First post, by TheMobRules
I've had a DTK PTM-1630 286 motherboard for a while, and I decided to set up a build with it. As expected, the original barrel battery had leaked so I had to do some trace repair in the area when I got the board, everything went well and now I'm working on connecting an external battery for the RTC and CMOS settings.
The manual calls for a 6V external battery, but when I tried one today (4xAA alkaline cells), but when measuring the current used by the RTC circuit it was around 330uA, which according to my calculations means the battery would be drained in around 6 months... it seems too much. Next, I tried a non-rechargeable 3.6V lithium battery (LS14250, 1/2AA cell) and with that one I got a more reasonable 100uA, but it still seems a lot considering the circuit is based on a Motorola MC146818A which according to the datasheet should use up to 50uA. And I'm not sure why using a 6V pack causes it to more than triple the amount of current used. Could there be current leakage somewhere in the circuit?
The rest of the circuit is pretty much the usual stuff: a 4069 inverter used to generate the oscillator input (with a 32.768kHz crystal) and STBY/CS pins on the RTC chip, a pair of NPN/PNP transistors to handle the switching between PSU and battery power, and a bunch of passives. None of that would seem hungry enough for that much current right?
I am attaching a diagram of the RTC + battery backup circuit I did to help me understand better while repairing traces, as far as I can tell all the components are working properly.
