Before you can even *THINK*of a substitute, you've got to know the operating frequency. If you know how to do so safely, measure it at the LQ1216 output (pin 5) on the working unit, under load. If you are unsure how to measure frequency safely on the primary side of a SMPSU, or don't have appropriate test equipment, scope the transformer end of one of the rectifier diodes on the secondary side. Getting the frequency seriously wrong will drastically reduce the output current, and may result in explosive failure of the MOSFET and control circuit!
You can *probably* substitute a UC384x series chip but its going to need several circuit changes including extra parts for the timing network, and either some track cuts and patch wires or a PNP current mirror to convert the opto output to pull up towards Vref rather than down towards ground, so a daughterboard is going to be essential to carry the extra parts and to wrangle the UC384x pinout to match. TI's
UCx84x datasheet is particularly helpful, especially Figure 25. Typical Application Design Example Schematic.
Unless the PSU is expensive, it probably isn't worth the effort, so measure the frequency and its Vcc voltage, and *hope* someone recognizes it from them and the partial pinout:
LQ1216 DIP-8 SMPS controller
Pin Function
---+--------
[code]
1 Vcc
2 ? (N/C)
3 Voltage Feedback (pulldown by opto)
4 Output
5 Current Sense (from MOSFET drain)
6 ? (N/C)
7 ? (N/C)
8 0V 'Gnd'