PS/55 note N23 SX (2nd Generation)

The N23 name comes from this machine's model type 5523. It was the second generation PS/55 Note (the 55xx series in Japan being similar to the Western PS/2 series). The first generation PS/55 Note came as two seperate boards in a sandwich configuration and thus didn't have room for both a floppy drive AND a hard drive, so you picked either as an option. The motherboard has the same EXCEL codename as the N33 16Mhz.

Side Note: Originally 5523 type was for the Notebook models and 5535 type was for Laptop models of the 55 Series.

The PS/55 N23 SX is a very close Japanese relative to the Western 16Mhz N33, although the Japanese N23SX is better because it had both the FDD and HDD built in. I theorise that as the 12Mhz PS/55 Note & N33 could not fit a both as HDD and FDD inside due to the two-part mainboards, so it had to have an external floppy The N33 16Mhz had it's floppy drive deleted to align both N33 machines so that both only had an external floppy connector. Although one could argue that having an internal floppy along with faster 16Mhz 386 and external video could have been a greater selling feature for the more powerful N33.

Some might consider this machine 'one' of the grandfathers of the IBM Thinkpad 700C due to it's dark case, bento-box form factor and 'nice' (but not quite brilliant) keyboard.

My one had the same blown cylinder fuse, as was inside my N33 16Mhz. After replacing this, it boots fine (with the battery pulled out). However it has no LCD.

Here is a picture of the inside, which, apart from the floppy drive is very similar to the 16Mhz N33:

And with the floppy drive and insulation moved to one side:

Here is a picture of the internal floppy drive - missing from the N33 models:

Memory  / RAM

On all the ISA notes between the very first PS/55 note through to both international N33 SX machines, these machines cam with 2Mb RAM onboard, which isn't a lot. These machine's are specified as needing official 4Mb 72-pin 80NS parity RAM sticks as an upgrade. These are hard to come by and we can do better.

I managed to get four sticks of 4Mb 70ns parity 72pin simms which are faster than the required spec so would, in theory, run cooler and at lower power (not that it matters). They needed two modifications to make them work on all these ISA 12 and 16Mhz notes:

Increase the notch:

Annoyingly, the official 72-pin sticks had a bigger keyed notch in the middle than nearly all other sticks. So I used a dremel to very very slightly increase the notch size, avoiding any nearby traces in the PCB. Alternatively I could have snipped out the keying plastic inside the memory bay, but trying to preserve the machine simply means not damaging it when I don't have to.

Bridging Detect Pins

Pins 67, 68, 69 and 70 are some kind of detection/verification pin and they can either be connected to ground or not. Most sticks need modifying to make them work without getting a 225 "memory error" on power up.

In my case, the sticks I got had the wrong pins grounded, so I removed the necessary o-ohm resistors (which are essentially metal bridges) and moving them to ensure that pins 69 and 70 were grounded.

Here is a close-up of the pins on the top left corner, with top to bottom 67-68 grounded and 70 grounded:

And here is after modifying to have just 69 and 70 grounded:

On another set of RAM, I did the same but the pins were in different original positions:

And after:

CMOS

You need a working external floppy drive (with 23mm connector) and a bootable PS/note option disk to setup the machine with the right time and configure some necessary bits like the internal hard drive. I have noticed that replacing the CMOS battery with every kind available does not retain the settings beyond perhaps 1 hour. I have double checked this across various PS note machines and batteries and I've checked the voltage all the way back to the pins inside the motherboard and whilst the CMOS battery retains power to the CMOS, the settings invariably get lost. So my conclusion is that a) there is no point trying to replace the CMOS, b) You need a working floppy disk and drive to make the machine usable (otherwise it just sits on a 161/163 error) and c) if the day comes where it won't even retain it's setup on a soft boot, the notes will become entirely unsusable.