Toshiba ESTUDIO170F, Service Manual

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e-STUDIO170F Circuit Description January 2005 © TOSHIBA TEC
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7.4.6 Hook Detect Circuit (US/CA models and SG/HK models only)
Fig.7-48
The hook detect circuit consists of the hook switch (HS1) installed on the TEL PBA, ASIC (I/O port:
IC38) on the Main PBA, and other peripheral devices to detect the hook status of the handset.
The hook detect circuit is provided on the US/CA models and SG/HK models only.
When the handset is replaced, the hook switch is pushed down by the handset. This causes the HOOK
signal to go HIGH and input to the ASIC to detect that the handset is replaced.
The hook status of the external telephone is detected by detecting current flowing through the line by
the line current detection circuit when the handset is lifted.
Signal Name Type Active Description Destination
Hook I H Hook detect signal ASIC
HOOK
21
CN8
J2
1
2
1
2
1
2
21 38
NCU PBA Main PBA
IC38
ASIC
(I/O port)
SG
CN9
CN16
+5VPS
R74
TEL PBA
Cradle
HS1
Modular jack