Acorn A5000 display problem

[Zelandeth]

Calling all Acorn experts!

I've got an old A5000 here at my parents place which I tend to use quite a bit at the weekends for word processing. I know I could use this PC for that...but I like using the A5000!

Recently, I picked up a TFT monitor for my PC at the flat - displacing it's decent 17" CRT one to this PC - so I was going to put its less decent one on the A5K, as it's old AKF18 has a few issues (focus is far from great, and lately has been suffering sporadic horizontal frame collapse - that's not the subject of this post though).

Mode selection was normally set to "auto" which worked fine with the AFK18. I set it to VGA however before connecting up the VGA monitor (Tiny WS771B). It worked brilliantly. Somehow having a decent refresh rate and a monitor that's actually sharp makes the whole user-interface thing so much more pleasant.

However, upon the next cold start, the monitor popped up a dialog complaining that the input was out of range (H=0.1kHZ, V=120.4Hz). "Hmm..." I thought, assuming that I'd forgotten to save the config or something, so still having the AFK18 on the desk I just switched the VGA leads over. ...and was rewarded with a picture which had somehow managed to "wrap" around three times vertically. No amount of mode switching restored any sort of sanity (I know my way around well enough to find my way into the display controls even in triple-o-vision). Powered off and on again, and all returned to normal...however if I power the system up with no monitor or the Tiny one plugged in, the graphics system seems to go nuts. Just tried it with this Dell E771, and it works perfectly. As this is the best monitor I've got here, I'd rather use it on the PC though!

Any ideas as to why this is happening? Equally to the point, anyone got any idea how to solve it?

[Vectrolosys]

Hello,

This is an odd one, I'll be honest, I have not seen it on any of my older Acorn equipment, which includes an A5000, but I tend to use the original monitors supplied by acorn, though I tend to avoid the AKF18 due to it's potential to catch fire, there was a massive recall on these back in the early 90's.

The video controller in the A5000, or VIDC10 as it is known, was designed to drive VDU's at a range of resolutions, up to around 800x600 in 256 colours, if I recall.

I'd be inclined to set the resolution (from the palette icon if I recall) to the lowest possible, i.e. 640x480 in 16 colours and gradually work up from there.

Not sure if this is RiscOS 3.5 onwards only, but I do remember having to play about with monitor definition files in order to use slightly spanglier monitors on my RiscPC, I can't remember if this was a RiscOS 3.5 thing onwards, or if 3.1 was similarly affected. It did allow you to get the best from the monitor and not over tax the VIDC controller chip.

The AKF18 had pretty poor focus out of the box to be honest, the AKF50 , if you can get hold of one, is a much better proposition, the AKF60 even more so. However, the ultimate for the Acorn A series machines, has to be the AKF85 which is a rebadged phillips of some sort.

The AKF18 would probably have thrown a wobbler as the VIDC was trying to drive it at a mode it did not support, 800x600 at 60hz tops on that one if I recall.

Anyway, to recap. Lower the res to 640x480 in 16 colours and plan to aim for an 800x600 in 256 colours (I think this is supported on these) as an optimum. If you can find one, on ebay, the add in card that Computer Concepts did for these, which would display 32K colour modes, this could be worth the hunt.

James

[Rat boy]

I've not had a good start here, being new, so bear with!! what was automatic in the day, is now a distant memory..

A suggestion, and only that; is that the computer and monitor aren't automatically syncing as they ought to; ie the monitor vesa line is looking for an input, and gets an unexpected input as the Acorn isn't supported as such(..) ..so a theory would be to power the monitor, and let it settle, and then power the computer, so that the monitor gets a 'clean' signal..?

Or visa versa..power the computer, let IT settle, and then power the monitor, that way they aren't interrogating each other as to screen refreshes etc, and fingers crossed...iirc Acorn and PC standard VGA connections differ somewhat? And the new vesa (power saving technology), will complicate further..?

As Mr Vectrolosys alludes to, many (if not all in my experience of repairing them), had Philips chassis, and in my experience, not the best? Latter Acorn branded were better however, but not on the scale of what you have now!

Disregard if I'm barking up the wrong tree however...must dig out the old service manuals...

[Zelandeth]

I think this is a problem with the monitor rather than the computer to be honest.

The screenmode at the moment is set to mode 31 - which if I remember rightly is 800*600 at 16 colours. Both monitors will quite happily display this.

If I power the A5000 up with no monitor plugged in, then plug one in (whether it's the AKF18 or the PC one), it throws a fit.

The same happens when I power on with the Tiny one plugged in. However if I start up with seemingly any other monitor I have plugged in, it'll then work from then on until the next hard reset.

I get the impression that the computer's looking for some sort of input from one of the pins on the VGA lead, which this monitor's failing to give, as such it might just not be compatible. Shame if that is the case, but it WAS free, so I can't complain that much.

The Automatic Mode Selection does still appear to work - the AFK18 starts up with it in one of the multiscan modes, and the Dell one starts up in the SVGA mode (easy to tell as the edges of certain things on screen like the icons on the taskbar are "cleaner" in VGA/SVGA mode).

The earlier Acorn machines used 8D connector for video, the A5000 according to my forgettory was the first one with the ability to drive off-the-shelf VGA monitors without adaptors and/or other tweaks.

Thanks for the heads up on the AFK18 as being the one that tends to catch fire...have to admit that I've always treated the switch with suspicion (worst contact bounce ever!), and it really doesn't look well ventilated...

Will have to keep my eyes out for something else, not to mention that Computer Concepts graphics card which I'd completely forgotten existed. Need to get a memory upgrade too...already got a 406Mb (Connor CFS420A if I remember rightly) harddrive in there, so there's no worries of ever running out of space! Is it just all the ones I have...or do ALL Connor harddrives sound like they have bearings made out of gravel?