Black square when Dragon 32 is starting

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luigi
Posts: 2
Joined: Wed Jan 29, 2014 11:00 pm

Black square when Dragon 32 is starting

Post by luigi »

Hi.

I'm new in this site. My name is Luis and I'm from Spain. I've bought a Dragon 32, I loved this computer when I was child. In addition Dragon 200 was manufactured in Spain, so it's special for me.

I've bought a new Dragon 32, in the original box, with de plastic bag, ... But the seller said me that the computer has been tested a few months ago but at this moment it has a problem starting. Nevertheless I decided buy it.

I'd like ask you if you know what can be the problem. The computer runs but in the screen you can only see the green border and a big black square in the center. The welcome message and the command console don't appear.

Is it a typical failure?

I hope your answers.

Long life to Dragon!

Best regards.
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robcfg
Posts: 1527
Joined: Sat Apr 04, 2009 10:16 pm
Location: Stockholm, Sweden
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Re: Black square when Dragon 32 is starting

Post by robcfg »

Hi Luis, and welcome to the forum!

I'd open the computer and press the socketed chips in case they got loose during transport.

If that doesn't fix the error, we should check the service manual for the possible solution.

Good luck!
luigi
Posts: 2
Joined: Wed Jan 29, 2014 11:00 pm

Re: Black square when Dragon 32 is starting

Post by luigi »

Hi!

I've been looking the sockets and all seem be fine.

Where can I get a service manual? Has anyone had a similar problem?

:o Ahhhh! I want to repair my Dragon! :D
zephyr
Posts: 1474
Joined: Mon Jul 21, 2008 1:18 am

Re: Black square when Dragon 32 is starting

Post by zephyr »

luigi wrote: Is it a typical failure?
I have bever seen these exact symptoms described before.
luigi wrote: I'd like ask you if you know what can be the problem. The computer runs but in the screen you can only see the green border and a big black square in the center. The welcome message and the command console don't appear.
Dragon faults are very often caused by a failed SAM (SN74LS783/MC6883), VDG (MC6847), or CPU (MC6809E) chip. I would tend to suspect a faulty VDG if you can hear the relay click inside the case after entering MOTOR ON and MOTOR OFF at the command prompt (You can also try entering SOUND1,200 etc ). I would suspect a possible faulty SAM or CPU if you don't get any response from the relay (or sound) test.

The SAM and CPU chips are usually socketed. The VDG chip usually has its legs soldered direcly to the PCB.
luigi wrote: Where can I get a service manual?
The only service information that I'm aware of is here.
http://archive.worldofdragon.org/index. ... =Technical

Which type of motherboard do you have?
http://archive.worldofdragon.org/index. ... d_Pictures
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Rolo
Posts: 228
Joined: Sun Feb 10, 2013 7:36 pm

Re: Black square when Dragon 32 is starting

Post by Rolo »

The computer runs but in the screen you can only see the green border and a big black square in the center
Normally the border is black and the background is green :?: How about a photo of the screen?

:?: Is the machine running (just without display) or completely dead?
:arrow: zephyr's MOTOR ON/OFF test and the clicking relays.
btw. Is the relay clicking when you turn on the computer. Mine does that.

:?: Do you have any auto starting cartridge to see if the computer is doing something reasonable, like playing music?

:?: Did you check all the voltages?
:arrow: The older Dragons 32 with M8116E 16k DRAMS needed all kinds of funny voltages (+12VDC and +5VDC and -5VDC). So does your computer really have any memory ;) ?

:?: Do you connect your TV via UHF-modulator or directly to VIDEO OUT (scart/composite)? Both outlets are dead?
:?: Did you re-adjust the two potentiometers (DC-level and phase adjust) of the video signal a little bit? In the machine I bought, both of them were severely deteriorated and dirty. Is your video signal making it through?

:arrow: I built a little board connected to the printer port with LEDs for every line. They flash for every key press and every key release. And they react to the joystick buttons.

Plastic bags and friction on styrofoam, building up charges, near to computers' ports is a sparkling idea. I successfully destroyed two expensive custom chips of my ATARI ST back in the day, with something like that. :oops:
ukretro
Posts: 9
Joined: Tue Sep 16, 2014 6:51 am

Re: Black square when Dragon 32 is starting

Post by ukretro »

Rolo wrote: :?: Did you re-adjust the two potentiometers (DC-level and phase adjust) of the video signal a little bit? In the machine I bought, both of them were severely deteriorated and dirty.
Interesting... I have a Dragon 32 with poor Composite video output while my Dragon 64 outputs a much clearer display.

Would adjusting these pots clean up the video output on the 32?

If so, where are they located on the board and how are they marked?
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Rolo
Posts: 228
Joined: Sun Feb 10, 2013 7:36 pm

Re: Black square when Dragon 32 is starting

Post by Rolo »

Sorry for the delay, I've been offline for a week.

Well I cannot garantuee :D.
I'd definitely gave it a try. You can not destroy anything by carefully turning the potis. Just remember the original positions.

You'll find them on the schematics on sheet 3 (i. e. OKI323.jpg), labelled as RV1 (carrier burst phase) and RV2 (DC level adjust).
On my board (D32) RV1 is located something like 2 cm behind (east to) the tape connector. RV2 is soldered in 2 cm "south" to the power connector (with the cables leading to the PSU-board). They are easy to find. There are no other potis on the board. On my board, they used housed versions with a silver-grey plastic housing. Little dirty things, covered with kind of crystalline powder (like on a dead, run-out battery).

I (still) have no D64, but I think I read somewhere in this forum, that the D64 had a better TV-picture, than the D32. Maybe somebody can confirm?

Just try and tell us. I remember, the adjustment was quite delicate. I could immediately see the slightest movement on my TV-screen.
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