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Thanks for checking my work Keith!

I guess this makes a case for silk screened component placement.

I made a mistake when installing C20.

Here is a photo of C20 placement on an ORIGINAL OSI 540B board:
Here is a before and after photo of my C20 placement:
I have added a '+' to my layout doc indicating the correct polarity of C20.

Regards!
/Jeff

I noticed that I haven't uploaded my full component layout, so here it is: I have a higher resolution version of this document. Just message me if you need it.

/Jeff

Hello Jeff,

C6 is jumpered and then to one leg of R7? (orange lines)

thanks,
Keith

Hi Keith,

Not sure what I was thinking there. I would just ignore the orange jumper lines. They are not jumped here on my board.

/Jeff

Many thanks!

How about the U4D to U5F (jumpered on orginal board (labeled))? Was it required to get your board working?

Keith

No.

This jumper (and cut) existed on my original board and I do not yet know or understand why.

/Jeff

I too have been building a 540 replica board.
After quite a bit of mucking around, and finding I had a number of dead components (not surprising as the board is mostly built from what I have in my parts bin), I am able to get a very unstable screen of tanks. (see photo)

I had a vague recollection of seeing a screen full of tanks somewhere before, and then I remembered its a milestone in the Superboard build process.

viewtopic.php?f=3&t=210&p=3076&hilit=ta ... V0CU#p3076)

Presently I have only the video board plugged into the backplane as my PSU blew up and my bench powersupply does not have enough power to drive the 540, 505 and the RAM card all at the same time. Having said that, I very briefly had all 3 boards plugged in before the PSU dies, and I still had screen of tanks, and reset did nothing

Now I was expecting a screen full of random characters as, from memory, that is what I get on my C4 if the only board plugged in in the 540.

Any advice would be greatly appreciated.

some progress,
I hooked a an ATX psu and was able to install all 3 cards.
Turning it on you can see the system reset (briefly shows garbage), then screen clears and goes to a blank screen. No Menu.
Manually reseting, again briefly shows garbage, and then to the blank screen. Voltages on the boards have dropped to 4.7V which probably isn't conducive to getting to the menu.

Any thoughts from the smart people

Did you switch the monitor ROM back to the standard SYN600? Or is this a different 505 board?

Actually, even if the 65A is still in place, you should see at least the "H" of "H/D/M?" on the 540 screen. If the serial port is looking for a /CTS signal and not getting it, that's as far as you'd get. Otherwise, you would see the full "H/D/M?", but there would be no response to anything typed on the 542 keyboard.

It seems very odd that the screen would clear, all the way down to the lower right, but you wouldn't see at least that "H". Is that really what's happening? I count 27 lines (or partial lines) of garbage in the picture you posted. Are there any cut off at the top? The "H" should be at location $D0C6, which is on the fourth line from the top of the 32 total lines of video memory, but only the second line from the top of the 30 lines that should actually be fully visible. Maybe it is being "displayed" above the top edge of your screen?

Hi Danny,
Much thanks for your reply
Just to quickly answer your questions...
Firstly, yes, I have changed out the ROM. I have tried both SYN600, and a copy of SYNMON that I got from a friend who said it worked with his 540/505 combo.
I did also think that the H/D/M was being displayed off screen. Using V-hold on the monitor I can make it the image scroll (and also wrap), but unfortunately no hidden text appears when I do this. Still, it doesn't mean that something isn't hidden somehow outside the display area.
Anyway, I do count 31 (maybe 32) lines of text (See photo). There is a little bit of weirdness at the top most and bottom most lines only being partially shown.
I don't yet have a keyboard built so I cant test if I can drop into monitor and see if anything shows on screen. I may try another monitor, but I don't think it'll change anything.
As for the screen clear, it certainly briefly shows the garbage screen and then clears, and also clears after reset is released. I think the clear screen is actually the system filling screen full of 'spaces', whether that's whats happening here is still unknown.

Did I mention that the screen is still relatively unstable and jitters a lot.

Will report back if I have any success.

EDIT...Second monitor is no different.
I should also add that I am using a 12mhz Xtal instead of 12.08Mhz, so that could have something to do with the screen jitter.