Product specifications
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 23 of 80
Faults in the Power Supply
High HT
In some cases the HT can rise to over 200V, this can cause damage to other parts of the circuitry. This is
normally caused by failure of IC705 - the power supply voltage regulation feedback opto coupler. The device is
easily damaged by excessive heat while soldering, so remember to keep your soldering iron turned down to 250
o
C
or below, and not to solder for more than 10 seconds on each leg. If these conditions are not met the
transparent barrier between the LED and opto transistor will be damaged. Note that sometimes the set will
work for several weeks or months before failing if the opto has been damaged during fitting.
To alleviate damage to other parts of the circuitry when the HT rises, an avalanche diode was fitted across the
main HT smoothing capacitor (C720) from late 1999 production. This device has a rated maximum voltage of
170V, and will go short circuit if this voltage is reached. If the avalanche diode was not fitted, it is worthwhile
to check the following components for damage before turning the set on. Note that this diode must be fitted to
all chassis (part number RH-EX0875BMZZ).
Reference Function Part Number Comment
Q601 Horizontal output transistor RH-TX0192BMZZ Leaky or short circuit
IC301/2 Audio output IC’s VHITDA7480/-1 Short circuit. Also check supply feed chokes
IC1801 CDA IC on CRT base PWB See previous list Short circuit. Check pin 5 to ground (<500Ω)
C720 HT reservoir capacitor RC-EZ0258CEZZ Physically damaged
IC1301 Centre channel amplifier VHITDA7480/-1 Short circuit. Located on centre speaker PWB
Q5407 Scan velocity modulator transistor VS2SA1837//-1 CRT PWB – short or open circuit
Q5408 Scan velocity modulator transistor VS2SC4793//-1 CRT PWB – short or open circuit
L315/6 IC302 feed chokes VP-CF3R3K0000 Open circuit
L350/1 IC301 feed chokes VP-CF3R3K0000 Open circuit
Figure 17: Location of D735 (note the
use of hot melt glue to prevent the diode
from shorting out to the tracking)
Sharp Electronics (UK) Limited - May 2003
Revision 3
Figure 18: Location of Audio Stage
components (Main PWB)