Fixing a dead Amstrad PCW9512+, Part 2

In my previous post I yanked enough of the PCW9512+ apart and debugged why the power supply just plainly wasn't working.

Now it's time to see if the rest of the board was working.

The first thing to do is test the power supply without having the 9512+ logic board (and the CRT side) powered up. The switch mode supply may not be happy with a load, so an initial failure isn't necessarily fatal.

So it mostly looked like this whilst I was testing it - with that EHT anode cap moved out of the way (just in case - it shouldn't have been powered!)

And honestly? The power supply just worked fine. The caps I tested were fine. All the rails tested fine. I'd have to test them under load to calibrate them, but before doing that I should verify that the 9512+ board and CRT hardware works fine.

So after a bunch of cleaning up, it was ready to put aside and test the mainboard. Testing the mainboard only required 5v - 12v is required for the earlier 3" drives but this drive doesn't require it, and the 28v rail is only used for the 9512+ daisywheel printer. I needed neither, so I just hooked up the 5v rail for testing.

.. and again, the mainboard tested fine. Here it is with the disassembled floppy drive for testing.

The board initialised and showed video/sync on the output side. Ok, great. It needed 800mA at 5v to power up, and it would peak above 1A to load from floppy disk. So pay attention to your power supply!

Next up the floppy drive. It had something in it.

I don't know how or why a sunglasses lens showed up in here, but ... well now I am its proud owner. So I removed that and plugged it all back in.

The motherboard and drive worked enough to fail booting a non-boot disk - and beeped loudly whilst doing so. That tells me the hardware is starting up fine and running the boot ROM code, but it's not reading from the drive.

And well, the drive was dead. The floppy drive rubber band was toast.

.. I could figure out the belt width (~2mm) and thickness but I couldn't figure out the size. The drive is a Citizen UODC-45A and I couldn't find any service manual / documentation on this drive at all.

But luckily someone had! And the belt he ordered from DataServe Retro is for a cassette deck - flat, 71mm diameter, 2.8mm wide, 0.6mm thick! And to make life easier, here's the link to the belt in question.

 

I recommend watching the video to get an idea of how to get the belt correctly around the capstan to line up the belt between the small motor and the large drive shaft. It's quite a squeeze.

First up was cleaning up the old bits.

First, the motor spindle.

Finding all the fun bits of the belt stuck in the drive - I had to shake it multiple times to get it all out.

And here's some on the drive spindle itself. In fact, after doing all of this I found more stuck UNDER the spindle which kept the drive from reliably spinning at the right RPM, resulting in loads failing! (Phew, I wasn't looking forward to having to calibrate it.)

In any case, once I had assembled the unit and stuck in a disk, it made the right kinds of seeking noises and .. well, I guess it had booted.

And .. well, it started booting fine. But the keyboard didn't work, and the display was way too bright and over-sized. Let's tackle the keyboard... oh it's just cracked solder joints. Easy.

And now the picture!

Now the important part - this is now under load, so I need to double and triple check the power supply calibration. If it's getting > 12v then this'll happen. So before you go and try re-calibrate your monitor, check the power rails.

And yup - it was dumping 14.5v into the monitor B+ rail. Things look MUCH better after calibrating this back to 12v.

No obvious calibration needed!

And finally, running a basic RAM test.

So, it boots fine, RAM tests fine, copies disks fine. I haven't yet dumped CP/M software on here to use - I think I'll make up a disk full of CP/M games.

The next post will cover MAKING a 720k CP/M boot disk for this thing - more of a pain in the rear than I'd like, even with a suitable MS-DOS 80386 IBM PC clone available.