Last week I mentioned I was repairing an HP9810 programmable calculator. I've now traced the last fault to the 74H52 AND-OR gate chip on the memory timing PCB (09810-66522). Needless to say this chip is unobtainable as far as I can see. I've worked out a kuldge using a 74LS51 which works in this circuit (as only 2 sets of inputs on the 'H52 were used). I'll stick details of that at the end of this message in case anyone else ever has to do the same repair (unlikely...). But the repair is a kludge, with wires flying everywhere. So does anyone have/know where to get a 74H52 chip? -tony ------------------------------- Replacing the 74H52 IC on the memory timing PCB (09810-66522) ------------------------------------------------------------- Well, have you ever tried to get one :-) However, _on this PCB_ it can be replaced by a 74LS51, suitably wired. Remove old IC carefully, in case it's still good. Bend out all pins of a 74LS51 apart from 1, 7, 14. Put this chip in place of the old one. Solder 1, 7, 14 to the PCB. Solder wires (wire-wrap wire is ideal) as follows : PCB 2 -> IC 13, IC 12 PCB 3 -> IC 11 PCB 4 -> IC 10 PCB 5 -> IC 9 IC 8 -> IC 2, IC 3, IC 4, IC 5 PCB 8 -> IC 6 mu(26)/ -------|\ | \ +---|\ ALU(0) ----+---| >-----+ | | >----+ | | / | +---|/ | +---|/ | | +---)\ +---)\ | ) >o---- TRegSin ) >o---+---|\ +---)/ mu(25+24/)/----|\ +---)/ | | >----+ | \ | +---|/ T(0)-----------| >------+ | / mu(26)---------|/