Hai the listing pointed out by GDX does exactly the same as the earlier listing with the added function of restoring the RAM. And this is exactly what my function does, as well. In my opinion also the most trusty way of checking if there is RAM on a page. One minor thing; the value put on the segment to test while reading back could also already be present at that value which could indicate a false positive. I added this in an earlier RAMtest function, it first tests if the value of the RAM location is equal to the test value. If so, i'll put in the negative value of that and read that back.
Either way, both basic listings do the same in function. As long as you use any address within the 16K segment. In these cases it's page 2: #8000-#BFFF. And to switch page 2 segments, you first have to move BASIC to another page. That's what line 10 does, in both cases. 
The plot thickens as I'm leaning towards hardware failure.
Alrighty then!
Simon (Retrofan) I got together today and had a great time. We live in the same city, easy! First of all, here's proof we actually did 
On the right is Simon holding his Panasonic fsa1f, on the left is yours truly
We got together to see if we could have a closer look at the memory mapper portion of this beautiful machine. I loaded up my dev environment on this machine and got cracking. And indeed found out some interesting stuff.
The gist of it, is that non existing segment mapping can result in a read-only mode (let's say ROM). The machine has main RAM in slots 3,0. That slot combo should never show ROM stuff, to start with.
I've been digging a bit and looked at the listings provided here earlier. We have to keep in mind, there's a difference in recognizing RAM and counting memory mapper segments. The first listing by Retrofan looks if a segment is RAM, the second by GFX counts segments.
A memory mapper works like this (*or should):
Mapping a RAM segment to a page (any) results in changing of RAM. It's a shadow RAM if you like. A segment is 16KB, so a machine with 128KB has 8 of them memory mapper segments. In that case, segments 0-7. You can access any of these segment by selecting the segment number on ports #FF (page 3), #FE (p2), #FD (p1), or #FC (p0). For example in BASIC, OUT(&HFE),3 will set memory mapper segment 3 on page 2 (#8000-#BFFF).
Here's the thing, when you set a segment higher than the max (in this case 7), say 8, it rotates and starts with segment 0 again. So segment 8 would be equal to segment 0, segment 9 = 1, etc. To count the memory mappers segments, we make use of that by checking segment 0 when writing to another segment. Say for example we write "1" to segment 8, then this actually writes to segment 0. If we encounter this, we know the segment count was reset. If we count the times we don't get the written value in segment 0, we know how many segment there are. That's what GFX his BASIC listing does, that's what I do too. We need to have the page set up to RAM beforehand, ofcourse.
Now, checking if a piece of memory (a page) is RAM is another matter. In that case, we write a value and read it back. If the read value differs from what we've written, it is not RAM. Simple.
So, back to the fsa1f machine.
This one has 128K, segment 0-7. But, when selecting segment 8 (which should be segment 0 again), it instead puts some ROM on the slots. Not expected behavior, for a memory mapper slot combo.
After some more checking, here's what I found on this 128K machine, setting memory mapper values:
0-7: RAM (mapper segments 0-7)
8-31: ROM
32-40 RAM (mapper segments 0-7)
41-63: ROM
etc
OR, 8 slots of RAM followed by 24 slots of ROM.
This is also the reason why a memory mapper counter will see 512 K. Because OUT #FE,32will result in segment 0 again (for the first time). The memory mapper checker will see the checksum value being written in segment 0 and knows the memory mapper cycle was reset, and counted 32vsegments. 32*16=512K
So, why did that listing Retrofan posted work? Well, because it checks for RAM and because segment 8 shows ROM it knows that there's just 8 pieces of 16K of RAM. This wil ONLY work on a machine that has this phenomena. Funny detail, on a turbo R in DRAM mode this will work too since the last four mappers are set in "ROM" mode then. But on any other machine it won't. So this basic listing was specially written for the ASF1 (check the link to see it was).
My conclusion: the machine has faulty behavior with memory mapper segment selection. Or, in other words, a hardware issue.
Can we work with that? Yes, in fact we can by combining the two search functions. So, during segment check we also need to check if it is actually RAM. In that case, all's fine.
I'll whip up a test case and send it to Simon later to test that theory.
