Dragon 32 Blank Screen Fault

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axeman
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Joined: Tue May 28, 2019 11:12 pm

Dragon 32 Blank Screen Fault

Post by axeman » Wed Feb 19, 2020 1:16 am

Hi,

I have a D32 which just displays a blank green screen. I've checked the +-5, 12 voltages which are all ok on the ram ,cpu, sam and various other places so I think the voltages are ok.

I've also swapped all the socketed chips into a working dragon and they all work ok.

Anyone got any ideas or troubleshooting tips?

Please excuse the colour on my TV as its been in a war with the ground and didn't fair to well.

Thanks in advance
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robcfg
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Joined: Sat Apr 04, 2009 10:16 pm
Location: Stockholm, Sweden

Re: Dragon 32 Blank Screen Fault

Post by robcfg » Wed Feb 19, 2020 11:33 pm

If you also swapped the rom chips, it may be that some ram chips are faulty.

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unumlapis
Posts: 97
Joined: Sat May 04, 2019 11:29 pm
Location: Malmo, Sweden

Re: Dragon 32 Blank Screen Fault

Post by unumlapis » Thu Feb 20, 2020 2:00 pm

This little YouTube video might come handy if you're into checking the memory.

axeman
Posts: 5
Joined: Tue May 28, 2019 11:12 pm

Re: Dragon 32 Blank Screen Fault

Post by axeman » Thu Feb 27, 2020 4:49 pm

Latest update to this issue is that I ended up not socketing and replacing the Ram as I thought I would first try socketing the right most ROM chip as some have said it is a major cause of such symptoms but that didn't help and the ROM was fine. I did however have a major breakthrough with getting this to work as when I touched the 14.218Mhz crystal (x2) I got a cursor to appear sometimes and then by gently pressing the crystal between finger and thumb I could get the machine to boot!!

It is very hit and miss (bit like holding up an antenna while standing on one leg sort of thing) but it is a big clue.

I've tried swapping the crystal but still the same so I'm going to do some testing of components connected to and around the crystal

axeman
Posts: 5
Joined: Tue May 28, 2019 11:12 pm

Re: Dragon 32 Blank Screen Fault

Post by axeman » Fri Feb 28, 2020 9:08 pm

Turns out touching the crystal to get it to boot wasn't a clue but it did allow me to test the keyboard.

I could only get key h,x,8,0 to work so this was a big clue. Traced the fault to the PIA 6821 IC26. Removed it and socketed then tested in a working machine and got the same fault, no boot up and blank green screen.

Replaced with a good pia and finally it works !!!!!

Thanks guys for all your help.

Another Dragon Lives....
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robcfg
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Location: Stockholm, Sweden

Re: Dragon 32 Blank Screen Fault

Post by robcfg » Fri Feb 28, 2020 11:07 pm

Great stuff!

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