Broken DVD Player part 2

Ordering those parts wasn't quite straightforward. The diodes, capacitor and fuse were all tuppenny parts and easy to find, but the 5L0165R is now more or less obsolete.  Nobody seems to stock the DIP-8 version in the UK, and carriage from the USA or China is crippling for 1 or 2 chips, so what to do?

Time to browse the manufacturers catalogues.  After much research, it turns out that Fairchild developed an updated version of the 5L0165R - the DL0165R.  This later chip has advanced features for improved control and optional current limit.  But they changed the pinout!  Then an even newer version was developed, the FSQ0165R.  This version adds valley-switching for quasi-resonant converter technology, and another pinout change!  Er, does that help?

Well, yes it does - for new designs - as it reduces EMI and reduces stress on other switching components.  The Q0165R is easily available and cheap.  It is possible to disable the valley-switching function with some loss of efficiency, but the main issue for this repair is the changed pinout.  Maybe it could be made to fit?

The printed circuit for the part of the circuit immediately adjacent to the chip was studied carefully.  Three pin assignments have moved along by 1 pin, that is Gnd from 2 to 1, Vcc from 3 to 2 and Vfb from 4 to 3.  A new Vstart function is added to previously unused pin 5.  Here's the relevant part of the circuit:

Two related changes would also be required: the 68k resistors would need to be disconnected at point A, and the 'hot' one fed to pin 5 for the revised start function.  Pin 4 - the valley-switching sync input - can be connected to ground as the original circuit was designed without that capability.  One other thing: the replacement chip oscillator frequency would be 55kHz instead of the previous 50kHz.  As the 5L0165R frequency tolerance is quoted as +/-5kHz, this should not cause problems.

So the necessary cuts and bridges were made to the circuit board.  These are shown in the annotated photo below

WARNING: the primary side of a switched-mode power supply has lethal voltages of several hundred volts, even when switched off and unplugged.  These circuits can kill.  Do not attempt these modifications unless you are absolutely certain you know what you are doing and follow strict safety precautions.

 Some of the details are omitted to discourage you; if you are competent, implementation will be obvious.

A shiny new IC was soldered in and - it worked!  Soak testing showed no overheating, though detailed measurements were not made because of the dangers outlined above.

The player is back with the user - total cost about £2.  But this repair just isn't value-for-money because at commercial rates the time charged would pay for several new DVD players!  But it was a fun job to do!