osiweb.org

Hi All,

I am planning on building a Replica 540 rev B video card.

This is part of a larger project described here: viewtopic.php?f=3&t=413

Does anyone know where I can get the 2 crystals?

X1 is listed as 12.08 Mhz and X2 is listed at 5.579545 Mhz.

/Jeff

I'm building one too.
so if anyone knows...

pass it on....

actually that might be a typo, i think it should b e 3.579xxx standard colour burst crystal.....
those are available pretty much everywhere.... I wonder if a good old fasioned 12 mhz crystal will work...

this is from the C4P service manual:

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.

/Jeff

Thank you
this will be very very helpful

Cheers.

Progress so far...
EDIT:
Keith opined out that C20 in the photo above was installed incorrectly. Here is a photo of my fix:
/Jeff

Finally all the IC's arrived from China and I had some time to populate it. /Jeff

While getting the board to operate, I discovered that R22 (10K Pot) should not be installed, and simply jumpered.

/Jeff

you got video?
can we see? he he (just excited not dubious)

I will have to start working on this board once we complete the colour board Steve Gray is working on.
we have yet to meet up and play we are going to do it together, Steve, Josh and I.

Cheers.

I have a screen full of random characters.

The board is not yet responding to instructions from the 502 CPU board.

/Jeff

The board is now displaying characters from the 502 board, (as opposed to garbage). The video is shaky and color isn't working yet, but at least *most* of it is working.

There were several changes needed to make the board match the schematic. All these changes apply to the original OSI PCB... and the replica faithfully reproduced them, so they need to be applied.
1: Missing trace: Just below C20, on bottom, add small jumper (just above pin 1 of U4H)
2: Missing trace: Add jumper from U4J pin 1 to U4J pin 4
3: Wrong trace: On the top of the board, cut the trace that leads to U4H pin 5. (This cut removes /02VMA signal from the pin, which should be S1)
4: Missing trace: Add jumper on bottom from U4H pin 5 to U4J pin 3 (use VIA next to U4I pin 5) This adds the S1 signal to that pin.

Here is a diagram of those fixes. I tracked down the issue of it not working at all to a missing resistor on the 502 board. Read this topic for details. viewtopic.php?f=3&t=503 I am in the process of documenting my adventure and I will post it here when done.

/Jeff