Sick Dragon 32

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

Post by sorchard »

Vyper68 wrote:Would the VDG carry on with Pin 20 disconnected ... ?
Pin 20 of the vdg is an unused output and should be left unconnected.
Stew
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Vyper68
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Re: Sick Dragon 32

Post by Vyper68 »

sorchard wrote:
Vyper68 wrote:Would the VDG carry on with Pin 20 disconnected ... ?
Pin 20 of the vdg is an unused output and should be left unconnected.
Well that is something i have not come across before so that's filed away for the future. :oops:
The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
sorchard
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Re: Sick Dragon 32

Post by sorchard »

I didn't explain that very well: I should have clarified that the pad isn't connected to anything, so it wouldn't make any difference whether the pin is soldered or not.

All the pins are normally soldered in so I guess something odd happened during production or there was some experimentation in the past.
Stew
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Vyper68
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Re: Sick Dragon 32

Post by Vyper68 »

sorchard wrote:I didn't explain that very well: I should have clarified that the pad isn't connected to anything, so it wouldn't make any difference whether the pin is soldered or not.

All the pins are normally soldered in so I guess something odd happened during production or there was some experimentation in the past.
I have to admit i was feeling hopeful i had found the problem. It had definitely parted company with the solder pad as the rest of the pin was still soldered in. The way the VDG is soldered in pins 21 - 40 are nice and straight. Pins 1 - 20 are curved quite badly so they are probably under a lot of tension and the heat cycles must have weakened the pin and it fractured although none of the others have failed yet.
The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
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Vyper68
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Re: Sick Dragon 32

Post by Vyper68 »

Well that was disappointing, i fitted a new LM1889N and the problem is still there. Does anyone have any ideas where to look next?

In the meantime i am going to replace all the electrolytic capacitors on the Power and Main PCB's i may also replace the Voltage regulators as well. Does anyone have a list of the Tantalum capacitors to hand rather than me tracking them down one by one? - Do they need to be Tantalum at all - can i fit Electrolytic capacitors instead???

Thanks again for you support and i hope you can help me get this back up and running.

Also the C7 seems to have no effect on the Video output at all would that affect the screen this much?
The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
Alastair
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Re: Sick Dragon 32

Post by Alastair »

Vyper68 wrote:The way the VDG is soldered in pins 21 - 40 are nice and straight. Pins 1 - 20 are curved quite badly so they are probably under a lot of tension and the heat cycles must have weakened the pin and it fractured although none of the others have failed yet.
If you have not already checked the solder connections of pins 1 to 19 (or at least those pins that matter - whichever they may be) with a multimeter then perhaps you should. I know from experience with SCART connectors that a solder joint may look fine to the naked eye but never-the-less can be sufficiently damaged that it will not carry the signal from the socket to the motherboard.
sixxie
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Re: Sick Dragon 32

Post by sixxie »

FYI, pins 9-11 are the chroma outs...
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Vyper68
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Re: Sick Dragon 32

Post by Vyper68 »

I think i might be getting somewhere now...

I have just bought another D32 ( this one is permatanned but came with Ghost Attack and some tapes ) - This is an Issue 2 Board with RV1 and RV2 ( this is the important part )

If i adjust RV1 on this Issue 2 Dragon too far i can get the same output as the Issue Six Dragon - so i need to find more out about RV1 and RV2.

If the RV1 in the Issue Six the same part of the circuit as RV2 in the Issue 2 PCB right up near the ribbon connector then i need to find out what replaced the RV1 circuit of issue 2 PCB's on Issue 6 PCB's as that seems to be the part that has cause the problems.
Anyone got any ideas which part of the Issue 6 board replaced the Variable resistor ???
The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
sorchard
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Re: Sick Dragon 32

Post by sorchard »

The ISS6 video circuit has a few differences compared to the ISS2. The biggest difference being the video output amplifier consisting of three transistors instead of an opamp. (Though strangely, some ISS2 boards do have the transistor version)

RV1 on the ISS2 boards adjusts a voltage that defines the chroma burst phase. On ISS6 boards this was replaced by the ØB signal from the 6847, making adjustment unnecessary. If not adjusted correctly, I would expect either weird colours, or the display device failing to lock on to the colour burst or otherwise failing to recognise a valid PAL signal.

RV2 on the ISS2 boards adjusts the DC offset of the video output. This is RV1 on ISS6 boards. An approximate adjustment usually works. Too far out gets you one of too bright/too dark/no colour/no video.

C7 fine-tunes the colour subcarrier frequency. If too far out then that can also result in no colour. Ideally it is adjusted to make the 'dot crawl' effect too fast to see, but drifts badly with time & temperature. It makes the Dragon display a special kind of special :)

The health or otherwise of the power supplies directly affects the video in a number of ways, so it would be wise to eliminate any problems with those first.
Stew
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Vyper68
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Re: Sick Dragon 32

Post by Vyper68 »

I have tried the power board and PSU from the fully working Issue 2 in the Issue 6 and that had no effect. I have replaced the Electrolytic Caps on the Issue 6. I was going to replace the Caps on the Power Board as well but it seems that wasn't needed ( still might do it though )
The PSU's check out as well so that is no the cause.
I will soldier on though.

This issue 2 is really early too the date code for the chips are week 44 1982 there are only 8 OKI chips as well.
The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
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