Trying to ID some hardware - RS232 Interface

[sup8pdct]

That jack could be power for the unit. pics of both the top and bottom would be most helpfull.

That was my first thought as well, but when I started looking at how it was wired that seemed very unlikely. Most of the circuit definitely takes all its power from the SIO port. I'm guessing it hooked up to some kind of circuit with a switch or a relay possibly built into the equipment it was hooked up to. Most likely a modem or dumb terminal of some kind.

Yes please, only if it isn't going to be too much trouble.

No real trouble, except for the closeups. I had to retake those several times before they were usable. Those were a real pain as it would either overexpose the flash or just not want to focus that close.

 

The two diodes, I can't make out the part number without removing them. I think they may be low value zeners as on both of them I got voltage drops of 0.7V forward biased and reverse voltage drops of 2.7V on one and 2.36V on the other. So they may be 2.5V zeners. Definitely silicon diodes of some sort.

 

The ICs are MC1489N (that's the marked package) and the unmarked package is probably a 74LS126. At least it looked like it was one as far as I had gotten tracing out the circuits myself. And those are the two used in the Megaterm interface that was referenced earlier. This circuit is very similar to that one.

 

If you do up a schematic I'd like to see it myself. Hopefully you can make heads or tails of it. Most of it makes sense to me, but not all of it. But then, when it comes to electronics I'm more of a repair than a design person. There's definitely some tricky klugery going on here that someone more designed oriented would understand that I don't. =^.^=;;

Have had a quick look and it appears the 2nd chip is a mc1488 rs232 driver. it requires both a positive and negative voltage of around 12V which would be supplied from the same place as the rs232 cable is plugged into. so it isn't anything like the rverter or megaterm interface.

Looking at the data sheet for the 1488 that actually makes some sense to me. Since even though the Atari SIO port could provide the Vcc+ from its +12V line it wouldn't be able to supply the Vcc- the 1488 needs. So an external power supply would required for the driver IC.

 

But what about those two diodes then? Like I said, they look to be 2.5V zeners by the voltage drops I got across them.

 

Interesting...

 

BobKat

judging by how they are connected, I would say they are protection diodes. the voltage across them would either be in the chip or maybe the caps.

 

James