USB Cable shield continuity
in [Design]
|
Prev: conservation of Euros
Next: Heat effect on FR4?
From: Paul E. Schoen on 11 Jun 2010 01:01 I have been having seemingly random noise problems where my PIC-based USB device will go into a USBSuspendControl state, and it requires the cable to be removed and replaced to reestablish communication. The problem usually occurs in the field where there is switching of high current and high voltage, but I was able to duplicate it to some extent by running the USB cable along an AC power line to a current source which I switched on and off. Recently I suspected that the USB cable itself might be at fault, because I had bought a batch of 100 pieces for $0.69 each (but now about $1.50) from www.CableWholesale.com, and several of these were sent to a customer who reported problems, while a previous customer with an older cable did not seem to experience this very much, and another customer replaced his cable with a longer one, and he said his unit was working OK. So, I dissected one of the new cables by removing the PVC jacket in the middle, and I found a substantial tinned copper braid shield, and an aluminized Mylar wrap under that. When I removed the shield I could see that the four USB conductors were twisted together, which is generally good for noise induced by strong magnetic fields. So far, so good. But when I measured continuity from the connector shells to the exposed shield, I got intermittent readings of about 3 to 30 ohms and sometimes an open circuit. Then I measured the continuity from shell to shell on a couple other USB cables I had been using, and I found that one showed an open circuit and the others showed intermittent. This was the case for two new cables from different sources. Yet I measured the shells of a USB cable for my Nikon digital camera (with a mini-USB on the camera end), and I got a solid connection of less than 1 ohm. I still need to do more testing and I may also purchase a high grade cable with gold plated connectors and better shielding. They are about $20. I will also have my customer check the continuity and try a better cable. Perhaps a USB 3.0 cable will work better. I removed the PVC molded cover for the male type "A" connector, and there is a metal shell that extends back and tapers to a smaller "neck" where the cable is clinched or crimped. By bending the ears on the crimp I was able to separate part of the metal housing to reveal where the shield has been folded back and exposed so that the inner surface of the housing presses against it. But it seems that the jacket of the cable is a continuous molding that fills the shell of the connector, and the crimp mechanism can only apply light force to the exposed part of the shield. So the actual connection may degrade with time as a non-conductive film may form on the metal surfaces, and mechanical flexing may further degrade the connection. Here are pictures of the cable after dissection and exposure of the crimped shield connection: http://cygnus.smart.net/~pstech/photos/USB_Cable_23.JPG http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_26a.JPG http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_27.JPG http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_28.JPG http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_29.JPG http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_30.JPG I think this is a design defect and I should be able to get a refund or credit for the unused cables. It may not be the reason for the problem but I should be able to determine that if my customers replace the cables with high performance versions and their problems are greatly reduced. Anyone else have experience with this? One member of the Microchip forums reported that he found the following with some new cables he had on hand: Poundland 1.8 m A-A(F) yellow 8 ohms Signalex 1.5 m A-A(F) white OPEN CIRCUIT! Signalex 1.5 m A-B white OPEN CIRCUIT! CPC 1.8 m A-B translucent yellow 18.5 ohms IXIOS 3 m A-A(F) translucent/silver grey gold plated connectors <0.5 ohms Paul
From: baron on 11 Jun 2010 10:48 Paul E. Schoen Inscribed thus: > I have been having seemingly random noise problems where my PIC-based > USB device will go into a USBSuspendControl state, and it requires the > cable to be removed and replaced to reestablish communication. The > problem usually occurs in the field where there is switching of high > current and high voltage, but I was able to duplicate it to some > extent by running the USB cable along an AC power line to a current > source which I switched on and off. > > Recently I suspected that the USB cable itself might be at fault, > because I had bought a batch of 100 pieces for $0.69 each (but now > about $1.50) from www.CableWholesale.com, and several of these were > sent to a customer who reported problems, while a previous customer > with an older cable did not seem to experience this very much, and > another customer replaced his cable with a longer one, and he said his > unit was working OK. > > So, I dissected one of the new cables by removing the PVC jacket in > the middle, and I found a substantial tinned copper braid shield, and > an aluminized Mylar wrap under that. When I removed the shield I could > see that the four USB conductors were twisted together, which is > generally good for noise induced by strong magnetic fields. So far, so > good. > > But when I measured continuity from the connector shells to the > exposed shield, I got intermittent readings of about 3 to 30 ohms and > sometimes an open circuit. Then I measured the continuity from shell > to shell on a couple other USB cables I had been using, and I found > that one showed an open circuit and the others showed intermittent. > This was the case for two new cables from different sources. Yet I > measured the shells of a USB cable for my Nikon digital camera (with a > mini-USB on the camera end), and I got a solid connection of less than > 1 ohm. > > I still need to do more testing and I may also purchase a high grade > cable with gold plated connectors and better shielding. They are about > $20. I will also have my customer check the continuity and try a > better cable. Perhaps a USB 3.0 cable will work better. > > I removed the PVC molded cover for the male type "A" connector, and > there is a metal shell that extends back and tapers to a smaller > "neck" where the cable is clinched or crimped. By bending the ears on > the crimp I was able to separate part of the metal housing to reveal > where the shield has been folded back and exposed so that the inner > surface of the housing presses against it. But it seems that the > jacket of the cable is a continuous molding that fills the shell of > the connector, and the crimp mechanism can only apply light force to > the exposed part of the shield. So the actual connection may degrade > with time as a non-conductive film may form on the metal surfaces, and > mechanical flexing may further degrade the connection. > > Here are pictures of the cable after dissection and exposure of the > crimped shield connection: > > http://cygnus.smart.net/~pstech/photos/USB_Cable_23.JPG > http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_26a.JPG > http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_27.JPG > http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_28.JPG > http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_29.JPG > http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_30.JPG > > I think this is a design defect and I should be able to get a refund > or credit for the unused cables. It may not be the reason for the > problem but I should be able to determine that if my customers replace > the cables with high performance versions and their problems are > greatly reduced. > > Anyone else have experience with this? One member of the Microchip > forums reported that he found the following with some new cables he > had on hand: > > Poundland 1.8 m A-A(F) yellow 8 ohms > Signalex 1.5 m A-A(F) white OPEN CIRCUIT! > Signalex 1.5 m A-B white OPEN CIRCUIT! > CPC 1.8 m A-B translucent yellow 18.5 ohms > IXIOS 3 m A-A(F) translucent/silver grey gold plated > connectors <0.5 ohms > > Paul Hi Paul, The figures above don't cause any surprise at all ! Part of the problem with USB cables is that the shield is not needed for the cable to work but is vital to prevent interference effecting the signals on the cable and by the same token preventing the cable radiating and causing interference to other things. I built a test rig that checks continuity of all four wires and the screen. I used a 100ma test current from a 12 volt source. I found that most of the cables tested showed 10 ohms or more between the ends of the shells and I found a number with varying resistance on the individual conductors of a similar order. I also found that some receptacles showed varying degrees of contact resistance with increasing usage. The type "A" being the most affected, type "B" being more robust. -- Best Regards: Baron.
From: Paul E. Schoen on 11 Jun 2010 12:41 "baron" <baron.nospam(a)linuxmaniac.nospam.net> wrote in message news:hutibu$vh4$1(a)news.eternal-september.org... > Paul E. Schoen Inscribed thus: > >> I have been having seemingly random noise problems where my PIC-based >> USB device will go into a USBSuspendControl state, and it requires the >> cable to be removed and replaced to reestablish communication. The >> problem usually occurs in the field where there is switching of high >> current and high voltage, but I was able to duplicate it to some >> extent by running the USB cable along an AC power line to a current >> source which I switched on and off. >> >> Recently I suspected that the USB cable itself might be at fault, >> because I had bought a batch of 100 pieces for $0.69 each (but now >> about $1.50) from www.CableWholesale.com, and several of these were >> sent to a customer who reported problems, while a previous customer >> with an older cable did not seem to experience this very much, and >> another customer replaced his cable with a longer one, and he said his >> unit was working OK. >> >> So, I dissected one of the new cables by removing the PVC jacket in >> the middle, and I found a substantial tinned copper braid shield, and >> an aluminized Mylar wrap under that. When I removed the shield I could >> see that the four USB conductors were twisted together, which is >> generally good for noise induced by strong magnetic fields. So far, so >> good. >> >> But when I measured continuity from the connector shells to the >> exposed shield, I got intermittent readings of about 3 to 30 ohms and >> sometimes an open circuit. Then I measured the continuity from shell >> to shell on a couple other USB cables I had been using, and I found >> that one showed an open circuit and the others showed intermittent. >> This was the case for two new cables from different sources. Yet I >> measured the shells of a USB cable for my Nikon digital camera (with a >> mini-USB on the camera end), and I got a solid connection of less than >> 1 ohm. >> >> I still need to do more testing and I may also purchase a high grade >> cable with gold plated connectors and better shielding. They are about >> $20. I will also have my customer check the continuity and try a >> better cable. Perhaps a USB 3.0 cable will work better. >> >> I removed the PVC molded cover for the male type "A" connector, and >> there is a metal shell that extends back and tapers to a smaller >> "neck" where the cable is clinched or crimped. By bending the ears on >> the crimp I was able to separate part of the metal housing to reveal >> where the shield has been folded back and exposed so that the inner >> surface of the housing presses against it. But it seems that the >> jacket of the cable is a continuous molding that fills the shell of >> the connector, and the crimp mechanism can only apply light force to >> the exposed part of the shield. So the actual connection may degrade >> with time as a non-conductive film may form on the metal surfaces, and >> mechanical flexing may further degrade the connection. >> >> Here are pictures of the cable after dissection and exposure of the >> crimped shield connection: >> >> http://cygnus.smart.net/~pstech/photos/USB_Cable_23.JPG >> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_26a.JPG >> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_27.JPG >> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_28.JPG >> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_29.JPG >> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_30.JPG >> >> I think this is a design defect and I should be able to get a refund >> or credit for the unused cables. It may not be the reason for the >> problem but I should be able to determine that if my customers replace >> the cables with high performance versions and their problems are >> greatly reduced. >> >> Anyone else have experience with this? One member of the Microchip >> forums reported that he found the following with some new cables he >> had on hand: >> >> Poundland 1.8 m A-A(F) yellow 8 ohms >> Signalex 1.5 m A-A(F) white OPEN CIRCUIT! >> Signalex 1.5 m A-B white OPEN CIRCUIT! >> CPC 1.8 m A-B translucent yellow 18.5 ohms >> IXIOS 3 m A-A(F) translucent/silver grey gold plated >> connectors <0.5 ohms >> >> Paul > > Hi Paul, > > The figures above don't cause any surprise at all ! > > Part of the problem with USB cables is that the shield is not needed for > the cable to work but is vital to prevent interference effecting the > signals on the cable and by the same token preventing the cable > radiating and causing interference to other things. > > I built a test rig that checks continuity of all four wires and the > screen. I used a 100ma test current from a 12 volt source. I found > that most of the cables tested showed 10 ohms or more between the ends > of the shells and I found a number with varying resistance on the > individual conductors of a similar order. > > I also found that some receptacles showed varying degrees of contact > resistance with increasing usage. The type "A" being the most > affected, type "B" being more robust. The overall resistance of the four conductors should be much more consistent if they are formed with a proper metal-to-metal crimp. Solder or tack weld would be even better but would be very costly. Here is the USB spec: Universal Serial Bus Specification 6.6.3 Electrical Characteristics ... The DC resistance from plug shell to plug shell (or end of integrated cable) must be less than 0.6 ohms. http://alsa.cybermirror.org/manuals/usb/usbcableecn_final.pdf The cables may work, but they do not meet specification. Your test at 100 mA is better than a simple ohmmeter check, but lower voltage might show poor connections better. I'm wondering if I could charge up a large capacitor and then discharge it through the cable shield so that a spot weld might occur at the junction of shield and shell. But it probably would not be very reliable long-term under normal use. Another "fix" might be to expose the shield near the connector and add a jumper to the shell, but that is ugly, time-intensive, and just plain wrong except to test if shield ground integrity improves the noise problem. I found some good deals on gold plated USB cables at www.monoprice.com and www.TriangleCables.com. Even if the same crimp was used, the gold plating might reduce the chance for oxides or other coatings to form at the junction. But the shield braid would also need plating. The manufacturer might be able to apply a drop of conductive paste at the junction point that would provide a decent connection and also exclude moisture and other contaminents. But there may be no reliable way to fix these cables as they are. Paul
From: IanM on 11 Jun 2010 13:05 Paul E. Schoen wrote: > > "baron" <baron.nospam(a)linuxmaniac.nospam.net> wrote in message > news:hutibu$vh4$1(a)news.eternal-september.org... >> Paul E. Schoen Inscribed thus: >> >>> I have been having seemingly random noise problems where my PIC-based >>> USB device will go into a USBSuspendControl state, and it requires the >>> cable to be removed and replaced to reestablish communication. The >>> problem usually occurs in the field where there is switching of high >>> current and high voltage, but I was able to duplicate it to some >>> extent by running the USB cable along an AC power line to a current >>> source which I switched on and off. >>> >>> Recently I suspected that the USB cable itself might be at fault, >>> because I had bought a batch of 100 pieces for $0.69 each (but now >>> about $1.50) from www.CableWholesale.com, and several of these were >>> sent to a customer who reported problems, while a previous customer >>> with an older cable did not seem to experience this very much, and >>> another customer replaced his cable with a longer one, and he said his >>> unit was working OK. >>> >>> So, I dissected one of the new cables by removing the PVC jacket in >>> the middle, and I found a substantial tinned copper braid shield, and >>> an aluminized Mylar wrap under that. When I removed the shield I could >>> see that the four USB conductors were twisted together, which is >>> generally good for noise induced by strong magnetic fields. So far, so >>> good. >>> >>> But when I measured continuity from the connector shells to the >>> exposed shield, I got intermittent readings of about 3 to 30 ohms and >>> sometimes an open circuit. Then I measured the continuity from shell >>> to shell on a couple other USB cables I had been using, and I found >>> that one showed an open circuit and the others showed intermittent. >>> This was the case for two new cables from different sources. Yet I >>> measured the shells of a USB cable for my Nikon digital camera (with a >>> mini-USB on the camera end), and I got a solid connection of less than >>> 1 ohm. >>> >>> I still need to do more testing and I may also purchase a high grade >>> cable with gold plated connectors and better shielding. They are about >>> $20. I will also have my customer check the continuity and try a >>> better cable. Perhaps a USB 3.0 cable will work better. >>> >>> I removed the PVC molded cover for the male type "A" connector, and >>> there is a metal shell that extends back and tapers to a smaller >>> "neck" where the cable is clinched or crimped. By bending the ears on >>> the crimp I was able to separate part of the metal housing to reveal >>> where the shield has been folded back and exposed so that the inner >>> surface of the housing presses against it. But it seems that the >>> jacket of the cable is a continuous molding that fills the shell of >>> the connector, and the crimp mechanism can only apply light force to >>> the exposed part of the shield. So the actual connection may degrade >>> with time as a non-conductive film may form on the metal surfaces, and >>> mechanical flexing may further degrade the connection. >>> >>> Here are pictures of the cable after dissection and exposure of the >>> crimped shield connection: >>> >>> http://cygnus.smart.net/~pstech/photos/USB_Cable_23.JPG >>> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_26a.JPG >>> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_27.JPG >>> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_28.JPG >>> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_29.JPG >>> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_30.JPG >>> >>> I think this is a design defect and I should be able to get a refund >>> or credit for the unused cables. It may not be the reason for the >>> problem but I should be able to determine that if my customers replace >>> the cables with high performance versions and their problems are >>> greatly reduced. >>> >>> Anyone else have experience with this? One member of the Microchip >>> forums reported that he found the following with some new cables he >>> had on hand: >>> >>> Poundland 1.8 m A-A(F) yellow 8 ohms >>> Signalex 1.5 m A-A(F) white OPEN CIRCUIT! >>> Signalex 1.5 m A-B white OPEN CIRCUIT! >>> CPC 1.8 m A-B translucent yellow 18.5 ohms >>> IXIOS 3 m A-A(F) translucent/silver grey gold plated >>> connectors <0.5 ohms >>> >>> Paul >> >> Hi Paul, >> >> The figures above don't cause any surprise at all ! >> >> Part of the problem with USB cables is that the shield is not needed for >> the cable to work but is vital to prevent interference effecting the >> signals on the cable and by the same token preventing the cable >> radiating and causing interference to other things. >> >> I built a test rig that checks continuity of all four wires and the >> screen. I used a 100ma test current from a 12 volt source. I found >> that most of the cables tested showed 10 ohms or more between the ends >> of the shells and I found a number with varying resistance on the >> individual conductors of a similar order. >> >> I also found that some receptacles showed varying degrees of contact >> resistance with increasing usage. The type "A" being the most >> affected, type "B" being more robust. > > The overall resistance of the four conductors should be much more > consistent if they are formed with a proper metal-to-metal crimp. Solder > or tack weld would be even better but would be very costly. Here is the > USB spec: > > Universal Serial Bus Specification > > 6.6.3 Electrical Characteristics > ... > The DC resistance from plug shell to plug shell (or end of integrated > cable) must be less than 0.6 ohms. > > http://alsa.cybermirror.org/manuals/usb/usbcableecn_final.pdf > > The cables may work, but they do not meet specification. Your test at > 100 mA is better than a simple ohmmeter check, but lower voltage might > show poor connections better. > > I'm wondering if I could charge up a large capacitor and then discharge > it through the cable shield so that a spot weld might occur at the > junction of shield and shell. But it probably would not be very reliable > long-term under normal use. > > Another "fix" might be to expose the shield near the connector and add a > jumper to the shell, but that is ugly, time-intensive, and just plain > wrong except to test if shield ground integrity improves the noise problem. > > I found some good deals on gold plated USB cables at www.monoprice.com > and www.TriangleCables.com. Even if the same crimp was used, the gold > plating might reduce the chance for oxides or other coatings to form at > the junction. But the shield braid would also need plating. > > The manufacturer might be able to apply a drop of conductive paste at > the junction point that would provide a decent connection and also > exclude moisture and other contaminents. But there may be no reliable > way to fix these cables as they are. > > Paul If the braid is pigtailed and crimped into the housing separately from the overall strain relief crimp there would be no problem. Unfortunately that would require an extra step on the assembly line. Sturgeon's Law applies . . . . -- Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED) ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- & [dot]=. *Warning* HTML & >32K emails --> NUL:
From: Baron on 11 Jun 2010 17:05
Paul E. Schoen Inscribed thus: > > "baron" <baron.nospam(a)linuxmaniac.nospam.net> wrote in message > news:hutibu$vh4$1(a)news.eternal-september.org... >> Paul E. Schoen Inscribed thus: >> >>> I have been having seemingly random noise problems where my >>> PIC-based USB device will go into a USBSuspendControl state, and it >>> requires the cable to be removed and replaced to reestablish >>> communication. The problem usually occurs in the field where there >>> is switching of high current and high voltage, but I was able to >>> duplicate it to some extent by running the USB cable along an AC >>> power line to a current source which I switched on and off. >>> >>> Recently I suspected that the USB cable itself might be at fault, >>> because I had bought a batch of 100 pieces for $0.69 each (but now >>> about $1.50) from www.CableWholesale.com, and several of these were >>> sent to a customer who reported problems, while a previous customer >>> with an older cable did not seem to experience this very much, and >>> another customer replaced his cable with a longer one, and he said >>> his unit was working OK. >>> >>> So, I dissected one of the new cables by removing the PVC jacket in >>> the middle, and I found a substantial tinned copper braid shield, >>> and an aluminized Mylar wrap under that. When I removed the shield I >>> could see that the four USB conductors were twisted together, which >>> is generally good for noise induced by strong magnetic fields. So >>> far, so good. >>> >>> But when I measured continuity from the connector shells to the >>> exposed shield, I got intermittent readings of about 3 to 30 ohms >>> and sometimes an open circuit. Then I measured the continuity from >>> shell to shell on a couple other USB cables I had been using, and I >>> found that one showed an open circuit and the others showed >>> intermittent. This was the case for two new cables from different >>> sources. Yet I measured the shells of a USB cable for my Nikon >>> digital camera (with a mini-USB on the camera end), and I got a >>> solid connection of less than 1 ohm. >>> >>> I still need to do more testing and I may also purchase a high grade >>> cable with gold plated connectors and better shielding. They are >>> about $20. I will also have my customer check the continuity and try >>> a better cable. Perhaps a USB 3.0 cable will work better. >>> >>> I removed the PVC molded cover for the male type "A" connector, and >>> there is a metal shell that extends back and tapers to a smaller >>> "neck" where the cable is clinched or crimped. By bending the ears >>> on the crimp I was able to separate part of the metal housing to >>> reveal where the shield has been folded back and exposed so that the >>> inner surface of the housing presses against it. But it seems that >>> the jacket of the cable is a continuous molding that fills the shell >>> of the connector, and the crimp mechanism can only apply light force >>> to the exposed part of the shield. So the actual connection may >>> degrade with time as a non-conductive film may form on the metal >>> surfaces, and mechanical flexing may further degrade the connection. >>> >>> Here are pictures of the cable after dissection and exposure of the >>> crimped shield connection: >>> >>> http://cygnus.smart.net/~pstech/photos/USB_Cable_23.JPG >>> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_26a.JPG >>> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_27.JPG >>> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_28.JPG >>> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_29.JPG >>> http://cygnus.smart.net/~pstech/photos/USB_Cable_Conn-A_30.JPG >>> >>> I think this is a design defect and I should be able to get a refund >>> or credit for the unused cables. It may not be the reason for the >>> problem but I should be able to determine that if my customers >>> replace the cables with high performance versions and their problems >>> are greatly reduced. >>> >>> Anyone else have experience with this? One member of the Microchip >>> forums reported that he found the following with some new cables he >>> had on hand: >>> >>> Poundland 1.8 m A-A(F) yellow 8 ohms >>> Signalex 1.5 m A-A(F) white OPEN CIRCUIT! >>> Signalex 1.5 m A-B white OPEN CIRCUIT! >>> CPC 1.8 m A-B translucent yellow 18.5 ohms >>> IXIOS 3 m A-A(F) translucent/silver grey gold plated >>> connectors <0.5 ohms >>> >>> Paul >> >> Hi Paul, >> >> The figures above don't cause any surprise at all ! >> >> Part of the problem with USB cables is that the shield is not needed >> for the cable to work but is vital to prevent interference effecting >> the signals on the cable and by the same token preventing the cable >> radiating and causing interference to other things. >> >> I built a test rig that checks continuity of all four wires and the >> screen. I used a 100ma test current from a 12 volt source. I found >> that most of the cables tested showed 10 ohms or more between the >> ends of the shells and I found a number with varying resistance on >> the individual conductors of a similar order. >> >> I also found that some receptacles showed varying degrees of contact >> resistance with increasing usage. The type "A" being the most >> affected, type "B" being more robust. > > The overall resistance of the four conductors should be much more > consistent if they are formed with a proper metal-to-metal crimp. > Solder or tack weld would be even better but would be very costly. > Here is the USB spec: > > Universal Serial Bus Specification > > 6.6.3 Electrical Characteristics > ... > The DC resistance from plug shell to plug shell (or end of > integrated cable) must be less than 0.6 ohms. Grief ! I never saw one less than an ohm. > http://alsa.cybermirror.org/manuals/usb/usbcableecn_final.pdf > > The cables may work, but they do not meet specification. Your test at > 100 mA is better than a simple ohmmeter check, but lower voltage might > show poor connections better. I measured the voltage drop across the cable. (1.5mt nominal length) > I'm wondering if I could charge up a large capacitor and then > discharge it through the cable shield so that a spot weld might occur > at the junction of shield and shell. But it probably would not be very > reliable long-term under normal use. You might find that it just blows the bad joint open. > Another "fix" might be to expose the shield near the connector and add > a jumper to the shell, but that is ugly, time-intensive, and just > plain wrong except to test if shield ground integrity improves the > noise problem. > > I found some good deals on gold plated USB cables at www.monoprice.com > and www.TriangleCables.com. Even if the same crimp was used, the gold > plating might reduce the chance for oxides or other coatings to form > at the junction. But the shield braid would also need plating. > > The manufacturer might be able to apply a drop of conductive paste at > the junction point that would provide a decent connection and also > exclude moisture and other contaminents. But there may be no reliable > way to fix these cables as they are. > > Paul I agree, they can't be fixed. All the cables that I built the tester for were of doubtful far east origin. The distributer had a financial agreement with what ever supplier, because the cables that were rejected didn't go back to the east. -- Best Regards: Baron. |