Surge Protection Relay - Toshiba TP43H60 Service Training

Surge Protection Relay

Figure 4 shows the surge protection operation. To
prolong the life of the power supply, a surge cir-
cuit reduces current through the main power sup-
ply at startup. When the television is OFF, relays
SR81 and SR82 are open. At turn-on, SR81
closes and the switching power supply begins to
operate. During this time, the power supply draws
a large amount of current. To reduce the current,
the ground path for bridge rectifier D801 is
through resistor R810. Once the power supply
becomes fully operational and produces output
voltages, one of these voltages is applied to the
base of transistor Q846. This voltage turns Q846
ON and allows current to flow through the coil of
SR82. SR82's switch closes and creates a direct
ground path for D801 by bypassing R810. SR82
remains closed during normal operation.
Main Power Supply
Relay
SR81
D801
R809
R810
Figure 4
Surge Protect
Troubleshooting Tip:
R810 is a fusible resistor. If SR82 does not close
after the power supply is fully operational, R810 even-
tually opens and prevents the power supply from op-
erating. Whenever troubleshooting the power sup-
ply, check R810 first. If R810 is open, replace it,
using Toshiba part number 24007061, and look for
cold solder joints around Q846 and R846.
Q801
and
T862
R846
Q846
SR82
6
125V
12V