In the summer of 2022 I bought a couple of ZX Spectrums on eBay, sold as seen, spares or repair. As it turned out both of them had lower RAM faults, so rather than wrestling with trying to fix the DC-DC converter circuitry and identifying the faulty DRAM ICs, I thought it'd just be easier to install a modern lower RAM module. This is a photo essay on how to do it.

A fault with the lower RAM on a ZX Spectrum manifests like this:

The ULA's video subsystem is reading from DRAM ICs which either aren't working a bit, or aren't working at all. What you get is patterns of garbage depending on what data the damaged ICs are returning. On this machine the DC-DC circuit wasn't supplying -5V correctly, which is frequently fatal for the MK4116 DRAMs. These DRAMS are the line of ICs seen in the bottom left of this image of the circuit board. One or more of them would be damaged, maybe all of them:

Replacing those ICs with a modern memory module board involves removing the originals, fitting sockets in their places, then plugging the new module into the sockets. So, the sockets have to go:

Each one is removed by clipping its legs with flush cutters:

All 8 must be removed, leaving the legs in the place:

Now the pins must be removed from the PCB. This is the bit that must be done carefully. The PCB is 40 years old and lifting one of those tracks is very easy. So one at a time, carefully does it:

16 pins per IC, 8 ICs, that's 128 pins to desolder:

Then the solder in each hole needs to be removed. I don't have a desolder station, just a desolder pump. Lots of mess:

Holding the board up to a light shows progress:

Solder splashes all over the PCB:

Each one needs to be removed with a nylon brush:

Test to see if the Spectrum has survived so far. With no lower RAM in place the ULA sees semi-random noise when it tries to read the screen image:

Well that seems OK, so it's time to put the sockets in place:

The lower RAM module needs all 8 fitted:

At which point it just plugs in:

Power it on, and hurrah! Another ZX Spectrum rescued!