Vintage Motor – Identifying Symbols on Old Milling Machine Schematic

In some cases it is possible to replace DRAM with SRAM, by adding some logic to latch the row address. Whether this will work in a particular circuit depends on the timing of the RAS, CAS, and /WR signals and how the SRAM responds to them. 1 bit DRAMs have separate data input and output pins. If these are not tied together in the circuit then you may also need a Tri-State buffer to bridge between them. Getting the timing right could be tricky.

Here are two examples that work:-

SRAM replacement for lower 16K ← ZX Spectrum

SRAM replacement for TMS99x8 VRAM

You may be able to use higher capacity DRAMs provided that they are compatible - compare their data datasheets to make sure. The main things to watch out for are RAS/CAS timing (Fast Page Mode, EDO etc.) and refresh requirements.

However replacing the the faulty DRAMs with correct equivalents would be much easier and more likely to succeed. Although these older DRAMs are no longer manufactured, many are still available on the second hand market - usually selling at much cheaper prices than when new.

You may not have found what you want because you haven't searched all the equivalent part numbers. eg. '41464' is equivalent to '4464'. Here are some selling on eBay right now:-

D41464C-10 NEC DIP18 10NS

5PCS KM41464AP-12

Just be aware that these chips may be refurbished and possibly remarked with different parts numbers. Usually they are equivalent, but sometimes not (I bought some 'MCM2114P20 1kx4 SRAM' chips that are actually BU2114F 8 bit shift registers!).

It's a thermal contact (Normally closed - thermal trip).

If OP Googles "contact switch symbols" and jumps to the Images, he/she can find a lot of symbol tables. Here's one OP could see: ibiblio.org/kuphaldt/electricCircuits/Ref/01053.png