The protective zener diode at 31V is broken
Posted: Mon Feb 17, 2025 3:40 am
(It is in the frame scan power supply circuit).The reason for its failure may be
an increase in voltage at the output of the power supply due to a periodic break in the zener diode in
the optocoupler control circuit.
Balance adjustment on Funai-MK10 can only be done with a remote control with teletext.
FUNAI-2000-MK7 periodically loses frame scanning. Does not depend on time,
can happen three minutes after switching on, can happen after 30 minutes. When a horizontal
strip appears, the frame microcircuit gets very hot, if you do not switch it off, the microcircuit flies out.
This complicates troubleshooting. The reason is capacitor C238.
FUNAI-2100 A MK8 Malfunction: increased brightness, sometimes even white screen,
the lines of the return path of the rays are visible.
Reason: reduced voltage (+ 200 v) of the power australia telegram data supply of video amplifiers due to
a defective capacitor C652 (4.7 x 100 v) of the volt-boost. This malfunction is typical for
100% of TVs of this model, since the other end of the TDKS winding for powering C652 is connected not to (+ 112
v) of the horizontal scanning power supply, but to the "circuit ground".In this regard, in the "STANDBY" mode, the C652
is recharged in reverse polarity through R652, R285, R286 and degrades over time.
Solution: C652 should be replaced with 1 mF x 250 v.
Cut off the pad with the negative terminal of the capacitor from the power conductor
(+ 112 v) with a scalpel and solder it to the "circuit ground" with a piece of wire or simply bend
the long negative terminal of the capacitor and solder it to the adjacent
pad of the "circuit ground".
FUNAI MK-8 . The power supply does not start. The fuse and all transistors are intact.
No short circuit in secondary circuits was detected. Detailed check showed that
there is no bias on the base of output transistor Q601 type 2SD734 (25V, 0.7A, 0.6W 250Mhz).
Bias is supplied via 4 series-connected resistors R620, R626, R627, R628, with a resistance of 56k each.
an increase in voltage at the output of the power supply due to a periodic break in the zener diode in
the optocoupler control circuit.
Balance adjustment on Funai-MK10 can only be done with a remote control with teletext.
FUNAI-2000-MK7 periodically loses frame scanning. Does not depend on time,
can happen three minutes after switching on, can happen after 30 minutes. When a horizontal
strip appears, the frame microcircuit gets very hot, if you do not switch it off, the microcircuit flies out.
This complicates troubleshooting. The reason is capacitor C238.
FUNAI-2100 A MK8 Malfunction: increased brightness, sometimes even white screen,
the lines of the return path of the rays are visible.
Reason: reduced voltage (+ 200 v) of the power australia telegram data supply of video amplifiers due to
a defective capacitor C652 (4.7 x 100 v) of the volt-boost. This malfunction is typical for
100% of TVs of this model, since the other end of the TDKS winding for powering C652 is connected not to (+ 112
v) of the horizontal scanning power supply, but to the "circuit ground".In this regard, in the "STANDBY" mode, the C652
is recharged in reverse polarity through R652, R285, R286 and degrades over time.
Solution: C652 should be replaced with 1 mF x 250 v.
Cut off the pad with the negative terminal of the capacitor from the power conductor
(+ 112 v) with a scalpel and solder it to the "circuit ground" with a piece of wire or simply bend
the long negative terminal of the capacitor and solder it to the adjacent
pad of the "circuit ground".
FUNAI MK-8 . The power supply does not start. The fuse and all transistors are intact.
No short circuit in secondary circuits was detected. Detailed check showed that
there is no bias on the base of output transistor Q601 type 2SD734 (25V, 0.7A, 0.6W 250Mhz).
Bias is supplied via 4 series-connected resistors R620, R626, R627, R628, with a resistance of 56k each.