I've built a RAM expansion cartridge for my VIC-20 computer.
It uses the CY62256L 32KB SRAM chip. It has been working fine except there's a quirk.
If I power off the computer, but leave the external disk drive powered, there is a small amount of current (apparently through the drive's reset line into the main Vcc) supplied to the expansion board still.
It is in the micro-watts but it is enough to keep the RAM chip in low-power standby.
Is there a way I can prevent this small amount of current from flowing?
Here is my circuit (please excuse its messiness):
Here's a clarification of what is going on. Here is a page from the schematic of the computer, which is powered off when the current leak happens.
The external drive is powered externally. The red circle is where it is sending +5V into the serial port while the computer is turned off, i.e. the reset line. The blue circle is where the reset line connects to my board.
However, the green circle is where the reset line is usually pulled up by the computer, and here I think is where it is leaking onto the Vcc. Which enters my expansion board at the purple circle.
It's Vcc that has current which is powering the RAM. The board's reset line is high too, but it's only connected to a switch.
Does that help explain?