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Author Topic: Test Equipment: Oscillocopes  (Read 42474 times)

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #45 on: February 18, 2015, 03:13:35 PM »
Hopefully they use nichrome coax cores.  Please let me know how they perform once you get them.

Most certainly will do.  If they aren't molded shut, I'll open them up and see what kind of coax core they have. 
The reason I went with those is because they've sold hundreds of them and have a 100% positive feedback rating, and are a top rated seller as well.   I have my fingers crossed they use nichrome........

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Re: Test Equipment: Oscillocopes
« Reply #45 on: February 18, 2015, 03:13:35 PM »

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #46 on: February 18, 2015, 07:51:48 PM »
Do the BNC patch cables that you use have nichrome coax cores?  Cuz I noticed that most BNC patch cables are RG58 or RG59.  I got some BNC/RG6 compression connectors at RadioShack, and I have several different kinds of RG6 - the best being XFT, and also Eagle Aspen 3.0Ghz RG6. All of it is 18AWG copper core, though.

Also, I took my scope apart and took the preamp board off.  I detailed everything with IPA and cleaned all the switch contacts and finger contacts with deoxit D5 and then IPA. I made sure I got the 91% IPA, which is pretty much the best I could find.  I'm not taking any of the other boards off unless I have to due to desoldering, but there is absolutely no visible damage to anything on the preamp board, so I switched the attenuators around from CH1 to CH2 and vice verse, so if CH2 works and CH1 doesn't, I know what part is broken.  Otherwise, I'm going to end up going thru all the tests/calibration steps one by one until I figure it out... since its $365 to calibrate professionally, and the service centers stopped doing repairs on the 465 in 1994...    If it isn't the attenuators and is something else, I will hook it up with a direct line to the calibrator and make a vid showing what it's doing.   Hopefully I've fixed the V/div issue at least, though.

One more thing, my unit has attenuators for 100X - so I guess it would automatically adjust the readouts for a 100X probe. Unless that means something completely different from what I am thinking.

Offline MarkE

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Re: Test Equipment: Oscillocopes
« Reply #47 on: February 19, 2015, 03:12:52 AM »
Most certainly will do.  If they aren't molded shut, I'll open them up and see what kind of coax core they have. 
The reason I went with those is because they've sold hundreds of them and have a 100% positive feedback rating, and are a top rated seller as well.   I have my fingers crossed they use nichrome........
I bought some "200MHz" probes that were about the same price, but the appearance is different.  They were very so-so.  Hopefully what you've bought will be better.

Offline MarkE

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Re: Test Equipment: Oscillocopes
« Reply #48 on: February 19, 2015, 03:22:16 AM »
Do the BNC patch cables that you use have nichrome coax cores?  Cuz I noticed that most BNC patch cables are RG58 or RG59.  I got some BNC/RG6 compression connectors at RadioShack, and I have several different kinds of RG6 - the best being XFT, and also Eagle Aspen 3.0Ghz RG6. All of it is 18AWG copper core, though.

Also, I took my scope apart and took the preamp board off.  I detailed everything with IPA and cleaned all the switch contacts and finger contacts with deoxit D5 and then IPA. I made sure I got the 91% IPA, which is pretty much the best I could find.  I'm not taking any of the other boards off unless I have to due to desoldering, but there is absolutely no visible damage to anything on the preamp board, so I switched the attenuators around from CH1 to CH2 and vice verse, so if CH2 works and CH1 doesn't, I know what part is broken.  Otherwise, I'm going to end up going thru all the tests/calibration steps one by one until I figure it out... since its $365 to calibrate professionally, and the service centers stopped doing repairs on the 465 in 1994...    If it isn't the attenuators and is something else, I will hook it up with a direct line to the calibrator and make a vid showing what it's doing.   Hopefully I've fixed the V/div issue at least, though.

One more thing, my unit has attenuators for 100X - so I guess it would automatically adjust the readouts for a 100X probe. Unless that means something completely different from what I am thinking.
You only want nichrome in the scope probes.  In the coax you want low loss copper.  The flattest response probe that you can get or make is called a transmission line probe:  The coax cable is matched by its characteristic impedance at the input to the scope: typically 50 Ohms.  $5000. and up scopes typically have a 50 Ohm / 1 MOhm input impedance control.  For the rest of us poor slobs, you can buy a male / female 50 Ohm through termination.  The coax cable would then load your circuit with 50 Ohms, which is a bit much for most circuits.  So, what Tek and Keysight offer are those kinds of probes with a series resistor.  A 450 Ohm series resistor makes a 10:1 voltage divider with the impedance of the cable and the circuit sees 500 Ohms instead of 50 Ohms.  The Tek probe is a P6150.  Keysight offers a probe with a 950 Ohm series resistor, that makes 1000 Ohms to the circuit and 20:1 attenuation.  It's a 1980's design.  I would have to look up the part number.  You can make a probe tip yourself or scrounge around eBay for one of the probes I mentioned.  Usually people want way too much money, but they pop up now and again for $100.-$150.

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #49 on: February 19, 2015, 09:44:06 PM »
So I have been doing a bit of research on what type of Coax wire to use for home-made probes.
This is the info I found, and the material I chose.   I want to see what you think about these materials.

https://en.wikipedia.org/wiki/Coaxial_cable

I chose RG316/U as the best possible candidate.
This type of cable is used in Nuclear Instrumentation Electronics.
Here is a link to an ebay item that has more info on the specs of the cable.

http://www.ebay.com/itm/10-ft-RG316-U-RG316-Equiv-Excellent-Quality-Coax-Cable-USA-SELLER-FREE-SHIPPING-/251237252458?pt=LH_DefaultDomain_0&hash=item3a7ee83d6a
http://www.ebay.com/itm/RG-316-MIL-C-17-Coax-Cable-50-Feet-/221625146764?pt=LH_DefaultDomain_0&hash=item3399e35d8c
I had to look up the "core material" - turns out SPCCS is Silver Plated Copper Coated Steel.


Here is some other cable with a much, much higher attenuation. It is "rg8X"
http://www.ebay.com/itm/USA-MADE-RG8X-95-SHEILDED-HAND-SOLDERED-50FT-CB-HAM-COAX-RADIO-CABLE-PL259-/170974652520?pt=LH_DefaultDomain_0&hash=item27cee22868

I wasn't able to figure out or find the exact kind of wire that is used for probes, so the only thing I can think of to find out would be to call Tek or another company that manufactures them and ask, or see if I could get one of the smaller probe manufacturers to tell me, which I doubt they would since there is only one reason why I would want to know - to get some and make my own!!

So what are your thoughts on this? I know that just buying some high quality probes is the best way to go, but what I am thinking about here is the possibility of making my own probes that are similar in performance to the extremely expensive probes that are on the market.  It'll be easy enough to make my own spring-loaded tips out of other types of hook tips that are out there, and easy enough to make my own connector base units for the resistors, caps, and adjuster.  If I don't feel like doing it by hand, I could just get someone with a small CNC machine to make them for me.    If this works out, and the performance is good, I'm sure this could turn into a new way for us who can't afford a $500+ dollar probe to make some that are "good enough".

Brian


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Re: Test Equipment: Oscillocopes
« Reply #49 on: February 19, 2015, 09:44:06 PM »
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Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #50 on: February 19, 2015, 10:34:24 PM »
Uhh..... no.

See the attachments below.

And also this document:
http://www.ece.vt.edu/cel/docs/TekProbeCircuits.pdf

If you insist on making your own, you might as well use the much cheaper RG174/U, I guarantee you will not be able to detect the difference between that and RG316/U on your oscilloscope, except that the 174 will be more flexible and easier to handle.

However... whatever floats your boat.

If I were you, though... I'd concentrate my efforts on troubleshooting and repairing and restoring the oscilloscope, using the probes you have already ordered to learn how to use it properly on various projects, and start saving money to buy your _next_ oscilloscope, or a more modern Function Generator with more waveform output choices. A good dual tracking powersupply is also an important investment for your electronics workbench.



Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #51 on: February 20, 2015, 02:37:28 AM »
Yeah, true.

I tend to get a little ahead of myself sometimes.

Thanks for the info.  I'm still working on cleaning this thing up and running some deoxit D5 into the pots and switches to clean out the contacts. Most of them caused the trace to "scratch around" a bit so I might as well do it while I have it open, and then I'm going to make sure I clean off any excess cleaner, hard to reach dust, etc with this CRC QD electronic cleaner that I picked up. Hopefully all works out well.  Then I can focus on learning how to use it....

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Re: Test Equipment: Oscillocopes
« Reply #51 on: February 20, 2015, 02:37:28 AM »
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Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #52 on: February 20, 2015, 08:40:10 PM »
well, now my scope has a new problem.
I think I may have managed to resolve most of the "noise" issues with the pots and switches, but now I've awoken a whole new problem.
GREAT.
I wish I could just go buy a brand new scope... I get the feeling I may never get this one working properly, especially since I don't have the testing equipment that the manual states is needed, and have absolutely no experience when it comes to diagnosing or fixing this complex of an electronic device.

https://www.youtube.com/watch?v=uOlpdG6qwpQ

I really hope someone has an idea about what is wrong with this thing.  At this point I wish I never would have even opened it up... or even got it for that matter.... :(

Thanks for the help thus far, and any help you are able to provide me in solving these issues....

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #53 on: February 20, 2015, 09:54:19 PM »
well, now my scope has a new problem.
I think I may have managed to resolve most of the "noise" issues with the pots and switches, but now I've awoken a whole new problem.
GREAT.
I wish I could just go buy a brand new scope... I get the feeling I may never get this one working properly, especially since I don't have the testing equipment that the manual states is needed, and have absolutely no experience when it comes to diagnosing or fixing this complex of an electronic device.

https://www.youtube.com/watch?v=uOlpdG6qwpQ

I really hope someone has an idea about what is wrong with this thing.  At this point I wish I never would have even opened it up... or even got it for that matter.... :(

Thanks for the help thus far, and any help you are able to provide me in solving these issues....

Don't get discouraged yet. When you can't get a beam at all, even with the Beam Finder,  that's when to get discouraged!

In the video it looks to me like you have the Timebase knobs set to "x-y" mode (all the way CCW.)  Is that right?

Please set the controls up like in the images below, and post a photo or new video of the traces you get.

Connect the CH 1 input to the calibrator. Just the center pin of the input jack to the calibrator bar, don't worry about a ground connection for now. I wouldn't even use a probe for this, just a cliplead from the cal bar to a wire stuck into the center pin of the CH1 input jack.



Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #54 on: February 20, 2015, 10:26:59 PM »
@Brian: Did you get the full Service Manual? There is a Troubleshooting guide in there. I've found that these guides are very good and will help you track down the problem to the board or even the component level.

http://elektrotanya.com/tektronix_465_oscilloscope_full_sm.pdf/download.html

A good DMM is probably all you'll really need to check it out. The very first things to check will be the power supply voltages, according to the instructions in the SM.

I'm surprised that the thing has "deteriorated" since you brought it home. Are you sure you didn't knock something loose, or leave a screwdriver inside, or something like that?
 :-\

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Re: Test Equipment: Oscillocopes
« Reply #54 on: February 20, 2015, 10:26:59 PM »
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Offline MileHigh

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Re: Test Equipment: Oscillocopes
« Reply #55 on: February 20, 2015, 10:32:26 PM »
Well I hope the scope is on X-Y but I am highly suspicious.   You have a dot in the center and you can see two pale filament curves going towards the bottom of the screen.  I am suspecting that perhaps the the scope is not on X-Y and the horizontal timebase is not working.  The explanation for the two pale filament curves is that normally the beam is pulled off the screen below the bottom of the display during the horizontal flyback.  If this is the case, as the timebase knob is switched to lower speeds you might see the two pale filament curves start to flicker.

If we assume that I am correct and there is no timebase sweep, and you see varying flickering speeds when you change the timebase, then that would be telling you that the horizontal timebase oscillator is most likely still working.  I think there is a good chance that it could then just be a mechanical contact problem somewhere inside the scope.  The next step would be to try whacking the side of the scope just like an old TV.  Do this very lightly at first and do not do it hard and do it at your own risk.  Try a light whack for different timebase settings.  If after a whack you see the beam do a normal horizontal deflection, even it it is just for a fraction of a second, then stop whacking and you are 90% of the way towards the solution.

The whacking made a failed electrical contact between the horizontal timebase oscillator and the horizontal deflection amplifier connect for a short time.  So then the next step would be to open up the scope and clean all of the contacts associated with the rotary timebase selector switch with Q-tips and WD40.

Here is a "big secret:"  Just put a very tiny tiny amount of WD40 on each contact point, then cover the opened up scope with something to prevent dust coming in and then just wait about two days.  The WD40 will do it's magic over the two days.

I learned this from this guy's channel:  https://www.youtube.com/user/AllAmericanFiveRadio

I have watched clips were he does just that.  Takes a tiny tiny amount of WD40, applies it to the bad contacts, waits two days, and then everything works fine.  When you do this instead of spraying you do not contaminate the inside of the scope with excess contact cleaner.

CAREFUL if you take my advice and whack the side of your scope.  Perhaps opening up the scope and just tapping on the rotary switch for the timebase selector with a piece of wood would be better.   All of my suggestions and advice are at your own risk.

MileHigh

P.S.:  Whenever you see a static dot on your scope display you should immediately turn the intensity way way down to protect the screen phosphor.

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #56 on: February 20, 2015, 11:42:59 PM »
Please read the SM from the link above about cleaning the switches and other contacts.  Sorry, but the SM specifically warns against things like Q-tips (they leave fibers behind which can cause intermittent contacts) and petroleum based solutions (they degrade certain circuit board materials used in the scope.)

I do agree with the gentle whacking, and the rest of the stuff in your post. The behavior of the scope has changed since Brian has cleaned it, so it's almost certain that he's managed to knock something loose,  disconnected or broken a wire,  or fouled a switch contact or something like that.

The first thing, though, is to get it out of X-Y mode if that's where it is, and see if any kind of trace makes sense. The fact that the display has the really bright spot on it is a little disconcerting, I don't know if the Intensity control is fouled or what.  I think at this point that there definitely is a problem inside, but also that the controls aren't set properly to produce an interpretable trace.


Offline MileHigh

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Re: Test Equipment: Oscillocopes
« Reply #57 on: February 21, 2015, 12:14:17 AM »
No Q-tips makes sense.  In that guy's channel that I linked to, he may have just put a tiny tiny drop of WD40 on the dirty contacts with the tip of a needle or a jeweler's screwdriver, and then he just touches the contact point.  When I saw that I was somewhat surprised and embarrassed because I have cleaned the pots in old 1970s amplifiers with very messy "brute force spraying."   :D

That's a great segue into some classic advice:  You want a good sound system for your main computer?   In the springtime go out to some garage sales and get a nice 1970s integrated amplifier or stereo receiver for $30 or less.  Clean the volume control knob and the input selector switch.  Get a decent set of stereo speakers and then you will be in computer sound system heaven.   It's getting pretty late now, so old amplifiers and receivers are probably getting scarce!

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #58 on: February 21, 2015, 12:14:32 AM »
AHA!! we have liftoff!!   still some kinks to work out it seems, but progress! 

I don't know if it was just be being dumb and not having the proper settings, but the only real difference between the settings before and the settings now is the coupling is set to AC instead of DC, and the input is also set to AC. oh, and the time/div to 1ms instead of X-Y... which must have been the major issue I suppose??
I did change the coupling to AC and input to AC before when I was trying to get it working, but not the time/div.  If not, maybe the gremlins inside the case fixed it while I was attempting to fix this 1000W amp unit.

One other thing that is different, which I mention in the vid, is where exactly I had the power plugged into.  before I had it plugged into an extension cord that also had a lamp plugged into it.  Now I have it plugged directly into the wall outlet, but it's the same outlet that I had the ext cord plugged into.

I'm going to go with the story that the tube gremlins fixed it....  so I don't feel so stupid!  :)
There are still a few kinks that those gremlins need to wrench on, though, such as the brightness of my vertical lines, the bad illumination bulb at the bottom of the CRT, and the pot noise.... haha

https://www.youtube.com/watch?v=M9slPe8A3lw

Thanks !! :) :) :) :)

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #59 on: February 21, 2015, 12:17:55 AM »
The video shows up as "private" so you have to put us on the list specifically by username. Or you could change it to "unlisted", then anyone with the URL can see it but it still won't appear on searches.

There is a difference between "Trigger coupling" and "input coupling". The input coupling is the one under the channel vertical scale knob. The Trigger coupling is over on the right in the trigger/timebase section. Also the trigger source should "not" be set to "line".

There is still something wrong because even the X-Y display should not look like that; with no inputs to the channels it should produce a single dot, that can be finely focussed to a point, without tails or bright blooming.


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Re: Test Equipment: Oscillocopes
« Reply #59 on: February 21, 2015, 12:17:55 AM »

 

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