To test, connect pin 14 to +5, pin-7 to ground and pin 8 is the output. Pin 1 is no connect.
tgerbic, ok, I think I get this now. There are only 4 actual pins, but their positions are mapped onto a 14 pin DIL package? So far corners would be 1, 7, 8 and 14 as indicated? You are correct that pin 7 is connected to ground. It isn't very visible but a continuity test confirms it.
So there is a very easy albeit brutal sounding way of dealing with removing DIL type chips:
I tried the de-soldering gun and solder sucker but this only removed solder from the top of the joint leaving the hole clogged. Similar problem with the IC pins. From one side the hole looked clean but the other side was still firmly soldered in place. Basically there is no chance of removing any DIL device from this board without a specialised DIL de-soldering tool or snipping pins so removal is going to be destructive and any replacement will have to go into a socket. With the crystal, the problem is that there is no access to the pins so the only way I could test was in situ by cutting the output pin track and soldering 3 short wires to the pins in question. Unfortunately this resulted in no output from the crystal.
My copy of the manual has U128 and U230 as 74S122 (not LS122), my memory says that most LS devices are rated to around 40MHz which is why I suggested HCT as a possible alternative.
Roger is quite correct. The ICs are 74S112. Earlier I had mistakenly stated 74LS112 but I had mis-read the diagram. Using 74HCT112's sounds like a good idea
Incidentally, why are the two caps on the 5V rail such specific values? They are marked Sprague 637D 540¦ÌF 25VDC and 672D 390¦ÌF 0-15VDC but no indication of tolerence. I couldn't find any data on these, but would 680¦ÌF and 470¦ÌF 105deg be suitable replacements?
I am just putting together an order to RS. Seems to work out cheaper than ordering individual bits from eBay. Also the 74LS112 is considerably cheaper than the 74HCT112 which I can only get on eBay.
