EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: gkmaia on December 31, 2019, 02:54:22 am
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I got a bit stuck on this one and that is probably a stupid question... as I am implying it is a diode. But could be something else, I am not sure.
The SG1 component seems to be open and not forwarding current in any direction on my curve tracer up to a 100V.
It is part of the primary block (auto voltage) of a flyback power supply of a TDS 2002C.
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More likely to be a zener for regulation. Trace the schematic out for the part of the circuit it sits in.
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That is NOT a diode, it's a spark gap, thus the "SG1" designation. Another common name for this is a GDT (gas discharge tube).
It's there for surge suppression and won't conduct until there's a fairly high voltage across it (hundreds of volts).
It is common to find these in various forms in the primary side EMI filtering circuit of SMPS. In low-cost SMPS they are usually in the form of pointy PCB traces but in better quality SMPS are a physical component which provides a more controlled spark-over voltage and are more durable. The modern version of discrete GDT usually use white ceramic as opposed to a diode-lookalike glass package.
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It is a spark gap device as TheMG wrote
Sevice manual, no schematics
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=17&cad=rja&uact=8&ved=2ahUKEwikhM64_d7mAhXlhOAKHcixCRkQFjAQegQIBBAC&url=https%3A%2F%2Fdownload.tek.com%2Fmanual%2F077044600web.pdf&usg=AOvVaw0s9h1CGOKtt7Cm91EAQr-x (https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=17&cad=rja&uact=8&ved=2ahUKEwikhM64_d7mAhXlhOAKHcixCRkQFjAQegQIBBAC&url=https%3A%2F%2Fdownload.tek.com%2Fmanual%2F077044600web.pdf&usg=AOvVaw0s9h1CGOKtt7Cm91EAQr-x)
page 6-37 you have voltages tests points
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Spark gap, in this case basically a glass encapsulated carbon film resistor that has had a groove ground or laser cut all the way around the circumference of the resistive layer, so that it will arc over at a well defined voltage around the 2-300V mark. Only way to test them is with a current limited ( under 1mA) high voltage supply, to see if it does break down and clamp to that high voltage, but they rarely fail unless physically broken or corroded through.
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Part datasheet can be found in this thread... https://www.eevblog.com/forum/beginners/identify-component-224708/ (https://www.eevblog.com/forum/beginners/identify-component-224708/)
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Part datasheet can be found in this thread... https://www.eevblog.com/forum/beginners/identify-component-224708/ (https://www.eevblog.com/forum/beginners/identify-component-224708/)
Thanks!!!!