Oscilloscope Series - Part 1 - DeVry Oscilloscope Repair & Restore
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- čas přidán 6. 09. 2024
- In part 1 of this series, we look at a vacuum tube oscilloscope from (I think) 1969. It was a kit made for the DeVry Institute electronics class. This was assembled, but never worked, as it was miswired. That's probably why this thing was in such good condition. Come follow along as we bring this thing to life and then see how it works.
One of your best video so far. Imagine the person initially assembling this kit would get to see this; probably someone in his seventies. Must be heart breaking.
1959Berre , Or older! ROFL
This was fun to watch, and to learn from. Looking for what may be wrong and you found plenty. Now a great old scope in new condition is up and working. Thank much.
I have a 1955 DTI Wideband on the bench. No documentation anywhere. Beautiful scope with art deco aesthetics.
You mentioned in the video if anyone had taken courses from Devry/Bell and howell and I took a correspondence course from them in the mid 1970s. The first thing you built was a transistorized multimeter that was used to test the follow on projects. The second was the oscilloscope. Both worked well and I used the meter up until 2019 when it stopped working. I am currently waiting for a couple of transistors for it. Then I got the scope off it's shelf as I have been thinking of getting it working again. The schematic and configuration matches mine exactly. I am waiting for new caps for it. One of those .1 @ 1600v caps was dead short so I will also be changing all the rest. It took me a week of looking to find a schematic and I saw the link to your video so now I am enjoying following your procedures to see what I can learn. Thanks for posting it!
that blue wire from the front panel to the Y output stage is meant to have very low stray capacitance. That's why it's a single wire out in the open away from other circuits. If you replaced it with coax you are going to drag down the high frequency response of the circuit because of the extra capacity of the coax you will add to the circuit. This type of thing is common in wide band circuits and also in video amplifiers with the leads feeding the picture tube cathode in a TV set.
abolutely
Yes. And much of the problem is caused by transformer's magnetic field accessing the cathode ray tube, not capacitively connected hum in the vertical amp circuit. Because even if you short vertical input connectors of the CRT, magnetic field of PT still causes problem if it is near the CRT.
fully correct!
1:32 - Those trimmer caps are used for compensation. Input a square-wave and adjust each for no over- or under-shoot
I too have a hungry floor too
54:30 - Oh it can get weirder; using the Oscilloscope to probe ITSELF!
Tony using a scope to fix a scope reminds me of a lathe. The only shop tool that can make all other shop tools is a lathe. So the oscilloscope is making another scope cycle the way it's supposed to from side to side. I remember a kid who was my friend who had just got his first scope. We were probably 13 or 14 at the time and he was so excited and said he could stop a missile in flight with his scope, (he later died in Vietnam as a medic on search and destroy missions). A wonderful person Ron Slane.
Great video Tony. I attended a DeVry school in the late '70's. In my city they were Bell and Howell but it was the same group. This scope predates me. We were building Heathkit DVM and bench power supplies. I still have both of mine and they keep ticking.
Very informative and educational. Keep up the good work. Jim WA5WRE
In my younger days I had put simple am radio transistor kits together and what you done here reminded me of the trouble I put the repairman thru to undo the mistakes I made. From putting in diodes backwards and transistors of course, to burning out capacitors from too much heat. He retired early because of me 😜. God bless him for his patience and yours too.
Also i would like to add that this guy is probably the best teacher on youtube.. i like the way you explain pretty much everything about everything. Thats greatly appreciated, thanks! You get a sub from me.
Tony, I went to United Electronics Institute in Louisville in 66 to 68 and we assembled a 3" scope. I still have and use it after a turned it into a component and transistor tracer and it is still working. I also have an old 5" Eico scope that I would like to go through. I will be watching your video series and look for your expertise restoring this one! Thanks for the great videos that I enjoy so much!!
Wasn't DeVry one of those places that advertised on matchbook covers?
This video gives me some help in getting my Goodwill scope fixed.I have lost the deflection in the horizontal section.I will try getting a scope kit from Bang Good to trace my scope's fault.
Back in the early 70s I took a two-year vocational electronics course at my high school. , and they used a DeVry learning program and test gear that included that very scope! That I used a lot ! I don't know if they bought or leased all as electronic learning program? But everything had a DeVry name printed or stamped on it? For our first year test to pass we had to build an AM Super Heterodine! Tube radio using point-to-point hand wired perf board! We had to tune it with that scope to be able to receive five stations to pass the class and I passed the test to move on to second year! I have had my eye open for one on eBay with no luck sofar!
In the summer of '81 I was given that exact scope and all the booklets needed to build it (a few dozen, it was broken down into modules to build!) The original owner had done all but the last few steps (add power cord and turn it on). Burnt up the rectifier tube first thing. My senior year of High school I took it to my vocational electronics class and once that was fixed, the trace would float off the top of scope when it warmed up. I will have to see if I still have it in storage as we were never abe to fix it. After finding your channel its definitely time to give it another shot after recapping it.
Hi Tony When I was in high school in the seventies I took a vocational electronic course that was sold to the school by DeVry. I used a DeVry scope just like that one! DeVry sold all the work stations, and test equipment and workbooks had DeVry name on it! it was a 3hour a day high school class! I assume it was sold to different schools as a package! Being high schoolers the equipment got a lot of abuse, I never seen any equipment failours so must be Farley well made! I learned more from that class then any other high school class I took by far! That might had to do with the instructor as well!
It's interesting that the scope uses a 1V2 as a HV rectifier. The 1V2 was originally used as a focus rectifier in the old 21 inch round color TV's. it provided the needed focus voltage to the CRT. Back in the 50's, many scopes used the 1V2 for the HV. The bigger scopes used a 1X2, and the older, larger scopes used a 2X2 (octal base) ST shape. AC coupled scopes had their limitations, but still had their uses. Interesting video. Brings back memories of when I started working in electronics :) I still have my old RCA WO51B and Eico 460. My favorite go-to scope is my Tek 2465B.
I really enjoyed watching you work through all the problems Tony. Great job my friend.
I can empathise with the person who tried to put this together the first time, wherever he or she may be now.
My best Tek is the 2465 BDM. Everything else I own is digital. I use the digital scopes for daily drivers, but I have a soft spot for the Tek.
Greetings:
I do not know how you feel about Dim bulb current limiters, but if the device-under-test draws too much current, the bulb will limit the current to that the bulb draws when used in a lamp.
A CL90 or CL90A has 120 ohms cold but drops to a much lower value as it passes current. In series with the transformer primary and power switch, it will help protect the rectifier feeding the input capacitor to the pi filter. (Even a 22ohm resister will help.)
1:34:47 ... Tell me about dropped hardware. I had a theory that when dropped on the floor, these components dissolve and exist in another dimension until some later date when you drop something else. Then you find the part you dropped earlier, but the current dropped part is nowhere to be found.
I know that one very well.
My first 'scope was a Tektronix Big-Ass 531, sitting out in Terry DeWick's shed. I mentioned I needed a 'scope, and he said "It's yours for $50."
And it was (this was around 1997 I think), and it still is, and it still works great.
It's a late serial number, so it too has a badwidth of a whopping 15MHz. (;^>)
Hi Tony,
I believe I have the complete DeVry document set for this O'scope. It shows the 6AN8 instead of the 6AF11 that your schematic shows. Let me know if your interested, and I will start scanning. It comes in 6 volumes, about 120 pages total. Give me a holler. It shows 1967 as the latest revised date. Oh, I have the scope to.
Tim,
Wow! That's really exciting news! If you have the ability to scan to PDF, that would be great (only if it's not too much trouble :) You can e-mail me at xtronixaudio@gmail.com . Thanks!!
At the going rate for reproduction manuals that should be $11/book, or $66 for the entire collection. do you want just the Schematic? :-) just kidding, but that is what I just paid for an old stereo service manual
Mic is fine, sounds crisp & clear.
I love my Tektronix 2245A!
Well, enjoy it while it lasts. Guarantee it will NOT be a long-term relationship!
😉
great fix Tony. Nice to see you DeFry the DeVry
Hi ya Tony, really great video to watch and follow, you make it all look so easy. My workshop floor is just the same as yours when ever I drop anything it seems to disappear for ever. I've now taken to sweeping the floor with a soft brush and actually inspecting the sweepings in the dust pan before binning it all. Thanks again.
Loved the video, thanks for that.
Had to laugh at the screw problem, my theory is if you watch a screw land it will land at your feet but if you miss it, it will be the other side of the room.
Amen to the last comment about thoughts being with the people who are contending with the Earth Quakes and Hurricanes. Thank goodness I live in the UK where we don't have this problem.
Awesome job. Really enjoyed watching your progress. I especially enjoy how you explain the circuit functions and your thoughts as you move through the repairs. Thanks for the video.
DeVry also sold their courses to other vocational schools! I took one of their 2year courses at a vocational school in Michigan back in the 70's and used one of their scopes just like the one you have that they must have provided to the school?I have no idea what kind of contract they had with the school but everything(books and equipment) was marked DEVry! It must have taught me something I still do and enjoy it as a hobby! WD8MBZ
how to explain how satisfying such repair :) Thanks sir!
@1:12:02 The tube is non conductive because the getter has not fired properly. That "burn" mark is a tiny splat of getter and it is not sufficient to harden the vaccuum which is why it has a discoloured halo around it. The HT wiring problem could not hurt the tube as it was shorted to ground.
Great video and methodical troubleshooting! Thanks also for the clear explainations!
This looks a little like my sencore oscope/vector scope. Cool vintage kit.
As a Kid the DeVry Head Hunters contacted me a number of times while in my last years of H.S. LOL I actually thought about it for a while. Joined the USAF shortly later 1979.
Great video. Chassis looks like it was 3-89. Keep up the outstanding videos!
@48:00 you mention that the 450v caps are only just high enough in voltage. Early electrolytics generally had an over-voltage capability to withstand surge voltages when equipment was warming up. Modern caps will fail with overvoltage. I remember 450 volts caps having a 500v short term ability which I doubt a modern cap would cope with.
I assume that you rotated the CRT about 2° or 3° clockwise to make the trace horizontal. BTW screws and nuts can be devilish and gone to an alternate universe. I have carpet, as bad as your floor pattern. If ferrite parts, a magnet can be your friend.
Vertical sensitivity on the panel of the schematic scope (model 34) reads 50 , 5 , .5 , .05
I would have centered all your adjust and cal pots prior to swapping out that resistor on your Vertical Gain but you got it right up on the line. I had a Unknown Flavor of scope quite close to being the same. I've used MILLIONS of dollars worth of test equipment over my life time in various jobs including the military. To this day I don't have a decent scope on my bench. LOL I never needed one. Always had access to the best of the best. Now Retired I'm screwed. LOL Maybe I'll get one before my End Game. Best thing I have at this time is a Hantek USB scope. Does fine on most Audio projects but I have nothing for RF of any flavor. That's what I miss .
pulsejet , Don't worry, Heaven has all top notch Keithley stuff, a few years from now they may even use this level stuff on earth!
@@BruceNitroxpro Don't know about Heaven but father time is going to call my ticket any day now.
@@pulesjet , Moi aussi. I'm probably older than you are! LOL I was born before Pearl Harbor.
@@BruceNitroxpro No you have me on that one. I was born in Wilford Hall on 911 57.
I am with you on the comment about the floor eating all screws that are dropped....
Hi Tony
Beautifully structured approach to teaching.
Totally engaging and edifying.
Thank you for taking the time to produce such enabling content.
Your work is a hobbyist dream.
Best wishes for your future, may you have a long and happy life.
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so basically, my Hickok OSK-4 with no schematic and my limited knowledge on oscilloscopes is gonna take forever.....but this video is very helpful for the journey
Try measuring the negative voltage rail ending on cathode resistor dividers network because i think thats it is not too steady and this creates signal not steady enough and looking a bit fade and as if there is a ghost trace bouncing around. This voltage is not regulated so it is very sensitive on electrolytics or high voltage caps that create it from the b+ through a reversed diode or in our case a rectifier tube. It is supposed to support static voltage on the crt though so it is not required to be loaded with any high current at all.
The sawtooth\sweep relation was todays revelation for me!
thanks so much, wish I could hit like multiple times.
Thanks for that - very interesting and well presented !
wow You brought it back to life!!!
I like the vice of Knowledge on Big Clive's Channel. I like the destructive nature of things.
Informative and entertaining, thanks. I am trying to resurrect an old Tektronix 7403 and am having issues of my own so good to see some of your troubleshooting techniques.
By the way, it looks like you need a magnet-on-a-stick!! :-)
Also, did I see my scope Tektronix 2465 DMS on top of all of your scopes? NICE! And my name is Tony also Tony!
I also have a floor that consumes mass quantities of hardware. And always the last piece. I don't even look down if the hardware launched into the ether was surface mount. Just grab another.
By replacing the wire that after as a noise aerial with shielded cable didn't you effectively attenuate the signal with its nominal 50 ohm impedance?
Nope. Less than 2 ft worth of coax would conform well to a lumped element model up to at least 30 MHz or so (going by a lambda/10 rule of thumb), and I highly doubt that this old kit scope would be faster than 5 MHz, if that. Capacitance of the coax may be higher than stock though, possibly reducing bandwidth even further.
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Great Video! Thank you for sharing.
The sweep generator ramp is not linear, and that might explain why the wave seems to be more "compressed" on the right of the screen. This is an annoying "feature" of many kit scopes. Nevertheless, good video and excellent repair!
Use a huge powerful magnet to find the dropped screw. Sweep the floor and use the magnet. You will likely find many screws nuts whatever.
I have a working one of this from my sister's husbands, great grampa, and need to find the manual but first heed the model, what is the model of this?
good job x-ray b. extra for a new old scope. it looked so good. never worked since built. makes me wonder how the guy passed his class. bet it was the end. a tech not fitting the job. took a penn state guy to figure out without a schematic, what the heck was going on here. lucky you took it up slow with an ammeter, but I didn't figure that dead tube from the miswire, I thought it was another wiring boner.
Mic sounds great!
Excellent!!
5:20 - trial by magic smoke
Sounds like Dave Jones!
XRAYTONEB, what circuit inside the oscilloscope will draw the horizontal voltage on the CRT screen?
Because there is no horizontal oscillator or vertical oscillator used inside an oscilloscope so how can it draw a SineWaveform on the CRT screen?
The Ramp circuit only controls the electron beam only to the CRT screen?
The horizontal circuit is technically measuring the voltage of the sawtooth waveform. As the voltage ramps up the trace moves across the screen in relation to that voltage. By changing the frequency (how fast) it ramps up it changes the amount of time it takes to move across the screen. A sine wave is tracing of sine voltage vs. time. The sine wave goes up and down over time so the horizontal amplifier circuit changes the trace position over time and the vertical amplifier moves the trace up and down as the sine voltage goes up and down. So there is a oscillator in an oscilloscope and it is generating the sawtooth wave pattern he was showing at 1:03:30.
Really nice video
and really interesting
CANNOT EVER BE A PART'S CHANGER! EVER!!!
I"m wondering if this scope wasn't used in instruction. Maybe these mis-wirings were deliberate. :)
That was excellent
I agree with an other viewer, the date, so called, code is 3-89 as it looks to me. At 15:30 its clearly 3-89, for what its worth. I wonder if its more a serial number or batch number.
I have couple old oscilloscopes: 1) Sencore PS148 - doesn't work at all 2) Simpson Model: 466 - this works now, but it is old and the pots needs cleaning....
Where can I buy replacement parts? Is there somewhere schematics with correct parts and modern replacements? Do you have a club or place on the Internet, like the Tektronix group? (I also have Tektronix 2465 DMS in working condition with P6407 RQAUS1). My modern oscilloscope is Aktakom 100 Mhz 2 channels. Thank for your video ! I'm now a subscriber.
I found a devry scope the other day as well
My floor eats the last screw as well... It's nature's way... No floor mat will solve this! 😅
I have acquired a scope exactly like this...where did you find the schematic? Thanks for the great video!
Great video I can't believe I just bought that very same oscilloscope from someone who sold it on Craigslist. mine has a couple of bugs but in general it's working okay. With your explanation I understand the layout of the circuit a whole lot better. I wish I had a copy of that schematic. Where did you find that and how close is it to the actual machine?
I'm going to do the same recap and wire replacement that you did I will also check all the ground connections.
my Trace is very noisy on the two highest vertical settings I think I might have a dirty switch but I'll get in there and see what's going on any help you can offer would be appreciated. I also went to DeVry Institute I forget when probably early 80s and I built the transistorized voltmeter in my class.
www.oscilloscopemuseum.com/uploads/8/9/7/7/89778727/hickok-osk-4-manual_part01.pdf
www.oscilloscopemuseum.com/uploads/8/9/7/7/89778727/hickok-osk-4-manual_part02.pdf
www.oscilloscopemuseum.com/uploads/8/9/7/7/89778727/hickok-osk-4-manual_part03.pdf
www.oscilloscopemuseum.com/uploads/8/9/7/7/89778727/hickok-osk-4-manual_part04.pdf
stevenjohnson.com/hickok/data/hickok-750-manual.pdf
I don't mind the new mic, but you seems to sound a little stuffier than before, like there's less of the midrange than before
The screw eating floor! My nemesis!
My question is it possible to record with this osciloscope? i dont know the exact term but what i mean is to record a brief sign wave? As in when something tries to turn on , you can go back and look at the sign wave... I have been thinking of buying one of these old ones since i cannot afford a new one , for repairs .
older scopes will not do what you ask. you would need a digital storage oscilloscope. you can find them on ebay fairly cheap now. i bought one for $50 on craigslist.
Hi Tony, I think I see another un-soldered joint on the back of the Horizontal adjust pot (anti clockwise end tag). I have a snap shot of the issue - is there a way for me to upload this?
I saw that as well. I'm not sure if he touched that one up or not.
15:04 that date you mentioned earlier is 3-89 not 3-69
I would love a copy of that schematic. Please.
www.oscilloscopemuseum.com/uploads/8/9/7/7/89778727/hickok-osk-4-manual_part01.pdf
www.oscilloscopemuseum.com/uploads/8/9/7/7/89778727/hickok-osk-4-manual_part02.pdf
www.oscilloscopemuseum.com/uploads/8/9/7/7/89778727/hickok-osk-4-manual_part03.pdf
www.oscilloscopemuseum.com/uploads/8/9/7/7/89778727/hickok-osk-4-manual_part04.pdf
stevenjohnson.com/hickok/data/hickok-750-manual.pdf
Bell and Howell btw.
Hi Tony, I have an old oscilloscope and the horizontal beam keeps jumping or floating off to the left even when there are no probes attached. Any idea what might be the problem? Thanks
Sounds like the gain on one of the amplifier stages is too high causing the signal to be divergent instead of convergent.
1:34:40 WE MUST BE RELATED! LOL!
Sure wish you were using a non-conductive pointer there, sir!
I enjoyed your video, very instructive. One safety suggestion is to remove rings and watches while doing troubleshooting, especially live circuits. A clip lead from high voltage to ground would be another backup safety measure.
Never worked since brand new and now calibrated.
I take it you would never try reforming the capacitors by slowing bringing up the voltage while monitoring the current
Only someone who has no idea how a capacitor works would do this.
update: my mom won't let me use it until I know how big of an explosion if the capacitors short out🙄
"Trying new mic, y'all let me know, We are doing a new series on oscilloscopes" then the program...
This was not a repair for a beginner.
The F student who assembled this went back to flipping burgers.
[written after less than twenty minutes into the video] One thing which you tend to perpetuate is an overwhelming sense of, "I HAVE to do this unpleasant job" (for example, recapping an OLD oscilloscope). You then use OLD caps for the most DEMANDING job IN the oscilloscope... the high voltage power supply. THEN, you use the SAME 450 vdc cap ratings on your replacements for the caps in the low voltage system, FORGETTING that the OLD caps were much wider in tolerance for overvoltage due to their old construction, not even showing us that they NEVER go over 450 volts or NEAR that voltage. I think you seem, despite your overwhelming knowledge of circuit design and breakdown methodology... you appear CHEAP. Yup... you don't want to spend a dime more than "just getting by," unless someone almost kills you. Is this TRUE? Pleasseeeee, say it isn't so!
I needed a filtering cap for a small 10volt transformer (that drived a relay) and had one 16v 3300uf. But i said screw it, why use such a fancy cap for such a small job and then i got 2 chinese 470uf caps in parallel and said, good enough.
Here's the Wiki on DeVry University. They've had quite a history, including lawsuits!
en.wikipedia.org/wiki/DeVry_University