EEVblog #804 - HP1740A Oscilloscope Repair - Part 2

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?
Original HP Journal article on the HP1740A:
How not to blow up your oscilloscope:

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[maccartier]

"It's permanently failed! Excellent!" Only Dave could say something so intuitively wrong, but practically right

[dorfschmidt]

Nothing more satifying than a successful repair.

[lentosy]

These kind of debugging videos are the very best. great work Dave.

[worroSfOretsevraH]

Everyone's favorite segment: Repair Videos!

[cyrex]

So happy to finally see a repair video that worked out.

[jonahansen]

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...

[jeromekerngarcia]

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!

[SatyajitRoy]

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.

[movaxh]

Finally. 800 videos, and finally we got a proper repairable repair. Very nice video.

[JoseHernandez-mdtv]

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!

[ixamraxi]

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.

[nplanel]

The first successful repair of the channel, congrats

[queuerious]

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!

[Tedybear]

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!

[therealjammit]

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.

[ChipGuy]

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 ;)

[turboslag]

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!

[dalebrooks]

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.

[DJX]

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!

[dave-d]

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!