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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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A colleague drops by my office toating a Tek R293 Programmable pulse generator and power supply and asks "Can I use a power supply?" followed by, I haven't turned it on in 35 years....
Having never seen one of these before (its circa 1966) and thought it might be an interesting thing to restore, even though I have never and probably will never have use for such a thing. Looking through the manual scanning for the semiconductor parts list (and looking for the 'special' Tek parts, I see designations on a number of diodes: Snap Diode, Check. No number of any sort. I never heard of one of these so google is my friend....(aka snap off diode or charge-storage diode or memory varactor) studied the schematics of the pulse generator a bit and realized what a neat device and interesting circuit design. It probably has a lot of bad parts, given the age, and while repair would be quite a learning experience, my basis questions a 1) how to determine the snap diode characteristics for this unique tek part? 2) and what are the chances of finding a reasonable substitute? Assuming one of the snap diodes in the unit still functions, I could use a curve tracer and get some general parameters: Breakover voltage, approximate current range, reverse blocking voltage, leakage, etc. But determining the switch time would be critical in this application as that dictates the pulse characteristics. Another thing that is of interest is this statement from Wikipedia: "The main phenomenon used in SRDs is the storage of electric charge during forward conduction, which is present in all semiconductor junction diodes and is due to finite lifetime of minority carriers in semiconductors." Finite lifetime of minority carriers....I assume when switching from forward conduction to reverse the minority carriers are quickly reversed in their flow given the abrupt change of voltage polarity? J |
#2
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On 2019/06/11 7:56 a.m., three_jeeps wrote:
A colleague drops by my office toating a Tek R293 Programmable pulse generator and power supply and asks "Can I use a power supply?" followed by, I haven't turned it on in 35 years.... Having never seen one of these before (its circa 1966) and thought it might be an interesting thing to restore, even though I have never and probably will never have use for such a thing. Looking through the manual scanning for the semiconductor parts list (and looking for the 'special' Tek parts, I see designations on a number of diodes: Snap Diode, Check. No number of any sort. I never heard of one of these so google is my friend....(aka snap off diode or charge-storage diode or memory varactor) studied the schematics of the pulse generator a bit and realized what a neat device and interesting circuit design. It probably has a lot of bad parts, given the age, and while repair would be quite a learning experience, my basis questions a 1) how to determine the snap diode characteristics for this unique tek part? 2) and what are the chances of finding a reasonable substitute? Assuming one of the snap diodes in the unit still functions, I could use a curve tracer and get some general parameters: Breakover voltage, approximate current range, reverse blocking voltage, leakage, etc. But determining the switch time would be critical in this application as that dictates the pulse characteristics. Another thing that is of interest is this statement from Wikipedia: "The main phenomenon used in SRDs is the storage of electric charge during forward conduction, which is present in all semiconductor junction diodes and is due to finite lifetime of minority carriers in semiconductors." Finite lifetime of minority carriers....I assume when switching from forward conduction to reverse the minority carriers are quickly reversed in their flow given the abrupt change of voltage polarity? J Not sure about the Snap Diodes - you might want to check archive.org or bitsaver.org for the Master Electronics Catalogs from that time for specs. Sound like fast recovery diodes to me... However in most cases running an ESR meter (Like Bob Parker's Blue ESR meter kit) over the various capacitors will find a few bad ones at which point the power supply may well work. Caps and electrical connections are the weak link in electronics... Just was playing with one of Bob's latest prototype ESR meter designs yesterday which is a talking ESR meter and working on a sound board with low volume. Having the meter talk to me (Bob's voice) was handy in that I didn't have to take my eyes off the job and things went very quickly. The meter going down to 0.001 ohms is handy too... Nag Bob if you want to see these in production, he isn't sure there is a market for a talking ESR meter... He is currently working on this version of a simple ESR meter kit: https://www.youtube.com/watch?v=o25gLeakcbM John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
#3
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On Tue, 11 Jun 2019 08:15:05 -0700, John Robertson
wrote: Just was playing with one of Bob's latest prototype ESR meter designs yesterday which is a talking ESR meter and working on a sound board with low volume. Having the meter talk to me (Bob's voice) was handy in that I didn't have to take my eyes off the job and things went very quickly. The meter going down to 0.001 ohms is handy too... Nag Bob if you want to see these in production, he isn't sure there is a market for a talking ESR meter... "Prototype "Blue2" talking ESR meter" https://www.youtube.com/watch?v=kYbsDlQ8nPg (1:23) It might be more useful it also announced if the capacitor was good, marginal, or bad. There are some talking multimeters available, mostly for the blind. http://www.mastrogippo.it/2014/03/a-talking-multimeter/ I played with one such home built meter that was built around a Speak-and-Spell toy. https://en.wikipedia.org/wiki/Speak_%26_Spell_(toy) I found the talking feature most useful when I couldn't read the multimeter LED display in bright sunlight, such as working under the hood of my car. I don't think there's a need for a talking ESR meter that works in bright sunlight. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#4
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Jeff Liebermann wrote:
..................... "Prototype "Blue2" talking ESR meter" https://www.youtube.com/watch?v=kYbsDlQ8nPg (1:23) It might be more useful it also announced if the capacitor was good, marginal, or bad. ** Or, in Aussie parlance that would be: "beauty", "dodgy" and "****ed". ..... Phil |
#5
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On 2019/06/11 4:41 p.m., Jeff Liebermann wrote:
On Tue, 11 Jun 2019 08:15:05 -0700, John Robertson wrote: Just was playing with one of Bob's latest prototype ESR meter designs yesterday which is a talking ESR meter and working on a sound board with low volume. Having the meter talk to me (Bob's voice) was handy in that I didn't have to take my eyes off the job and things went very quickly. The meter going down to 0.001 ohms is handy too... Nag Bob if you want to see these in production, he isn't sure there is a market for a talking ESR meter... "Prototype "Blue2" talking ESR meter" https://www.youtube.com/watch?v=kYbsDlQ8nPg (1:23) It might be more useful it also announced if the capacitor was good, marginal, or bad. There are some talking multimeters available, mostly for the blind. http://www.mastrogippo.it/2014/03/a-talking-multimeter/ I played with one such home built meter that was built around a Speak-and-Spell toy. https://en.wikipedia.org/wiki/Speak_%26_Spell_(toy) I found the talking feature most useful when I couldn't read the multimeter LED display in bright sunlight, such as working under the hood of my car. I don't think there's a need for a talking ESR meter that works in bright sunlight. I use an ESR meter for things besides caps, this chatty one that goes down to 0.001 ohms is handy for finding shorts between traces, and other jobs, not just testing caps. Maximum is around 90 ohms. Bob's newest ESR project (He didn't think the talking meter would sell) is an EasyESR which has three LEDs and three different tones depending on the result. So there is your point, however the value of the cap is taken into consideration so the middle LED if on is good if under 1000ufd but questionable if over 1000ufd. Here is the prototype: https://www.youtube.com/watch?v=o25gLeakcbM Send him a note if you want it built! John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
#6
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On Tue, 11 Jun 2019 17:17:41 -0700, John Robertson
wrote: I use an ESR meter for things besides caps, this chatty one that goes down to 0.001 ohms is handy for finding shorts between traces, and other jobs, not just testing caps. Maximum is around 90 ohms. Yet another idea. Most supercaps have an extremely low ESR. For example, Murata claims 40 to 300 milliohms (measured at 1KHz). https://www.murata.com/~/media/webrenewal/products/capacitor/edlc/techguide/electrical/c2m1cxs-053.ashx Ask Bob Parker if he can build something to test those. I have no clue how to build probes with that low a contact resistance. Fat copper wires with silver contacts? I don't have an immediate application or market, but I keep running into supercaps with no way to test them for anything more than capacitance. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#7
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On 2019-06-12 18:05, Jeff Liebermann wrote:
On Tue, 11 Jun 2019 17:17:41 -0700, John Robertson wrote: I use an ESR meter for things besides caps, this chatty one that goes down to 0.001 ohms is handy for finding shorts between traces, and other jobs, not just testing caps. Maximum is around 90 ohms. Yet another idea. Most supercaps have an extremely low ESR. For example, Murata claims 40 to 300 milliohms (measured at 1KHz). https://www.murata.com/~/media/webrenewal/products/capacitor/edlc/techguide/electrical/c2m1cxs-053.ashx Ask Bob Parker if he can build something to test those. I have no clue how to build probes with that low a contact resistance. Fat copper wires with silver contacts? I don't have an immediate application or market, but I keep running into supercaps with no way to test them for anything more than capacitance. One would use Kelvin connections - probe resistance is not a major issue then. https://en.wikipedia.org/wiki/Four-terminal_sensing Arie |
#8
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On Tue, 11 Jun 2019 08:15:05 -0700, John Robertson wrote:
Nag Bob if you want to see these in production, he isn't sure there is a market for a talking ESR meter... Just the thing for a blind repair tech! :-) Jonesy |
#9
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On 6/11/19 10:56 AM, three_jeeps wrote:
A colleague drops by my office toating a Tek R293 Programmable pulse generator and power supply and asks "Can I use a power supply?" followed by, I haven't turned it on in 35 years.... Having never seen one of these before (its circa 1966) and thought it might be an interesting thing to restore, even though I have never and probably will never have use for such a thing. Looking through the manual scanning for the semiconductor parts list (and looking for the 'special' Tek parts, I see designations on a number of diodes: Snap Diode, Check. No number of any sort. I never heard of one of these so google is my friend....(aka snap off diode or charge-storage diode or memory varactor) studied the schematics of the pulse generator a bit and realized what a neat device and interesting circuit design. It probably has a lot of bad parts, given the age, and while repair would be quite a learning experience, my basis questions a 1) how to determine the snap diode characteristics for this unique tek part? 2) and what are the chances of finding a reasonable substitute? Assuming one of the snap diodes in the unit still functions, I could use a curve tracer and get some general parameters: Breakover voltage, approximate current range, reverse blocking voltage, leakage, etc. But determining the switch time would be critical in this application as that dictates the pulse characteristics. Another thing that is of interest is this statement from Wikipedia: "The main phenomenon used in SRDs is the storage of electric charge during forward conduction, which is present in all semiconductor junction diodes and is due to finite lifetime of minority carriers in semiconductors." Finite lifetime of minority carriers....I assume when switching from forward conduction to reverse the minority carriers are quickly reversed in their flow given the abrupt change of voltage polarity? J SRDs have been used for aeons. Besides pulsers, as in the 20-ps-class Tek SD24 TDR sampling head, SRDs are used as high-order frequency multipliers. You can still get them from Microsemi and maybe elsewhere--Arrow has 433 Microsemi GC2510 devices in stock. One of my first engineering tasks back in 1981 was to rebias an X-band waveguide frequency multiplier using an SRD--we were changing from a Microwave Associates device to a Gigahertz Devices one. The SRD was self-biased with a thick-film conductive ink drop on the side of the ceramic package. I used a soft pencil to make the resistive shunt on the new device, and varied it till I found the value that produced the highest efficiency. The job was complicated by the tendency of the graphite to ablate. ![]() Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
#10
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On Tue, 11 Jun 2019 07:56:08 -0700 (PDT), three_jeeps
wrote: I never heard of one of these so google is my friend....(aka snap off diode or charge-storage diode or memory varactor) Which diodes are you referring to? I checked the R293 manual at: http://w140.com/tekwiki/wiki/R293 http://w140.com/tek_r293.pdf In the description, it refers to "avalanche diodes". In the parts list, they are "Snap off, Checked" whatever that means. D224, D240, D274, and D290. http://w140.com/tekwiki/wiki/Step_recovery_diode It probably has a lot of bad parts, given the age, and while repair would be quite a learning experience, my basis questions a 1) how to determine the snap diode characteristics for this unique tek part? I don't know. Start digging: http://w140.com/tek_xref_free.pdf http://w140.com/Tek_RPR_152-_Diodes.pdf Maybe more he http://w140.com/tekwiki/wiki/Reference_material 2) and what are the chances of finding a reasonable substitute? Marginal. Finding an exact replacement, impossible. The TEK part number in the manual for these "snap" diodes is 153-0023-00. Google doesn't seem to find anything. The Tek to vendor cross reference lists the part number as a "selected part" and "Sig, Snap off" with a vendor number of "Ref. only". That's not very useful information. This rather smells of bin selected parts in matched pairs, which is going to be difficult to substitute without know what parameters are being matched. When you remove the diodes for testing in the R293, be sure to mark them with their original Rxxx reference designator so that the return to the same location on the PCB. Looks like some of the microwave semiconductor houses still make step recovery diodes for use in comb generators, frequency multipliers, sub-harmonic generators, and maybe pulse generators: https://www.microsemi.com/product-directory/varactor-diodes/3150-step-recovery-diodes https://www.macom.com/products/diodes/multiplier-step-recovery-diodes https://www.semigen.net/step-recovery-diodes/ http://www.advancedsemiconductor.com/diodes/step_recovery.shtml etc. You probably don't need rise times suitable for generating microwave frequencies. Assuming one of the snap diodes in the unit still functions, I could use a curve tracer and get some general parameters... Are you sure that there's something wrong with the original step recovery diodes? They might all be good and no replacement is needed. Maybe ask the same questions in one of the Tek specific Yahoo Groups? -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#11
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On Tuesday, June 11, 2019 at 9:03:43 PM UTC-4, Jeff Liebermann wrote:
On Tue, 11 Jun 2019 07:56:08 -0700 (PDT), three_jeeps wrote: I never heard of one of these so google is my friend....(aka snap off diode or charge-storage diode or memory varactor) Which diodes are you referring to? I checked the R293 manual at: http://w140.com/tekwiki/wiki/R293 http://w140.com/tek_r293.pdf In the description, it refers to "avalanche diodes". In the parts list, they are "Snap off, Checked" whatever that means. D224, D240, D274, and D290. http://w140.com/tekwiki/wiki/Step_recovery_diode It probably has a lot of bad parts, given the age, and while repair would be quite a learning experience, my basis questions a 1) how to determine the snap diode characteristics for this unique tek part? I don't know. Start digging: http://w140.com/tek_xref_free.pdf http://w140.com/Tek_RPR_152-_Diodes.pdf Maybe more he http://w140.com/tekwiki/wiki/Reference_material 2) and what are the chances of finding a reasonable substitute? Marginal. Finding an exact replacement, impossible. The TEK part number in the manual for these "snap" diodes is 153-0023-00. Google doesn't seem to find anything. The Tek to vendor cross reference lists the part number as a "selected part" and "Sig, Snap off" with a vendor number of "Ref. only". That's not very useful information. This rather smells of bin selected parts in matched pairs, which is going to be difficult to substitute without know what parameters are being matched. When you remove the diodes for testing in the R293, be sure to mark them with their original Rxxx reference designator so that the return to the same location on the PCB. Looks like some of the microwave semiconductor houses still make step recovery diodes for use in comb generators, frequency multipliers, sub-harmonic generators, and maybe pulse generators: https://www.microsemi.com/product-directory/varactor-diodes/3150-step-recovery-diodes https://www.macom.com/products/diodes/multiplier-step-recovery-diodes https://www.semigen.net/step-recovery-diodes/ http://www.advancedsemiconductor.com/diodes/step_recovery.shtml etc. You probably don't need rise times suitable for generating microwave frequencies. Assuming one of the snap diodes in the unit still functions, I could use a curve tracer and get some general parameters... Are you sure that there's something wrong with the original step recovery diodes? They might all be good and no replacement is needed. Maybe ask the same questions in one of the Tek specific Yahoo Groups? -- 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 anything is wrong with this thing. I have degrees in Electrical Computer engineering and focus on CPU architecture and hardware design, and control theory. As an EE, yea, designed/built lots of digital and analog 'stuff' but never dabbled with microwave 'stuff' and the SRD was something I've never come across till I was looking at the schematics and tech manual for this device. Personally, I have no use for it and lots of other things to devote my time to, but I thought I'd ask some questions about these devices on the off chance I'd do something with it. I did go down the route of looking up the tek cross to commercial parts and found nothing, so I am even more inclined not to deal with this thing. Given that is vintage 1965 and hasn't been turned on in 30+ years, chances are components are non-functional. Thanks for all the insights. J |
#12
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On 6/11/2019 7:56 AM, three_jeeps wrote:
A colleague drops by my office toating a Tek R293 Programmable pulse generator and power supply and asks "Can I use a power supply?" followed by, I haven't turned it on in 35 years.... Having never seen one of these before (its circa 1966) and thought it might be an interesting thing to restore, even though I have never and probably will never have use for such a thing. Looking through the manual scanning for the semiconductor parts list (and looking for the 'special' Tek parts, I see designations on a number of diodes: Snap Diode, Check. No number of any sort. I never heard of one of these so google is my friend....(aka snap off diode or charge-storage diode or memory varactor) studied the schematics of the pulse generator a bit and realized what a neat device and interesting circuit design. It probably has a lot of bad parts, given the age, and while repair would be quite a learning experience, my basis questions a 1) how to determine the snap diode characteristics for this unique tek part? 2) and what are the chances of finding a reasonable substitute? Assuming one of the snap diodes in the unit still functions, I could use a curve tracer and get some general parameters: Breakover voltage, approximate current range, reverse blocking voltage, leakage, etc. But determining the switch time would be critical in this application as that dictates the pulse characteristics. Another thing that is of interest is this statement from Wikipedia: "The main phenomenon used in SRDs is the storage of electric charge during forward conduction, which is present in all semiconductor junction diodes and is due to finite lifetime of minority carriers in semiconductors." Finite lifetime of minority carriers....I assume when switching from forward conduction to reverse the minority carriers are quickly reversed in their flow given the abrupt change of voltage polarity? J Back then, TEK made many of their own diodes and transistors because they could not get the quality and specs they wanted. They later made their own ICs. We use one of their stencil machines today to screen solder paste on PC boards. Paul |
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