7 ms·

HP/Agilent E3631A Rotary Knob Repair

70 points by parsecs 6y ago

userbinator 5y ago
I'm curious to see what the inside of the rotary encoder looks like; I've revived a few of those by just cleaning and relubricating them, if the contacts haven't completely worn away.
- smiley1437 5y ago
  I've never had much luck permanently fixing either rotary encoders or potentiometers, a cleaning and relube has only ever restored function briefly. When they're worn, they're worn. On the other hand, I can't remember encountering a worn-out optical rotary encoder - can they even wear out?
  - corty 5y ago
    They can get dust or lint in them, making skips (if the dust blocks parts of the rotor) or erratic misbehaviour. But unless you fix that in some destructive way there is no real wear.
- tverbeure 5y ago
  Here are the pictures of the one that was broken... https://twitter.com/tom_verbeure/status/1384010826177122306?s=21 https://twitter.com/tom_verbeure/status/1384010826177122306?...
  - zoomablemind 5y ago
    Does it look worn out or oxidized? Wonder what sort of grease do these usually use?
jonhohle 5y ago
Many "broken" electronics have fixes as simple as this. There are a lot of cheap kits on Ali Express to practice solder if its something you'd find interesting. One of the benefits of YouTube is the depth of videos featuring diagnosis and fixing of obscure issues on rare hardware.
- walrus01 5y ago
  I have seen claims that as many as 80% of "dead" flat screen TVs are just a dead component in the AC-to-DC power supply. Assuming it's a problem where it doesn't power on at all, not some weird visual artifacting or physical damage to the screen. Sometimes as simple as just desoldering and replacing some capacitors... For anyone that's ever repaired a more complex power supply, the AC to DC units in a typical flat screen TV are usually really simple and easy to understand.
  - lmm 5y ago
    An AC power supply is one of the most dangerous places for a beginner to try electronics repair - the capacitors can easily be holding a lethal charge even though the device is unplugged.
    - bartvk 5y ago
      It's good that you mention it, but it shouldn't deter anyone really interested. The power quickly dissipates (over the course of minutes), but you should short it with a resistor before working on it, of course.
      - hyperman1 5y ago
        Don't bet your life on minutes. As a 10 year old kid, I had an old (tube) TV that had been standing on a table for months. I wanted to unsolder some component out of it, and thought it should be safe by now. But as an extra safety measure, I decided to short the big capacitors with my metal screwdriver. Most were as dead as can be. One however, decided to surprise me with a big arc/flash that scared me stiff.
        jmrm 5y ago
        I had the same experience as a child but with an old camera flash. While cutting a big capacitor I accidentally shorted both of the terminals. Since them I have a lot of respect to electricity.
myself248 5y ago
Can confirm, the knobs on those things are turds. Kinda embarrassing for such an otherwise-nice piece of equipment, too. There clearly are better ways to build rotary encoders, and for a unit with a four-figure MSRP, they could've specified a better encoder! Like the ones Rohde & Schwarz use. I think the detents are magnetic or something; they feel magical.
- spoonjim 5y ago
  The butter smooth encoder is the Grayhill 62M.
  - lmilcin 5y ago
    I use exclusively Grayhill encoders and pots on my projects. Which is to say I don't mind paying extra for a knob that I will be regularly using but probably would be revisiting the choice if I had to make 100 thousand of these.
    - spoonjim 5y ago
      Yeah, a 62M will cost you ~100 dollars in single unit quantities.
      - lmilcin 5y ago
        I sometimes wonder who buys that kind of parts. I mean I know why I buy them. Because I just like the feel of it and am not restricted by cost. My time is more valuable than dealing with cheap stuff. Military? Aerospace?
        spoonjim 5y ago
        I think the dominant market is industrial controls. The cost to have a line down or a technician sent out dwarfs the component cost.
        5y ago
tn1 5y ago
I love these power supplies! An awesome feature is the GPIB port on the back (it's basically a parallel port with a specific command set). In college I bought a USB to GPIB adapter on ebay for like $100 and a few cables (you can daisy chain them together) and wrote some VBA macros to automatically sweep the voltage output over a range, and also connected to a frequency generator & oscilloscope to capture the data. My EE labs were done in a fraction of the time compared to my classmates!
- the_only_law 5y ago
  I have a ton of old HP/Agilent equipment for my current project and most of it has GPIB connectivity. It seems like a neat protocol and I also finally got an HP-85 with the serial/GPIB modules which have been on my wishlist for a while. Might try to turn it into a controller for some of the equipment.
  - bartvk 5y ago
    The protocol isn't too bad but that humongous connector... hoo boy. I think everyone nowadays just hooks it up with those USB-to-GPIB connectors, but the drivers under Linux are often iffy: if you get the wrong one, you need to supply a blob to it, in order to fully boot.
    - the_only_law 5y ago
      I have so many V.35 cables laying around the GPIB feels small.
- tverbeure 5y ago
  Yeah, one of the reasons to buy this PSU was the GPIB interface. I already had the expensive ($100+) USB to GPIB interface anyway. Earlier, I wrote a blog post about controlling my TDS 420 oscilloscope through GPIB: https://tomverbeure.github.io/2020/06/27/Tektronix-TDS420A-Remote-Control-over-GPIB.html https://tomverbeure.github.io/2020/06/27/Tektronix-TDS420A-R....
- Mauricebranagh 5y ago
GuB-42 5y ago
I had an old home cinema amp with a finicky encoder. The only thing I did was to remove the knob, douse the encoder in contact cleaner and put the knob back. I didn't even open the case. It took a few times to get it back to fully working but in the end, it worked surprisingly well, and it seems to last. Replacing the part is obviously better, but contact cleaner can do wonders if you want to try a cheap and dirty solution. Note: I used the 3-in-1 (WD-40) brand because it is what they have in my local hardware store. I suppose that DeOxit and other brands work just as well if not better.
greatartiste 5y ago
Sadly not all Agilent/HP equipment uses rotary encoders like this. One of their function generators was brought to me with a clear rotary encoder fault. I opened it up expecting to find a rotary encoder like this. But instead found they had implemented it using circular tracks on the PCB and the knob turned a metal wiper which shorted out the tracks as it turned. After a couple of years of use the tracks start to develop grooves and wear out. There isn't much you can do without replacing the entire front panel which wasn't economic to do. I think within 5 years we binned 15+ of those units. Old HP/Agilent equipment was beautifully made but in the few years before the sale to Keysight quality took a real dive.
- NovemberWhiskey 5y ago
  >Old HP/Agilent equipment was beautifully made but in the few years before the sale to Keysight quality took a real dive. Keysight was actually formed by spinning-off Agilent's electronics test-and-measurement businesses (leaving behind really I think just the life-sciences stuff?) so there was no sale per se.
  - simlan 5y ago
    Correct! But the "just" life science business is actually bigger than the electronics equipment part.
PostThisTooFast 5y ago
"If your PSU is still under warranty, expect it to be void after doing stuff like this!" Ugh, I wish people would stop believing and propagating this falsehood (at least in the U.S.). Your right to warranty service is protected by federal law even if you modify a device, by the Magnuson-Moss Warranty Act.
mkesper 5y ago
Not directly this machine but you can do fantastic things with old test equipment: https://www.youtube.com/watch?v=hdQnpg7b3Vw https://www.youtube.com/watch?v=hdQnpg7b3Vw https://www.youtube.com/watch?v=MfH53a9xAjo https://www.youtube.com/watch?v=MfH53a9xAjo
unixhero 5y ago
This is kind of like an Arcade game repair mission.
puzzlingcaptcha 5y ago
For anyone interested in repair of vintage HP instrumentation (among other things) I recommend CuriousMarc on youtube (a good place to start e.g. https://www.youtube.com/watch?v=CeXYZKg5jdo&list=PL-_93BVApb5_e9h-vqKn1FPUg9WnzFL20 https://www.youtube.com/watch?v=CeXYZKg5jdo&list=PL-_93BVApb... )
hellbannedguy 5y ago
If you tinker with electronics, buy a dc power supply. I've been meaning to buy one for years, and only bought one recently at an estate sale for 30 buck. It's just so convienant having the right voltage for testing, and repair.
- sokoloff 5y ago
  Not only the right voltage, but a bench supply will have current limiting as well. (It will be constant voltage up to a settable current limit and then will let the voltage drop off to maintain that max current set. You can short the output together and set the max current.)
  - lmilcin 5y ago
    > You can short the output together and set the max current. Please, read user manual first. Not all bench supplies are safe to be shorted. Also there might be a small current peak that might be damaging your device over time without you even noticing it. For example, my PSU has a special button to press and you dial in current limit while the button is pressed. You can do it without interrupting supply to the load but more importantly it does not stress components.
- mindcrime 5y ago
  Another really useful thing to have is a programmable load[1]. It's sort of the inverse of a power supply... it's a power sink that you can control. It's really handy to dial up a constant current setting and plug in a power supply that is under test, and observe how it behaves. They're good for testing batteries, solar panels, and most power supply related things. One example that I'm familiar with (it's what I use on my bench at home) is the Rigol DL3021A[2]. There are a lot of choices out there though, spanning a wide range of price / capability / power handling points. [1]: https://en.wikipedia.org/wiki/Programmable_load https://en.wikipedia.org/wiki/Programmable_load [2]: https://www.rigolna.com/products/dc-power-loads/dl3000/ https://www.rigolna.com/products/dc-power-loads/dl3000/

70 points by parsecs 6y ago

I'm curious to see what the inside of the rotary encoder looks like; I've revived a few of those by just cleaning and relubricating them, if the contacts haven't completely worn away.

smiley1437 5y ago
I've never had much luck permanently fixing either rotary encoders or potentiometers, a cleaning and relube has only ever restored function briefly. When they're worn, they're worn. On the other hand, I can't remember encountering a worn-out optical rotary encoder - can they even wear out?
- corty 5y ago
  They can get dust or lint in them, making skips (if the dust blocks parts of the rotor) or erratic misbehaviour. But unless you fix that in some destructive way there is no real wear.
tverbeure 5y ago
Here are the pictures of the one that was broken... https://twitter.com/tom_verbeure/status/1384010826177122306?s=21 https://twitter.com/tom_verbeure/status/1384010826177122306?...
- zoomablemind 5y ago
  Does it look worn out or oxidized? Wonder what sort of grease do these usually use?

jonhohle 5y ago

Many "broken" electronics have fixes as simple as this. There are a lot of cheap kits on Ali Express to practice solder if its something you'd find interesting. One of the benefits of YouTube is the depth of videos featuring diagnosis and fixing of obscure issues on rare hardware.

walrus01 5y ago
I have seen claims that as many as 80% of "dead" flat screen TVs are just a dead component in the AC-to-DC power supply. Assuming it's a problem where it doesn't power on at all, not some weird visual artifacting or physical damage to the screen. Sometimes as simple as just desoldering and replacing some capacitors... For anyone that's ever repaired a more complex power supply, the AC to DC units in a typical flat screen TV are usually really simple and easy to understand.
- lmm 5y ago
  An AC power supply is one of the most dangerous places for a beginner to try electronics repair - the capacitors can easily be holding a lethal charge even though the device is unplugged.
  - bartvk 5y ago
    It's good that you mention it, but it shouldn't deter anyone really interested. The power quickly dissipates (over the course of minutes), but you should short it with a resistor before working on it, of course.
    - hyperman1 5y ago
      Don't bet your life on minutes. As a 10 year old kid, I had an old (tube) TV that had been standing on a table for months. I wanted to unsolder some component out of it, and thought it should be safe by now. But as an extra safety measure, I decided to short the big capacitors with my metal screwdriver. Most were as dead as can be. One however, decided to surprise me with a big arc/flash that scared me stiff.
      - jmrm 5y ago
        I had the same experience as a child but with an old camera flash. While cutting a big capacitor I accidentally shorted both of the terminals. Since them I have a lot of respect to electricity.

myself248 5y ago

Can confirm, the knobs on those things are turds. Kinda embarrassing for such an otherwise-nice piece of equipment, too. There clearly are better ways to build rotary encoders, and for a unit with a four-figure MSRP, they could've specified a better encoder! Like the ones Rohde & Schwarz use. I think the detents are magnetic or something; they feel magical.

spoonjim 5y ago
The butter smooth encoder is the Grayhill 62M.
- lmilcin 5y ago
  I use exclusively Grayhill encoders and pots on my projects. Which is to say I don't mind paying extra for a knob that I will be regularly using but probably would be revisiting the choice if I had to make 100 thousand of these.
  - spoonjim 5y ago
    Yeah, a 62M will cost you ~100 dollars in single unit quantities.
    - lmilcin 5y ago
      I sometimes wonder who buys that kind of parts. I mean I know why I buy them. Because I just like the feel of it and am not restricted by cost. My time is more valuable than dealing with cheap stuff. Military? Aerospace?
      - spoonjim 5y ago
        I think the dominant market is industrial controls. The cost to have a line down or a technician sent out dwarfs the component cost.
        5y ago

tn1 5y ago

I love these power supplies! An awesome feature is the GPIB port on the back (it's basically a parallel port with a specific command set). In college I bought a USB to GPIB adapter on ebay for like $100 and a few cables (you can daisy chain them together) and wrote some VBA macros to automatically sweep the voltage output over a range, and also connected to a frequency generator & oscilloscope to capture the data. My EE labs were done in a fraction of the time compared to my classmates!

the_only_law 5y ago
I have a ton of old HP/Agilent equipment for my current project and most of it has GPIB connectivity. It seems like a neat protocol and I also finally got an HP-85 with the serial/GPIB modules which have been on my wishlist for a while. Might try to turn it into a controller for some of the equipment.
- bartvk 5y ago
  The protocol isn't too bad but that humongous connector... hoo boy. I think everyone nowadays just hooks it up with those USB-to-GPIB connectors, but the drivers under Linux are often iffy: if you get the wrong one, you need to supply a blob to it, in order to fully boot.
  - the_only_law 5y ago
    I have so many V.35 cables laying around the GPIB feels small.
tverbeure 5y ago
Yeah, one of the reasons to buy this PSU was the GPIB interface. I already had the expensive ($100+) USB to GPIB interface anyway. Earlier, I wrote a blog post about controlling my TDS 420 oscilloscope through GPIB: https://tomverbeure.github.io/2020/06/27/Tektronix-TDS420A-Remote-Control-over-GPIB.html https://tomverbeure.github.io/2020/06/27/Tektronix-TDS420A-R....
Mauricebranagh 5y ago

GuB-42 5y ago

I had an old home cinema amp with a finicky encoder. The only thing I did was to remove the knob, douse the encoder in contact cleaner and put the knob back. I didn't even open the case. It took a few times to get it back to fully working but in the end, it worked surprisingly well, and it seems to last. Replacing the part is obviously better, but contact cleaner can do wonders if you want to try a cheap and dirty solution. Note: I used the 3-in-1 (WD-40) brand because it is what they have in my local hardware store. I suppose that DeOxit and other brands work just as well if not better.

greatartiste 5y ago

Sadly not all Agilent/HP equipment uses rotary encoders like this. One of their function generators was brought to me with a clear rotary encoder fault. I opened it up expecting to find a rotary encoder like this. But instead found they had implemented it using circular tracks on the PCB and the knob turned a metal wiper which shorted out the tracks as it turned. After a couple of years of use the tracks start to develop grooves and wear out. There isn't much you can do without replacing the entire front panel which wasn't economic to do. I think within 5 years we binned 15+ of those units. Old HP/Agilent equipment was beautifully made but in the few years before the sale to Keysight quality took a real dive.

NovemberWhiskey 5y ago
>Old HP/Agilent equipment was beautifully made but in the few years before the sale to Keysight quality took a real dive. Keysight was actually formed by spinning-off Agilent's electronics test-and-measurement businesses (leaving behind really I think just the life-sciences stuff?) so there was no sale per se.
- simlan 5y ago
  Correct! But the "just" life science business is actually bigger than the electronics equipment part.

PostThisTooFast 5y ago

"If your PSU is still under warranty, expect it to be void after doing stuff like this!" Ugh, I wish people would stop believing and propagating this falsehood (at least in the U.S.). Your right to warranty service is protected by federal law even if you modify a device, by the Magnuson-Moss Warranty Act.

mkesper 5y ago

Not directly this machine but you can do fantastic things with old test equipment: https://www.youtube.com/watch?v=hdQnpg7b3Vw https://www.youtube.com/watch?v=hdQnpg7b3Vw https://www.youtube.com/watch?v=MfH53a9xAjo https://www.youtube.com/watch?v=MfH53a9xAjo

unixhero 5y ago

This is kind of like an Arcade game repair mission.

puzzlingcaptcha 5y ago

For anyone interested in repair of vintage HP instrumentation (among other things) I recommend CuriousMarc on youtube (a good place to start e.g. https://www.youtube.com/watch?v=CeXYZKg5jdo&list=PL-_93BVApb5_e9h-vqKn1FPUg9WnzFL20 https://www.youtube.com/watch?v=CeXYZKg5jdo&list=PL-_93BVApb... )

hellbannedguy 5y ago

If you tinker with electronics, buy a dc power supply. I've been meaning to buy one for years, and only bought one recently at an estate sale for 30 buck. It's just so convienant having the right voltage for testing, and repair.

sokoloff 5y ago
Not only the right voltage, but a bench supply will have current limiting as well. (It will be constant voltage up to a settable current limit and then will let the voltage drop off to maintain that max current set. You can short the output together and set the max current.)
- lmilcin 5y ago
  > You can short the output together and set the max current. Please, read user manual first. Not all bench supplies are safe to be shorted. Also there might be a small current peak that might be damaging your device over time without you even noticing it. For example, my PSU has a special button to press and you dial in current limit while the button is pressed. You can do it without interrupting supply to the load but more importantly it does not stress components.
mindcrime 5y ago
Another really useful thing to have is a programmable load[1]. It's sort of the inverse of a power supply... it's a power sink that you can control. It's really handy to dial up a constant current setting and plug in a power supply that is under test, and observe how it behaves. They're good for testing batteries, solar panels, and most power supply related things. One example that I'm familiar with (it's what I use on my bench at home) is the Rigol DL3021A[2]. There are a lot of choices out there though, spanning a wide range of price / capability / power handling points. [1]: https://en.wikipedia.org/wiki/Programmable_load https://en.wikipedia.org/wiki/Programmable_load [2]: https://www.rigolna.com/products/dc-power-loads/dl3000/ https://www.rigolna.com/products/dc-power-loads/dl3000/