Hi,

At https://easthope.ca/RyobiScrollSawSC164VS.jpg part of the power
board from a Ryobi scroll saw is visible. A dime is there for scale.

Is the blue thing a diode? Search for C702 produced many citations;
none seeming particularly relevant.

Thanks, ... P.





--- PyGate Linux v1.5.14
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On 5/6/2026 8:13 PM, peter@easthope.ca wrote:

Hi,

At https://easthope.ca/RyobiScrollSawSC164VS.jpg part of the power
board from a Ryobi scroll saw is visible. A dime is there for scale.

Is the blue thing a diode? Search for C702 produced many citations;
none seeming particularly relevant.

Thanks, ... P.

Likely a DIAC
Ed

--- PyGate Linux v1.5.14
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

In article <10tgrsa$11ss$1@ehsjr.eternal-september.org>, ehsjr <ehsjr@verizon.net> wrote:

Likely a DIAC

Thanks Ed.

A sketch of the circuit is here. https://easthope.ca/RyobiScrollSawSC164VSboard.jpg

A search for "DIAC C702" gave these pages.

https://www.aliexpress.com/s/wiki-ssr/article/db3-c702-diode https://www.st.com/resource/en/datasheet/db3.pdf

In one of the documents, mention of a DIAC feeding the gate of a TRIAC
is consistent with the observed circuit.

In a week or two, can check Lee's Electronic Components here in
Vancouver for a replacment; a C702 or a DB3.

Meanwhile I'm curious about the circuit. R5 adjusts the voltage
delivered to the gate of the TRIAC. What do C2, R3, R4 and R6 add to
that?

Thanks, ... P.



--- PyGate Linux v1.5.14
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On 5/7/2026 2:54 PM, peter@easthope.ca wrote:

In article <10tgrsa$11ss$1@ehsjr.eternal-september.org>, ehsjr <ehsjr@verizon.net> wrote:

Likely a DIAC

Thanks Ed.

A sketch of the circuit is here. https://easthope.ca/RyobiScrollSawSC164VSboard.jpg

A search for "DIAC C702" gave these pages.

https://www.aliexpress.com/s/wiki-ssr/article/db3-c702-diode https://www.st.com/resource/en/datasheet/db3.pdf

In one of the documents, mention of a DIAC feeding the gate of a TRIAC
is consistent with the observed circuit.

In a week or two, can check Lee's Electronic Components here in
Vancouver for a replacment; a C702 or a DB3.

Meanwhile I'm curious about the circuit. R5 adjusts the voltage
delivered to the gate of the TRIAC. What do C2, R3, R4 and R6 add to
that?

Thanks, ... P.

They control the timing (what phase angle) of the trigger to the triac.
Maybe the simplest way to think of it is to picture 180 degrees of a
sine wave and consider how long the triac conducts if the trigger is
applied at 0 degrees, 1 degree, 2 degrees etc. When the trigger pulse "arrives" at the gate, the triac turns on and stays on as long as a
certain minimum current, called the "holding current" flows. When the
sine wave reaches 180 degrees there is no current so the triac turns
off. The sooner in the cycle the triac is triggered the longer it
conducts, providing input to the bridge and therefore power to the
motor, thus controlling its speed. There's a lot more that could be
said about triacs but that's a small overview.
Ed

--- PyGate Linux v1.5.14
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

In article <10tiqi5$11st$1@ehsjr.eternal-september.org>, ehsjr <ehsjr@verizon.net> wrote:

They control the timing (what phase angle) of the trigger to the triac.
Maybe the simplest way to think of it is to picture 180 degrees of a
sine wave and consider how long the triac conducts if the trigger is
applied at 0 degrees, 1 degree, 2 degrees etc. ...

Ed, thanks for the explanation. Very helpful.

My immediate challenge is to find a replacement for the C702.
From Web based documentation, DB3 is somewhat equivalent and
may substitute.

Thx, ... P.


--- PyGate Linux v1.5.14
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On 5/11/2026 1:22 PM, peter@easthope.ca wrote:

In article <10tiqi5$11st$1@ehsjr.eternal-september.org>, ehsjr <ehsjr@verizon.net> wrote:

They control the timing (what phase angle) of the trigger to the triac.
Maybe the simplest way to think of it is to picture 180 degrees of a
sine wave and consider how long the triac conducts if the trigger is
applied at 0 degrees, 1 degree, 2 degrees etc. ...

Ed, thanks for the explanation. Very helpful.

My immediate challenge is to find a replacement for the C702.
From Web based documentation, DB3 is somewhat equivalent and
may substitute.

Thx, ... P.

Good luck with the repair - my bet is that you'll succeed. :-)
That was a nice schematic you drew.
Ed

--- PyGate Linux v1.5.14
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)