Variation on A4000 dark gray screen problem

[ali1234]

Sorry to bump this year old thread, but I just had exactly the same situation that OP described, and it turned out to be something nobody mentioned yet in this thread. So for the next person to have this problem and search Google, check your VGA adapter:

Problem was caused by my VGA adapter which was just a straight cable adapter inside. When connected to my LCD monitor the A4000 displays only a dark grey screen unless I pull the chip RAM, then it shows a green screen. If I power it on with the monitor disconnected, wait a few secnds, and then plug the monitor, I see the "insert disk" animation and everything works as expected.

I was able to solder in a buffer chip to my adapter on the sync lines and now everything works fine.

[ali1234]

Which signal lines need the buffer chip? and what buffer chip did you use?

Where do you get the power? (from the HD15 VGA connector?)

I followed these instructions:
http://www.ntrautanen.fi/computers/hardware/misc/a4000_vga_cable.htm

Buffer goes on the sync lines only. Power comes from the Amiga monitor connector, and I used a 74LS244 chip, because I have hundreds of the things.

Here is a picture. Before modification there was only the grey wires between the two connectors.
https://plus.google.com/117474986382867317779/posts/Y4Btkm6ZVx9

[ali1234]

Certainly seems to be exactly the same symptoms. The plugging in of the monitor after booting sounds like a great trouble shooting technique. Well done!

Another is to revert to a 15khz capable Commodore monitor and standard Amiga video cable. Which I think we all assumed orb85750 was already doing.  If not, and it is the same problem as you had, then it's a good reminder to always give an overview of your system and it's connectivity before relating the problem.  Removes a lot of educated guessing. Even electronics professionals like Castellan can't read people's minds from a post. Face to face maybe.

I wonder if Orb85750 ever solved his problem....

My old 15kHz CRTs died years ago unfortunately. My nice new Dell U2410 does support 15kHz though. It even handles NTSC interlace correctly, but not PAL interlace (fields are spatially swapped).

[ali1234]

Can't see it..

Perhaps a image host without all the javascript would do it?

You're not missing much.
http://al.robotfuzz.com/~al/random/adapter.jpg