Dragon64

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Dragon64UK
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Joined: Sun Sep 29, 2019 6:32 pm

Dragon64

Post by Dragon64UK » Sun Sep 29, 2019 6:48 pm

Purchased a Dragon 64 at the begining of the year to add to my collection. The machine worked for approx 5hrs and then stopped. The issue I have is the Dragon Turns on and displays the Dragon basic Screen for a second and then goes to an orange screen. I have checked all the supplies are correct. So I am getting the 5V,12V and -12V from the PSU board inside the machine.

The machine will display a Cartridge correctly.So I suspect in may be a ram issue, but cant think of a way really to prove this. Any suggestions to help get this working again would be much appreciated?

sixxie
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Re: Dragon64

Post by sixxie » Mon Sep 30, 2019 11:54 am

RAM's quite a common thing to fail, but cartridges do also make use of it.

It's just possible your BASIC ROM is failing?

As it's a Dragon 64, try typing EXEC after it powers on to switch to 64K mode BASIC (which sits entirely in RAM) and see if the same thing happens?

Dragon64UK
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Joined: Sun Sep 29, 2019 6:32 pm

Re: Dragon64

Post by Dragon64UK » Tue Oct 01, 2019 7:58 am

Thanks for the suggestion.

I tried this but no change, but to be honest the keyboard on this machine wasnt great when it worked so its possible its not registering all the keys I'm pressing. I did try cload before this as I was hoping to hear the relay click.

Might try the Dragon 64 rom in a Dragon 32 to see if the fault shows on that, with this rom chip installed. But will check the pinouts are the same on the schematics first. Suspect they are, will also need to confirm which rom chip is holding the 32K rom and which is holding the 64K rom on the schematic, but will give me something else to try :-).

bluearcus
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Joined: Wed Sep 07, 2016 4:45 pm

Re: Dragon64

Post by bluearcus » Tue Nov 05, 2019 8:59 pm

Hi D64UK,

You'll not have any luck swapping the ROMs over... they are different pin counts and pinouts - Dragon 32 uses 2x8k 24 pin mask ROMs, Dragon 64 uses a pair of 16k 28pin EEPROMs. And the initialisation code which brings the machines up differs between the two ROMs as well.

Can you post a video somewhere of the failure occurring - that might help. It sounds an unusual failure mode - is always consistent?

Good luck

Mike

Dragon64UK
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Joined: Sun Sep 29, 2019 6:32 pm

Re: Dragon64

Post by Dragon64UK » Sun Dec 01, 2019 12:17 pm

Sorry for the delay I have only just seen your reply. I am suspecting the dragon is running some sort of memory test on boot up and displays the orange screen as it fails the test, but this is just a guess. As the basic Rom messages does show briefly. I will set it up and take a recording and post a link to it. Thanks in advance for any help.

bluearcus
Posts: 64
Joined: Wed Sep 07, 2016 4:45 pm

Re: Dragon64

Post by bluearcus » Mon Feb 03, 2020 5:46 pm

This is interesting - I have a Dragon 32 which I've just acquired that displays EXACTLY the same symptom.

It boots normally, then after a very short time, the screen instantly changes colour set and clears.

Haven't had time to investigate further, certainly a strange one.

Dragon64UK
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Joined: Sun Sep 29, 2019 6:32 pm

Re: Dragon64

Post by Dragon64UK » Sun Mar 29, 2020 12:38 am

Sorry about the delay in replying. Hoping you can see the two video's I have shared. One shows the Dragon 64 starting up issue and the other the Dragon 64 working correctly with a Cart installed.

https://drive.google.com/drive/folders/ ... sp=sharing


Any ideas on what you think is causing the Dragon 64 to start and then quickly change to an orange screen??????

Thanks in advance for any advice. Please note the display is fine when running a Cart Game.

sorchard
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Location: Norwich UK

Re: Dragon64

Post by sorchard » Wed Apr 01, 2020 9:24 am

My guess is ROM or RAM seems most likely, the orange screen being a symptom of a crash rather than a direct symptom of a fault.

If you're able to get your hands on a cartridge based machine code monitor, (and if it works!), you would be able to inspect the rom contents and check out the ram.

I remember doing this with an alldream cartridge to diagnose a bad rom in a D32 years ago. I think I had to do something with the /cart line to get it to autostart, then ignore the error messages from the assembler to get to the debug prompt where I could then inspect the rom contents. I eventually found a single faulty byte causing a crash during the startup sequence.
Stew

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