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Author Topic: Test Equipment: Oscillocopes  (Read 61905 times)

Offline poynt99

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Re: Test Equipment: Oscillocopes
« Reply #105 on: February 22, 2015, 07:59:08 PM »
PW,  ;)

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Re: Test Equipment: Oscillocopes
« Reply #105 on: February 22, 2015, 07:59:08 PM »

Offline picowatt

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Re: Test Equipment: Oscillocopes
« Reply #106 on: February 22, 2015, 08:08:41 PM »
I would strongly advise against that.  If there are little trim pots all over the boards in your scope that typically means that the boards had to be tuned and aligned with the trimpots as part of the manufacturing process.  Changing a cap could adversely affect the tuning and alignment of your scope.  I am being cautious and very generic in my statement.

And you don't want to take a chance of cracking or pulling out a plated thru hole or lifting a pad if you don't have to. 

Brian said he is blowing out the solder (I assume with compressed air or Dust off) which is OK if you know where the solder is going!  Don't let it blow onto a board somewhere where it will short out something causing another problem.

When solder sucking or blowing out plated thru holes, it may be necessary to resolder the lead and do it again if you don't see daylight around the lead the first time.  Resoldering allows the joint to wet again.  Also, it is always a good idea to snap the lead loose from the side of the plated thru hole using a small flat bladed screwdriver or small needle nose plier and sideways force.  Resist the temptation to pull on the part until you can easily wiggle all leads, otherwise you may pull out a small copper cylinder that was once the thru hole plating.  Sometimes it is best just to carefully cut the part's leads first and then pull each lead out of the board one at a time while applying heat.  After all the leads are out, the hole can be cleared of solder (via sucking, blowing, or wicking).  This is particularly advisable with leads that are a tight fit in the PCB hole that do not allow sucking out the solder all that well. 

PW

Offline MileHigh

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Re: Test Equipment: Oscillocopes
« Reply #107 on: February 22, 2015, 08:20:17 PM »
PW:

Funny story.  That repair tech guy had a fail.  My first thought was to take my variable bench power supply and inject some current and put a few watts in and then do a "laying on of hands" to find the cap acting like a toasty resistor.  Your way was quite dramatic.

My semi-related story was running a boom box off a Radio Shack power inverter circa 1980.  This was in a big private bus going down the highway.  We heard this incredibly loud boom.  It was so loud that we all thought a tire blew out.  There was a big non-polarized electrolytic cap (I think) in the inverter that blew up.

Yes about those tants.  They look like mysterious gooey stuff must be encapsulated in there.  A dangerous thing is inserting radial tantalum caps manually into boards on a push line.  A very nice lady in a blue frock may make a mistake and it's had to detect.  I don't think a reversed-biased tantalum cap turns into a gooey mess right away when it is wrongly inserted so it can make it into a shipping box.

MileHigh

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Re: Test Equipment: Oscillocopes
« Reply #107 on: February 22, 2015, 08:20:17 PM »
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Offline picowatt

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Re: Test Equipment: Oscillocopes
« Reply #108 on: February 22, 2015, 08:27:51 PM »
PW:

Funny story.  That repair tech guy had a fail.  My first thought was to take my variable bench power supply and inject some current and put a few watts in and then do a "laying on of hands" to find the cap acting like a toasty resistor.  Your way was quite dramatic.

My semi-related story was running a boom box off a Radio Shack power inverter circa 1980.  This was in a big private bus going down the highway.  We heard this incredibly loud boom.  It was so loud that we all thought a tire blew out.  There was a big non-polarized electrolytic cap (I think) in the inverter that blew up.

Yes about those tants.  They look like mysterious gooey stuff must be encapsulated in there.  A dangerous thing is inserting radial tantalum caps manually into boards on a push line.  A very nice lady in a blue frock may make a mistake and it's had to detect.  I don't think a reversed-biased tantalum cap turns into a gooey mess right away when it is wrongly inserted so it can make it into a shipping box.

MileHigh

MH,

With the supply folded back, nothing was getting all that warm (including the supply).

And yes, a backwards installed tant tends to first get a bit warm, then get very noisey, and then finally will usually short.  If they are of sufficiently high V rating relative to the rail, they can, as you say, survive long enough to QC the equipment and get it out the door. 

And then, of course, there is infant mortality...

PW

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #109 on: February 22, 2015, 09:06:02 PM »
@MH and PW: I suggest you look at the videos Brian has posted. The scope is a Tek 465 and the SM can be downloaded from the link I posted earlier in the thread, so that you can be "on the same page" as we are, so to speak.

I've located the caps in question on the parts list and on the schematics in that version of the SM. The questionable C1476 cap referred to is indeed listed as a ceramic and the photo listing in the parts source that Brian found looks very much like the cap photo on the board. It is a multilayer ceramic, and its position in the circuit leads me to think that it could indeed be causing at least one of the glitches that he has shown in the videos.

All help is of course appreciated, and I'm especially glad that PW is interested. He may be able to tell much more from the schematic and the behaviour as shown in the  video than I can.

Those old doublesided circuit boards are usually very robust. PW's advice about clipping the component leads off very short is a good one, and then the remainder can be pushed out with a wooden toothpick while heating the pad with the iron. This process is actually recommended by Tek for the plated thru-holes, to clear them for reinstallation of a new component.

Making sure that the removed solder doesn't get on anything is a rather elementary caution.

@Brian: the board images that I see: some of them are quite readable but others are not. I really don't think it's a problem with my software or the use of it.

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Re: Test Equipment: Oscillocopes
« Reply #109 on: February 22, 2015, 09:06:02 PM »
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Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #110 on: February 22, 2015, 09:10:51 PM »
I would strongly advise against that.  If there are little trim pots all over the boards in your scope that typically means that the boards had to be tuned and aligned with the trimpots as part of the manufacturing process.  Changing a cap could adversely affect the tuning and alignment of your scope.  I am being cautious and very generic in my statement.
I think this is unlikely in this case. Take a look at the schematic to see the function of these tantalums in the circuit.

Offline picowatt

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Re: Test Equipment: Oscillocopes
« Reply #111 on: February 22, 2015, 09:37:02 PM »
I think this is unlikely in this case. Take a look at the schematic to see the function of these tantalums in the circuit.

TK,

Where is a video of the current state of this scope?  Last one I saw was with severe blooming with what looked like horiz scan issues.  Is there a newer video showing the scope functioning a bit better?

Has Brian posted any DC measurements of at least the LV rails?  'Tis the best place to start.

I doubt that tant is the only +5 rail decoupling cap, but if it is noisey, it might be glitching the line.  Temporarily replacing it with an electrolytic or even just attaching one across the rail may assist diagnostics.  In the absence of a scope for diagnostics, MH's suggestion of looking at the 5V rail with a voltmeter set to low AC volts might be revealing if the rail is glitching/noisey.

C1476, is that it in your parts layout to the left of the number "89" arrow.  If it is, it looks fairly skinny on the drawing you posted.  What board is that on?

Which cap does he state has the lead arced open and on what board is that cap?  A burnt/arced off lead sounds like a smoking gun.

PW

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Re: Test Equipment: Oscillocopes
« Reply #111 on: February 22, 2015, 09:37:02 PM »
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Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #112 on: February 22, 2015, 10:00:24 PM »
TK,

Where is a video of the current state of this scope?  Last one I saw was with severe blooming with what looked like horiz scan issues.  Is there a newer video showing the scope functioning a bit better?
I think the blooming is just the intensity setting up too high. The scope produced a "perfect" image of the calibrator trace on CH1, but had some strange periodic glitch, like half a second interval, of a sharkfin-type trace that looked like it might be on the unblanked return of the beam.
Quote
Has Brian posted any DC measurements of at least the LV rails?  'Tis the best place to start.
No, not to my knowledge yet. I also have been asking for these, and I found in the manual which the testpoints are and the voltages/tolerances for them.
Quote
I doubt that tant is the only +5 rail decoupling cap, but if it is noisey, it might be glitching the line.  Temporarily replacing it with an electrolytic or even just attaching one across the rail may assist diagnostics.  In the absence of a scope for diagnostics, MH's suggestion of looking at the 5V rail with a voltmeter set to low AC volts might be revealing if the rail is glitching/noisey.
Yep.
Quote
C1476, is that it in your parts layout to the left of the number "89" arrow.  If it is, it looks fairly skinny on the drawing you posted.  What board is that on?

Which cap does he state has the lead arced open and on what board is that cap?  A burnt/arced off lead sounds like a smoking gun.

PW
That is the one, C1476. It is on the A9 interface board. See the schematic excerpt below, from p. 228 in the pdf SM.


ETA:  http://www.youtube.com/watch?v=C8WUWgIVG0A

Offline picowatt

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Re: Test Equipment: Oscillocopes
« Reply #113 on: February 22, 2015, 10:18:50 PM »
TK,

If it was me, besides already knowing the rail voltages, if I suspected the caps that are highlighted, I would temporarily replace them with something from my on hand parts bins.  The two tants in question could be replaced with 47uf at anything over 10V electrolytics and that ,1uf ceramic with any ceramic of similar or greater uf and voltage rating should work OK as well (I think I would stay under .47uF).  it would at least help identify if those are bad caps.

You say one channel actually shows the calibrator signal OK?  I would think a problem with the highlighted caps would affect both channels.

Maybe you or Brian could post a link to the video of the calibrator signal.  I thought things got worse after he cleaned the scope.

PW

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Re: Test Equipment: Oscillocopes
« Reply #113 on: February 22, 2015, 10:18:50 PM »
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Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #114 on: February 22, 2015, 10:39:17 PM »
I wish I could just get a whole freakin' day to myself to sit here and test everything on this scope so I don't have to keep putting stuff away and taking it back out.  Things would get done a whole lot faster.   
Anyway, I should have the next couple hours at least free to do this....
I have 3 DMMs here and am going to check all the rail voltages. 
I have used page 240 aka section 12 diagram as my reference for the test point to voltage matching.

Do you want me to also check all the rails on low V AC settings for "noise"?   And this noise would be any unstable reading, correct?

I am going to do my best to record all of this procedure. I am first going to record a new vid of the calibrator trace from CH1 and CH2 separately and upload it, so we can get this rolling now that more people are interested.

Thanks for all the help everyone, and sorry it's been taking me so long to get the necessary info out here.

Brian

Offline picowatt

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Re: Test Equipment: Oscillocopes
« Reply #115 on: February 22, 2015, 10:47:44 PM »
I wish I could just get a whole freakin' day to myself to sit here and test everything on this scope so I don't have to keep putting stuff away and taking it back out.  Things would get done a whole lot faster.   
Anyway, I should have the next couple hours at least free to do this....
I have 3 DMMs here and am going to check all the rail voltages. 
I have used page 240 aka section 12 diagram as my reference for the test point to voltage matching.

Do you want me to also check all the rails on low V AC settings for "noise"?   And this noise would be any unstable reading, correct?

I am going to do my best to record all of this procedure. I am first going to record a new vid of the calibrator trace from CH1 and CH2 separately and upload it, so we can get this rolling now that more people are interested.

Thanks for all the help everyone, and sorry it's been taking me so long to get the necessary info out here.

Brian

Brian,

Please do check the supply rails and write down your measurements.  When checking the DC rails with the voltmeter set to AC, anything over a few tens of millivolts is likely indicating a problem.  You may have some noise pickup using unshielded test leads, but just get some rough DC and AC measurements for now (ideally, your AC readings will be close to zero).  Pay particular attention to the 55 volt rail, it is used as the reference for four other supply regulators.  Any noise or problems with that rail will affect the other four that use it as a reference.  Since you've already had the scope on several times, I would not bother with the shutting down between measurements, unless it will take a significant amount of time or difficulty getting to the next measurement point.  Consider using a clip lead to attach your meter negative lead to the supply common so you only need to probe with and concentrate on the other DVM lead.  Be careful probing, don't slip and short something with the probe. If a TP is hard to get to, turn off the scope and use a spring hook or small clip lead to attach your meter to the scope.  Happy hunting, look forward to your measurement results.

I am not sure I would bother making a video of you doing the supply measurements.  If you use a tripod and having a camera on you does not make you nervous or distract you, go for it.  But when working on the scope, you need to focus ONLY on working on the scope.

Can you provide a link to a video that most accurately reflects the current state of or problems the 'scope is having?

PW

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Re: Test Equipment: Oscillocopes
« Reply #115 on: February 22, 2015, 10:47:44 PM »
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Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #116 on: February 22, 2015, 11:01:04 PM »
http://i1081.photobucket.com/albums/j347/Brian_Bloom/Scan1_zpsyc0entbh.jpg

http://i1081.photobucket.com/albums/j347/Brian_Bloom/Scan2_zpshoyjanxs.jpg


Scans of A9 layout.  They didn't turn out too great, but they seem better than the one you posted before.
I had to darken the contrast a bit to get the outlines, and it blurred some of the text.

PW -
here is a link to the most recent video.  About to check it again and see if it's still the same and record that. Also I want to get a visual of channel 2 posted.

https://www.youtube.com/watch?v=C8WUWgIVG0A

Brian

Offline picowatt

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Re: Test Equipment: Oscillocopes
« Reply #117 on: February 22, 2015, 11:23:10 PM »
http://i1081.photobucket.com/albums/j347/Brian_Bloom/Scan1_zpsyc0entbh.jpg

http://i1081.photobucket.com/albums/j347/Brian_Bloom/Scan2_zpshoyjanxs.jpg


Scans of A9 layout.  They didn't turn out too great, but they seem better than the one you posted before.
I had to darken the contrast a bit to get the outlines, and it blurred some of the text.

PW -
here is a link to the most recent video.  About to check it again and see if it's still the same and record that. Also I want to get a visual of channel 2 posted.

https://www.youtube.com/watch?v=C8WUWgIVG0A

Brian

Brian,

That video looks like the scope is mostly working.  Does channel two function correctly?  If not, what are its symptoms.  Also, does selecting ALT or CHOP affect the channel one display adversely?

Do not attempt to measure the high voltage for now, you seem to have plenty of it.  Just get some measurements of the low voltage supplies for now (from the 110 volt rail on down).

Is that extreme brightness/blooming just a camera artifact?  I keep wanting to reach for the brightness control and turn it down!

PW

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #118 on: February 22, 2015, 11:42:03 PM »
https://www.youtube.com/watch?v=nMcNEvQ4b4o


Well it appears that everything is working perfectly now.  I guess whatever was wrong was fixed when I removed the trigger/sweep boards and cleaned them up.  There was a decent amount of gunk on the switch drums, so I'd imagine there was a good bit on the finger contacts as well.  I couldn't get a good view of them, but I took a small camel hair brush and IPA and gently cleaned them by pushing the bristles in under the contacts back and forth, and turning the drum to the next setting and repeating.  I also gently wiggled around the transistors and made sure they were fully seated. 
Anyway, it must have been either a bad connection somewhere, or some dust or grime shorting something out or something along those lines....  cuz she works, and channel two works fine also.

I've had 'er sitting here running for the last ten min and everythings fine, so no heat problems either apparently.  Should I even bother to check the rail voltages anyway?

The only thing I see is that there is a wee bit of a wave effect going on with the trace. Don't know if thats to be expected.  Also, call me dumb but I don't know how to get both calibrator traces on the screen at the same time, unless they overlap on analog scopes instead of the shots I've seen of digital scopes where the top half shows one trace and the bottom another.

Either way I'm thrilled it's working and I don't have to replace anything.  good thing I didn't order anything yet!!   Plus, I got my new probes in the mail today, too!

Thanks for all the help!!!  Now I get to learn all of the functions of it!

Brian


Ah.. figured it out.   "CHOP" & "MIX" and then having them on two different V/div settings does the trick.

Offline picowatt

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Re: Test Equipment: Oscillocopes
« Reply #119 on: February 23, 2015, 12:06:40 AM »
Brian,

It sounds like you figured out how to display the two channels at the same time.  Typically you will use ALT most of the time and CHOP for lower frequency signals.

Using your clip leads/wires, short each channels' BNC center contact to ground (BNC collar or the scope's ground lug) and with the channel gains turned up, switch between AC, DC, and GND on the input coupling switch.  The trace should not move up or down while doing this.  Any movement means there is offset in the input amp that needs calibration.  Check the manual regarding this.  You will likely need to switch your trigger source to LINE or switch to "free run" so that the trace appears with no signal applied.

As for the waviness, I assume this video was made with the scope covers on.  If so, there is likely some supply ripple on one of the supplies.  Your scope appears to be working sufficiently to use it to look at its own low voltage rails when you get a probe.  Likely you have a little AC at line frequency riding on a rail, unless the video was made with the cover off.  I have some scopes that will ripple a bit with the lid off.

Do you still get a weirdness when cranking on the trigger hold off?

Congrats, all in all it is looking pretty good.

PW

 

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