vanop
http://old.nabble.com/SCI-615-Multitrak-battery-drain....-td8384504.html :
Do you have the schematics? Makes things a bit easier. But thea are not absolutely necessary.
Several parts in the
MultiTrak are powered by the NV power, among those is the CD4022 for the keyboard scanner. I absolutely don't know a reason for this, but okay, i have to accept it. Besides this, the RESET line of the CD4022 is pulled high when main power is absent. Due to this, the 4022 pulls CARRY and Q0 high (got this from the datasheet). On the CARRY line, there is a pullup resistor to the main 5V supply. And exactly this is the problem. The power from the high signal of the CD4022 is lead to the main 5V circuits over this resistor. The leakage is not very big, in my measurements with worn test batteries, i measured 200µA, and the voltage drop on this resistor was around 2V, and using Ohm's law with this 10K resistor, all of those 200µA were drawn by this resistor and the main electronics being fed accidentally by it. The workaround was desoldering the resistor end off the main power and putting it to the NV power. Now, my
MultiTrak draws about 1µA from the
battery. If they wouldn't self-discharge, this
battery would keep up the memory for 50-100 years now
What to do:
You know how to disassemble your
MultiTrak. So do this now, disconnect the keyboard connector and put the electronics in front of you, connectors away from you, circuit boards upwards. Remove the voice board (the upper large board) to reveal the CPU board below it. In the left area, near the keyboard connector, you find a 40pin chip, a mask programmed 6801, and right of the connector, you see the CD4022. Maybe it has other letters, but 4022 has to be there. Left of this 4022, you find 2 resistors, both of them 10KOhm. The left resistor (the one more away from the 4022) is the problem. You see the thick trace at the front end of those resistors connecting both. This is the main power. Desolder the left resistor from this trace (or cut it off very neat the PCB, we need to connect it elsewhere). Now use some isolation tape or adhesive tape to make sure the resistor doesn't touch the board or it's neighbour resistor. Connect the now open end of the resistor to pin 16 of the CD4022. Eventually, you want to use some hot-melt glue or so to
fix everything, i just used a wire stiff enough to keep the resistor in place, and put some isolation tape on top of it.
That's all.
If you want to check everything out, use your Amperemeter to check the current drawn from the
battery before and after this modification. If you see a very large difference (200µA versus 1µA), everything worked. You can also check if your moved resistor end now has a bit below 3V when power is switched off, it should have a bit below 5V when power is on.
