Back in the 90s I had the mechanical data of the ZIP RAM package from one of those fearsome memory data books supplied by the likes of Hitachi and Toshiba, usually scrounged off a visiting rep. The information was clear and consistent in that the pin spacing on each row was 0.1", the row spacing was 0.1" and the offset between rows 0.05". The thickness of the pins was a nominal 0.01" or 0.25mm.
I think the problem for these A3010 RAM upgrades was partly due to the crummy sockets used by Acorn. They were the same style as the ones used in the 400/1 series, just more contacts. The force needed to insert a single 256kx16 RAM was easily double that required for the 256kx4 used in the 400/1. The pins on many of these 4MB modules are about 0.02" (0.5mm) diameter, twice the thickness of the IC pins for which the sockets are designed.
It is also likely that, prior to soldering, the sockets are a loose fit in the motherboard hole. So it is not impossible that during the wave soldering process the two sockets could move relative to one another. It would only want one to move 0.01" in one direction and the remaining socket the same distance in the other, and straight away you have a significant change in separation distance of 0.02". That's enough to cause pin misalignment on these plug-in boards and you can't do much about this.
One of the upgrades from the 90s had four 512kx8 SOJ RAMs to provide 2MB. A combination of the onboard 1MB, two extra 256kx16 ZIP RAMs and the 2MB just mentioned gave the full 4MB. I remember having one returned which was 'faulty'. In fact, what had happened was the user has pressed down hard on the SOJ chips in order to install it. This had squashed the J-lead RAMs right down onto the PCB and pulled up a few tracks/pads in the process. The board+RAM was a write off.
The long term solution was to change the type of pins used, specifically a smaller diameter of 0.45mm. This may not sound much but obviously each pin would now fit more easily. The total reduced installation force was then multiplied by 80. The use of gold finish on the pins may have been helpful too, not so much over contact issues but possibly resulting in a lower insertion force due to a malleable coating.
Most problems went away overnight with the different pins.
I think the problem for these A3010 RAM upgrades was partly due to the crummy sockets used by Acorn. They were the same style as the ones used in the 400/1 series, just more contacts. The force needed to insert a single 256kx16 RAM was easily double that required for the 256kx4 used in the 400/1. The pins on many of these 4MB modules are about 0.02" (0.5mm) diameter, twice the thickness of the IC pins for which the sockets are designed.
It is also likely that, prior to soldering, the sockets are a loose fit in the motherboard hole. So it is not impossible that during the wave soldering process the two sockets could move relative to one another. It would only want one to move 0.01" in one direction and the remaining socket the same distance in the other, and straight away you have a significant change in separation distance of 0.02". That's enough to cause pin misalignment on these plug-in boards and you can't do much about this.
One of the upgrades from the 90s had four 512kx8 SOJ RAMs to provide 2MB. A combination of the onboard 1MB, two extra 256kx16 ZIP RAMs and the 2MB just mentioned gave the full 4MB. I remember having one returned which was 'faulty'. In fact, what had happened was the user has pressed down hard on the SOJ chips in order to install it. This had squashed the J-lead RAMs right down onto the PCB and pulled up a few tracks/pads in the process. The board+RAM was a write off.
The long term solution was to change the type of pins used, specifically a smaller diameter of 0.45mm. This may not sound much but obviously each pin would now fit more easily. The total reduced installation force was then multiplied by 80. The use of gold finish on the pins may have been helpful too, not so much over contact issues but possibly resulting in a lower insertion force due to a malleable coating.
Most problems went away overnight with the different pins.
Statistics: Posted by ctorwy31 — Fri Nov 28, 2025 6:04 pm