Tektronix 465 repair help needed! - Page 1
Forum section: electronics / repair

author: joeferg1801@gmail.com
author_rank: Newbie
timestamp: December 23, 2019, 08:17:52 pm
content: Hello all, this is my first time ever posting on this forum site so please forgive me if I'm doing this wrong, but I seem to have messed up my "new" tektronix 465 oscilloscope.The story goes that I bought it off of a gentleman on craigslist for $40 and it was a little beat up, but still functioning. So, like I always do with any electronics that aren't brand new, i started cleaning it up with some 97% isopropyl alcohol. I then moved on to cleaning the pots by removing the knobs and using (plastic safe) contact cleaner and contact lubricant on the pots as some were causing some 'noise' on the display. Through all of this I didn't even need to open it up so I didn't, that is until when I was re-attaching the dials and I noticed that the threads for the nuts behind the 'position' dials had sunken back into the internals. So, I simply slid the case off, nudged them back enough to screw the nuts back on and boom, it all looked great!The problem came when i plugged it back in and turned it on, everything started up and glowed like before except now there's no trace at all :c I've noticed that when you initially turn it on, you do get a blinding green dot but only for about a second and then nothing. Now, I love projects and I'm used to doing some work on vintage receivers, but this was not something I planned on needing to fix so soon as I just wanted a cheap scope to play with and learn on as I'm a broke college student so I don't have much of a budget for this. While I do have some experience with repairs, this one seems quite intimidating and I can't figure out what I screwed up while cleaning it! Any advice would be much appreciated!

author: PaulAm
author_rank: Frequent Contributor
timestamp: December 23, 2019, 09:04:53 pm
content: Make sure the sweep mode switch is in "auto", you won't get a trace otherwise.Make sure the intensity control is turned up sufficiently.Make sure the V and H position controls put the beam on screen.The odds are you just messed up the controls when cleaning it.Do not, under any circumstances, shoot contact cleaner into the attenuators , sweep range switch or other front panel controls. The pots generally clean up with some exercise as do the various switches. There's a fiddly cleaning procedure for the attenuators detailed in the service manual which uses IPA only. Don't bother if they're working fine.Although this was an inexpensive scope, it is by no means "cheap". When new, it cost about as much as a small car. It does have a couple of known failure modes, particularly the filter caps drying out, but those are pretty cheap to replace and more or less expected for that vintage gear. They may be fine for years yet, so only replace when they fail.

author: joeferg1801@gmail.com
author_rank: Newbie
timestamp: December 23, 2019, 11:15:38 pm
content: Thanks for the advice! I just adjusted the V and H positions to no avail, I guess I should have also mentioned that the 'beam finder' button also does not show anything either. After looking around it a bit I'm still not sure what you mean by the sweep mode switch? I can't find anything like that. I was also thinking that I just messed up the controls but after playing with them for quite a while and watching videos of people explain the machine, as far as I can tell everything is in the correct position or at least should be enough to display a trace for more than the one second dot that disappears :/

author: med6753
author_rank: Super Contributor
timestamp: December 24, 2019, 12:35:50 am
content: It appears you lost one of the supply voltages or the HV. So you'll have to start with the basics.Completely remove the case and do a quick visual to make sure you didn't disturb/damage anything during your partial removal.Download a service manual here:http://w140.com/tekwiki/wiki/465Make sure it's the 465 manual, not the 465B manual (They are different)The power supply test points are on the bottom main board. You should have:+120V (unregulated, may read high)+55V This is the reference for all the supply voltages.+15V+5V-8VStart with that and report back.

author: andy3055
author_rank: Super Contributor
timestamp: December 24, 2019, 02:18:21 am
content: Quote from: joeferg1801@gmail.com on December 23, 2019, 11:15:38 pmCheck this page and follow the info to get to the basic display.

author: joeferg1801@gmail.com
author_rank: Newbie
timestamp: December 24, 2019, 04:31:02 am
content: Thank you for the advice, but I re-checked everything according to that page and still no progress :c

author: joeferg1801@gmail.com
author_rank: Newbie
timestamp: December 24, 2019, 04:33:07 am
content: Quote from: med6753 on December 24, 2019, 12:35:50 amOk after taking a bit to figure this out I measured these voltages compared to what the service manual said and here's what I got (expected values first, actual second)(tp1536) +55v = +54.9v (tp1548) +15v = +14.9v (tp1558) +5v = +5v(tp1568) -8v = -0.049v(tp1518) +110v = +109.0vSo the obvious standout here is -8v rail, I just finished getting these readings so I haven't had time to research what that means but I thought I'd give you an update with voltages.

author: bob91343
author_rank: Super Contributor
timestamp: December 24, 2019, 05:00:15 am
content: It's possible you have some broken controls; the unit may have been dropped on its face. Your comment regarding the knobs makes me think so.It that's the case, you may be in trouble. Those switches are special and complex; abuse is death, generally speaking.

author: med6753
author_rank: Super Contributor
timestamp: December 24, 2019, 05:28:54 am
content: Quote from: joeferg1801@gmail.com on December 24, 2019, 04:33:07 amAs I suspected. Chances are you have a shorted beaded tantalum capacitor holding down the -8V rail. Extremely common issue. In the service manual there is a section on how to isolate each board to determine which one has the short. Follow those directions and happy hunting.

author: andy3055
author_rank: Super Contributor
timestamp: December 24, 2019, 06:08:30 am
content: Here is the page that was referred to by Med6753.

author: Dacke
author_rank: Regular Contributor
timestamp: December 24, 2019, 08:05:03 am
content: Nice scope for $40. 465/475's can be absolute maintenance whores though, especially if you buy one that has been used and abused. The upside is that there is no shortage of people that can help you get them working again and they are well documented. There was a 475A (a similar scope) that I worked on where a main filter electrolytic had turned itself into a resistor, pulling the 5V rail down to less than a volt. I would check those as well. Watch your transistors and ICs, as most of them will be socketed. It's not that difficult to bump one out of position and create a bad connection. Tantalum failures as mentioned are also really common. Just be gentle with the scope, they're bordering 50 years old and can be a bit touchy. More so than others I've worked on.

author: med6753
author_rank: Super Contributor
timestamp: December 24, 2019, 10:05:18 am
content: Quote from: Dacke on December 24, 2019, 08:05:03 amAbsolutely....475A, apparently received light use. Proactively changed many tantalums and general clean up. Works fine.465B, this one apparently had many hours but was treated well. Proactively changed many tantalums but also had to replace the CRT due to focusing issues.465B/DM44, must have been owned by a group of baboons. Dirty and general cleanup. Replaced all the filter caps and many tantalums. Had to replace the entire channel 2 attenuator switch deck assembly due to a poor repair attempt by some gorilla who damaged it beyond repair. The vertical output board was grossly maladjusted. Almost gave up on this one several times but it's now working.Spare parts are a must. Have a junker 465 and 465B. Plus a fully functional spare DM44 that has a broken front bezel.

author: Dacke
author_rank: Regular Contributor
timestamp: December 25, 2019, 11:33:10 pm
content: Quote from: med6753 on December 24, 2019, 10:05:18 amGood times. Yes, having a donor scope helps immensely. Here's part of a repair log I kept from the last 475A that I had a few months ago, I think I picked up the scope for $35. I don't usually make logs for repairs, but this one was a bit exceptional and I have a terrible memory. Once I got the scope fully functional, I just ended up donating it to someone because I was just over it at that point.

author: joeferg1801@gmail.com
author_rank: Newbie
timestamp: December 27, 2019, 06:42:31 am
content: Quote from: andy3055 on December 24, 2019, 06:08:30 amThank you for finding that for me! Sorry I went MIA during the holidays, but after getting back into this now I'm not sure that I understand how to interpret the instructions? What manual exactly did you get this from? I think there must be something missing..

author: PaulAm
author_rank: Frequent Contributor
timestamp: December 27, 2019, 02:11:53 pm
content: You need to find out why the -8V isn't correct. This is likely a shorted tantalum, but check the ripple on the supplies with another scope. The service manual lists the specs, but they should be under 15 mV I think (varies with supply). If you see a large ripple value, it means the filter cap is most likely failed. These scopes don't work at all if the power supplies aren't right.Tracking a shorted cap can be difficult. You'd localize it to a board by disconnecting the -8V supply on each board in turn and measuring resistance until you find the short. Sometimes a failed part will have physical evidence, sometimes not. It may get hot, so that might be a clue. If you have a milliohm meter you can use that to track it down. The tantalums that fail are the epoxy drop type. Once you have the board, worse case you can lift one leg of those and check for shorts.

author: andy3055
author_rank: Super Contributor
timestamp: December 27, 2019, 07:03:50 pm
content: Quote from: joeferg1801@gmail.com on December 27, 2019, 06:42:31 amGot it from the service manual.

author: Unknown
author_rank: Unknown
timestamp: March 21, 2020, 10:41:50 pm
content: Hi all,was just about to open a new thread when I came across this thread, which is a very similar problem to mine, so perhaps we can help others in the future by keeping a'low -8v on a 465'in one thread?Last night I was taking pictures of my lovely old 465 as I intend to sell it, and took some pictures of perfect square waves on the CRT, then just left it running whilst doing other stuff.When I next checked - perhaps an hour later - the trace had disappeared!Upon further inspection and with the Intensity increased, however, there is still one small dot - with, or without the beam-finder.As the case was already off, a thorough search for burnt or blown caps or components revealed nothing out of the ordinary. What was out of the ordinary was TP1568, the minus 8v Test Point, which had been minus 7.9v or so and now reads minus 4.89v.This is why I am here...Reading through earlier posts in this thread, there was a page linked with the procedures for isolating the low-voltage power supplies (see attachment), which says to unsodler (it does) one end of various components, and this is where I became confused. One of the components is R1445...R1445 is a three pin trimpot!(*Edit... just realised that the linked page is for scopes above S/N B250000 - Mine is 100123)Furthermore, using continuity on a DMM there seems to be no connection between TP1568 and any of the components listed in that page of the manual, so how would that help?No component seems to be overheating although two PNP's Q1262 and Q1282 are too hot to touch, but test totally fine.I have spent all day reading different versions of the 465 SM, without finding any version with that particular page, nor clear instructions as to how to progress, so am having to put my hands up, as short of removing and testing every single component I can identify in the -8v line, I don't know where to test.Someone must have some CLEAR idea of how to resolve this problem.Many thanks in advance.

author: med6753
author_rank: Super Contributor
timestamp: March 21, 2020, 11:53:17 pm
content: OK, first...do you have a 465 or 465B? Two completely different scopes on the inside. Make sure you download the correct manual.Chances are high (99%) that you have a shorted tantalum capacitor. Finding it can be tedious but the excellent schematics can be your guide. They clearly show the entry point for the supply voltages for each board. What you need to do is isolate each board until you identify which one has the short. Then lift and test the tantalum capacitors on the -8V bus.And remember that since this is -8V the capacitor will be oriented with the plus side to ground and the new one oriented the same.

author: andy3055
author_rank: Super Contributor
timestamp: March 21, 2020, 11:57:22 pm
content: The attached shows the low voltage supply including the -8v section. Perhaps this will help you to trace back/forward. I would isolate the -8v supply from the rest of the circuitry to make sure it is up to spec and then re-introduce the loads one section at a time.

author: Unknown
author_rank: Unknown
timestamp: March 22, 2020, 06:36:47 am
content: Quote from: med6753 on March 21, 2020, 11:53:17 pm465 (pre S/N B250000 without options)QuoteI have a fresh head today. It took me a while to realise that there different manuals depending on the serial number and the first manual found for this S/N only had one small board section in it.Think I have the correct manual now.

author: Unknown
author_rank: Unknown
timestamp: March 22, 2020, 06:37:52 am
content: Quote from: andy3055 on March 21, 2020, 11:57:22 pmBut the attached is for S/N B250000 and up...

author: Unknown
author_rank: Unknown
timestamp: March 22, 2020, 08:40:36 am
content: Quote from: med6753 on March 21, 2020, 11:53:17 pmCan't seem to find how to do that...But have been sifting through the schematics for all caps grounded from the -8v rail.QuoteAnd now have a list of ten caps which I shall do exactly that, and see where we get to...

author: Unknown
author_rank: Unknown
timestamp: March 22, 2020, 09:09:07 am
content: Mmm...!!The images of the boards and components in the manual don't all match up with the board traces, components, nor positions on the actual scope...Mmmm???!!Now what did I do with that drawing board?...(Edit ...Gonna bell test between the -8v TP and the tantalums and electrolytics to see which are directly connected)

author: Unknown
author_rank: Unknown
timestamp: March 22, 2020, 10:19:34 pm
content: So, did that.There were 3 tantalums on the Interface board and two on the sweep board, however none of them came up as bad when tested with an ESR70.Couple of things;One, in the process of pulling components I realised that the legs of many of the fet's are not gonna be giving the best contact, so tomorrow, I plan to remove and clean every last one.Elsewhere, I came across this thread here...https://www.eevblog.com/forum/testgear/tektronix-465-without-trace-just-a-dot/Although his LV supply was ok... His problem was U870 on the sweep board...If anyone has ten cents they wish to chuck in, then please feel free.And if anyone knows where to get the Service Manual (not the above B250000)

author: andy3055
author_rank: Super Contributor
timestamp: March 22, 2020, 10:58:12 pm
content: Try this:http://bama.edebris.com/manuals/tek/465(2)/Go to the end of the page "Files."Check the manual: 070-1330-00_465Service.pdf

author: Unknown
author_rank: Unknown
timestamp: March 23, 2020, 08:24:59 am
content: Quote from: andy3055 on March 22, 2020, 10:58:12 pmThis is the manual I have.For some reason the Interface board traces and trigger amplifier board are different and some components are either not shown or absent entirely. It's a shame this manual does not show the pcb traces and components like other manuals.Gonna clean those fet's and keep poking around...I do have another scope available if that would help?

author: PaulAm
author_rank: Frequent Contributor
timestamp: March 23, 2020, 01:27:20 pm
content: You may not have a shorted tant. When those short the rail voltage typically goes close to 0. You may have some other failed component. You need to identify which board has the problem. See if you can disconnect the -8V supply from each board until the problem goes away.

author: Unknown
author_rank: Unknown
timestamp: March 23, 2020, 03:39:07 pm
content: Quote from: PaulAm on March 23, 2020, 01:27:20 pmBeen trying to find out how to do that.According to the Tektronix 'Troubleshooting Your Oscilloscope', the problem is in the Horizontal section, so shall look a bit closer there. Doesn't help that the 070.1330.00 manual doesn't correspond to the scope, but never mind.

author: Unknown
author_rank: Unknown
timestamp: March 24, 2020, 08:57:58 am
content: Thanks for all the input so far.Anyway, nothing apparent on the horizontal board, so rewound into this thread and followed the instructions to isolate the boards as detailed earlier in this thread.. (see attachment)But still short of minus 8v (-4.89v).Unless anyone has any fresh ideas as to what might be causing this, gonna pack this scope away and get on with something else.

author: med6753
author_rank: Super Contributor
timestamp: March 24, 2020, 09:08:41 am
content: Did you check C1569 (33uf) on the A9 Interface board? Might also want to check the 3 transistors plus C1562.Find out at which point the -8V leaves the A9 Interface board and pull that connection. See if the -8v comes up. If it doesn't you've isolated the short to the A9 board. If it does then you still have a short on one of the other boards.

author: Unknown
author_rank: Unknown
timestamp: March 24, 2020, 09:56:08 am
content: Already checked C1569 and C1562. All ok.Not sure I can get the transistors out to check themBut did, and they tested fine.Seen people following the trace with another scope. Think I should look into that...Has to be something simple... Floopin thing was working great the other day.

author: Unknown
author_rank: Unknown
timestamp: March 24, 2020, 07:31:02 pm
content: Quote from: med6753 on March 24, 2020, 09:08:41 amNot so simple to do, that as there are plug-in sockets connecting the interface and sweep boards together.Never done that before and it llike it would entail a lot of delicate work. Maybe I'll just sell it for spares?

author: Unknown
author_rank: Unknown
timestamp: March 25, 2020, 01:06:40 pm
content: Saw mentioned that the zeners can fail in the horizontal section.Anyone have any experience with this?I've packed the scope away now. Doh!

author: mzacharias
author_rank: Frequent Contributor
timestamp: March 27, 2020, 11:33:39 pm
content: I have seen bridge rectifiers fail open circuit on these. That could produce the lack of -8 volt line.If that line isn't shorted, that is what I would check.If the -8 line isn't shorted, and still no output, it almost has to be the rectifier.

author: Unknown
author_rank: Unknown
timestamp: March 28, 2020, 09:22:42 am
content: Hi fella,thanks for the input. Just looking through the schematic I have again.It is not shorted, it measures around -4.89v.Won't get a chance to look again for a a few days but shall have a look at the rectifier.

author: charlyd
author_rank: Frequent Contributor
timestamp: March 28, 2020, 10:17:21 am
content: contact cleaner and electronics...it is like a car mechanic and a hamer.use the right things like 99% isopropyl alc.contact cleaner gets sticky after a while and that is what you don t want

author: Unknown
author_rank: Unknown
timestamp: March 28, 2020, 12:46:49 pm
content: Quote from: charlyd on March 28, 2020, 10:17:21 amNo contact cleaner here... only Isopropyl alcohol

author: mzacharias
author_rank: Frequent Contributor
timestamp: March 28, 2020, 01:15:45 pm
content: Quote from: Gazucha on March 28, 2020, 09:22:42 amIf not shorted but you have the 4.89 volts DC there, the filter cap is more likely.C1562, 3000uF.Pretty much one or the other, though.

author: jxjbsd
author_rank: Regular Contributor
timestamp: March 28, 2020, 02:10:05 pm
content: After reading your description, I think it may be that the pins behind some potentiometers are short circuited. These potentiometers use - 8V.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: March 28, 2020, 03:02:27 pm
content: Cap testing for ESR is not appropriate to find a leaky cap. You have to put DC voltage on the cap and see if it draws current.Likewise for Zeners that may be out of spec.Wally KC9INK

author: WaveyDipole
author_rank: Frequent Contributor
timestamp: March 28, 2020, 04:19:04 pm
content: Indeed, tantalum caps usually fail dead short so easy to find with just a DMM. On mine, the filter cap on the 8v rail became intermittent and dragged the 8v rail down after a few minutes warm up.

author: Unknown
author_rank: Unknown
timestamp: March 29, 2020, 10:39:43 pm
content: Quote from: Wallace Gasiewicz on March 28, 2020, 03:02:27 pmThat can be done, when I get back to the scope in a few days.

author: Unknown
author_rank: Unknown
timestamp: March 29, 2020, 10:42:07 pm
content: Quote from: jxjbsd on March 28, 2020, 02:10:05 pmIt does not appear to be experiencing a 'short', more something 'leaking' or failing.But great. Thanks for the input!

author: Unknown
author_rank: Unknown
timestamp: April 05, 2020, 06:00:23 pm
content: Update;Pulled the 3000µF filter cap and connected it up to my bench power supply, with a resistor in series and left it for a few hours to allow the electrodes to electrochemically reform (if necessary)Then drew up a list of every component within the minus 8v power rail and proceeded to test each and every one.R1656 literally separated in the middle as the solder heated. It must have had the finest of hairline breaks as it looked fine to the eye....so a new one of those is in the post...And by swapping the two identical dual op-amps U1554 and U1524, it became clear that they weren't behaving indentically....so two of them are also on their way to postman Pat.I'll report back when he arrives.

author: ko4nrbs
author_rank: Regular Contributor
timestamp: April 25, 2021, 08:24:21 pm
content: Any luck? I've got the same problem.Bill