FYI, most Canadian autoparts stores are selling the boards (89-95) for nearly $100 now, as they are not a common item. 88's and some 89's had the old style "pulse" motor, has a round cover instead.
GM had cheap solder, and the joints cracked. Easiest way to dianose this problem; next time they quit working, pop the hood and give the board cover a good smack with your hand, they start right up again and quit again when ever they want.
I had 8 cracked solder joints on the board, first time I removed it, I only soldered the main one (Cavalry has highlighted) and had to do it again. Look real close at every joint.
REMOVE THE OLD SOLDER!!! Don't just gob on top, or it will crack underneath the new solder!
Easy fix, takes no more than 10 min to solder the joints. Save your money for a box of beer.
92 k1500, 305TBI; Ultimate TBI mods, K&N, 700R4; B&M shift kit, Posi-lok, 32x11.50 BFG A/T's, 15x8 AR767's. Barely cranked and blocked.