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#1
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
We have about 10 Agilent 33120A frequency-generator / synthesizers
in our lab, and a few other similar synthesizers. They feature a convenient digital frequency and amplitude programming knob that's based on optical encoders. A pair of left-right pushbuttons sets which decade you're adjusting with the knob, and over or underflows operate on the next higher decade. There's a little indent near the edge of the knob so you can spin it with your fingertip. You can also use up-down pushbuttons or directly punch in numbers, but the spinning knob is very convenient. Typically such encoders have 16 or 32 ticks per revolution. A very nice design feature. The optical shaft encoders were originally made by HP, but now of course they're made by Avago. Sometimes they call these a digital potentiometer or a "Panel Mount Optical Rotary Encoder". For example, the HRPG-AD16 product line, about $34 each at Mouser. http://www.mouser.com/Search/Refine....word=HRPG-AD16 http://www.avagotech.com/pages/en/mo.../hrpg-ad1616c/ Since they use an optical 2-bit quadrature grey-code (as opposed to using a pair of switch contacts), they're supposed to be extremely reliable. But recently I've encountered two instruments with identical tuning-knob failures, one in an elegant 33250A 80MHz model that's on my bench, and the other in one of our standard 33120A 15MHz instruments. In both cases the knob seems 'stuck" and not to work as you turn it, except every now and then you'll get one or two increments or decrements. Totally useless. I'm wondering if anyone else has encountered this failure? -- Thanks, - Win |
#2
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
Winfield Hill wrote in message
... We have about 10 Agilent 33120A frequency-generator / synthesizers in our lab, and a few other similar synthesizers. They feature a convenient digital frequency and amplitude programming knob that's based on optical encoders. A pair of left-right pushbuttons sets which decade you're adjusting with the knob, and over or underflows operate on the next higher decade. There's a little indent near the edge of the knob so you can spin it with your fingertip. You can also use up-down pushbuttons or directly punch in numbers, but the spinning knob is very convenient. Typically such encoders have 16 or 32 ticks per revolution. A very nice design feature. The optical shaft encoders were originally made by HP, but now of course they're made by Avago. Sometimes they call these a digital potentiometer or a "Panel Mount Optical Rotary Encoder". For example, the HRPG-AD16 product line, about $34 each at Mouser. http://www.mouser.com/Search/Refine....word=HRPG-AD16 http://www.avagotech.com/pages/en/mo...cts/rotary_swi tches/hrpg-ad1616c/ Since they use an optical 2-bit quadrature grey-code (as opposed to using a pair of switch contacts), they're supposed to be extremely reliable. But recently I've encountered two instruments with identical tuning-knob failures, one in an elegant 33250A 80MHz model that's on my bench, and the other in one of our standard 33120A 15MHz instruments. In both cases the knob seems 'stuck" and not to work as you turn it, except every now and then you'll get one or two increments or decrements. Totally useless. I'm wondering if anyone else has encountered this failure? -- Thanks, - Win Its probably patentable so is there a patent outline for them somewhere, to show what the innards are? |
#3
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
On 8 Aug 2011 00:12:54 -0700 Winfield Hill
wrote in Message id: : We have about 10 Agilent 33120A frequency-generator / synthesizers in our lab, and a few other similar synthesizers. They feature a convenient digital frequency and amplitude programming knob that's based on optical encoders. A pair of left-right pushbuttons sets which decade you're adjusting with the knob, and over or underflows operate on the next higher decade. There's a little indent near the edge of the knob so you can spin it with your fingertip. You can also use up-down pushbuttons or directly punch in numbers, but the spinning knob is very convenient. Typically such encoders have 16 or 32 ticks per revolution. A very nice design feature. The optical shaft encoders were originally made by HP, but now of course they're made by Avago. Sometimes they call these a digital potentiometer or a "Panel Mount Optical Rotary Encoder". For example, the HRPG-AD16 product line, about $34 each at Mouser. http://www.mouser.com/Search/Refine....word=HRPG-AD16 http://www.avagotech.com/pages/en/mo.../hrpg-ad1616c/ Since they use an optical 2-bit quadrature grey-code (as opposed to using a pair of switch contacts), they're supposed to be extremely reliable. But recently I've encountered two instruments with idenical tuning-knob failures, one in an elegant 33250A 80MHz model that's on my bench, and the other in one of our standard 33120A 15MHz instruments. In both cases the knob seems 'stuck" and not to work as you turn it, except every now and then you'll get one or two increments or decrements. Totally useless. I'm wondering if anyone else has encountered this failure? I have not seen a failure on the 33XXX series of generators, but the part # is 0960-0892. Looking at the picture on the find-a-part website shows it as a mechanical encoder. http://www.home.agilent.com/myagilen...te=u4p3ex5iq_4 Which is obsolete and replaced by 0960-2545, also a mechanical one. It looks like its the same as used on the 65XX and 66XX power supplies. I do know that the older 65XX and 66XX do use the (obsolete) optical ones. It is possible to use the mechanical ones to fix the obsolete optical ones with a bit of hacking, but the mechanical ones need more turns to change the output of the supplies for a given amount. Are you sure it's an optical encoder you're looking for? |
#4
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
JW wrote...
Winfield Hill wrote, The optical shaft encoders were originally made by HP, but now of course they're made by Avago. Sometimes they call these a digital potentiometer or a "Panel Mount Optical Rotary Encoder". For example, the HRPG-AD16 product line, about $34 each at Mouser. http://www.mouser.com/Search/Refine....word=HRPG-AD16 http://www.avagotech.com/pages/en/mo.../hrpg-ad1616c/ Since they use an optical 2-bit quadrature grey-code (as opposed to using a pair of switch contacts), they're supposed to be extremely reliable. But recently I've encountered two instruments with identical tuning-knob failures, one in an elegant 33250A 80MHz model that's on my bench, and the other in one of our standard 33120A 15MHz instruments. In both cases the knob seems 'stuck" and not to work as you turn it, except every now and then you'll get one or two increments or decrements. Totally useless. I'm wondering if anyone else has encountered this failure? I have not seen a failure on the 33XXX series of generators, but the part # is 0960-0892. Looking at the picture on the find-a-part website shows it as a mechanical encoder. http://www.home.agilent.com/myagilen...te=u4p3ex5iq_4 Indeed. Which is obsolete and replaced by 0960-2545, also a mechanical one. It looks like its the same as used on the 65XX and 66XX power supplies. I do know that the older 65XX and 66XX do use the (obsolete) optical ones. It is possible to use the mechanical ones to fix the obsolete optical ones with a bit of hacking, but the mechanical ones need more turns to change the output of the supplies for a given amount. Thanks, great info! Are you sure it's an optical encoder you're looking for? No, and as you say, the service manual identifies the mechanical one as the part, now that I bothered to look. Given the failures, perhaps being mechanical makes sense. I had just assumed that because HP long-ago developed and manufactured a fine optical part, they'd use it in their expensive premium instruments. Heck, I've long used their expensive optical encoder in my own designs! The mechanical part looks much smaller than the optical one, which might not fit as an upgrade replacement. Hmm, their mechanical part looks a lot like the ones Spehro was selling as excess inventory. BTW, as you can see at my Mouser link, the HRPG optical encoder is not obsolete (yet). Hah, it costs $34 instead of $4.23. Do we get what we pay for? http://www.home.agilent.com/myagilen...mber=0960-2545 -- Thanks, - Win |
#5
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knobfailure
Winfield Hill wrote: JW wrote... Winfield Hill wrote, The optical shaft encoders were originally made by HP, but now of course they're made by Avago. Sometimes they call these a digital potentiometer or a "Panel Mount Optical Rotary Encoder". For example, the HRPG-AD16 product line, about $34 each at Mouser. http://www.mouser.com/Search/Refine....word=HRPG-AD16 http://www.avagotech.com/pages/en/mo.../hrpg-ad1616c/ Since they use an optical 2-bit quadrature grey-code (as opposed to using a pair of switch contacts), they're supposed to be extremely reliable. But recently I've encountered two instruments with identical tuning-knob failures, one in an elegant 33250A 80MHz model that's on my bench, and the other in one of our standard 33120A 15MHz instruments. In both cases the knob seems 'stuck" and not to work as you turn it, except every now and then you'll get one or two increments or decrements. Totally useless. I'm wondering if anyone else has encountered this failure? I have not seen a failure on the 33XXX series of generators, but the part # is 0960-0892. Looking at the picture on the find-a-part website shows it as a mechanical encoder. http://www.home.agilent.com/myagilen...te=u4p3ex5iq_4 Indeed. Which is obsolete and replaced by 0960-2545, also a mechanical one. It looks like its the same as used on the 65XX and 66XX power supplies. I do know that the older 65XX and 66XX do use the (obsolete) optical ones. It is possible to use the mechanical ones to fix the obsolete optical ones with a bit of hacking, but the mechanical ones need more turns to change the output of the supplies for a given amount. Thanks, great info! Are you sure it's an optical encoder you're looking for? No, and as you say, the service manual identifies the mechanical one as the part, now that I bothered to look. Given the failures, perhaps being mechanical makes sense. I had just assumed that because HP long-ago developed and manufactured a fine optical part, they'd use it in their expensive premium instruments. Heck, I've long used their expensive optical encoder in my own designs! The mechanical part looks much smaller than the optical one, which might not fit as an upgrade replacement. Hmm, their mechanical part looks a lot like the ones Spehro was selling as excess inventory. BTW, as you can see at my Mouser link, the HRPG optical encoder is not obsolete (yet). Hah, it costs $34 instead of $4.23. Do we get what we pay for? http://www.home.agilent.com/myagilen...mber=0960-2545 Hello, Win. I haven't seen you around for quite a while. The only failed optical encoders I've seen either had a failed incandescent lamp (Very early type of encoder). The other was when they were dropped on the shaft, which shatters the code wheel. These use a thin glass disk that rotated through a pair of photo interrupters. The shock of impact hit the disks at both photo interrupters, making it unrepairable. A failed photo interrupter can be replaced in some units, but it takes more time than it's usually worth. The mechanical encoders are a lot smaller than the optical, so some designs use them just to save space. I prefer optical encoders with a fairly heavy knob so you can give it a spin, and stop it with your finger when it gets close. If you can get that part from Agilent for $4.23 I would get at least half a dozen while they re availible. -- It's easy to think outside the box, when you have a cutting torch. |
#6
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
Winfield Hill wrote:
I'm wondering if anyone else has encountered this failure? I bought a power supply E3647A and the encoder feels like very bad quality. My boss bought the same power supply six month ago and the encoder feels much better. So I thought the quality of HP goes south and I bought the freq generator from Rigol. When HP is selling the quality of Rigol now, I dont like to pay the price for HP anymore! Olaf |
#7
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
On 8 Aug 2011 05:47:44 -0700, Winfield Hill
wrote: http://www.home.agilent.com/myagilen...mber=0960-2545 That part looks very familiar. I'll guess that it's a mechanical encoder made by CUI. http://onlinecatalog.digikey.com/WebProject.asp?CodeId=7.4.4.28&pagelabel=2365# I don't know the coding or counts per turn, so I can't find an exact substitute. However, at $3.60 ea, you could probably buy an assortment. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#8
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
On Mon, 08 Aug 2011 08:51:31 -0700, Jeff Liebermann
wrote: On 8 Aug 2011 05:47:44 -0700, Winfield Hill wrote: http://www.home.agilent.com/myagilen...mber=0960-2545 That part looks very familiar. I'll guess that it's a mechanical encoder made by CUI. http://onlinecatalog.digikey.com/WebProject.asp?CodeId=7.4.4.28&pagelabel=2365# I don't know the coding or counts per turn, so I can't find an exact substitute. However, at $3.60 ea, you could probably buy an assortment. CUI AZ16 data sheet: http://products.cui.com/getpdf.aspx?fileID=6206 Catalog page: http://products.cui.com/adtemplate.asp?invky=103924&brand=motion-control&catky=112362&subcatky1=994182&subcatky2=99 7832&subcatky3=953473 -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#9
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
On 8 Aug 2011 05:47:44 -0700 Winfield Hill
wrote in Message id: : JW wrote... Winfield Hill wrote, The optical shaft encoders were originally made by HP, but now of course they're made by Avago. Sometimes they call these a digital potentiometer or a "Panel Mount Optical Rotary Encoder". For example, the HRPG-AD16 product line, about $34 each at Mouser. http://www.mouser.com/Search/Refine....word=HRPG-AD16 http://www.avagotech.com/pages/en/mo.../hrpg-ad1616c/ Since they use an optical 2-bit quadrature grey-code (as opposed to using a pair of switch contacts), they're supposed to be extremely reliable. But recently I've encountered two instruments with identical tuning-knob failures, one in an elegant 33250A 80MHz model that's on my bench, and the other in one of our standard 33120A 15MHz instruments. In both cases the knob seems 'stuck" and not to work as you turn it, except every now and then you'll get one or two increments or decrements. Totally useless. I'm wondering if anyone else has encountered this failure? I have not seen a failure on the 33XXX series of generators, but the part # is 0960-0892. Looking at the picture on the find-a-part website shows it as a mechanical encoder. http://www.home.agilent.com/myagilen...te=u4p3ex5iq_4 Indeed. Which is obsolete and replaced by 0960-2545, also a mechanical one. It looks like its the same as used on the 65XX and 66XX power supplies. I do know that the older 65XX and 66XX do use the (obsolete) optical ones. It is possible to use the mechanical ones to fix the obsolete optical ones with a bit of hacking, but the mechanical ones need more turns to change the output of the supplies for a given amount. Thanks, great info! You're welcome. Are you sure it's an optical encoder you're looking for? No, and as you say, the service manual identifies the mechanical one as the part, now that I bothered to look. Given the failures, perhaps being mechanical makes sense. Could be, but I've yet to see a mechanical one go south unless there was some abuse. Even then they are sometimes repairable. The bend over tabs that hold the encoder together come apart a bit when the shaft is hit at a right angle, which seems to happen all the time on the power supplies I mentioned. I've lost count on the number of times I've repaired them. After repair I solder two 24ga pieces of bus wire across the top from tab to tab which helps sturdy them up a bit. I had just assumed that because HP long-ago developed and manufactured a fine optical part, they'd use it in their expensive premium instruments. Heck, I've long used their expensive optical encoder in my own designs! The mechanical part looks much smaller than the optical one, which might not fit as an upgrade replacement. If you *do* have an optical one, it may depend on whether it solders directly to a PCB, or is panel mounted. If the latter, it probably has a cable which attaches to a PCB, and you should be able to adapt the mechanical one. If you go that route, I've found that it is important to ground the case of the encoder. You'll probably have to fiddle around with the wires to get the order right. Trial and error... |
#10
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
On Mon, 08 Aug 2011 09:39:32 -0400 "Michael A. Terrell"
wrote in Message id: : The only failed optical encoders I've seen either had a failed incandescent lamp (Very early type of encoder). And what a pain in the butt to get to on a 6034A! I wish I could find a "side firing" LED that would not only fit in that little slot, but also be the right wavelength for it to work correctly. I've experimented a bit with this, but never been successful. |
#11
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
"JW" wrote in message
... On 8 Aug 2011 05:47:44 -0700 Winfield Hill wrote in Message id: : JW wrote... Winfield Hill wrote, The optical shaft encoders were originally made by HP, but now of course they're made by Avago. Sometimes they call these a digital potentiometer or a "Panel Mount Optical Rotary Encoder". For example, the HRPG-AD16 product line, about $34 each at Mouser. http://www.mouser.com/Search/Refine....word=HRPG-AD16 http://www.avagotech.com/pages/en/mo.../hrpg-ad1616c/ Since they use an optical 2-bit quadrature grey-code (as opposed to using a pair of switch contacts), they're supposed to be extremely reliable. But recently I've encountered two instruments with identical tuning-knob failures, one in an elegant 33250A 80MHz model that's on my bench, and the other in one of our standard 33120A 15MHz instruments. In both cases the knob seems 'stuck" and not to work as you turn it, except every now and then you'll get one or two increments or decrements. Totally useless. I'm wondering if anyone else has encountered this failure? I have not seen a failure on the 33XXX series of generators, but the part # is 0960-0892. Looking at the picture on the find-a-part website shows it as a mechanical encoder. http://www.home.agilent.com/myagilen...te=u4p3ex5iq_4 Indeed. Which is obsolete and replaced by 0960-2545, also a mechanical one. It looks like its the same as used on the 65XX and 66XX power supplies. I do know that the older 65XX and 66XX do use the (obsolete) optical ones. It is possible to use the mechanical ones to fix the obsolete optical ones with a bit of hacking, but the mechanical ones need more turns to change the output of the supplies for a given amount. Thanks, great info! You're welcome. Are you sure it's an optical encoder you're looking for? No, and as you say, the service manual identifies the mechanical one as the part, now that I bothered to look. Given the failures, perhaps being mechanical makes sense. Could be, but I've yet to see a mechanical one go south unless there was some abuse. Even then they are sometimes repairable. The bend over tabs that hold the encoder together come apart a bit when the shaft is hit at a right angle, which seems to happen all the time on the power supplies I mentioned. I've lost count on the number of times I've repaired them. After repair I solder two 24ga pieces of bus wire across the top from tab to tab which helps sturdy them up a bit. I had just assumed that because HP long-ago developed and manufactured a fine optical part, they'd use it in their expensive premium instruments. Heck, I've long used their expensive optical encoder in my own designs! The mechanical part looks much smaller than the optical one, which might not fit as an upgrade replacement. If you *do* have an optical one, it may depend on whether it solders directly to a PCB, or is panel mounted. If the latter, it probably has a cable which attaches to a PCB, and you should be able to adapt the mechanical one. If you go that route, I've found that it is important to ground the case of the encoder. You'll probably have to fiddle around with the wires to get the order right. Trial and error... I see mechanical ones go bad ALL THE TIME. I even keep a few of the more common ones in stock. I was going to mention this sooner, but it was said that there was a pushbutton function on the OP's unit which the encoders I see don't have, but one of the pics previously posted look like some I stock (and pay about 1.00 each for). They go bad from tarnished contacts, in my opinion, but my friend Arfa opines that it is the migration of silicon lubricant that is the root of the problem. Mark Z. |
#12
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
On Tue, 9 Aug 2011 06:21:23 -0500, "Mark Zacharias"
wrote: I see mechanical ones go bad ALL THE TIME. I designed one into a marine radio and regretted it. If it moves, it breaks. After about 10 years, all the encoders have probably been replaced at least once. I also have a few ham radios (Icom IC-735) with genuinely horrible mechanical shaft encoders, but that respond well to cleaning. ... but it was said that there was a pushbutton function on the OP's unit which the encoders I see don't have, but one of the pics previously posted look like some I stock (and pay about 1.00 each for). The CUI data sheet shows versions with a push button option. They go bad from tarnished contacts, in my opinion, but my friend Arfa opines that it is the migration of silicon lubricant that is the root of the problem. In my never humble opinion, y'er both right. It's both tarnishing and the silicon grease that causes problems. http://en.wikipedia.org/wiki/Polydimethylsiloxane It tends to absorb aromatic hydrocarbon solvents. It also tends to have residual acetic acid used in the manufacture. Both are very mild oxidizers that will eventually rot the surface of any metal contacts. Once pitted, the contact area is reduced. Silicon grease enters the voids, and since it's an insulator and incompressible, eventually ruins the electrical connection. Using soft metals, such as PCB copper, for contacts helps because the wiper scrapes away any surface pitting. That only works until the copper is worn away. I've seen encoders with grooves worn into the PCB traces. In desperation, I found that cleaning off the grease from the copper with alcohol, and tinning the copper PCB traces, actually works fairly well. The problem was that when I lifted the soldering iron, there would always be a small solder points left behind, resulting in multiple bumps as the encoder rotated. I managed to file or press down the points, but the bumps are still obvious. One of my radios was repaired in this manner several years ago and is still functional (although the bumps are irritating). -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#13
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
Jeff Liebermann wrote in message
... On Tue, 9 Aug 2011 06:21:23 -0500, "Mark Zacharias" wrote: I see mechanical ones go bad ALL THE TIME. I designed one into a marine radio and regretted it. If it moves, it breaks. After about 10 years, all the encoders have probably been replaced at least once. I also have a few ham radios (Icom IC-735) with genuinely horrible mechanical shaft encoders, but that respond well to cleaning. ... but it was said that there was a pushbutton function on the OP's unit which the encoders I see don't have, but one of the pics previously posted look like some I stock (and pay about 1.00 each for). The CUI data sheet shows versions with a push button option. They go bad from tarnished contacts, in my opinion, but my friend Arfa opines that it is the migration of silicon lubricant that is the root of the problem. In my never humble opinion, y'er both right. It's both tarnishing and the silicon grease that causes problems. http://en.wikipedia.org/wiki/Polydimethylsiloxane It tends to absorb aromatic hydrocarbon solvents. It also tends to have residual acetic acid used in the manufacture. Both are very mild oxidizers that will eventually rot the surface of any metal contacts. Once pitted, the contact area is reduced. Silicon grease enters the voids, and since it's an insulator and incompressible, eventually ruins the electrical connection. Using soft metals, such as PCB copper, for contacts helps because the wiper scrapes away any surface pitting. That only works until the copper is worn away. I've seen encoders with grooves worn into the PCB traces. In desperation, I found that cleaning off the grease from the copper with alcohol, and tinning the copper PCB traces, actually works fairly well. The problem was that when I lifted the soldering iron, there would always be a small solder points left behind, resulting in multiple bumps as the encoder rotated. I managed to file or press down the points, but the bumps are still obvious. One of my radios was repaired in this manner several years ago and is still functional (although the bumps are irritating). -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 I don't know if its relevant with these encoders but a few times I've found with preset size pots that appear in audio mixers. The grease hardens and then lifts the very feeble wipers of the pots. No track wear at all as the wiper action is so slight , so why the grease ? |
#14
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
"N_Cook" wrote in message
... Jeff Liebermann wrote in message ... On Tue, 9 Aug 2011 06:21:23 -0500, "Mark Zacharias" wrote: I see mechanical ones go bad ALL THE TIME. I designed one into a marine radio and regretted it. If it moves, it breaks. After about 10 years, all the encoders have probably been replaced at least once. I also have a few ham radios (Icom IC-735) with genuinely horrible mechanical shaft encoders, but that respond well to cleaning. ... but it was said that there was a pushbutton function on the OP's unit which the encoders I see don't have, but one of the pics previously posted look like some I stock (and pay about 1.00 each for). The CUI data sheet shows versions with a push button option. They go bad from tarnished contacts, in my opinion, but my friend Arfa opines that it is the migration of silicon lubricant that is the root of the problem. In my never humble opinion, y'er both right. It's both tarnishing and the silicon grease that causes problems. http://en.wikipedia.org/wiki/Polydimethylsiloxane It tends to absorb aromatic hydrocarbon solvents. It also tends to have residual acetic acid used in the manufacture. Both are very mild oxidizers that will eventually rot the surface of any metal contacts. Once pitted, the contact area is reduced. Silicon grease enters the voids, and since it's an insulator and incompressible, eventually ruins the electrical connection. Using soft metals, such as PCB copper, for contacts helps because the wiper scrapes away any surface pitting. That only works until the copper is worn away. I've seen encoders with grooves worn into the PCB traces. In desperation, I found that cleaning off the grease from the copper with alcohol, and tinning the copper PCB traces, actually works fairly well. The problem was that when I lifted the soldering iron, there would always be a small solder points left behind, resulting in multiple bumps as the encoder rotated. I managed to file or press down the points, but the bumps are still obvious. One of my radios was repaired in this manner several years ago and is still functional (although the bumps are irritating). -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 I don't know if its relevant with these encoders but a few times I've found with preset size pots that appear in audio mixers. The grease hardens and then lifts the very feeble wipers of the pots. No track wear at all as the wiper action is so slight , so why the grease ? I think the silicon grease is there to provide the "feel" when you turn the controls. Mark Z. |
#15
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
Mark Zacharias wrote in message
om... "N_Cook" wrote in message ... Jeff Liebermann wrote in message ... On Tue, 9 Aug 2011 06:21:23 -0500, "Mark Zacharias" wrote: I see mechanical ones go bad ALL THE TIME. I designed one into a marine radio and regretted it. If it moves, it breaks. After about 10 years, all the encoders have probably been replaced at least once. I also have a few ham radios (Icom IC-735) with genuinely horrible mechanical shaft encoders, but that respond well to cleaning. ... but it was said that there was a pushbutton function on the OP's unit which the encoders I see don't have, but one of the pics previously posted look like some I stock (and pay about 1.00 each for). The CUI data sheet shows versions with a push button option. They go bad from tarnished contacts, in my opinion, but my friend Arfa opines that it is the migration of silicon lubricant that is the root of the problem. In my never humble opinion, y'er both right. It's both tarnishing and the silicon grease that causes problems. http://en.wikipedia.org/wiki/Polydimethylsiloxane It tends to absorb aromatic hydrocarbon solvents. It also tends to have residual acetic acid used in the manufacture. Both are very mild oxidizers that will eventually rot the surface of any metal contacts. Once pitted, the contact area is reduced. Silicon grease enters the voids, and since it's an insulator and incompressible, eventually ruins the electrical connection. Using soft metals, such as PCB copper, for contacts helps because the wiper scrapes away any surface pitting. That only works until the copper is worn away. I've seen encoders with grooves worn into the PCB traces. In desperation, I found that cleaning off the grease from the copper with alcohol, and tinning the copper PCB traces, actually works fairly well. The problem was that when I lifted the soldering iron, there would always be a small solder points left behind, resulting in multiple bumps as the encoder rotated. I managed to file or press down the points, but the bumps are still obvious. One of my radios was repaired in this manner several years ago and is still functional (although the bumps are irritating). -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 I don't know if its relevant with these encoders but a few times I've found with preset size pots that appear in audio mixers. The grease hardens and then lifts the very feeble wipers of the pots. No track wear at all as the wiper action is so slight , so why the grease ? I think the silicon grease is there to provide the "feel" when you turn the controls. Mark Z. I'd not thought of that as a reason but it makes some sort of sense. I suppose the first pot one ,I cleared the grease out with meths and reassembled dry, refitted, and returned to owner must be about 5 years ago. That one and subsequent ones, have not bounced back with worn tracks , so superfluous as far as electrical function is concerned , IWS. I suppose someone will now tell me I should have replaced like for like, not going against the "designer's" wishes. |
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
On Wed, 10 Aug 2011 08:17:53 +0100, "N_Cook"
wrote: I don't know if its relevant with these encoders but a few times I've found with preset size pots that appear in audio mixers. The grease hardens and then lifts the very feeble wipers of the pots. No track wear at all as the wiper action is so slight , so why the grease ? Good question. You might need a microscope to see the groves. My guess(tm) would be to prevent oxidation and prevent the small amounts of the resistance material from landing across contacts. I also recall reading that it reduces pot noise improves the "feel" by adding some drag, but that's mostly on the shaft, not the wiper. This explains much: http://www.nyelubricants.com/lubenotes/Lubenote_Potentiometers.pdf Looks like they have different greases for different problems: http://www.nyelubricants.com/applications/sensor_potentiometer.shtml -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
On Wed, 10 Aug 2011 12:51:27 +0100, "N_Cook"
wrote: I'd not thought of that as a reason but it makes some sort of sense. I suppose the first pot one ,I cleared the grease out with meths and reassembled dry, refitted, and returned to owner must be about 5 years ago. That one and subsequent ones, have not bounced back with worn tracks , so superfluous as far as electrical function is concerned , IWS. I suppose someone will now tell me I should have replaced like for like, not going against the "designer's" wishes. I've had good luck disassembling and cleaning these types of mechanical encoders that are often used as volume controls. They have to be disassembled. Using something like deoxit will work for a while, but it's not usually a lasting fix. I do normally replace the grease since I figure it was there for a reason (probably lubrication, and possibly to prevent oxidation of the contacts). I recently repaired a 33120A, and the encoder was just held together with bent metal tabs, and should be easy to disassemble. |
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
Jeff Liebermann wrote in message
... On Wed, 10 Aug 2011 08:17:53 +0100, "N_Cook" wrote: I don't know if its relevant with these encoders but a few times I've found with preset size pots that appear in audio mixers. The grease hardens and then lifts the very feeble wipers of the pots. No track wear at all as the wiper action is so slight , so why the grease ? Good question. You might need a microscope to see the groves. My guess(tm) would be to prevent oxidation and prevent the small amounts of the resistance material from landing across contacts. I also recall reading that it reduces pot noise improves the "feel" by adding some drag, but that's mostly on the shaft, not the wiper. This explains much: http://www.nyelubricants.com/lubenotes/Lubenote_Potentiometers.pdf Looks like they have different greases for different problems: http://www.nyelubricants.com/applications/sensor_potentiometer.shtml -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 Of course being a seller of lubricants there is no tabling of the long-term performance as far as immunity to hardening. That "velvet feel" becoming gumming up the works . And pot track lubrication being insufficient to cause "aquaplaning" and then with aging/ chemical reaction, hardening and forming a wedging under the wiper and so loosing contact for all or most of the track run. A job for tomorrow is to take some measurements of one of those tiny preset size pots. The wiper arcs are something like 3 off 10mm long , and section .2x.4mm IIRC but I will try and measure the contact force , I'm guessing at this stage of order 10 gm. Once one wiper lifts I imagine its not long before all 3 lift at some part of their travel. |
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optical knob encoder: HP/Agilent 33120A freq generator,tuning-knob failure
On Monday, August 8, 2011 3:12:54 AM UTC-4, Winfield Hill wrote:
We have about 10 Agilent 33120A frequency-generator / synthesizers in our lab, and a few other similar synthesizers. They feature a convenient digital frequency and amplitude programming knob that's based on optical encoders. .... Since they use an optical 2-bit quadrature grey-code ... But recently I've encountered two instruments with identical tuning-knob failures... In both cases the knob seems 'stuck" There's two optointerruptors out-of-phase with a toothed wheel (or somesuch, like in the old mice). Your symptom is of one blocked or dim lamp. |
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optical knob encoder: HP/Agilent 33120A freq generator,tuning-knobfailure
whit3rd wrote: On Monday, August 8, 2011 3:12:54 AM UTC-4, Winfield Hill wrote: We have about 10 Agilent 33120A frequency-generator / synthesizers in our lab, and a few other similar synthesizers. They feature a convenient digital frequency and amplitude programming knob that's based on optical encoders. ... Since they use an optical 2-bit quadrature grey-code ... But recently I've encountered two instruments with identical tuning-knob failures... In both cases the knob seems 'stuck" There's two optointerruptors out-of-phase with a toothed wheel (or somesuch, like in the old mice). Your symptom is of one blocked or dim lamp. His encoder is mechanical, as he stated later in the thread. -- Politicians should only get paid if the budget is balanced, and there is enough left over to pay them. |
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
N_Cook wrote in message
... Jeff Liebermann wrote in message ... On Wed, 10 Aug 2011 08:17:53 +0100, "N_Cook" wrote: A job for tomorrow is to take some measurements of one of those tiny preset size pots. The wiper arcs are something like 3 off 10mm long , and section .2x.4mm IIRC but I will try and measure the contact force , I'm guessing at this stage of order 10 gm. Once one wiper lifts I imagine its not long before all 3 lift at some part of their travel. Alpha type 4D3-11 pot , footprint 9.6x 11.2mm. 2 wiper arcs about 7 and 9 mm long. Wiper metal 0.1mm thick x 0.3mm. Could not measure contact force in-situ. With wiper removed from recess, 10 gm would visibly move one wiper relative to the other. No visible track scoring under a x30 magnification. Of course , those old enough, would have come across the effect of hardening grease in cassette tape mechanisms then VCR. Where an arm pivots on an axle and return action is just a light torsion spring. |
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optical knob encoder: HP/Agilent 33120A freq generator,tuning-knob failure
On Aug 8, 1:19*am, "N_Cook" wrote:
Winfield Hill wrote in message ... We have about 10 Agilent 33120A frequency-generator / synthesizers *in our lab, and a few other similar synthesizers. *They feature a *convenient digital frequency and amplitude programming knob that's *based on optical encoders. *A pair of left-right pushbuttons sets *which decade you're adjusting with the knob, and over or underflows *operate on the next higher decade. *There's a little indent near *the edge of the knob so you can spin it with your fingertip. *You *can also use up-down pushbuttons or directly punch in numbers, but *the spinning knob is very convenient. *Typically such encoders have *16 or 32 ticks per revolution. *A very nice design feature. *The optical shaft encoders were originally made by HP, but now of *course they're made by Avago. Sometimes they call these a digital *potentiometer or a "Panel Mount Optical Rotary Encoder". *For *example, the HRPG-AD16 product line, about $34 each at Mouser. *http://www.mouser.com/Search/Refine....word=HRPG-AD16 http://www.avagotech.com/pages/en/mo...r_products/rot... tches/hrpg-ad1616c/ *Since they use an optical 2-bit quadrature grey-code (as opposed *to using a pair of switch contacts), they're supposed to be *extremely reliable. *But recently I've encountered two instruments with identical *tuning-knob failures, one in an elegant 33250A 80MHz model *that's on my bench, and the other in one of our standard *33120A 15MHz instruments. *In both cases the knob seems 'stuck" and not to work as you *turn it, except every now and then you'll get one or two *increments or decrements. *Totally useless. *I'm wondering if anyone else has encountered this failure? -- *Thanks, * * - Win Its probably patentable so is there a patent outline for them somewhere, to show what the innards are? Lots of video editing gear uses optical shaft encoders. Typical failure is bushing wearout that alters the alignment of the rotary vs fixed disk. You'll find excess axial 'play' and often side-side play as well. Some decent lubricant early on sold have increased the life. G² |
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
FWIW, the acrylic "body" of manu LEDs can be resized.. and leaving the
emitting surface area untouched generally won't reduce the output. I've reduced the diameter of common LEDs to fit where they normally wouldn't. The tiny emitting chip is very small compared to the size of the outer diameter of the acrylic. A pin vise can be used to hold the leads of a common (thru-hole) LED. There are some applications where the tiny chips are used without acrylic bodies, and the very fine gage gold leads are attached directly to gold plated circuit board pads. A home bathroom scale had what looked like a 3-digit 7-segment display, but the separate LED chips were mounted to the board, and a plastic housing was placed over the LED chips (with colored film) which made it appear to be a normal 3-digit module. -- Cheers, WB .............. "JW" wrote in message ... And what a pain in the butt to get to on a 6034A! I wish I could find a "side firing" LED that would not only fit in that little slot, but also be the right wavelength for it to work correctly. I've experimented a bit with this, but never been successful. |
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optical knob encoder: HP/Agilent 33120A freq generator,tuning-knobfailure
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
On Wed, 10 Aug 2011 17:15:35 +0100, "N_Cook"
wrote: Of course being a seller of lubricants there is no tabling of the long-term performance as far as immunity to hardening. NYE also sells laser printer fuser grease. After several aborted attempts at finding a cheaper substitute, I've resigned myself to using the overpriced real thing. In a past life, I designed marine radios. Pots were always a problem. If "sealed", they would eventually condense some water out of the air, and rot. If vented, salt encrustation and corrosion would become a problem. Sealing the shaft was a big help, but re-lubrication was tricky. However, ignoring all these mechanical problems, we did have problems with the grease on the resistance material. It would develop dead spots, where the wiper would not make contact, usually where the volume and squelch controls spent most of their time. It was obviously a lump of grease that the wiper was riding on top of, but what was the cause? Basically, silicon grease (PDMS) will absorb small amounts of water and aromatic solvents. These bring with it salt from the marine atmosphere. The salt crystallizes out of solution, the grease encapsulates it, and we have a lump. I played around with various microscope filters for hours until I could see the tiny salt crystals imbedded in the grease. Nye sent us some sample greases, which were a big improvement and which became standard for re-lubrication. That "velvet feel" becoming gumming up the works http://www.nyelubricants.com/products/damping.shtml You won't appreciate proper pot lube until after you try to operate a mobile radio or HT when it's really cold, and find all the controls stuck in place due to thickening of the lubricant. And pot track lubrication being insufficient to cause "aquaplaning" and then with aging/ chemical reaction, hardening and forming a wedging under the wiper and so loosing contact for all or most of the track run. I've never seen this wedging. I have seen salt lumps formed when the pot is left in one position for long periods, in a hostile atmosphere. A job for tomorrow is to take some measurements of one of those tiny preset size pots. The wiper arcs are something like 3 off 10mm long , and section .2x.4mm IIRC but I will try and measure the contact force , I'm guessing at this stage of order 10 gm. Once one wiper lifts I imagine its not long before all 3 lift at some part of their travel. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
Jeff Liebermann wrote in message
... On Wed, 10 Aug 2011 17:15:35 +0100, "N_Cook" wrote: You won't appreciate proper pot lube until after you try to operate a mobile radio or HT when it's really cold, and find all the controls stuck in place due to thickening of the lubricant. Easily dissimilar metals , Al and brass and sliding fit , then the naval saying. Cold enough to freeze the (iron canon) balls off a brass monkey (trivet) |
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
On 8 Aug 2011 00:12:54 -0700, the renowned Winfield Hill
wrote: We have about 10 Agilent 33120A frequency-generator / synthesizers in our lab, and a few other similar synthesizers. Hey, Win:- We had a mechanical encoder failure on a 33220A arb function generator. It is a known issue with these encoders and Agilent sent a repair kit gratis (or we could have sent it in). It's an easy fix, so I elected to do it myself. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
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optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure
On Fri, 12 Aug 2011 19:36:51 -0400 Spehro Pefhany
wrote in Message id: : On 8 Aug 2011 00:12:54 -0700, the renowned Winfield Hill wrote: We have about 10 Agilent 33120A frequency-generator / synthesizers in our lab, and a few other similar synthesizers. Hey, Win:- We had a mechanical encoder failure on a 33220A arb function generator. It is a known issue with these encoders and Agilent sent a repair kit gratis (or we could have sent it in). It's an easy fix, so I elected to do it myself. Here's the service note: http://cp.literature.agilent.com/lit...33220A-02B.pdf The expiration for free service or parts is February 1, 2012. |
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