Replacing Transistor Z330 - Philips PM 5775 Manual

'. REPLACING TRANSISTOR Z330
Between transistor Z330 and the printed wiring board a beryllium oxide (BeO)
heat sink disc is mounted.
To improve the thermal conductivity of this disc, a special silicone heat sink
compound (Midland Silicones Ltd., Type MS 2623) should be applied at both
sides of the disc.
Note 1: Beryllium oxide dust is dangerous to inhale. Do not grind the discs.
Note 2: The silicone compound should not be applied at soldering points or the
transistor leads since this make soldering impossible.
Proceed as follows:
— Remove the faulty transistor. Clean the old BeO heat sink disc and, if necessary,
the printed wiring board with isopropyl alcohol.
— Mount the disc on the leads of the new transistor and hold it between your
thumb and forefinger as shown in Fig. VIII-6a.
Apply a thin coating of the silicone compound on the transistor bottom by
means of a piece of wire which is flattened in one end. Do not overdose.
— Press the disc firmly against the transistor and apply a thin coating of the silicone
compound on the heat sink disc (Fig. VHI-6b).
— Mount the transistor tight to the printed wiring board (Fig. VII-6c). Ensure that
- the soldering is proper by bending the transistor slightly from side to side. An
overdose of the silicone compound may cause bad soldering.
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Fig. VII-6. Applying of the silicone compound