8-bit acorn hardware • Re: Another RAM issue, or is it?

I have tested it with another keyboard and now do have activity on the Caps and Scroll Lock key.
Could somebody please confirm that in removing all the "lower ram" (yellow) and testing it, that should have resulted in the machine booting with 16k assuming the jumper (is it S26) was positioned south?
For reference I used this image:
pxl_20240121_172450697_ram-1.jpg

You can use the following S25 options:

• north: 32K, CAS0 lower, CAS1 upper RAM (default model B config)

• south: 16K, CAS1 RAM (default model A config)

• removed: 16K, CAS0 RAM

• inverter applied on north pins: 32K, CAS1 lower, CAS0 upper RAM

For more details on how this works, see the this post on the fault finding index.

The yellow highlighted ICs are IC53-IC60. These are CAS1. If you set S25 south, you configure the BBC to use CAS1 only (effectively model A config).
Some PCBs have the purple ram chips (IC61-IC68 CAS0) socketed, but in most computers IC53-IC60 are soldered in.
In other words, no, if you remove the yellow (CAS1) chips and set S25 south, the computer will not boot (it will have no RAM).

Assuming you only removed the socketed RAM IC's, for clarity; which IC numbers are socketed on your board?

RAM is not the most likely culprit imo, Tricky's ROM validated the vitals.
Did you try a known-good OS in this board?


Useful resource: the BBC B Mapped Motherboard on the 8BS site.

Statistics: Posted by DutchAcorn — Wed Jan 28, 2026 7:03 am

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