dragon 32 fault

[thecaver99]

Hi All

first thanks for letting me join the community.

i have just got a dragon 32 boxed but it has a fault.

i have attached a pic of the screen, the dragon powers on and has all voltages as it should, the green screen comes on and has some text
but the screen is covered in ( and i am able to type but the first time i press a letter like L i get a letter D the and L.

i am unable to run any programs or type any commands.

would any one have any advise on where to look please.
the board is an issue 5

i have repaired many different retro computers over the years but i have never owned a dragon but have used them in the 80s.
looking forward to getting this running.


Graham

[thecaver99]

my apologies i realised i should have posted this in the hardware section.

[robcfg]

Is it frozen or can you type something?

Try CLS 2 and see if the screen turns yellow.

It looks like faulty ram or maybe any chip that controls the ram.

[thecaver99]

if i type cls or cls 2 it drops to next line and shows DG that's it.
if i press clear it locks up but when press reset its back to the same screen as here,
i can type about 10 or 12 characters then it locks up and i have to reset again.

[sixxie]

It's slightly baffling that it gets as far as it does - you'd expect either working-but-duff-video or not-working-at-all.

FMEA probably going to be quite difficult with this one - have you looked around the board for all the obvious stuff? ICs loose, scorch marks, that sort of thing

As has been noted in the Other Place, the corruption isn't as predictable as RAM faults usually end up looking (but it's the same corruption across groups of 12 scanlines reading the same addresses, which kinda makes "weak signal" seem less likely to me).

If you're up for the challenge, maybe start by tracing signal into/out of the SAM - get a scope on the data in/out pins of the RAM ICs, that sort of thing. But I can't even hazard a guess based on what we see there

[robcfg]

Could it be a corrupted rom?

[noggin32]

Long time lurker here. If you look at the differences it looks like bit 3 is always low.
It can't be the ROM if it's getting this far. Probably not RAM either.

Maybe the VDG chip connection to the data bus? Try cleaning the MC6847 socket.

"DRAGON" => "DRAGGN". G=O
"BASIC" => "BA[AC". [=S and I=A
"1982" => "1182". 9=1

Code: Select all

        v
    76543210
G = 01101111
O = 01100111

[ = 01011011
S = 01110011

I = 01101001
A = 01100001

9 = 00111001
1 = 00110001

[wayland]

Hello Graham,

My first approach would be that I don't actually care specifically what it's doing, it's simply getting corrupted. Some kind of noise or faulty signal is getting into the otherwise smooth operation of the computer.

A simple but tiresome job would be to replace all the capacitors. One of them maybe not smoothing the power properly. You could start with the easy ones on the PSU.

Another source of noise could be a dodgy connection on a socketed IC. Remove the IC and re-insert it thus improving the connection.

If the above no-brainer actions don't fix it then you will have to get smart and diagnose what's going on. At that point it's possibly a faulty IC.

[thecaver99]

it definitely is a ram fault, i removed the ram and fitted dual wipe sockets and eventually got the normal screen but turned out the sockets were garbage and i and suffering to remove them and fit turned pin ones.
i can feel the dragon wanting to breath fire once more getting close

[dublevay]

Great news. Well done!