I bought what was claimed by the seller to be an Issue 4S Spectrum 48k.
I tried loading games and some worked while others didn't. Turns out it was the 16k ones that worked and 48k didn't. This pattern took a while to work out because the tapes were old as was the tape player. I put those that worked in one pile, with the others in another pile. And tried and tried again, in the time honoured fashion, changing volume, leads, cleaning. Games like Atic Atac would appear to load then reset the machine.
Others would fail with RAMTOP no good errors on the BASIC loader. Errors I had rarely seen before.
Others with other memory errors like Out of Memory.
I suspected a memory problem.
So I tried POKEing and PEEKing to all of upper memory with 255. Checked out OK.
POKEing 0 to 32768 PEEKed as 4. 128 gave 132 and so on.
So I checked the P-RAMT system variable. 23732+23733*256 gave 32767.
So it looked like a 16k but was claimed and sold to me as a 48k.
Various weirdness occurred. Then it occurred to me from looking at how the ROM RST 0 (hard reset) worked that it might be certain bits working while others failed. Hence why 255 worked but 0 did not.
The common element here appears to be that bit 2 stays on, no matter what. (using convention that bits are 0-7. That is, the bit that adds 4 to the binary number represented in decimal.
This masks 255 and other values, as per the screenshots. But most values fail.
This same problem occurs at 32768, 32768+8191, 32768+16384, and other addresses in upper RAM that I've checked.
According to the seller this is definitely a 48k Spectrum. He asked me to open it up and check and I did. The chips are there.
What could have caused this? Damage in the post? Old capacitors? Damage when the seller did the composite video modification?
And what about the bulging or solder damage to C64? No, not a Commodore 64 the capacitors marked c64?
Now trying to show the dirty and shiny side of the ICs. I apologise for the iPad 2 poor quality photo. I will post a better photo if I can get one.