Product specifications

DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 36 of 80
CRT PWB
There are two types of CRT PWB fitted to this chassis. One is for use with the 66cm and 76cm versions of this
chassis and the other is for the 56FW53H only. The major difference is that the 56cm model does not have a
scan velocity modulator or picture rotation circuits on this PWB. This means that it is physically smaller than the
other models.
Note that the CDA IC, IC1801, can be one of three types – see note in IC Identification section.
Figure 33: 66cm and 76cm CRT PWB
Figure 34: 56FW53H CRT PWB
Faults on the CRT PWB
It is possible for the grey scale to wonder, picture brightness to ramp up or down. If the G2 is set correctly,
IC1801 is suspect. Check by substitution.
If the reference voltage on pin 2 of IC1801 is about 10V, picture smearing will occur. This is normally on the red
channel. If the voltage is below 9V the picture will blank. In both cases, Q912 or its associated components can
be responsible. This transistor can get hot during operation (especially on the GF models due to more current
being drawn through the device). If you suspect that the transistor may fail due to its temperature being too
high it is permissible to fit a 68Ω, 0.5W resistor between the collector and emitter of Q912. It is easier to fit
this resistor to the print side of the PWB.
Sharp Electronics (UK) Limited - May 2003
Revision 3