Tektronix 465 Oscilloscope Troubleshooting

[DanielSpokane]

Got the cap out. Pictures are posted below. Went pretty easy... the only thing is one of the ground traces lifted just as Addicted2AnalogTek warned. You can see it in the last picture (looking down at the bottom next to the other PS filter caps). The trace goes to a ground screw that connects the side and bottom PCBs. I'm thinking I will glue the trace down with super glue (will have to drum up a curved stick or something to apply the glue to the underside of the trace). The only thing is... part of the hole tore off with the capacitor (you can see in the last picture )... thus it seems like there is a chance the ground connection isn't made when I solder the new cap in since I will be soldering from the bottom side opposite of the ripped hole trace. Hmmmm. I can test and make sure there is ground continuity... but worried it might be a weak connection. What do you think? Other than that... went well

[Addicted2AnalogTek]

It looks to me like that ground trace may have burned up prior to your removal of the capacitor.  Upon comparison with a spare board, it looks like that trace runs to the cathode of CR1569, the anode of CR1549, and then on to the ground TP/screw hole in front of Q1546.  That's also where the notorious little 3uF 150V wet tantalum capacitor ( C1534 ) is grounded, but the ground trace between that area and CR1569 is a lot smaller, so I'd be expecting that to burn first if something in that area had failed. I'd check all of those components just to be safe.  Others might have some ideas as to what caused that trace to burn - if that's what happened.

You may have to remove the trigger board for this, but one way to solve that problem is to gently scrape all the crud off of the board with a flat tip screwdriver, clean up with IPA, and then lightly scrape some of the good trace so you can solder some stranded wire down to it. Then just run the wire from the good trace and thru the hole. You could actually just use some used solder-wick instead of wire since it's a short run.  Personally, I would feel that to be a more stable solution than trying to repair the damaged trace.

Good job on getting that sucker out, though! It's a monster compared to it's replacement!

[DanielSpokane]

Thanks for the input. Yes I like the idea of running a wire on the trace. Maybe I solder it to the trace and through the hole then bridge the wire back to one of the other ground holes. Then run another wire from the other hole up to the new capacitor (and bridge the grounds on the cap). Seems like that would hold well and then I wouldn't have to worry about connecting the hole with the damaged trace directly to the capacitor. Seems like that might simplify the mechanical dexterity needed to do this.

Replacement capacitor is scheduled to arrive Friday!

[DanielSpokane]

Also, I will check those other parts shortly to see if there is any sign of damage, etc. Thanks for the heads up.

[DanielSpokane]

Got the new capacitor in. Overall it wasn't too bad. I was able to re-glue the damaged trace; then used wire and solder for belt and suspenders just incase the trace was damaged or not fully intact. The new capacitor had two leads (instead of 4). Installed the 2 leads in existing holes then jumpered the other two open ground locations. Had to drill a couple holes in the ground trace to get everything to set... but worked well. After that... turned it on and works like a charm! Thanks guys! See pictures and video:



A couple things (which can be seen in the video):
1. When I move the trace for either channel up and down the screen there appears to be some visual distortion for a second that goes away. Any idea what is causing that?
2. Also, the intensity of the screen is really really bright. I have it at about 25% and that looks great. When I move it to 100% it gets insanely bright. Not a big deal... I guess I just want to make sure something else isn't out.

Overall a pretty sweet scope for $20 (at a thrift store) plus the price of a capacitor and a little elbow grease. Thanks again for all your help.   

[tautech]

1. When I move the trace for either channel up and down the screen there appears to be some visual distortion for a second that goes away. Any idea what is causing that?
2. Also, the intensity of the screen is really really bright. I have it at about 25% and that looks great. When I move it to 100% it gets insanely bright. Not a big deal... I guess I just want to make sure something else isn't out.

All looks perfectly normal.

WRT CRO Intensity/brightness, you need good brightness when using delayed timebases and that's really the only time. Generally Service manual adjustment specifies that when set to Min the trace should just disappear and an additional bias pot is normally fitted on the PCB to get the brightness range correct.
It's a good idea to get into the habit of using only enough Intensity/brightness to see the trace clearly in order to preserve CRT life.

So now use it for a bit as your main scope, why ?.....well in order to get used to properly driving a scope instead of using Autoset. This is/isn't a dig so much as an experienced recommendation and it will help you later when using your DSO.

[DanielSpokane]

Thanks for the info... and thanks for the recommendations regarding learning to drive a scope. Will do!! Looks like this is my new baby for a while!

[Miti]

If you want my opinion, if this cap was dead, the others are most likely on their last legs as well. If I were you, i'd replace them too.

2. Also, the intensity of the screen is really really bright. I have it at about 25% and that looks great. When I move it to 100% it gets insanely bright. Not a big deal... I guess I just want to make sure something else isn't out.

Apply 100MHz with X10 MAG, is it bright?

[Addicted2AnalogTek]

A couple things (which can be seen in the video):
1. When I move the trace for either channel up and down the screen there appears to be some visual distortion for a second that goes away. Any idea what is causing that?

This is typical of one of these scopes that's sat for a long period of time without use and should improve (for the most part) as you use the scope.  It's being caused by some oxidation or buildup on the contacts inside of the vertical position pots.  There's likely some other dirty contacts you'll discover soon enough, which also will likely improve with use.

Overall a pretty sweet scope for $20 (at a thrift store) plus the price of a capacitor and a little elbow grease. Thanks again for all your help.

Congratulations on your successful repair! That's one heck of a deal - $20 for the scope and maybe $10 for the capacitor after shipping, plus a little bit of time and effort!

If you want my opinion, if this cap was dead, the others are most likely on their last legs as well. If I were you, i'd replace them too.

I've found an easy way of discerning whether a supply cap is "on the fritz" from my time inside of a 468.  The 468 manual has waveforms for the unregulated power supply rails which I haven't found in any other manuals.  Upon probing the positive terminal of each cap with the same setup you would use for ripple measurements, you'll see if the cap is discharging smoothly or not.  Now, if the ripple is in spec but the unregulated supply waveform doesn't look "clean", I'll just replace the cap.  But of course, you need a second scope for that.  Other than wholesale tantalum cap replacement (when they're obviously from the 70's-80's), I avoid wholesale parts replacement tasks. It just seems to be a waste of money when the OEM parts, if still good, may last at least several more years.

[DanielSpokane]

Thanks again for all the help. I really appreciate it. You guys sure know your stuff!! This scope sure looks sweet on my bench now!

I will keep an eye on the other components and will replace when needed. I did buy another 5600uF cap just in case

[Addicted2AnalogTek]

But of course, you need a second scope for that.

I completely forgot that you can use the scope to check itself! I just double checked on a 465B.  Just be careful probing! Make 100% sure that your ground lead DOES NOT TOUCH anything that is not a ground test point or the frame!!!   In order to check the caps the way I described above, you just need to use a 1X probe and set bandwidth limit to 20Mhz.  The settings you'll want to use are shown in the pictures I'm adding to the post.


>The first picture is the waveform you'll see when probing a good cap. This is what your new cap will look like.
>The second picture is the waveform of an acceptable cap (to me, anyway), but one I'd keep an eye on. If it were any worse, I'd just change it.
>The third picture is a bad cap, and one that I'll replace immediately.  This bad cap is on the +15V rail, which measured less than 2mV ripple on the regulated output. It's still "acceptable" to the scope's power supply, but I wouldn't expect it to stay that way for long if I left it in.

If you decide to go ahead and check them out, I'd download the 468 service manual volume 2 from the TekWiki site and go to pages 169/171. You can then apply that info to your 465.  If you haven't already, you should download or buy the manual for your scope and familiarize yourself with everything. Also download and read "Troubleshooting your oscilloscope: Getting down to basics" by Tektronix. It's a lifesaver!  This way you'll be nearly ready when the time comes to tackle another repair.

EDIT  The orientation of the photos has been changed when uploading and I'm not sure how to make them the proper orientation on here after they're attached.   

[tautech]

But of course, you need a second scope for that.

See reply #34.

[Addicted2AnalogTek]

But of course, you need a second scope for that.

See reply #34.

Oh!! My mistake!   I probably need sleep.. It's 4AM here.

[tautech]

But of course, you need a second scope for that.

See reply #34.

Oh!! My mistake!   I probably need sleep.. It's 4AM here.

No matter buddy, you were a bit late to this party and probably missed the first few posts. 

[tautech]

EDIT  The orientation of the photos has been changed when uploading and I'm not sure how to make them the proper orientation on here after they're attached.   

Yeah my iPhone does that dumb trick too.
I import them into a pic viewer and flip them right side up, save and then post.

BTW, what phosphor is in your Tek ?
I do like those trace colors. 

[MarkL]

A couple things (which can be seen in the video):
1. When I move the trace for either channel up and down the screen there appears to be some visual distortion for a second that goes away. Any idea what is causing that?

This is typical of one of these scopes that's sat for a long period of time without use and should improve (for the most part) as you use the scope.  It's being caused by some oxidation or buildup on the contacts inside of the vertical position pots.
...

You can also just operate the controls to their extremes 10 or 20 times or until the problem subsides enough to clear the wiper.  But it's usually only a temporary fix and the jumpiness will be back.

[bd139]

Sometimes that works. The vertical pots on mine are beyond that unfortunately.

[Addicted2AnalogTek]

EDIT  The orientation of the photos has been changed when uploading and I'm not sure how to make them the proper orientation on here after they're attached.   

Yeah my iPhone does that dumb trick too.
I import them into a pic viewer and flip them right side up, save and then post.

BTW, what phosphor is in your Tek ?
I do like those trace colors. 

It's a 485 with option 4 (EMI filtering) and option 78 (P11 phosphor). It's got the CRT mesh filter, which makes the blue seem even more brilliant!   It's great for pictures (as that's it's intended purpose), but I didn't realize just how unfriendly P11 phosphor is on the eyes.  It plays tricks with my vision and drives my eyes out of focus if I'm looking at it for more than just a couple seconds.

 

Sometimes that works. The vertical pots on mine are beyond that unfortunately.

I've had success with "repairing" these pots. It's just time consuming is all. Here's a quick run-down of what I've done:

1- remove vertical board, desolder pots, disassemble them and remove the part of the pot that holds the wiper. I like to put the rest of it back together to maintain orientation, and so I don't lose anything....
2- soak the wiper assembly in 99% IPA for a bit (usually an hour or so).  After the initial soak, grab one of the leads with pliers and "whip" it to fling out the IPA.
3- repeat #2 two or three more times
4- Blast out with compressed air - I use canned air so I don't have to worry about the moisture & oil that comes out of an unfiltered compressor.
5- Reassemble, install, and test.

I don't clean the lube out from around the shaft unless it's dirty.  I did clean it out on an intensity pot assembly once and the dielectric grease that I used to replace it just didn't seem to allow smooth operation. It's not noticeable on the display, but when I went to adjust the grid bias and Z axis, the darn thing was so stiff that I had to fiddle with it for some minutes before I got it to the correct voltage.  Maybe some contaminants remained behind before I re-lubed it, maybe I used the wrong stuff, or maybe I used too much - but now I just leave the original lube in there and only clean out the wiper assembly. Fortunately I've only had to do this 3 or 4 times, but it would seem I'm about to be doing it again with some of the "sealed" Allen Bradley type vertical position pots.   I'd rather do that than dish out $30 for a pair of "new" ones or raid another scope for replacements, though!!

It's a lot easier to do if they're the A-B type with the four slotted screws holding it together. It can be performed on ones with the plastic pins as well, you just have to either glue or melt it back together afterwards. The Bourns pots with aluminum dowel pins I haven't attempted yet, but I'm confident those can be done as well - it could be as simple as finding some screws and nuts small enough to replace the aluminum dowels. 

[bd139]

Thanks for the tips. These are the old black AB ones with screws fortunately. Not sure I fancy taking the vertical amp to bits yet to get them out. Honestly I was hoping for another 465 to turn up as a parts mule so I have some backup pots first

[Addicted2AnalogTek]

IIRC, the 311-1311-00 pots are in all of the 400 series scopes except for the 468 and 485.  The problem with using ones from a parts mule is that you're risking the chance of ending up with pots that are just as bad or worse than the ones you already have!     I have a 465 parts scope with known good vertical position pots, and if I don't end up needing them for the 465B that's on the bench right now, I'd be willing to part with them.   I'd understand if you'd rather hold out for a complete parts scope for all the extra replacements it contains! 

[bd139]

Plan was to test and refurbish the ones in the parts mule scope and then substitute them in. Path of least risk there. Annoyingly the entire scope is immaculate and looks like new (even feet are intact!) so I’m not sure why the pots are so scratchy. Probably why Bourns do the later model ones!

Thanks for the offer but alas I am waiting for a complete scope as I need some spares around. This is the first time I think I’ve had only one tek scope on hand and I’m never happy with that situation.

[DanielSpokane]

You guys are a wealth of information!

Ok... here's a little less technical question.

Any idea where I can get 2 replacement cabinet feet (See picture). Mine has 2 but is missing the 2 rear feet. The screws are there for the missing feet... but the feet are gone. Almost looks like a kid or someone unscrewed the 2 right before I found it and bought it. I searched for a bit on the internet but couldn't find anything in stock. I was thinking about making something.... 

[tautech]

You guys are a wealth of information!

Ok... here's a little less technical question.

Any idea where I can get 2 replacement cabinet feet (See picture). Mine has 2 but is missing the 2 rear feet. The screws are there for the missing feet... but the feet are gone. Almost looks like a kid or someone unscrewed the 2 right before I found it and bought it. I searched for a bit on the internet but couldn't find anything in stock. I was thinking about making something....

Google for 'wall skirting door stop' and get one of the 'squat' (short) varieties.
They should really be non-conducting ......from the age when it was normal to float a scope.

[Addicted2AnalogTek]

Any idea where I can get 2 replacement cabinet feet (See picture). Mine has 2 but is missing the 2 rear feet. The screws are there for the missing feet... but the feet are gone. Almost looks like a kid or someone unscrewed the 2 right before I found it and bought it. I searched for a bit on the internet but couldn't find anything in stock. I was thinking about making something....

I'm about to send some out today to someone for reproduction, actually. If they are successful, replica replacements should be available in a couple weeks.  They appear to be part number 348-0080-00 (according to the 485 manual).  Until the reproductions are available, the only way I know of to score these is to take them from a spare case.

Be sure to put something over those studs to protect the threads until you have suitable replacement feet - if the threads get damaged, they'll probably need to be chased (cleaned with a die).  It could be as simple as a wine bottle quark that you've cut to a decent height and then screwed onto the studs.

There's some similar ones listed on the evil auction site P/N 348-0187-00, but I have no idea if those ones have the correct threads to match up to the studs mounted to the 400 series scope cases. I don't think I'd want to pay $21.00 for two replacements that may not fit, though!   It's great that your case still has the aluminum studs still attached - I have a 485 which had the two rear feet completely ripped off!

[bd139]

Only about 20% of the scopes I’ve had over the years have had feet. First thing that buggers off usually!

Edit: when I sold my parts mule 465b ages ago I got the most money for the multiplier and feet (20 quid for the feet).