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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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SMPS wall wart failure.
"N_Cook" wrote in message ... On 07/06/2015 04:41, David Farber wrote: I have a Netgear cable modem. It is powered by a Jentec Technology AF1205-B power adapter. The adapter failed and I replaced it with another adapter but of course I was curious what the fault was. I opened up the case and found a bad (bulging) 1,000uF 10V filter cap. I did some other circuit tests to make sure there were no shorts because I was getting extremely low ESR readings (less than 0.1 ohms) around the bad cap, Eventually I found an SMD zener diode that was shorted. There are no identifying marks on the diode other than its color which is the standard looking orange. I am fairly sure it's a zener because the pc board has it marked as ZD-2. Its location in the circuit is in parallel with the 5 volt power supply diode that comes off of the secondary of the switching transformer. The power diode has two sets of numbers. The top row is marked 540 (perhaps an SB540?) on the bottom row is marked 849. That diode is ok. Only the zener is shorted. I was wondering if there was some ballpark zener voltage that I could use to replace the old one. It's always good to have a spare 5V supply. Thanks for your replies. Could it be a VTS, ie designed to go short circuit in overvoltage situation? Perhaps the ovelay component character set does not allow for VTS . I had to look that up. You mean TVS. Gareth. |
#2
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SMPS wall wart failure.
On 07/06/2015 09:53, Gareth Magennis wrote:
"N_Cook" wrote in message ... On 07/06/2015 04:41, David Farber wrote: I have a Netgear cable modem. It is powered by a Jentec Technology AF1205-B power adapter. The adapter failed and I replaced it with another adapter but of course I was curious what the fault was. I opened up the case and found a bad (bulging) 1,000uF 10V filter cap. I did some other circuit tests to make sure there were no shorts because I was getting extremely low ESR readings (less than 0.1 ohms) around the bad cap, Eventually I found an SMD zener diode that was shorted. There are no identifying marks on the diode other than its color which is the standard looking orange. I am fairly sure it's a zener because the pc board has it marked as ZD-2. Its location in the circuit is in parallel with the 5 volt power supply diode that comes off of the secondary of the switching transformer. The power diode has two sets of numbers. The top row is marked 540 (perhaps an SB540?) on the bottom row is marked 849. That diode is ok. Only the zener is shorted. I was wondering if there was some ballpark zener voltage that I could use to replace the old one. It's always good to have a spare 5V supply. Thanks for your replies. Could it be a VTS, ie designed to go short circuit in overvoltage situation? Perhaps the ovelay component character set does not allow for VTS . I had to look that up. You mean TVS. Gareth. Brain-fart, I end up typing VTS a lot in another subject area of marine flooding issues, standing for (Southampton) Vessel Traffic Services, and also Voltage Transient sounds more appropriate than Transient Voltage |
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