Today I decided to prepare the Spectrum motherboard for the replacement RAM chip (IC16). To make things easy, I’ve decided to be brutal and cut the faulty chip out.
Like most things, that was easier said than done. My cutters were too large to attack the pins. Thankfully the pins are made out of quite soft metal, so 15 minutes with a small saw along the top of the pins sorted the left hand side of the chip. I then repeatedly kept bending the chip along the right hand side of pins until they snapped.
I was left with a space where IC16 used to be with 16 short pins sticking up out of the board. At this point I decided to repair some of the tracks cut whilst I was diagnosing the board, so tracks to pin 8 of IC7 and pin 16 of IC25 had a quick blob of solder applied.
This picture shows the gap where IC16 used to be along with the track repair to IC7. I’ll repair the final track (Pin 8 to IC16) when I replace that chip as it is quite likely the solder blob will have to go to the leg of the socket.
The next stage was to remove the remaining pins from the board and ensure that all the pads for IC16 are clear and have holes ready to accept a socket.
Half an hour with a solder sucker, soldering iron and a piece of thin, stiff wire (to poke through the holes on the board) sorted that out.
As a final check before powering up I checked for short-circuits by visually inspected the board (with a magnifying glass) around the removed RAM chip and tested with a multimeter on continuity test. Thankfully this all passed.
Upon powering up the Spectrum I was greeted with the copyright message which is a good sign. There is always the worry when fixing a board whether you’re going to destroy another chip by heat or static. A quick PEEK at the system variable RAMTOP returned 32767, so the Spectrum still thinks it’s a 16K Spectrum. This is a good sign; the bootup RAM test has clearly got to the first byte of the 32K bank of RAM (32768), tested (by reading and writing a byte) and finding that bit 1 (represented by IC16) is not working.
I’ll pick up a socket from the local electronics store at the weekend and will solder that in place. My final job will be to order a replacement 4532 RAM chip and keyboard membrane as the ribbon cable for the keyboard has gone brittle due to age.