I have a telephone circuit (Model No. Panasonic KX-TS500MXB) which has following item between TIP and Ring. Do you have any idea what it might be? At first I thought it might be a back to back zener diode but after some testings I doubt if I am correct. enter image description here

The following item is as well unknown to me. I have searched the part number but I couldn't find any item similar to this!! enter image description here

EDIT: Here is the symbol that corresponds to first image:

Thanksenter image description here

  • \$\begingroup\$ @tuskiomi Thanks for quick reply, please check the symbol I have added to the question, This symbol makes me doubt that if this element is anything lile resistor or so. \$\endgroup\$ – Farzan Jun 23 '17 at 19:10
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    \$\begingroup\$ Is there a reference designator on the board by the symbol? This question indicates it may be a spark gap. Not sure how to interpret the colored bands, though. \$\endgroup\$ – Cheibriados Jun 23 '17 at 19:12
  • \$\begingroup\$ @tuskiomi sounds like you still have no clues. Bear in mind that saying you don't know what something is provides no help at all and begins to look like a desperate attempt to make friends or be amusing. \$\endgroup\$ – Andy aka Jun 23 '17 at 19:13
  • \$\begingroup\$ @Cheibriados Yes, there are reference designator on the board for both of them. SA1 is for the first image and D17 is for the second one. Seems Andy-aka is right about the second one. \$\endgroup\$ – Farzan Jun 23 '17 at 19:38

The first item is a spark gap device i.e. over-voltage protector. The symbol clinched it for me. I have no definite thoughts about the second picture but it might be a bridge rectifier given the + symbol on the top right pin. Modern telephones use bridges of course, usually two; one for the speech circuit and one for the ringer circuit.

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  • \$\begingroup\$ Andy, thanks for your answer. Does a spark gap fries in case of over-current as well? I am asking this because I common-grounded the board with an arduino board and out of sudden even after the board was working for a few days the spark gap fried! I want to make sure it doesn't happen again. Since Arduino working voltage is 5V I now think that the spark gap failure was due to a over-current rather than a over-voltage. Any idea? \$\endgroup\$ – Farzan Jun 23 '17 at 19:48
  • \$\begingroup\$ BTW, If spark gap is going to protect the circuit then why when I replaced it (Took the replacement item from another functional board) after it fried the board is not functioning again? \$\endgroup\$ – Farzan Jun 23 '17 at 19:54
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    \$\begingroup\$ If a protection device fails whilst "protecting" then it no longer protects and something else will fail. It's a bit like a blow out going round a corner, control becomes so erratic in the next second that another tyre is likely to blow out. \$\endgroup\$ – Andy aka Jun 23 '17 at 20:06

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