Building up a 540B video board

[gekaufman]

I'm trying to get a 540B to work with a 502 CPU board. I've followed Jeff's very helpful notes and made his corrections in the note above.

The CPU board is tested in another system, works fine.

I've built up the board for B&W only, so the U1 row is unpopulated, as are U6B, U6E and U6F. I believe I have the correct jumpers for B&W usage. They match my other board.

The video is rock solid, but the random character display never clears with reset. I do get some change in the display with Reset. I can see the output enable pins (1,15) on the 8T26's flash with reset.

Have I missed any other known issues with this board, or errata? Any help very appreciated!

- Gary

[Jeff]

Gary, did you add the resistor to the 502 board?
/Jeff

[gekaufman]

Jeff -

I did, and the 502 board works fine with my original 540B board.

= Gary

[musovern]

Is there a link for the character generator 2716 hex or bin file any where.

I've just started this board as well.

Regards
Vernon

The character generator will need to be a 2716 EPROM, so a trace cut and a jumper will be needed.

I created a layout that illustrates the needed mod.

540B 2716 Chargen Mod.png


/Jeff

[dave]

Welcome to the board!

You've uncovered an oversight. I'll add a copy to the archive. Here's a hex file:

Code: Select all

:020000040000FA
:200000005A7E5A18185A7E5A427E5A18185A7E42814224242424428181423C00003C4281D4
:2000200000000024995AFF00800000C0C0FCFEFC01010103C7FFFF7F808080C0E3FFFFFE4B
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:00000001FF

[Jeff]

Here is the Character Generator ROM image. It should be burned into a 2K EPROM. It is the same Character ROM that is used in the Superboard 600.

/Jeff

[Jeff]

Just a note to myself and anyone else interested.

The Transistor Q1 is labelled differently on different schematics. The part I used was a 2N5225.

/Jeff

[Jeff]

Here is my parts list and assembly log.

540B Assembly Instructions and Log.xlsx.zip

(15.8 KiB) Downloaded 870 times

/Jeff

[dave]

Jeff, that's really nice--thanks so much for sharing!

Dave

[keith_r25]

Many thanks Jeff. The pics and assembly log were invaluable while building up my own video board.

I was wondering about the negative terminal connection of C20. The schematic shows it connected to ground and the owners manual pic shows an axial type reaching to a grounded two pin vertical.