Using an ICL7660 to feed -5VDC to 4116 DRAMs?

On Wed, Jul 02, 2008 at 06:13:22PM -0700, Scanning wrote: OK. I don't have _that_ 4116 datasheet to reference, but that does sound familiar. Looking carefully at the Commodore power supply schematics from zimmers.net, I don't see anything that would bring up Vbb first or remove it last. To all appearances, it's all three at once. I don't know of any voltage priority in the Apple II, either (as an example of a contemporaneous design to the dynamic PET), so presumably, "at the same time" suffices. The unanswered (unanswerable?) question is then how close is close enough. Given the replies, I think I'm going to try the ICL7660. It means that I can run the board off a dual supply instead of trying to find other means. There is a remote chance that it could blow all the 4116s on a semi-common PET 3032 motherboard and I'll have to extract the chips - not a preferred outcome, but it seems no more risky than the factory supply. The safest alternative appears to be to remove the DRAM in the first place and run a static chip on a ROM/RAM board, but that still involves a lot of work on the board. What is clear is that providing +5V and +12V without covering the -5V requirement is _not_ a reasonable option. As originally manufactured by Commodore, the chips have 0.1 uF on both the +12V and +5V rails. They are so notoriously cheap that I take it as proof that they are required. Fortunately, we have this nice warm indoor space - _I_ get to walk ~10 hrs/week outside, but the classic toys stay inside where it's nice and toasty. Thanks for all the advice, -ethan -- Ethan Dicks, A-333-S Current South Pole Weather at 3-Jul-2008 at 03:39 Z South Pole Station PSC 468 Box 400 Temp -83.2 F (-64.0 C) Windchill -121.6 F (-85.3 C) APO AP 96598 Wind 10.1 kts Grid 45 Barometer 681.6 mb (10568 ft) Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html