Displaying old computers on new TVs

[RWAP]

Rich,
do you plan do produce a video mod?

BTW, how do you know board's issue?

The ZX81 motherboard has the issue stamped on it....

Yes, we are working on a video mod The design is complete - I need to chase up what is happening!

[angus]

OK I performed the mod on my early ZX81 (ULA dated 12th week 1981) using a BC108 transistor and 100 Ohm resistor.

Success. Here are two photos of the display on a TV where the RF input produced a very dark and partially inverted screen. The display was adjusted with max brightness and contrast, zero colour and zero 'sharpness'. It looks nice, is 100% stable without any odd artifacts. The zeddy had been running 30 minutes when the photos were taken.

Next is to try with LCD and plasma.

(photos reduced to 800x600)

[angus]

Took the Zeddy home to meet my other Zeddy (hmm, will they reproduce if I give them some privacy?) and to hook the modded machine up to my AOC LCD television.

Curious. Hooked up direct to the TV I get a very nice picture, totally stable with no strobing or other effects apart from small background pattern such as you see in the Eight One emulator if you play with the TV emulation settings. Without any adjustment of my TV the picture is very acceptable. It's better than I usually got back in the day via RF.

However, if I go via my VCR or DVD recorder I get no usable picture. Nothing at all via the VCR and a blank white screen via the DVD recorder.

Even more curious if I add a 16K RAM pack known to be working (I tested it on Monday) I lose all picture even hooked directly to the TV.

I've got two working RAM packs now, a Sinclair and a Memotech and both have the same effect. I am baffled.

[angus]

OK tried the modded ZX81 on my LCD television at home for a longer period and it worked pretty well for 20 minutes, then started jumping around and showing a yellow background.

And even when working fine, if I add a RAM pack (obviously while the power is off) the image disappears. I get a pattern slowly rolling down the screen. Really strange how can a RAM pack affect the composite output? Any ideas?

Here are some photos.

[angus]

Has anybody tried something like this

http://www.ebay.co.uk/itm/Composite-RCA ... 500wt_1156


For connecting a modded ZX81 to a VGA monitor? If so, did you have any success?

[Slipstreem]

I've not tried one yet, but I'll definitely bid on it if you're not. There's no point in us trying to outbid each other for it, so let me know if you're not bidding and I will.

[angus]

I'm not bidding for now so go ahead. I'm still investigating with my two Zedddies where they do and don't work (one modded for composite, one not)

[Slipstreem]

OK. If it goes for £15 or less then I'll grab it. If it comes apart without breaking the case, I'll take some photos of its intestines too and post them here for others to disect.

[angus]

Other vendors are selling what looks visually to be a similar or identical article, posting from the far East. They have good feedback so I imagine the unit works for hooking up VCR, DVD or digiboxes to VGA monitors. If it works for vintage computers with composite outputs then it may have found a considerable niche market!

[Slipstreem]

Yes. The one we were looking at went for more than I'm prepared to spend, but THIS one appears to be the same for just over £14 new delivered. I've ordered one as it'll come in handy for connecting my old Freeview box to the bedroom PC monitor even if it doesn't like the ZX81, so it won't go to waste whatever. I'll report back when it gets here.