Tektronix 2215 dead - Page 1
Forum section: electronics / repair

author: bob91343
author_rank: Super Contributor
timestamp: May 28, 2019, 05:57:26 pm
content: My 2215 will not turn on. Power switch is good.The diagram shows an inductor off board that measures open but my unit has an FET there instead. I broke one lead of it while poking around. It's an IRF820 and I have an IRF740 I could put in there if appropriate.Or I could jumper around it. I don't know the rules here and wonder what to do to get this unit going.All help appreciated.

author: pbarton
author_rank: Frequent Contributor
timestamp: May 28, 2019, 07:20:43 pm
content: I have looked at the schematic diagram and I don’t see an off board inductor. However, Q9070 is the pre-regulator. It’s an IRF820 and is good for 500V.Your IRF740 is only good for 400V, so its not suitable for use in this application.No, you can't jumper around a PWM pre-regulator!I suggest you follow the following informationhttp://www.hakanh.com/dl/docs/troubleshooting_tips_on_2200_ps.pdf

author: David Hess
author_rank: Super Contributor
timestamp: May 28, 2019, 08:26:10 pm
content: There are two versions of the 2213/2215 power supply with one using a thyristor and inductor preregulator and MOSFET current limiter and the upgraded one using a MOSFET switching preregulator like the later 2235/2213A/2215A oscilloscopes.The commonly available 2215 service manual shows both.

author: bob91343
author_rank: Super Contributor
timestamp: May 28, 2019, 08:30:48 pm
content: Look here

author: bob91343
author_rank: Super Contributor
timestamp: May 28, 2019, 08:31:42 pm
content: Where is 'the currently available' schematic and parts list?

author: bd139
author_rank: Super Contributor
timestamp: May 28, 2019, 08:35:55 pm
content: See my thread herehttps://www.eevblog.com/forum/testgear/tektronix-2235-repair-thread/This covers 2235 which is same power supply.Basically there's a cascade of destruction if the FET goes bang or is broken. In my case I knocked the FET while recapping it and it exploded violently taking out driver transistor and a diode.Try and bring the scope up on ~43V DC first then debug the preregulator when you're sure that works.You will need to go parts shopping to fix this. It's VERY fussy about what it will not routinely blow the shit out of.

author: bob91343
author_rank: Super Contributor
timestamp: May 28, 2019, 08:41:22 pm
content: I don't see a diagram there.I downloaded the 2235 service manual but could not locate the power supply diagram. The manual is very unfriendly for me at least.

author: bob91343
author_rank: Super Contributor
timestamp: May 28, 2019, 08:48:50 pm
content: Incidentally there wasn't any kind of traumatic failure. For a while the scope would be balky in turning on or off and I thought the power switch was faulty. Then it finally wouldn't turn on any more.With my erroneous schematic I found what I described above. So a proper diagram is needed. I don't mind buying the right FET and in fact I may be able to repair the old one if enough metal shows to take some solder. I am concerned that the little black box housing it was such a mess, looks like it has been abused physically but the rest of the unit is pristine so I wonder. In the box is also a shield plate. I don't know how this is supposed to go back together or if it even can. I probably will end up with some kind of workaround, not sure yet. I don't need to have this original but I'd like it to work.Before it stopped working, it seemed in good order, no other sign of deterioration except a few seemingly unrelated issues regarding focus and intensity at different settings.

author: David Hess
author_rank: Super Contributor
timestamp: May 28, 2019, 08:56:10 pm
content: Quote from: bob91343 on May 28, 2019, 08:31:42 pmThis copy of the manual from Tektronix shows both the original design and at the end, the later improved power supply.https://download.tek.com/manual/tek_2215_service.pdf

author: bob91343
author_rank: Super Contributor
timestamp: May 28, 2019, 09:05:19 pm
content: Okay thank you. My unit apparently contains the current limit board A19. It's an early s/n but has Option 48 whatever that is.So I am back to square one for the time being. I probably won't have a chance to get back into it today but who knows.

author: pbarton
author_rank: Frequent Contributor
timestamp: May 28, 2019, 09:06:40 pm
content: Quote from: David Hess on May 28, 2019, 08:26:10 pmDavid, you are quite correct, there are two versions of the power supply, as you describe.However, as bob91343 has an off board IRF820 FET, then he must have the "upgraded one using a MOSFET switching preregulator like the later 2235/2213A/2215A oscilloscopes."Unfortunately bob91343 is looking at (and attached to this thread) the "power supply with one using a thyristor and inductor preregulator".

author: David Hess
author_rank: Super Contributor
timestamp: May 28, 2019, 09:38:22 pm
content: Quote from: pbarton on May 28, 2019, 09:06:40 pmI was just being systematic to avoid confusing between the two versions.Quote from: bob91343 on May 28, 2019, 09:05:19 pmOption 48, linked below, is a modification to fix a problem with the early versions of these oscilloscopes where the heater voltage to the CRT was high causing short life.http://www.hakanh.com/dl/docs/kitinstructions/045-0034-00.pdf

author: bob91343
author_rank: Super Contributor
timestamp: May 28, 2019, 10:09:31 pm
content: Okay I was able to resolder the IRF820 lead so I don't have to worry about finding a replacement. Unless of course it's defective, which could be the problem.Now on to figuring out what's wrong. Any tips to troubleshoot?

author: bob91343
author_rank: Super Contributor
timestamp: May 29, 2019, 01:31:10 am
content: I do have the later board, the A18.

author: bob91343
author_rank: Super Contributor
timestamp: June 01, 2019, 10:30:04 pm
content: I bypassed the A18 board and the scope worked with 40 V.Then I replaced the broken FET.I plugged it into the mains and it works!I reassembled much of it, less some of the shields and covers, and all is well.Thanks to all for the help; I probably couldn't have done it otherwise.Bob

author: bd139
author_rank: Super Contributor
timestamp: June 01, 2019, 11:25:15 pm
content: Nice one. Good to hear