I'm totally unfamiliar with the Dragon 32, but I'm hoping someone with more technical insight into how or what the problem with it might be could offer any advice.
By looking at the picture you posted on stardot, and assuming the ram chips are ok, my guess would be that the sam chip is damaged or maybe there's a shorted track somewhere.
Sam chips can be found relatively cheap, so I'd start by replacing it and see what happens.
I've gone through some of the tests outlined in the post above and I've drawn a blank with those also. I have noticed however that Pin 20 on the MC6847P is broken off right at the body of the chip and theres no way it can make contact with the socket. Is it supposed to be broken off or lifted?
I've got the another 7 RAM chips to take off, socket and test but I don't think they've gone bad(Famous last words!!! ) Can anyone suggest a good place to pick up replacement SAM and 6847 IC's?
martinjharvey wrote:
I've gone through some of the tests outlined in the post above and I've drawn a blank with those also. I have noticed however that Pin 20 on the MC6847P is broken off right at the body of the chip and theres no way it can make contact with the socket. Is it supposed to be broken off or lifted?
Pin 20 is DA11, which shouldn't be used in the Dragon as the SAM generates the video addresses.
I've got the another 7 RAM chips to take off, socket and test but I don't think they've gone bad(Famous last words!!! ) Can anyone suggest a good place to pick up replacement SAM and 6847 IC's?
It is possible that if one of them is bad it is causing the RAM address lines to become "corrupted" for example if it was pulling it perminently high or low.
It should also be possible to run the machine with just one bank of 4116s installed though obviously you'll only get 16K or RAM.
prime wrote:Pin 20 is DA11, which shouldn't be used in the Dragon as the SAM generates the video addresses.
As I've not worked on a Dragon before, I wasn't sure if the missing pin was down to someone else handywork somewhere along the line
prime wrote:It is possible that if one of them is bad it is causing the RAM address lines to become "corrupted" for example if it was pulling it perminently high or low.It should also be possible to run the machine with just one bank of 4116s installed though obviously you'll only get 16K or RAM.
Took the first bank of RAM out and powered on and all the garbage on screen has gone but theres nothing much of anything else happening. No prompt, cursor or anything. Just a solid border with a blank solid orangey centre.
I'll get all the RAM socketed and tested then. I did piggyback a good 4116 on the ones soldered in to see if that showed anything up, but I suppose if more than ones gone kaput then that test would have missed it.