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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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Dual output supply dead
Hi,
I use a lot of external disk/tape/etc. enclosures or my computer peripherals. These typically have ~60W, dual output (5/12) supplies in them. They are a "popcorn part" so, when one fails, it is usually easier to grab a spare out of my junk pile and replace the entire power supply than waste time trying to repair it. However, I have one such supply that is dead AND has an atypical form factor (long and skinny). So, finding a suitable spare in my junk pile has been a problem : (the supply in question is a Autec UPS65-2002) It is functionally equivalent to the dozens of other supplys that I have so I have temporarily replaced it with one of those. I figured it might be worth a few minutes to poke around it and see if I can steal some components off another supply to breathe new life into this one. (If not, I'll just pull the disks/tape out of the enclosure and throw the whole thing out in favor of another enclosure). A quick look at the types of components on the PCB leads me to make some guesses as to what the circuit topology is. It looks like mains power passes through an input filter (choke, snubber, etc.) and then rectified. Switching transformer primary is chopped and controlled by a sense winding on the xformer. "Center" tapped secondary (no doubt assymetrically tapped) two legs are rectified and then LC filtered to provide the final output. I assume some sort of OVP watches one or both outputs as I see optoisolator feedback across the transformer no doubt to shutdown the chopper. Can someone confirm my guesswork to be correct? Nothing is visibly toasted. And, assuming this topology, I'd guess the chopper is "opened". Of course, it is possible that there is a failure elsewhere on the board/load but I suspect it may have just opened from fatigue, etc. I.e. is it worth hunting down a replacement part (out of the scrap bin) for a "quick fix"? Or, are these a bit more complicated to repair (in which case, tossing it all in the hazardous waste recycling bin is more expedient). Recall I am *not* particularly "attached" to this enclosure... : Thanks! --don |
#2
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Dual output supply dead
Don wrote:
Hi, I use a lot of external disk/tape/etc. enclosures or my computer peripherals. These typically have ~60W, dual output (5/12) supplies in them. They are a "popcorn part" so, when one fails, it is usually easier to grab a spare out of my junk pile and replace the entire power supply than waste time trying to repair it. However, I have one such supply that is dead AND has an atypical form factor (long and skinny). So, finding a suitable spare in my junk pile has been a problem : (the supply in question is a Autec UPS65-2002) It is functionally equivalent to the dozens of other supplys that I have so I have temporarily replaced it with one of those. I figured it might be worth a few minutes to poke around it and see if I can steal some components off another supply to breathe new life into this one. (If not, I'll just pull the disks/tape out of the enclosure and throw the whole thing out in favor of another enclosure). A quick look at the types of components on the PCB leads me to make some guesses as to what the circuit topology is. It looks like mains power passes through an input filter (choke, snubber, etc.) and then rectified. Switching transformer primary is chopped and controlled by a sense winding on the xformer. "Center" tapped secondary (no doubt assymetrically tapped) two legs are rectified and then LC filtered to provide the final output. I assume some sort of OVP watches one or both outputs as I see optoisolator feedback across the transformer no doubt to shutdown the chopper. Can someone confirm my guesswork to be correct? Nothing is visibly toasted. And, assuming this topology, I'd guess the chopper is "opened". Of course, it is possible that there is a failure elsewhere on the board/load but I suspect it may have just opened from fatigue, etc. I.e. is it worth hunting down a replacement part (out of the scrap bin) for a "quick fix"? Or, are these a bit more complicated to repair (in which case, tossing it all in the hazardous waste recycling bin is more expedient). Recall I am *not* particularly "attached" to this enclosure... : Thanks! --don Circuit sounds about right, though there will likely be overcurrent protection as well. As far as repair goes, just bin it, theyre often sods to do. NT |
#3
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Dual output supply dead
Check the fuse?
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#4
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Dual output supply dead
"Ancient_Hacker" writes:
Check the fuse? Might also be as simple as an open startup resistor. But as someone else suggested, may not be worth the trouble. For now, if you need to get your system back up, move the drives to another enclosure. Then, later if you want a challenge, try to repair it. --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
#5
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Dual output supply dead
Sam Goldwasser wrote:
"Ancient_Hacker" writes: Check the fuse? Might also be as simple as an open startup resistor. Nope on both counts. When I removed it from the enclosure, I made the mistake of picking it up a short time later and sitting down on the couch to have a look at it. Quite annoying to get "bit" from a small device with no wires attached! (of course, the input filter was still charged : ) But as someone else suggested, may not be worth the trouble. For now, if you need to get your system back up, move the drives to another enclosure. Then, later if you want a challenge, try to repair it. Unfortunately, this enclosure handles *3* half height drives (instead of the one or two typically supported) so I have to look for a more creative packaging option. Or, leave the replacement supply sitting atop this enclosure until I find something else, suitable. |
#6
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Dual output supply dead
"Don" none@given wrote in message ... Sam Goldwasser wrote: "Ancient_Hacker" writes: Check the fuse? Might also be as simple as an open startup resistor. Nope on both counts. When I removed it from the enclosure, I made the mistake of picking it up a short time later and sitting down on the couch to have a look at it. Quite annoying to get "bit" from a small device with no wires attached! (of course, the input filter was still charged : ) until I find something else, suitable. You can't say " nope " for the contention of open startup resistor, as the main primary filter cap remaining charged ( often for hours ) is a totally typical symptom of this failure. Couple of quick checks would be to follow the print from the " + " terminal of the primary filter cap, and see if a high-ish value resistor is hooked to it on its way to one of the chopper tranny pins. Another possibility which is very common on all switchers, and will also leave the main filter cap charged due to the chopper oscillator not running, is defective primary-side electrolytics. Look for any small electros, particularly if they are positioned close to the heatsink or anything else that gets hot, and ESR them. If you haven't got an ESR meter, just replace them. It's worth going that far, but beyond that, commit it to landfill ... Arfa |
#7
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Dual output supply dead
Arfa Daily wrote:
"Don" none@given wrote in message ... Sam Goldwasser wrote: "Ancient_Hacker" writes: Check the fuse? Might also be as simple as an open startup resistor. Nope on both counts. When I removed it from the enclosure, I made the mistake of picking it up a short time later and sitting down on the couch to have a look at it. You can't say " nope " for the contention of open startup resistor, as the main primary filter cap remaining charged ( often for hours ) is a totally typical symptom of this failure. Couple of quick checks would be to follow the print from the " + " terminal of the primary filter cap, and see if a high-ish value resistor is hooked to it on its way to one of the chopper I repeat, "Nope". : The fuse is known good (since the input filter would never charge through an open fuse). And, this topology does not employ the sort of startup resistor you are expecting. I.e. there is no DC path to the SMPS controller's "power" pin from the input filter. (I assume you are expecting a ~1W dropping resistor between the input filter and the SMPS controller) To be precise, there are exactly 5 connections to the input filter: - the input filter cap's + terminal - the bridge's '+' output terminal - one side of the transformer primary - one side of an RC snubber across the xformer primary (which is *two* components/connections) in series with catch diode I'll drag out a DVM and verify power is available at the SMPS controller, though... tranny pins. Another possibility which is very common on all switchers, and will also leave the main filter cap charged due to the chopper oscillator not running, is defective primary-side electrolytics. Look for any small electros, particularly if they are positioned close to the heatsink or anything else that gets hot, and ESR them. If you haven't got an ESR meter, Aside from the input filter (180uF 400VDC) and secondary output filters, there are exactly two electrolytics in the design. The first serves as a filter on the sense/feedback coil. I haven't yet tracked down the role of the second... just replace them. It's worth going that far, but beyond that, commit it to landfill ... This looks tiny enough that I can probably trace the circuit topology in half an hour. I'll photocopy the foils and see how quick i can reconstruct the basic design... |
#8
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Dual output supply dead
Don wrote: Arfa Daily wrote: "Don" none@given wrote in message ... Sam Goldwasser wrote: "Ancient_Hacker" writes: Check the fuse? Might also be as simple as an open startup resistor. Nope on both counts. When I removed it from the enclosure, I made the mistake of picking it up a short time later and sitting down on the couch to have a look at it. You can't say " nope " for the contention of open startup resistor, as the main primary filter cap remaining charged ( often for hours ) is a totally typical symptom of this failure. Couple of quick checks would be to follow the print from the " + " terminal of the primary filter cap, and see if a high-ish value resistor is hooked to it on its way to one of the chopper I repeat, "Nope". : The fuse is known good (since the input filter would never charge through an open fuse). And, this topology does not employ the sort of startup resistor you are expecting. I.e. there is no DC path to the SMPS controller's "power" pin from the input filter. (I assume you are expecting a ~1W dropping resistor between the input filter and the SMPS controller) To be precise, there are exactly 5 connections to the input filter: - the input filter cap's + terminal - the bridge's '+' output terminal - one side of the transformer primary - one side of an RC snubber across the xformer primary (which is *two* components/connections) in series with catch diode I'll drag out a DVM and verify power is available at the SMPS controller, though... tranny pins. Another possibility which is very common on all switchers, and will also leave the main filter cap charged due to the chopper oscillator not running, is defective primary-side electrolytics. Look for any small electros, particularly if they are positioned close to the heatsink or anything else that gets hot, and ESR them. If you haven't got an ESR meter, Aside from the input filter (180uF 400VDC) and secondary output filters, there are exactly two electrolytics in the design. The first serves as a filter on the sense/feedback coil. I haven't yet tracked down the role of the second... just replace them. It's worth going that far, but beyond that, commit it to landfill ... This looks tiny enough that I can probably trace the circuit topology in half an hour. I'll photocopy the foils and see how quick i can reconstruct the basic design... I assume you checked ALL solder connections for bad joints? And put your meter on all higher current film resistors and compared the measured value to the color code? Bob ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
#9
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Dual output supply dead
ok question. we may have to step up a notch now.
What kind of SMPS controller does it have? is the controller and chopper transistor seperate, or is it an all-in-one such as a VIPIR or STR regulator. those are notorious for dying out. "Bob Urz" wrote in message ... Don wrote: Arfa Daily wrote: "Don" none@given wrote in message ... Sam Goldwasser wrote: "Ancient_Hacker" writes: Check the fuse? Might also be as simple as an open startup resistor. Nope on both counts. When I removed it from the enclosure, I made the mistake of picking it up a short time later and sitting down on the couch to have a look at it. You can't say " nope " for the contention of open startup resistor, as the main primary filter cap remaining charged ( often for hours ) is a totally typical symptom of this failure. Couple of quick checks would be to follow the print from the " + " terminal of the primary filter cap, and see if a high-ish value resistor is hooked to it on its way to one of the chopper I repeat, "Nope". : The fuse is known good (since the input filter would never charge through an open fuse). And, this topology does not employ the sort of startup resistor you are expecting. I.e. there is no DC path to the SMPS controller's "power" pin from the input filter. (I assume you are expecting a ~1W dropping resistor between the input filter and the SMPS controller) To be precise, there are exactly 5 connections to the input filter: - the input filter cap's + terminal - the bridge's '+' output terminal - one side of the transformer primary - one side of an RC snubber across the xformer primary (which is *two* components/connections) in series with catch diode I'll drag out a DVM and verify power is available at the SMPS controller, though... tranny pins. Another possibility which is very common on all switchers, and will also leave the main filter cap charged due to the chopper oscillator not running, is defective primary-side electrolytics. Look for any small electros, particularly if they are positioned close to the heatsink or anything else that gets hot, and ESR them. If you haven't got an ESR meter, Aside from the input filter (180uF 400VDC) and secondary output filters, there are exactly two electrolytics in the design. The first serves as a filter on the sense/feedback coil. I haven't yet tracked down the role of the second... just replace them. It's worth going that far, but beyond that, commit it to landfill ... This looks tiny enough that I can probably trace the circuit topology in half an hour. I'll photocopy the foils and see how quick i can reconstruct the basic design... I assume you checked ALL solder connections for bad joints? And put your meter on all higher current film resistors and compared the measured value to the color code? Bob ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
#10
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Dual output supply dead
Mike wrote:
ok question. we may have to step up a notch now. What kind of SMPS controller does it have? is the controller and chopper transistor seperate, or is it an all-in-one such as a VIPIR or STR regulator. those are notorious for dying out. 3842 driving a discrete FET (can't see the P/N on the FET since it is hiding behind the input filter). And, to answer "Bob's" questions, below (his post hasn't made it to my news server): - first thing I did was reflow all the solder joints (since it is so easy to do and I've seen problems with fatigue in the past) - there are only two "higher current" (wattage) resistors on the board: one in the snubber and the other in the current sense leg. The current sense R was verified as "approximately the right value"; the snubber was ignored. I made a photocopy of the foil patterns last night and will trace it out this evening if I have time. In the late evening quiet, I also was able to notice a "ticking" sound -- as if the switcher was starting up and then shutting down again. I'll pay closer attention to the current sense circuit when I am tracing the foil patterns tonight -- along with the OVP shutdown (as those are the two things that come to mind that could cause this cyclic start-shutdown behaviour). But, tomorrow brings another surplus equipment auction so I may stumble on a suitable replacement and just pitch this... :-/ "Bob Urz" wrote in message I assume you checked ALL solder connections for bad joints? And put your meter on all higher current film resistors and compared the measured value to the color code? Bob |
#11
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Dual output supply dead
"Don" none@given wrote in message ... Mike wrote: ok question. we may have to step up a notch now. What kind of SMPS controller does it have? is the controller and chopper transistor seperate, or is it an all-in-one such as a VIPIR or STR regulator. those are notorious for dying out. 3842 driving a discrete FET (can't see the P/N on the FET since it is hiding behind the input filter). If it uses a 3842 / FET circuit, then it just abiut *must* have a startup resistor and supply pin decoupling cap somewhere, otherwise, how does it get a supply to the IC to start it up ? If it's ticking, my money is still on a cap ... Arfa |
#12
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Dual output supply dead
Arfa Daily wrote:
"Don" none@given wrote in message ... Mike wrote: ok question. we may have to step up a notch now. What kind of SMPS controller does it have? is the controller and chopper transistor seperate, or is it an all-in-one such as a VIPIR or STR regulator. those are notorious for dying out. 3842 driving a discrete FET (can't see the P/N on the FET since it is hiding behind the input filter). If it uses a 3842 / FET circuit, then it just abiut *must* have a startup resistor and supply pin decoupling cap somewhere, otherwise, how does it get a supply to the IC to start it up ? Trust me, I can eyeball a 1.5" length of foil with 5 holes in it! : As I said in a previous post, only two R's larger than 1/10W: one as the current sense R; the other as the snubber (it's REALLY easy to see an RC-D across the primary ... you don't even have to look hard! : ) If it's ticking, my money is still on a cap ... My first guess would be the current sense resistor being open and immediately shutting the controller down. But, I haven't yet traced the foils to see what else is going on. |
#13
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Dual output supply dead
"Don" none@given wrote in message ... Arfa Daily wrote: "Don" none@given wrote in message ... Mike wrote: ok question. we may have to step up a notch now. What kind of SMPS controller does it have? is the controller and chopper transistor seperate, or is it an all-in-one such as a VIPIR or STR regulator. those are notorious for dying out. 3842 driving a discrete FET (can't see the P/N on the FET since it is hiding behind the input filter). If it uses a 3842 / FET circuit, then it just abiut *must* have a startup resistor and supply pin decoupling cap somewhere, otherwise, how does it get a supply to the IC to start it up ? Trust me, I can eyeball a 1.5" length of foil with 5 holes in it! : As I said in a previous post, only two R's larger than 1/10W: one as the current sense R; the other as the snubber (it's REALLY easy to see an RC-D across the primary ... you don't even have to look hard! : ) If it's ticking, my money is still on a cap ... My first guess would be the current sense resistor being open and immediately shutting the controller down. But, I haven't yet traced the foils to see what else is going on. Did you get to the bottom of it yet, Don ? I'm always interested in SMPS faults as I do a lot of work with them, and any info that saves a few minutes, is extra money in the bank ... Arfa |
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