exxos's Atari, Amiga & retro forum

Argh, another orientation question.

The quad 2-input multiplexers (U3, U4, U5) don't have an indent on the chip. They do have printing on the top of the package, including a vertical bar, but no dot for pin 1. I would like to assume that the bar is in the direction of pin 1, except for the fact that on the underside of the package, there's an embossed asterisk near the opposite corner of the package.


So, is this pin 1?

Or is this pin 1? (Sorry, no camera adapter for my microscope!)

It looks in Icky's build like his are oriented like the first picture, but it's not entirely clear that they're even the same chips.

@derkom - The vertical bar is the indicator thus your first picture is correct. Chip Pin 1 identifiers are an interesting subject and if there is no ident at all then the text orientation is all you can go off of.

Thanks @Icky!

There's loads of odd ways manufactures do it. With a dot which is the norm. Or a line across the front of the chip. Or a line down the left side of the chip. Or no lines at all and the edge of the if is slanted one side.

@derkom - when you get to soldering in sockets dont solder in the Flashy Clock one yet. https://www.exxosforum.co.uk/forum/viewt ... 229#p28915

SMT work mostly complete. It'll be a minor miracle if I didn't cook any of the ICs, but we'll see. :)


I'm missing the 47/50 pF caps, which I'll acquire later. Turns out the 50s I had on hand were 50 nF, not pF. Oops. Not too difficult to add those later, though, as long as I hold off on mounting the monitor port. And exxos said they're nearly optional anyway. :)

@Icky , thanks for the heads up on the Flashy Clock socket. Noted.

derkom wrote: 22 Nov 2019 14:14 SMT work mostly complete. It'll be a minor miracle if I didn't cook any of the ICs, but we'll see. :)

@Icky , thanks for the heads up on the Flashy Clock socket. Noted.

Nice - I did think that about mine last night. Note to self don't do SMT work with a hot bed whilst drinking a large G&T. The board got quite hot and thought it had warped at one point.

Various sockets installed, as well as all the discrete resistors, save two of them that might need some careful placement with respect to a couple of missing sockets.

Regarding those missing sockets, I've realised that I failed to order new sockets for most of the unique chips, as they didn't have part numbers on the BOM. Not sure how I missed that, because I spent quite a lot of time finding part numbers for a lot of miscellaneous, but somehow I failed to notice those.

I'll put everything else on the board and then decide whether I prefer to strip the sockets off the alpha board (generously donated to me by Atarian Computing) or if it's better to make a relatively long trip to the nearest shop that stocks such things. But I can put that decision off for later. :)

Looking pretty nice!

Hey, @exxos, it occurred to me while thinking about my missing sockets that I don't have a TOS ROM specifically for this board. Will the ROM from the Alpha board work in H4, or do I need to get a new chip?