ZX Spectrum 48K Issue 3 thinks its a 16K

[vdpuser]

Hi,

I recently purchased a ZX Spectrum 48K Plus, issue3 mb but for some reason it thinks its a 16K machine,
If I run

PRINT PEEK 23732 + PEEK 23733 * 256

I get the answer

32767

I've replaced all the upper 32K Memory modules and it has made no difference
I've checked the links at the top of the board and they look correct


Anyone any ideas where to look next?
Thanks
Gareth

[Tiger]

For Issue 3 boards it is essential that all extension RAM ICs must be of the same type.
Possible that one of this ICs is broken: IC 23 (74LS32), IC 24 (74LS00) or IC 25, IC 26 (74LS157 NOT National Semiconductor)
Also possible is a broken PCB connection...