Restoring an HP 150A Oscilloscope (Part 4) – Victory!

It was a brutally long repair, but we got there! I won’t spoil too much, but in our diagnosing process we traveled all over the scope, replacing a litany of parts, but in this episode, we finally crack the code and emerge victorious. It’s a good day indeed!

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Music:
Artist: Gux
Title: Secret of Mana "Smooth Mana"

Intro Music adapted from:
Artist: The Runaway Five
Title: The Shinra Shuffle

Thanks for watching!

Chapters
0:00 Intro
1:48 The Game Plan
4:18 Recapping
5:16 Testing
7:41 Intensity Issues
11:46 HV Section Rework
13:18 Testing Again
14:12 Oopsie
15:23 HV Section Rework… Again
16:17 Even More Testing
18:21 Vertical Tuning
19:37 Horizontal Tuning
21:26 Victory
24:08 Bunny!

[RWBHere]

Who else was shouting at the screen, 'Turn the brightness down! You're burning the phosphor on an expensive and hard to replace tube.' The brightness should be no higher than the display on your modern 'scope. Any brighter and it begins to defocus as the trace spreads across the phosphor. That threshold should be your guide. That said, it's great that you managed to fix the Old Lady. 🙂👍

[mauriciosinigaglia]

Good job. It is very gratifying to see such a quality equipment back in action. Nowadays, you can buy a good oscilloscope for a few hundred dollars. But 60 years ago, few people or institutions had the capital to pay for such equipment. They were works of art that brought together the cutting edge technology of their time.

[pragmatologist]

I enjoyed this series, having enjoyed working with HP stuff of this vintage years ago as a service tech. What surprised me is your reticence to 'shotgun' replace all of the paper caps at once. As my hobby these days is restoring old amateur and test gear--those caps have either failed, changed, or are not far from it. My first order of business is to first make a parts list of the caps and then check any high-ohm resistors for tolerance. Then add the inevatible ones to the list. Follow up with a thorough internal cleaning of control contacts and potentiometers--followed by tube testing. Although such does not create as many "interesting" adventures in troubleshooting--that way of doing things saves a lot of time and smoke--and usually leads directly to the alignment. Anyway, keep on enjoying these beasts!

[CuriousMarc]

Nice! The rabbit works again at the end, I see.

[brianclimbs]

You inspired me to have another look at why my Tektronix 561A wasn't working, and I figured out the "on" switch just needed some contact cleaner!

[tomohlsson]

I'm so glad you never gave up! I just grinned along with you there at the end. Wow, well done, well done indeed!

[lovatomi]

Honestly the most emotionally resonant oscilloscope repair mini-series I could possibly imagine. This is prime-time stuff. Nicely done!

[akkudakkupl]

Selenium rectifier (gray plates stack close to power supply), lets pray it doesn't overheat, otherwise you will have to live with a terrible rotten smell for some time until it goes away. Big Clive did a video on them some time ago.

[stanbrow]

Lots more interactions than I would of thought. Really appreciate your patience. And hard work.

[akkudakkupl]

Flux your desoldering braid and it will suck up solder like crazy. I usually heat up some flux with my soldering iron (rosin flux) and dip a few centimeters of braid as needed. The difference is colossal.

[Pulverrostmannen]

yep and the golden rule about all vintage gear such as this here, never trust the capacitors because they will have excessive leakage which will fry resistors and other stuff on the way. the bumblebee or black beauty as you call them and wax caps allways need replacing but also electrolytic etc tend to be gone too. you can normally trust most Mica style which is the square ones you can see in the device and or mustard caps and film caps generally don´t fail as often as the other ones, except Rifas, oooo the shivers I get from these Rifa ones, destroyer of equipment and ruins of life. they must be replaced on sight! but I did not see any here because your device is a bit older than these caps anyway. good job restoring it in the end!

[paulawillaminachandler-ren]

April 1956 not 70 year old yet. This was a very enjoyable series. Well done!

[stanbrow]

I am impressed by your collection of replaced/bad parts.

[iygor]

Well done. . . Well done sir. Never doubted you would find the issues with this esoteric piece of hardware. Again Well done.

[frankowalker]

Brilliant. What an EPIC success. Realy well done on bringing this beautiful HP scope back to life.

[vicmiller]

You could enjoy a conversation with the YouTuber Mr Carlson lab. This guy is a genius when it comes to tubes for all kinds of stuff. And he has one of largest TEK scope collection i have ever seen . And if they work and most if not all do work he has done his magic to restore them and make then as if they just came off the factory floor... nice video and thanks for sharing... Vic

[docfoot]

I can see the light, well done and you stuck with it .

[acoustic]

Your videos are amazing! You're sharp and very resourceful. I once worked an engineer who was like you and really learned a lot from him. I miss those days.

[justovision]

That scope is a beast! Congrats on taming it!

[ckie]

Brilliant! Thanks for bringing us along on your rollercoaster journey. Great to see it so rock solid stable at the end. Well done!