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- เผยแพร่เมื่อ 27 ส.ค. 2024
- Follow Dave as he tracks down an elusive intermittent thermal fault in a HP1740A analog oscilloscope.
Can you figure out the culprit before Dave does?
Part 1: • EEVblog #803 - HP1740A...
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Original HP Journal article on the HP1740A:
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How not to blow up your oscilloscope:
• EEVblog #279 - How NOT...
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"It's permanently failed! Excellent!" Only Dave could say something so intuitively wrong, but practically right
doing IT work I say everyday "if its not broken right now there is not much I can do we need to wait until it gets worse"
These kind of debugging videos are the very best. great work Dave.
+lentosy100 Unfortunately they aren't always this interesting!
+EEVblog Yeah... thisone was gr8 , but mostly murphy will get u .... but @this time.. he went to have some lunch :D
These are the most educational videos from an applied or practical point of view. Gives the watcher the chance to get intimately involved and test their logical skills...
Nothing more satifying than a successful repair.
Revised troubleshooting guide:
1. RTFM
2. RTFM
3. To be sure, RTFM again
4. Check voltages
5. Check connections
+leppie and then the documentation lies :(
RTFM means "Read The Fantastic Manual" (in THIS case, anyway ;) )
Everyone's favorite segment: Repair Videos!
Favourite segment, "Dave talking about repairing electronics". Well, actually just "Dave talking about electronics". Well, I guess we could still compress it to "Dave talking". Well, actually, I think "Dave" is good enough to make the best videos :)
Best channel on TH-cam!
So happy to finally see a repair video that worked out.
Double thumbs up Dave. It was more like a detective story than just a troubleshooting repair video. You just cant leave until you find the clue. Enjoyed truly.
+Satyajit Roy Thanks. Yes this one luckily turned into an a rather interesting detective story.
Cool story time.
I had a home component CD player go dead. It had been hit by lightning on the AC mains and it had a linear power supply. It used discreet glass diodes for rectification. I opened the case and plugged it in and I noticed one of the glass diodes was glowing like an LED. It wasn't getting hot, it actually gave off a red light. I replaced the diode turned LED and the CD player worked.
Great one Dave, as many people have probably already said.
Great job demonstrating methodology over "jumping down every rabbit hole"!
Ive been into electronics since age 12 and a working EE since 1975, wouldn't trade it for all the tea in China.
I probably learned more about electronics while troubleshooting failed equipment, than designing new.
Best 2 questions to keep in mind when troubleshooting; "What do we know?" and "How do we know it?"
Thanks again Dave, keep up the great work!
The first successful repair of the channel, congrats
Thank God the man is getting to what we want to see.
BER = "Beyond Economical Repair" Dave, how did you know in 2015 the Berlin airport will never get fixed?
This video is gona stay in my top ranking ones. Thing of beauty, joy for ever!
I have never known a rectifier to fail this way. Normaly when they fail they permanently fail. It's a lesson to not rule out in the future. Nice one Dave it's been a good and interesting diagnosis.
Finally. 800 videos, and finally we got a proper repairable repair. Very nice video.
That was fascinating! After seeing the circuit breakdown and the fault mode, my inclination was the bridge rec or a leaky electrolytic. The dry joints were a surprise, recently I saw similar joints on an automotive relay. It was a timer relay for the headlamp washers on a friends car. I diagnosed the problem but the dealer quoted £85 for a new replacement, fortunately with a 3 week delivery! My friend declined to order it and told me. So, I broke the seal on the faulty relay and closely examined it. There was a fair bit of circuitry inside and quite a nice relay, all in a cube about 30mm square. To the naked eye all looked fine, but when I looked through a magnifier at the base connection pins, 3 of the 4 were dry and loose. Re soldered, sealed back up and winner winner, chicken dinner, as Dave would say! Said friend was both delighted and impressed!
How do you tell a newbie youtuber apart from one that has done almost 1000 vids: "I will be yapping for another 5 minutes, maybe 10...." I call that self confidence ;)
Don't worry about the time for locating the fault. You showed how you choose your direction for the repair and the thought process. Excellent job! (And I love the posts...."I knew it...Had this happen on a lawn tractor's alternator with a rubber dillydoo sitting on a fence...." Yeah that is a sarcastic remark. ) Have a good day!
Fantastic. Thank you Dave, this was excellent. Always a pleasure to watch your videos.
I love someone who actually LOOKS for things going wrong... doesn't "expect" things to NEVER fail. But fail it did!
Really enjoyed watching you hunt down the problem.
Great repair Dave would never have thought a diode bridge, my hats off to you. I was assuming as you were indicating, and thats
wrong on my part. Will remain opened minded with your next repairs.
never believe in diode bridge! )))
+T Komoski I thought it could be a diode bridge, but maybe shorting in some way. I didn't figure it would be a partial high impedance fault, that was a curveball.
+EEVblog yeah I've never seen such a vicious failure mode neither...
Congratulations Dave!!! You finally lifted the repair curse!
Really glad you were able to get a win. Successful repair videos that include the debugging and procedure are some of my favorite types of videos on youtube. Really hope you get some more wins in the future.
Need more meters there Dave. Joking aside, good to see you taking care of some old gear. They need a good hug every now and then for their faithful service.
Totally entertaining both part one and part two. Thumbs up on the isolation transformer when testing with the oscilloscope. I literally blew up the earth probe on a HP osc. Technicians came running in to see if the apprentice was dead or alive. The noise was like a gun going off.
I just bought one of these at a hamfest in Canada. I watched Dave's two videos before even turning it on, with some trepidation. Anyway it seems to work perfectly. But now I have Dave's guide in case it goes awry. I already have six DMMs.
This was a super entertaining video. More troubleshooting video please :)
+Mazsul Unfortunately rarely do they turn out to be this exciting.
+EEVblog They are always pure entertainment, at least. This one has been epic!
That was very cool. I have put off going out to do my grass (which has shot up in past 2 days) to watch this adventure.
It is good to see a quality product from the inside too. So even there less than adequate solder joints had enough residual quality to last all that time.
Very entertaining, thanks.
Nice job. Glad I'm not the only one who lifts the occasional land (pad) on these old boards. I do think for these old well-documented electronics R'ingTFM is a good start. Please keep up the repair vids, especially for the older equipment. Thanks!
I definitely watched the whole video.
There's your succesfull repair video you have been waiting for Dave! Congrats!
+Necessaryevil 86 *phew*
Great video, I have not seen a diode or bridge unit fail this way my self and I have worked in this field for over 40 years. Thanks for sharing this information with all of us. Will look for more.
Nice one, Dave! This has to be one of the best videos from you that I've seen. Great job curing that sick puppy.
Hey Nice work Dave ! You covered a very complete troubleshooting process at last! Shariar beware! Dave is back! And he's hungry for more...
Looking at the schematic at 18:20./ lower right - seems like the +15V regulator is powered by the 5V rail... that would explain the cascaded failure.
+vintagepc64 The -15V rail is, but not the +15V rail.
+EEVblog D'oh... you're right.
Have a tek and spent last weekend tracing down a touching but broken lead to the CH2 vertical knob. The manual has a great piece of advice on troubleshooting - it sums up as "milk the front panel for all it's worth" - narrow down the fault as much as you can before you so much as crack the cover. Was surprisingly effective too, once you take a moment to step back and note ALL of the symptoms. The longest part of finding that fault was disassembly. Just goes to show how easy it is to jump from one conclusion to another when you've actively got eyes on all the innards... and you easily miss the big picture from all the symptoms together.
Great video, as usual - Thanks for making us unwashed masses just a little bit smarter with each one :)
"A wiggle and a jiggle." Dave might have a hit single on the charts!
Really enjoyed the story of the scope,, the problem solving and example of how to trouble-shoot. You demonstrated more than that which you expressed in your commentaries and summary: a skilled and experienced professional at play with something he loves. Thank you Dave for sharing the adventure, as well as your infectious enthusiasm for electronics!
Awesome video. As an undergraduate soon to enter the industry, I find the in-depth explanation of your troubleshooting process to be invaluable. Hope you get more broken stuff!
"Murphy is on his lunch brake." Dave, you're hilarious! These repair videos are really fun.
There are few things more satisfying than a good repair! Nicely done.
Service work may not be a good business, but it puts all your neurons to work ! Love these 2 videos on 1740 repair, the pursuit of the failure is just like a suspense movie, until you find the culprit. Congratulations and thanks Dave.
Always good watching the tracking of a problem and then the fix. Good video Dave.
Hi Dave - thanx for this one, as it shows a common fault on old/vintage stuff.....
If a unit fails - regardless of its kind - check the power supply first. Usually 90% of the synths i get in for a repair/or bought in non working condition, suffer from a gone bad power supply and some have gone bad IC sockets, main switches, connectors (i´ve done a video in where i show a worn out ribbon cable connector on my MK-1 synth.... and the like as well...
Always make sure that the mechanical side (cables,interconnections,sockets,switches) is alive and working first, and that make further tests...I also had seen some IC factory-sides put in sockets with one or more pins bent with 90degrees pointing into the inner mid of the socket and not into the socket´s pin....so intermitened connection was bult in as well...
Hard to trace down....
Im my hammond X-5 i needed to replace nearly the complete wiring loom (between keycontacts and soundsource) due to broken inner copper, replaced one, fixed that problem, two/three month later a similar fault occurs (of curse at another key/octave), replaced the next wire...after the 4th error of the same kind i´ve chosen the long road and rewired the whole thing....
Next in line are some hohner RDM1000 (first gen digital audio delay) i got three of them - all with the same error: 5 up to 20 minutes after PowerOn they go nuts, the 5V rail dropps, DSP and uC go mad...the last one came with schematics, now i can try to fix them;)
I was going to play Dead Space tonight, but that has now changed.
I think Dave is flexing on us with his multimeter collection
Thank you so much for this. This video will be helpful when I get around to repairing my two dead HP 1740A scopes.
Good job, that was a well hidden intermittent problem!
+youbecha64 Well hidden indeed.
+EEVblog It looks like it acts as a half wave rectifier when it fails, so I think that internally there's a diode what is being open when the temperature reach certain point. It cooldowns and recovers until coming hot again. And that's the failure mode of that bridge rectifier. Very uncommon, and It's only a theory, what do you think? PS: Sorry for my bad english, I'm from South America, hope you will understand :)
+youbecha64 Intermittent issues can make you throw adorable kittens off a cliff.
Thanks so much Dave. Had one of these scopes for a few years and love the trace quality. The new DSO gets a good work out but this old one is a fave. It died a while back and I just delved in there today. Discoloration round the same bridge! The trace just went "crinkley" and disapeared off to the top left one day. Will be taking a very close look at those through holes tomorrow. R3 on the HV board failed previously. Youre a star. Excellent videos as usual. Pointing all my proto-geek friends at your channel!
wow... went to videos on your channel: nothing. went to the repairs playlist: 1 new vid, out since 1sec. good timing :D
One of your best troubleshooting video
Excellent video! I ALWAYS check power supply before I troubleshoot any other part of a device. I've seen many others waste so much time tracking a problem down when it actually came back to a power issue!
I repair a lot of guitar amps and the bad solder joint issue is a prevalent issue! Especially on large filter caps and such that suffer from vibration issues.
GREAT JOB!
I love a good mystery! So much to be learned! Great job Dave.
Man I love these troubleshooting repair videos with schematics and reasoning faults out. Thanks!
that was great fun. ya got the little bugger. it was so satisfying seeing that little rectifier caught in the act with its pants down. ripper video once again!
That was fun to watch the whole process of figuring it out and repairing it.
great repair! I work on broadcast transmiters and if the part doesn't vaporize when it fails I am usually stuck!
Dead Dingo's Donger ... absolutely loved it every time it was said
This was fantastic. You did an awesome job and kept it entertaining too. Thanks.
I love doing my homework while watching your videos! Really takes time off my mind.
Boy Dave that was fun, I did get a bit confused at times but kept up OK. Thanks from Va. U.S.A.
Hi Dave, fantastic :o I'm 53 years old since I was interested in electronics, but I never, really never seen Graetz like this.
Have a nice day wishes ;) Tom
Ahoj Dave, tak od minulého týdne patřím mezi elitu v můstkových usměrňovačích 😁
Koupil jsem 10 SMD můstkových usměrňovačů pro 230V LED pro svůj nový projekt. Osadil jsem desky plošných spojů, vše zkontroloval a uvedl ne zcela zakryté zařízení do zkušebního provozu, po dvou dnech jedna kontrolka zhasla, ovládání jsem vypnul a zapnul na měření - kontrolka svítila, vše jsem zkontroloval a zjistil žádný problém. Po půl hodině světlo zhaslo a na filtračním kondenzátoru bylo místo 1,8V 0,5V, můj nápad - kondenzátor selhal - má vývod (1µ / 63V), zahřál jsem kondenzátor a bingo - tma. Výměna kondenzátoru a tma zase za hodinu, na tvoji záhadu s můstkem jsem už dávno zapomněl, napětí jsem měřil osciloskopem a vše v normě, asi po 5 minutách se na záporné větvi objevil divný ocásek a napětí spadlo na 0,5V - sakra, po výměně OK. Za tři dny další světlo po setmění a úplně stejná řeč, vystřídal jsem je všechny a je klid. Dnes jsem shlédl toto video a vzpomněl jsem si, že jsem ho viděl a dokonce jsem ho i komentoval. Nedalo mi to a musela jsem vám svůj příběh, i když ve velmi jednoduchém spojení, odvyprávět a se stejnou vadou, abyste věděli, že v tom nejste sami 😁
I'm sorry for my English, Google Translate helps me.
I wish you all the best in the new year and many successes in the further creation of your fantastic videos 🙂 Tom from Prague
Thanks Dave, realy love your repair videos, i am realy learning a lot from them, love that you tell us what you are thinking, and the reasoning for the things you do, combined with showing us the schematics.
Greatings from Denmark.
Morten
I own a HP 1740A and i was just looking around in net to see about info... just curious... untill i dropped in your channel... I was letterally captured by your nice explanation on the fault analysis!
It was better than to watch a thriller or spy movie!
To make all more interesting is the video quality, and the very good explanation that pointing on schematic.
I'm not English mother language so it was a little hard somethimes to follow your fast speaking... but fortunately i get it all.
Thank you for your passion, and for sharing your knowledge.
and... "Bingo".... I subscribed in your channel !
Nice! I'd have suspected/looked at the voltage reg first, but it proves even a simple device that should just never go wrong still can :)
Well tracked down Dave! I had a very similar intermittent fault on a Marshall guitar amp here in the UK. It looked as if thermal expansion had caused the bridge rectifier to de-solder its dry as a dead dingo's donger joints. (!) But after re-soldering it transpired that it was the bridge itself. It had failed in almost the same way as yours - so maybe not that unusual.
It's always a treat to restore test equipment!
Really neat to see all this test gear being used in anger. Had never seen stuff like oscilloscopes used for anything non trivial.
These videos are always fun.
Glad to see you cracked and repaired it. Now to get the big screen TV cracked.
Excellent video Dave. One of your best!
Any video featuring the phrase "dryer than a dead dingo's donger" is OK by me. Great fix.
25 years ago, when I worked in electronic service I had a lot of problem with diodes bridges. Of course this were polish bridges that were produced behind the Iron Curtain :)
finally another totaly engrossing repair video. i enjoy the review and teardowns but the repairs are real winners. Lets have more in the future.. Karl
Thanks for another great video. Never heard the phrase "Dead dingos donger", but I love it. Your word choice keeps it interesting. Keep up the great work. Your videos inspire me to keep learning.
Nice epic 90 mins of mystery. I enjoyed that - especially with the schematic shots and 6 DMM array and scope to show the various voltage rails (and the current test). Visually Rich. Fulfilling. Glad you solved it, man. ...Diode bridge? Didn't suspect it (very seriously, confirmed) until you tested the transformer output. Nice job.
always fun to watch! if I'm diagnosing something that is intermittent I won't charge the customer unless I know for sure what the problem was. just like you testing the bridge after I have to know what the problem is.
Well done Dave !!
Superb video Dave. I learn so much from these videos!
Another awesome repair video, especially that the curse has been lifted! Keep doing these repair videos, even when it's not a great repair!
Wire traces and components can be bad in electronics...I knew this from many years in my youth...Great lesson Dave!!!
Good work Dave; I thoroughly enjoyed the video and the detailed troubleshooting you put into the project, all good points made throughout had me thinking all along the process.
Actually those little round bridges are usually very sneaky in the way they fail. My first one had me busier than a one-legged dog in a tug-o-war. Also Molex connectors, especially old ones will fail as the plating erodes where male meets female. Just pull out a bit and watch. A metered variac would have told you straight away during transition to failure if you were dealing with a short or open condition. As for the through holes, the interface between the hole and the pad is very thin. If it's not tinned as is typical when flat bottomed components are mounted in this way the copper will oxidize at that corner first leaving the service trace on the top out of circuit.When we must do like they did we provide a redundant via adjacent to the component and solder pin it. Very nice video.
Fantastic! A successful troubleshoot and repair. And now a brilliant working piece of electrical engineering history the HP1740A 'scope. You should keep that old Fluke you got sent (rather than giving it away) and build up a little mini museum of historic EE pieces, which you can take to events and show.
+Samgab It's more useful to a beginner.
It would be interesting to hook the individual diodes up to an analyzer and plot characteristic curves of each diode in the bridge cold & hot to get an idea of what is going on in the bridge....
GREAT debug video by the way...
(Love all your vids.)
thx Dave
Old Engineers never die, they just have slower rise times....
At 37:00 , according IPC, solder on the pads on the solder target side is not a requirement.
(and i am sure it was too when they did assemble the scope)
Congratulations Dave! In Germany most times we said: Small cause, big effect...;-)
Might be interesting to hook up the diode bridge to a scope (instead of just a DMM) and see if it jumps from "camel" to "dromedary" rectification. I suspect there might be one diode or diode-pair failing, so that it essentially becomes a half rectifier.
+Henner Zeller
Looks to me like some weird zener-effect. The ripple after the bridge dropped nearly to zero. As one way rectifier the ripple would have gone up with half the frequency.
Good point, I didn't got back and watch the ripple frequency on the scope.
+Andreas Dill I kept watching for that, too, as I'd already suspected a bridge, having had one fail in the past. (See my comments on Part 1).
But it does look like it always stayed full wave on the ripple. It went down, probably because the load had dropped, but it sure looked like 100Hz, working or flaky. and, IIRC, the load on the transformer also dropped, which would seem that it was going high resistance. (Tho the other supplies dropping V would also drop I, and that might unload the tranny enuff to swamp what the 5v winding was doing.) Very wierd, those bridges. I see others in the comments have had odd HP problrms in the past. Maybe HP got a bunch of dead dingoes? Sure have never seen fails in other items with the same rectifiers... Can't say this wasn't a good puzzle! Stu
Honestly I had something like that on a old motorcycle that i had, it had pickup coils off the crankshaft for the coils to fire, there was 2 of them but when i rode it for about an hour the bike would just die, but after setting for about a half hour it would fire right up, but once it heated up it shut down, i know it isn't the same but it ended up being the rectifier for the pulse signal coils.... go figure..... nice troubleshooting and solving it, great job Dave :)
Awesome, entertaining video Dave, but the OCD in me really wanted the money shot at the end of the thing sitting on the bench, re-assembled, bit of a wipe over and working :)
Another thing i noticed is when you were looking at the ripple, it seems that the working bridge had a 120Hz ripple as it should, but the failed one had a 60Hz ripple.
I do enjoy your verbal ?? sayings ?? as much as your theory. I spent 20 years between a instrument repair lab and a electronics calibration lab for nuclear subs BUT I still think it was that "dead dingos' doner" caused the trouble. lol Thanks Leo
Oh man Sweet Part 2! Grats on finding it.. I love these vids so much.... someday Ill snag me a scope like that beauty..love the older stuff!
Good show, Dave!
I repair old analog music synthesizers from the same era and had seen quite a few of those cylinder diode rectifiers acting weird. Enough to start replacing them the moment I see them. Investigating what that dodgy diode rectifier is actually doing with IV curve tester may be an interesting video.
+kvitekp Yeah, curve tracer would be nice.
Really enjoyed the diag and fix on this one!!
Good job Dave. Very interesting indeed.
Great video Dave! You doing a great service for hobbyists like me!
You actually managed to fix something! YAY! Celebrations :) Great video.
Thanks Dave.
Awesome repair Dave. Thumbs up