Much progress has been made since my last post!
The board was (almost) fully assembled ready for testing at the weekend:
(and yes, that board is totally coated in flux so every little bit of crud on my desk sticks to it which is lovely..... this board really needs some quality time in the ultrasonic)
On testing this I got.... Nothing. The PSU didn't even start up (and yes I did remember to fit that missing HC132 before testing
)
Much probing and staring at the board layout in sprint revealed loads of missing traces a number of which where in the startup circuit (there where also a couple around the RAM address mux's and a few elsewhere)
This got the board powering on but with no chime and no video, A little bit of probing later and it turns out the ASC wasn't connected to 5V, oops! One bodge wire later and the board was producing beautiful clear.... death chimes.
I spent hours trying to figure this out without being able to find any further issues with the board when I started thinking about my IIx, it's a pretty much identical machine hardware wise and I had a similar issue which after months of troubleshooting turned out to just have a bad ROM, maybe this was the same....
I stuck a ROM Simm socket on the board and chucked a SE/30 ROM in it and.....
More investigation revealed ROM MH at UA2 was bad, one 27C512 later and the board was booting with the onboard ROM
This was the point I did something I probably should have done earlier and test fitted the board in the case, whatever I did it just would not lay flat and I just couldn't figure out why......
Ahh yes, it helps if you remember to put all the locking slots in the board!
Never mind, I can vaguely hack a slot out the board
And it fits!
And even boots Mac OS
The board is bit of a tight fit in the case so needs to be slimmed down a tad and the latching slots are also a bit short making the speaker quite a tight fit so some adjustments are in order for the next revision
That should have been then end of it for now but just as I was about to go to bed last night I found two odd faults: first off only the left NuBus slot worked, installing the graphics card in either of the other slots gave a gray screen for a second then the computer would hang and installing two cards in any slots gave death chimes. Secondly I found setting the volume level lower than 2 made it lock up and then give death chimes on boot until the PRAM was reset which is a odd fault to say the lest!
The NuBus issue turned out to be that different arrangement's of ground pins are used on each slot to identify them and I had just copied the same arrangement for all 3 slots. a quick bodge wire got a second slot working (getting the third to work would require removing the connector form it which I'm not going to do)
The weird sound issue also had a simple fix: it turns our I had forgot to solder one side of the right sound chip, I'm guessing that when the volume was set to a low level the chip would glitch out and start yanking on the reset line (the machine was not resetting, but this is the only way I can really think of that one of the sound chips could crash the machine) Rectifying this allowed me to set the volume as low as I liked
That's it for now
the board still needs some more testing but It'll probably be a week or two before I get around to finishing it
Did some sketches for the layout last night at work. Should porobably start a new topic hereabouts to get feedback/suggestions when I've got something ready for prime time.
