Sick Dragon 32

A place to discuss everything Dragon related that doesn't fall into the other categories.
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Vyper68
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Sick Dragon 32

Post by Vyper68 »

Hi

Just wondering if anyone has any experience of or come across this issue and what can you do to resolve it.

I just bought a Dragon 32 off eBay and it's in a really nice condition. So i was pleased when it worked. I loaded a few tapes and it was fine. Then today i loaded a tape off the laptop and it started to play as normal ( Green,Red,Yellow,Blue ) then it flicked to a fuzzy white/black. Nothing i did outside externally would make it change.

I opened it up and it is an Issue Six board with the Daughter board others have referred to and is shown in the archive. Everything looked OK until i got up to the variable 10K resistor RV1 which was all covered in a white furry substance a bit like when a battery leaks. I cleaned it if the front of the resistor and there was no corrosion on the tracks.

I have ordered a like-for-like replacement of this part but it's coming from the Netherlands so it may take a few days. Just wondering if anyone
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sorchard
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Re: Sick Dragon 32

Post by sorchard »

The white powder is pretty common - I've seen it in just about every machine I've opened.

I think it's most likely to be tin oxide forming on the plating, but could just as easily be lead salts or some other form of slow corrosion going on. The safest thing to do is brush it off while collecting the dust with a vacuum cleaner.

The component itself is usually fine. In the case of variable resistors, I've seen it a couple of times that turning them a very small amount and then returning to the original position is enough to go from no video to fully working.

Is this the same machine that had the suspect keys?
Stew
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Vyper68
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Re: Sick Dragon 32

Post by Vyper68 »

Yes it is!
Odd thing is when it got here the suspect keys were fine there was no problem with any of the Keyboard. The reset button was a bit iffy so i ordered some contact cleaner for that which has yet to arrive.

I had bought a MC6821 just in case that was the problem with the keyboard.

I seemed odd that i loaded Rommels Revenge in off my laptop as an EXEC .WAV ran it and got to the menu screen and just the same as in Xroar and then i looked down and back up and the whole thing had gone to a fuzzy/dot crawl Black & White. I tried turning the the resistor and it went from black to grey-white and to black. I will try again over the next couple of days while i am waiting for a new one.
Is there any other part of the Video circuit i should concentrate on.... My real experience is Atari 8-Bit's but i have always wanted a Dragon because of the 6809 CPU
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sorchard
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Re: Sick Dragon 32

Post by sorchard »

Nice result on the keys. Could be a soldered joint on the PIA or keyboard ribbon connector that was open circuit and was temporarily fixed by vibration in transit. If the problem comes back then it may be possible to figure out where to look from the pattern of affected keys.

Regarding the video, it's worth having a look at the trimmer cap C7 just below the crystal between the reset button and the power connector. This fine-tunes the colour carrier frequency. An incorrect adjustment will result in no colour, so make a note of the original position in case the problem is elsewhere.

Also worth trying on a different monitor. The Dragon's video signal doesn't follow the PAL spec to the letter and some devices might not like it. I have a cheap converter that randomly decides the signal is SECAM and gives a grainy monochrome image.
Stew
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Vyper68
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Re: Sick Dragon 32

Post by Vyper68 »

Well so far i have tried tuning RV1 & C7 neither have any effect on the output and it remains Black & White. I have also tried different TV's and both have the same problem and i have also tried the RF output as well as i was using the Composite output and both TV's using both outputs show the same issue.

I am waiting on a new RV1 coming from the Netherlands and in the meantime i have ordered a new LM1889N IC as if i have understood this correctly the LM1889N adds the Chrominance to the video signal and the VDG the Luminance. The only other thing is to trace the Video signal back and check each component. It feels like something has failed as it was quite happily playing DunJunz on Day One and then after a few attempts at loading Wommel's it loaded and then went like this.
At first i thought i had turned a NTSC toggle on/off but realised there was none.

Just out of interest what does a NTSC Dragon look like on a UK TV???

Last straw would be replace the VDG - then the SAM, I know the CPU is good as i have fitted my HD63C09
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robcfg
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Re: Sick Dragon 32

Post by robcfg »

Can you take a picture of the screen and the boards inside your Dragon?

If the picture on the screen looks like a square instead of a rectangle, then it’s most probably a ntsc machine.
sixxie
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Re: Sick Dragon 32

Post by sixxie »

But there were no NTSC Dragon 32s...
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robcfg
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Re: Sick Dragon 32

Post by robcfg »

That’s why we need the pictures ;)

I think that the small chip on the top left corner of the board may be missing or damaged thus giving a gray picture.
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Vyper68
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Re: Sick Dragon 32

Post by Vyper68 »

Hi Guys
Thanks for all the input i have uploaded the pictures of the PCB today these were taken a few days ago when i was cleaning it on arrival the white corrosion on RV1 can be seen and was cleaned off and the Dragon played DunJunz quite happily all afternoon that day. The output from Video would be tomorrow at the earliest.

Image
Image
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sixxie
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Re: Sick Dragon 32

Post by sixxie »

I'm unable to help, others will know far more (but I think the LM1889s *do* die, so you never know...)

But interesting motherboard photo. Is the daughterboard doing the same fix that was needed in some CoCos? The HSync pulse would vary a bit due to heat or somesuch, and not necessarily trigger IRQs, so latches were put in to clean up the signal (if I'm remembering right). It does look that way, but seems a bit weird if this was already Mk II of the board design.

Also interesting that there are ferrite beads on yours, but the archive picture just has link wires. I'd guess due to the markings that maybe they assumed the beads were necessary but later found they weren't?
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