Tektronix 2336YA repair - Page 1
Forum section: electronics / repair

author: Haatveit
author_rank: Regular Contributor
timestamp: June 09, 2018, 09:57:30 pm
content: I've been fixing a Tek 2336, the previous owner seems to have had a catastrophic ground lead vaporization event on Ch. 1And I've slowly been tracing my way through the input circuitry.So far I've replaced the attenuator assembly entirely, it was blown apart.I've traced out a few more faulty components, by comparing to Ch. 2 (which works just fine). But so far they all seem to be very expensive or unobtainium...Parts I need to replace:Q4, dual "ultra matched" FET >>>>(Red)Q10, dual NPN BJT >>>>(Green)CR1 & CR2 Diodes,>>(Blue) >>PhotoThis is "ground zero" on Ch 1 that I'm trying to repair.CR3 is also dead, but it's actually a reasonable part#, 1N4152R. Which I presume can be replaced with anything roughly equivalent. Don't know what the R at the end means. But 1N4152's are available.Variable cap C1 seems to be fine. But I'm not sure I trust it, since it was directly in the path of destruction. But I guess, I'll leave it as-is for now.Q4 and Q10 can be found online, but they cost 11$ a pop, used but tested. Since these seem to be super duper special matched pairs, I guess I'm screwed when it comes to finding a modern / new replacement?The CR1 & CR2 (same type) diodes appear to be unobtainium. I can't find any information at all, other than that they're out of stock in every spare parts store, and that the service manual refers to them being used as protection diodes. Can I just replace these with generic small signal silicon diodes? Since they're sitting in reverse straight across the input to Ground, I guess that the total series reverse voltage needs to exceed the max spec for the input?Any help appreciated!PS.Oh, and I've always wondered aboutthese old Sprague capacitors... I see them everywhere in old gear. They don't seem to go bad. Are they not liquid electrolytic? Are they generally considered good unless proven otherwise?

author: tautech
author_rank: Super Contributor
timestamp: June 10, 2018, 08:58:37 am
content: This list might help with finding equivalents:http://www.sphere.bc.ca/test/tekequiv.htmlBut there's a much better one at the foot of that page that Sphere ask not to be linked.Sorry, that's all I've got time for ATM.

author: floobydust
author_rank: Super Contributor
timestamp: June 10, 2018, 04:56:46 pm
content: Tektronix used the best semi's out there.151-0725-00 Plessey SL360 Dual-NPN RF ultra-matchedfT=2.2GHzTO-99Found the datasheet but nothing for a substitute in through-hole with fT that high.There are SMT parts that look fine but maybe need an adapter PCB or dead bug.NXP BFU520SMT SOT-363,On-semi MCH6001152-0323-00 GE/Sprague DE102, GE S365 silicon diode 50V20pA@-20V 100mA 3.7pF Vf=1.1V@100mA DO-7 low leakageThis is the lowest leakage diode Tek had in their catalog! Most modern low leakage diodes are 1,000pAOnly thing like it is Siliconix/Linear Systems JPAD20 or PAD2 familyI will look for the dual JFET

author: Haatveit
author_rank: Regular Contributor
timestamp: June 10, 2018, 06:15:23 pm
content: Quote from: floobydust on June 10, 2018, 04:56:46 pmThanks, at least you found some of the critical specs, that helps! I'm not afraid to bodge something in there. I don't really require this scope to work perfectly to spec I guess, but getting it as close as I reasonably can would be nice.I don't have time right now but I'll look for some replacements. Thanks for the ones you linked, I'll check those out as well!

author: Haatveit
author_rank: Regular Contributor
timestamp: June 12, 2018, 04:34:52 pm
content: Well, today I transplanted the diodes and transistors from Ch 2 onto Ch 1, and ...... nothing, still the same problem I had with the old faulty parts installed.The problem with the channel 1 trace is that it IS visible, but only if you hold down Beam Find, and it's all the way at the bottom. Basically maximum negative vertical deflection is being applied. Adjusting the Position control does nothing, however it can be moved horizontally.I don't believe that the actual display drive circuitry is faulty in any way, because it works great on Channel 2. And since this scope can only ever show 1 trace at a time (or chop / alternate) I just don't believe there could be anything wrong with that circuit, since Ch 2 shows up fine.So I've been focusing on the vertical pre-amps. As mentioned in the first post, I found the Ch 1 input attenuator to be basically partially vaporized (see pictures). I replaced it. Nothing changed.I've tried to do sort of a circular search around the dead input transistors and diodes, but haven't found any more faults.Just to mention it, I have checked power supplies and they all seem perfectly fine. The voltages on Ch 1 are mostly wrong, but I think that's because there's something, somewhere, pulling them high or low, I thought for sure the transistors and diodes I replaced (the diodes in particular, they were dead shorts to Gnd!) would fix this issue, but it didn't change anything at all. Very disappointing...Any suggestions would be very welcome...!

author: Old Printer
author_rank: Frequent Contributor
timestamp: June 14, 2018, 02:23:59 pm
content: You probably already considered this, but it sounds like you replaced the attenuator as a unit. If so, are you sure it is good? Often I get in deep and don't see the forest for the trees.

author: Haatveit
author_rank: Regular Contributor
timestamp: June 15, 2018, 03:00:55 am
content: Quote from: Old Printer onTodayat 12:23:59 amTo be completely honest, I haven't checked it - but it's fairly complex so I'm not completely sure how I would check it. But, it was sold as guaranteed working. But, it's a good idea so I shall put that on the list of things to check!