PK87.6 Remove the EPROM and put aside, it is needed once more for testing. Using a sharp knife cut the track on the underside going to pins 1 and 2 of U 8 (74LS139) and put in links on the underside between pin 1 of U 8 and adjacent ground track and between pin 2 of U 8 and the adjacent ground track. This alters the address decoding to the RAM in U 3 to A 15 only. Cut out out and desolder the pins of U 3 and U 4, the 8K RAMs. It is better to destroy the ICs than the printed circiut board !!!. Cut the thick track on the underside of the board going to pin 26 of U 3. Solder the 32K RAM in place of U 3 or solder in a good quality 28 pin IC socket (e.g. Turned pin). Link pin 26 of U 3 (RAM) to pin 26 of U 2 (EPROM socket) and link pin 1 of U 3 (RAM) to pin 27 of U 2 (EPROM socket). This adds the two extra address lines needed by the bigger RAM. Now insert the 32K RAM if a socket was used. Replace the PK-87 EPROM in its socket and check the board carefully for any shorts, bent pins or solder spldo link them up as below:- EXT MODEM 5 pin DIN 25 D connector 1 16 TX 4 o____ / _____ \ / / ___ ==\ O [ [ [ / \\ [[ [ [ [ [ O= \======== [ [ \ \ +--------------- FIG 1 o 1 U 5 8530A continued in file pk87.3 Downloaded From P-80 International Information Systems 304-744-2253