequent Contributor
timestamp: December 29, 2020, 07:52:47 am
content: ...ouch

author: bd139
author_rank: Super Contributor
timestamp: December 29, 2020, 10:27:05 am
content: As long as you didn’t go down the stairs with it then it’s a good day

author: TERRA Operative
author_rank: Super Contributor
timestamp: December 29, 2020, 03:43:41 pm
content: Time to sell the parts that are still good.....PCB's, knobs, undamaged case parts, etc

author: bd139
author_rank: Super Contributor
timestamp: December 29, 2020, 04:01:01 pm
content: Probably worth more like that anyway