Electron with odd video issue

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Sampull-MC
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Electron with odd video issue

Post by Sampull-MC » Fri Jan 10, 2020 6:42 pm

Hi all. Wondering if anyone has any thoughts about this little problem of mine.

My Elk has started outputting an NTSC signal from the Composite port. No idea why (PAL machine obviously). rather annoying since I bought an RGB - Scart cable and my TV isn't exactly the most forgiving in that sense. any ideas where to start? my only thought would be the clock crystal?

not to sound annoying but, suggestions with an oscilloscope are impossible to me as I don't have one.

if it helps, ISS 6 motherboard.

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Re: Electron with odd video issue

Post by 1024MAK » Fri Jan 10, 2020 9:47 pm

What makes you think that it is a NTSC signal?

Mark

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Re: Electron with odd video issue

Post by Sampull-MC » Fri Jan 10, 2020 10:01 pm

1024MAK wrote:
Fri Jan 10, 2020 9:47 pm
What makes you think that it is a NTSC signal?

Mark
my TV has a very handy function that it will detect and recognise the frequencies and show me what they are, just not display them properly/at all. my Elk has what I call a "Collapse Effect" it just appears then falls off the bottom of the screen like a mouse scroll wheel with a motor attached to it. that's how I know. what causes it? no clue. worked fine as a PAL machine for about a month and then just did a complete flip. and now I'm here.......

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Re: Electron with odd video issue

Post by mr-macrisc » Fri Jan 10, 2020 10:26 pm

I reckon it’ll still be pal but whatever has changed/failed has cause it to look like ntsc due to way tv detects it rather than actually being one.

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Re: Electron with odd video issue

Post by Sampull-MC » Fri Jan 10, 2020 10:32 pm

mr-macrisc wrote:
Fri Jan 10, 2020 10:26 pm
I reckon it’ll still be pal but whatever has changed/failed has cause it to look like ntsc due to way tv detects it rather than actually being one.
I do see your point here, but I have tried it on 2 other TVs of varying ages and all register as NTSC or in one other case SECAM. so I doubt it's my TV detection being an issue.....

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Re: Electron with odd video issue

Post by 1024MAK » Fri Jan 10, 2020 11:35 pm

Yeah, the reason I asked, is that there are timing differences between 625 line and 525 line. Then the colour encoding system for PAL is different to NTSC and both are different to SECAM.

It sounds like there is a hardware fault with your Electron.

Can you post a photo of the large square chip (the ULA) please.

Mark

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Re: Electron with odd video issue

Post by Sampull-MC » Fri Jan 10, 2020 11:40 pm

1024MAK wrote:
Fri Jan 10, 2020 11:35 pm

Which issue board is it? Can you post a photo of the large square chip (the ULA) please.

Mark
Issue I can answer quickly. ISS 6. ULA I can't right now, will do tomorrow. By the sound of it, it seems you may have an idea or two, am I right there?

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Re: Electron with odd video issue

Post by mr-macrisc » Sat Jan 11, 2020 9:20 am

So it’s a pal computer and two detect as ntsc and one secam. Defo sounds like the timing has gone well out and it’s just detecting mistakenly based on the dodgy timed output.

What output you using? RGB to RGB scart? Ah I see you say composite. Have you got a cable to try Rgb scart?

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Re: Electron with odd video issue

Post by Sampull-MC » Sat Jan 11, 2020 11:38 am

mr-macrisc wrote:
Sat Jan 11, 2020 9:20 am
Have you got a cable to try Rgb scart?
It's in the post as we speak, got bored of the monochrome composite. Which as we established isn't working very well.
If the RGB detects as something stupid, what should I try next? New clock crystal?

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Re: Electron with odd video issue

Post by Sampull-MC » Sat Jan 11, 2020 12:36 pm

Ok update time. Just got the cable and plugged everything in, cable works fine but the video still has a "Collapse Effect" (see one earlier post for that). TV Does properly detect it as an RGB signal though. so that's good.
Where do we go from here? I can only think clock crystal or something more expensive...

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Re: Electron with odd video issue

Post by danielj » Sat Jan 11, 2020 5:08 pm

If the elk is booting then it's either ULA or something related or something around the video timing.

https://www.4corn.co.uk/archive/diagram ... %20PCB.jpg

I'd check LK2 and what the deal is with IC11? If you have a scope you can at least check what's coming out of the crystal?

d.

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Re: Electron with odd video issue

Post by hoglet » Sat Jan 11, 2020 5:10 pm

Can you post a photo of the "collapse effect"?

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Re: Electron with odd video issue

Post by Sampull-MC » Sat Jan 11, 2020 5:12 pm

as requested. ULA. and motherboard/powerboard as well if it helps.
IMG_1358.JPG
IMG_1362.JPG
IMG_1361.JPG
IMG_1360.JPG
IMG_1359.JPG

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Re: Electron with odd video issue

Post by Sampull-MC » Sat Jan 11, 2020 5:14 pm

danielj wrote:
Sat Jan 11, 2020 5:08 pm
If you have a scope you can at least check what's coming out of the crystal?
as was stated in the first post I made here, I don't unfortunately. would have tried otherwise
hoglet wrote:
Sat Jan 11, 2020 5:10 pm
Can you post a photo of the "collapse effect"?
I can indeed. gimme a moment

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Re: Electron with odd video issue

Post by Sampull-MC » Sat Jan 11, 2020 5:30 pm

Here's the "Collapse Effect"
IMG_1363_Trim_Trim.mp4
(3.07 MiB) Downloaded 35 times

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Re: Electron with odd video issue

Post by 1024MAK » Sat Jan 11, 2020 6:12 pm

danielj wrote:
Sat Jan 11, 2020 5:08 pm
If the elk is booting then it's either ULA or something related or something around the video timing.
danielj wrote:
Sat Jan 11, 2020 5:08 pm
I'd check LK2 and what the deal is with IC11? If you have a scope you can at least check what's coming out of the crystal?
But from what I can see, LK2 and IC11 only affects the RF/UHF output and the optional colour feed to the composite output. The problem is affecting the monochrome composite output and the RGB output.

Hence I thinking that either there is a fault with the ULA or a USA version of the ROM is in use. But as it’s a U.K. spec. machine, that rules out the ROM (unless there is a strange partial failure).

Mark

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Re: Electron with odd video issue

Post by Sampull-MC » Sat Jan 11, 2020 6:15 pm

1024MAK wrote:
Sat Jan 11, 2020 6:12 pm

Hence I thinking that either there is a fault with the ULA or a USA version of the ROM is in use.

Mark
I doubt there is a US ROM in there, it's been a PAL machine all it's life from new.
which means I probably need a new ULA to fix the issue... ah well. at least an answer has been reached.

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Re: Electron with odd video issue

Post by 1024MAK » Sat Jan 11, 2020 6:15 pm

See edit...

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Re: Electron with odd video issue

Post by Sampull-MC » Sat Jan 11, 2020 6:18 pm

I'm guessing you can't piggy-back a ULA, can you?

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Re: Electron with odd video issue

Post by 1024MAK » Sat Jan 11, 2020 6:22 pm

Not recommended...

Mark

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Re: Electron with odd video issue

Post by Sampull-MC » Sat Jan 11, 2020 6:27 pm

so that leaves me with 2 options. a new ULA or a scart NTSC/PAL switchbox. at least I have an answer after boring myself with symptoms and schematics. lol.

Thanks for the help. much appreciated!

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Re: Electron with odd video issue

Post by danielj » Sat Jan 11, 2020 7:00 pm

Was there ever a US version of the Electron ROM? I don't think there was :?

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Re: Electron with odd video issue

Post by 1024MAK » Sat Jan 11, 2020 7:17 pm

danielj wrote:
Sat Jan 11, 2020 7:00 pm
Was there ever a US version of the Electron ROM? I don't think there was :?
I’ve not heard of one, but given the effort Acorn went to with providing a possible NTSC video output with the hardware, you never know...

Mark

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Re: Electron with odd video issue

Post by 0xC0DE » Sat Jan 11, 2020 7:24 pm

I have to ask. Does every Electron (every issue #) have the ability to output NTSC by design?
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Re: Electron with odd video issue

Post by 1024MAK » Sat Jan 11, 2020 7:47 pm

I’m guessing (as I don’t have the time to read through the thread about the detailed workings of the Electron’s ULA) that the U.K. / European version uses a ULA that only has PAL video timing. Presumably if Acorn had attempted to launch an overseas NTSC version of the Electron, it would have had a ULA with NTSC video timing.

Also please note that PAL and NTSC are colour encoding systems. The original monochrome video standards are 625 line (15625Hz line, 50Hz field frequency, 25Hz frame frequency) which in the U.K. is ITU system “I” and 525 line (15750Hz line, 60Hz field frequency, 30Hz frame frequency) which in the U.S.A. is ITU system “M”.

When colour is added, the U.K. standard becomes “PAL-I” and the U.S.A. system becomes “NTSC-M”. Note that the “NTSC-M” standard uses a slightly different line frequency (15734Hz) and a slightly different field frequency (59.94Hz) compared to the monochrome standard.

It is possible to use NTSC colour encoding with a 625 line system and it is also possible to use PAL colour encoding with a 525 line system (known as PAL-M, as used in Brazil).

Mark

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Re: Electron with odd video issue

Post by Sampull-MC » Sun Jan 12, 2020 4:10 pm

Right, Final update for this little journey of mine.

Since there isn't a scart compatible NTSC/PAL switcher, I have finally got colour out of it with the famous "LK4 and the paperclip" trick.
not quite what I thought I would be doing, but thanks for helping me finally figure out what the heck was up with it!

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Re: Electron with odd video issue

Post by Sampull-MC » Mon Jan 13, 2020 1:02 am

Just one last question for this post, Should the ULA finally kick the electric bucket, anyone know where I could source a replacement? Or is my best shot taking a gamble with a spares machine on ebay?

I know where to get some obscure parts, (spectrum ULAs, etc) but the ULA for the electron has evaded me. any thoughts?
Last edited by Sampull-MC on Mon Jan 13, 2020 4:45 pm, edited 1 time in total.

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Re: Electron with odd video issue

Post by Richard Russell » Mon Jan 13, 2020 2:19 pm

Sampull-MC wrote:
Fri Jan 10, 2020 10:32 pm
I have tried it on 2 other TVs of varying ages and all register as NTSC or in one other case SECAM. so I doubt it's my TV detection being an issue.....
SECAM has identical timings to PAL (they are both 625-line 50-fps standards, differing only in colour encoding) so the fact that one TV registers it as SECAM supports the theory that, whatever has happened, the output isn't NTSC. Rather, the timing has gone astray and it's confusing the TVs' detection mechanisms. An NTSC-to-PAL converter wouldn't help.

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Re: Electron with odd video issue

Post by Sampull-MC » Mon Jan 13, 2020 2:24 pm

Richard Russell wrote:
Mon Jan 13, 2020 2:19 pm
An NTSC-to-PAL converter wouldn't help.
Well, I do have an NTSC/PAL converter already that uses Composite, and the "Collapse Effect" that I have mentioned a few times is eliminated entirely, with the only drawback being a *barely* noticeable drop in the sharpness. only reason I asked if anyone had any ideas to fix it is because I was completely bewildered and curious, but at the same time, didn't really care if no one had any ideas since the computer itself still worked with that.
Last edited by Sampull-MC on Mon Jan 13, 2020 4:18 pm, edited 1 time in total.

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Re: Electron with odd video issue

Post by Richard Russell » Mon Jan 13, 2020 2:30 pm

1024MAK wrote:
Sat Jan 11, 2020 7:47 pm
Also please note that PAL and NTSC are colour encoding systems.
Well, if we're being pedantic. PAL is indeed a colour encoding system but NTSC isn't. The National Television System Committee was established in 1940 and was responsible for the monochrome TV broadcasting standards in the US long before they decided on the colour encoding standard more than a decade later. Yes, if one is specifically talking about colour encoding systems then 'NTSC' is well understood in that context, but it's not what the initials necessarily imply.

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