Master has a jumpy screen

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KarateEd
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Master has a jumpy screen

Post by KarateEd » Thu Mar 08, 2018 7:51 am

Hi Folks,

When I do a *HELP or *IMPORT on my Datacentre or play an 'active' game on my Master the screen jumps like crazy.

I've posted a couple videos on YouTube to show what I'm talking about.

Does anyone have an idea what I should check first? I connect up with a GBS-8200 and I know it works well as I've tested it on a Beeb.

Thanks for any help anyone can give.

Ed...... :-)

Links to vids.

https://youtu.be/D0iNNsVa6jI
https://youtu.be/z9klEjMoOZo

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hoglet
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Re: Master has a jumpy screen

Post by hoglet » Thu Mar 08, 2018 7:56 am

Is this a new problem, or has it always done this?

Does it do it with the Data Centre unplugged and *HELP?

It could be power supply related.

Another possibility... How is the 1MHz Bus cable routed? I had a problem with mine as I had routed it under the Beeb's circuit board, and a sharp lead on the PCB had managed to pierce one of the the cables.

Dave

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danielj
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Re: Master has a jumpy screen

Post by danielj » Thu Mar 08, 2018 8:02 am

I suspect it'll be something causing some level of interference somewhere :/ - my master's display via a GBS8200 gets jumpy as hell when the MDFS is next to the master, it's fine when it's a bit away - but I never managed to bottom it out precisely...
d.

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Re: Master has a jumpy screen

Post by KarateEd » Thu Mar 08, 2018 10:21 am

hoglet wrote:Is this a new problem, or has it always done this?
It did have some very small symptoms originally but very minor. They have gotten much worse.
hoglet wrote:Does it do it with the Data Centre unplugged and *HELP?
I've disconnected the DataCentre completely and it's still doing it. I just ran a simple program printing 10000 lines and it's jumping all over the place.
hoglet wrote:It could be power supply related.
I did change the caps, also some power output caps I think, it's a while ago so don't really remember.
hoglet wrote:Another possibility... How is the 1MHz Bus cable routed? I had a problem with mine as I had routed it under the Beeb's circuit board, and a sharp lead on the PCB had managed to pierce one of the the cables.

Dave
My DataCentre is external so the cable routes under the machine. The cable appears clear of punctures or abrasions.

Thanks for the reply Dave....

Not sure what caps other than the usual ones could cause something like this.

Ed...... :-)

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KarateEd
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Re: Master has a jumpy screen

Post by KarateEd » Thu Mar 08, 2018 10:23 am

danielj wrote:I suspect it'll be something causing some level of interference somewhere :/ - my master's display via a GBS8200 gets jumpy as hell when the MDFS is next to the master, it's fine when it's a bit away - but I never managed to bottom it out precisely...
d.
Yeh, don't think this is the problem here Daniel. Moving the GBS around hasn't helped and there is no other interference closer than about 3 or 4 feet so I don't see that as being a problem.

Ed...... :-)

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Re: Master has a jumpy screen

Post by cmorley » Thu Mar 08, 2018 10:35 am

I've seen similar when connecting a SEGA Megadrive/Genesis (with a 50Hz/60Hz switch) to a Pioneer Plasma TV with a SCART lead. In auto signal detect mode it would roll and then pop back to the top again when switched to 60Hz. Forcing PAL mode on the TV synced perfectly for either 50/60Hz.

I also have two flat screen TVs which dislike syncing to a B output. (One drops sync and you need to cycle through the inputs to get it back, the other blanks when it drops sync) IIRC it is not quite PAL timing but close enough for CRTs... perhaps your screen is borderline too and now is dropping the sync?

Do you have another screen you can try?

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Re: Master has a jumpy screen

Post by KarateEd » Thu Mar 08, 2018 10:47 am

I'm wondering about my monitor cable.... el cheapo work one (when I used to do such a thing). I'll try to find a more robust monitor cable just to rule that out.

I've never had a problem with my GBS-8200s, have had a couple running with no issues. I doubt they are the problem.

Ed...... :-)

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Re: Master has a jumpy screen

Post by KarateEd » Thu Mar 08, 2018 10:49 am

cmorley wrote:I've seen similar when connecting a SEGA Megadrive/Genesis (with a 50Hz/60Hz switch) to a Pioneer Plasma TV with a SCART lead. In auto signal detect mode it would roll and then pop back to the top again when switched to 60Hz. Forcing PAL mode on the TV synced perfectly for either 50/60Hz.

I also have two flat screen TVs which dislike syncing to a B output. (One drops sync and you need to cycle through the inputs to get it back, the other blanks when it drops sync) IIRC it is not quite PAL timing but close enough for CRTs... perhaps your screen is borderline too and now is dropping the sync?

Do you have another screen you can try?
I do have another screen to try, in fact also have 1 CRT just to check so being it's almost 3AM, even retired guys have to get some sleep but I'll do that tomorrow and let people know the results.

I suppose if these don't pan out then it's down to something in the Master.

Ed...... :-)

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Re: Master has a jumpy screen

Post by KarateEd » Fri Mar 09, 2018 4:13 am

Hi Folks,

A bit of an update.

I put my CRT with it's VGA cable on the Master and it's still very jumpy.

I talked with Mark Haysman of Retroclinic fame about something I saw about resistors in the cable from the RGB port to the GBS-8200 port and he said there should be 200 ohm resistors on the sync and RGB lines of the cable.

I will do that next, it'll probably take 1 or 2 days to get that organized. I first have to search out 200 ohm resistors. I may have some hiding in the shed but it's a bit of a mess so it will be a chore to find them.

Anyway, once I've re-done the cable with the resistors, I'll post back here to the results.

Ed...... :-)

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1024MAK
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Re: Master has a jumpy screen

Post by 1024MAK » Fri Mar 09, 2018 4:34 am

If you can't find any 200 ohm resistors, use 220 ohm resistors. Even 270 ohm should do.

For the red, green and blue lines though, they are less important, as these inputs go via the variable preset resistors (pots) on the GBS-8200 board, so adjusting these has a similar function.

You should however use a resistor in the sync line.

Good luck :wink:

Mark
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KarateEd
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Re: Master has a jumpy screen

Post by KarateEd » Sun Mar 11, 2018 1:22 am

Hi Folks,

As promised, an update after rebuilding my video cable with, in this case, 220 ohm resisters on the sync and RGB lines. The jumpiness has mostly gone away.

With Gyroscope, the screen jumps anyway when you move down it so it's not maybe the best test but..... it was playable and I got over 3000 on the first try on my Master.

Currently, I've done a *HELP MOS and not let it go all the way through, it's holding just before the last few commands and - very little jumpiness when before it was going nuts. It still jumps about every 20 or 30 seconds. Other than that it's rock solid. That's something I can live with, it could be anything, after all, these are pretty old computers and maybe if I was super ambitions, I'd replace every cap in the beast but I've not got the confidence that that would be a good idea.

Anyway, resistors on the lines seems to be the fix for this issue.

Thanks everyone for their well-wishes and help to resolve this.

Ed...... :-)

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marcusjambler
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Re: Master has a jumpy screen

Post by marcusjambler » Sun Mar 11, 2018 1:35 am

Recently I had problems with RGB sync with a B+....
I socketed a new IC26 ( 74s04 ) and replaced C13 ,C16,R30,R31 & R35 clock circuit components.
Now its steady as a rock.

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Re: Master has a jumpy screen

Post by KarateEd » Sun Mar 11, 2018 2:14 am

marcusjambler wrote:Recently I had problems with RGB sync with a B+....
I socketed a new IC26 ( 74s04 ) and replaced C13 ,C16,R30,R31 & R35 clock circuit components.
Now its steady as a rock.
Ah, thanks for that. That is something I could tackle on this Master. It's relatively easy to replace the clock circuitry components and wouldn't be too onerous a task.

Ed...... :-)

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