Dragon 64 - Charset issue

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ZahrlAn
Posts: 22
Joined: Tue Jan 08, 2019 1:02 pm

Dragon 64 - Charset issue

Post by ZahrlAn »

Hello.

I have a Problem with my Dragon 64.
One moment to another the picture was gone and two Caps on the Powerboard where gone. C5 and C8. I replaced the two Caps and the C6 and C9 Caps too. Still no picture.

Then i pulled out the two socket IC 38 and IC 39 and reseated it. Then i finally got a picture.

My Screen is showing wired chars, The Dragon itself is working.
FBA14DBA-D4F7-448A-BE28-9BA7A92DAC61.jpeg
FBA14DBA-D4F7-448A-BE28-9BA7A92DAC61.jpeg (4.99 MiB) Viewed 3761 times
Loading OS9 with Zaxxon Disk Interface shows this:
358C5F5C-B07D-4ED9-BF7B-EE50A1E67141.jpeg
358C5F5C-B07D-4ED9-BF7B-EE50A1E67141.jpeg (2.98 MiB) Viewed 3761 times
Seems that the output is somehow distorted.

Can someone help me to sort that out?

Regards
Andreas
ZahrlAn
Posts: 22
Joined: Tue Jan 08, 2019 1:02 pm

Re: Dragon 64 - Charset issue

Post by ZahrlAn »

My Mainboard is an Issue 3.

As you can see in the first Picture, i pushed the first two lines of the keyboard.
Numbers are shown mostly correct but the normals chars are wrong.
sixxie
Posts: 1181
Joined: Fri Jul 18, 2008 8:36 am
Location: Hertfordshire
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Re: Dragon 64 - Charset issue

Post by sixxie »

Looks like a fault between RAM chip for bit 4 through the video data latch through to DD4 (pin 7) on the VDG, seeing as everything else is functioning.
ZahrlAn
Posts: 22
Joined: Tue Jan 08, 2019 1:02 pm

Re: Dragon 64 - Charset issue

Post by ZahrlAn »

So, for a beginner, that means maybe i should check the connection of pin 4 of the VDG and follow the line to the RAM?
Sorry to ask in that dump behavior.

Regards
Andreas
sixxie
Posts: 1181
Joined: Fri Jul 18, 2008 8:36 am
Location: Hertfordshire
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Re: Dragon 64 - Charset issue

Post by sixxie »

ZahrlAn wrote: Thu Sep 17, 2020 6:50 am So, for a beginner, that means maybe i should check the connection of pin 4 of the VDG and follow the line to the RAM?
Sorry to ask in that dump behavior.
Well, it might not be this, but the first thing I'd be checking is pin 7 of the VDG (IC10) to pin 5 of the data latch chip (IC20, a 74LS273). It looks like something is pulling this line high. It's bit 4 of the data bus as presented to the VDG.

If you try the following little 1-liner after starting up an emulator, you'll probably recognise the pattern:

Code: Select all

FORI=1024TO1535:POKEI,PEEK(I)OR&H10:NEXT
ZahrlAn
Posts: 22
Joined: Tue Jan 08, 2019 1:02 pm

Re: Dragon 64 - Charset issue

Post by ZahrlAn »

Thanks a lot, i will try to check that on the weekend.
ZahrlAn
Posts: 22
Joined: Tue Jan 08, 2019 1:02 pm

Re: Dragon 64 - Charset issue

Post by ZahrlAn »

It‘s gotten worse.

Next time i turned on the Dragon it showed me this picture:
1FC98634-477C-49A9-8B10-148CF25BC17F.jpeg
1FC98634-477C-49A9-8B10-148CF25BC17F.jpeg (4.15 MiB) Viewed 3658 times

When i softly touch IC10 this is shown on the screen:
D9697760-61B0-46DD-819E-130BB356C06D.jpeg
D9697760-61B0-46DD-819E-130BB356C06D.jpeg (4.81 MiB) Viewed 3658 times
This doesn't appear when touching other ICs or anything.

So, could anyone help me with this? Probably send my Mainboard to you and you gonna try and fix it?
Or maybe some other things i can try?
sixxie
Posts: 1181
Joined: Fri Jul 18, 2008 8:36 am
Location: Hertfordshire
Contact:

Re: Dragon 64 - Charset issue

Post by sixxie »

Looks like uninitialised RAM, except bit 4 is still stuck high!

Now I'd be checking the CPU and SAM are still socketed ok - you mentioned reseating them before.

Some board photos might be informative... never know.

I can't offer to attempt repair, though there are others on here who might.
ZahrlAn
Posts: 22
Joined: Tue Jan 08, 2019 1:02 pm

Re: Dragon 64 - Charset issue

Post by ZahrlAn »

I did a reeseating of IC 38 and IC39, but that changed nothing.

Here are some Photos.
E49B4B7D-A3D6-48E7-902F-8FF61638ED67.jpeg
E49B4B7D-A3D6-48E7-902F-8FF61638ED67.jpeg (3.23 MiB) Viewed 3588 times
F9170DC6-EA9A-4B23-82CD-58922DF5261D.jpeg
F9170DC6-EA9A-4B23-82CD-58922DF5261D.jpeg (3.58 MiB) Viewed 3588 times
DD8AAF51-7572-4A1A-990D-2B0506BE4445.jpeg
DD8AAF51-7572-4A1A-990D-2B0506BE4445.jpeg (2.65 MiB) Viewed 3588 times
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