Home-brew Atari TT ECL VGA Adapter

[Icky]

Today I had a go at building an Atari ECL (TT-High) to VGA adapter using the diagrams on the Atari-forum http://www.atari-forum.com/viewtopic.ph ... CL#p286175

I used the option suggested by Frank Lucas at the bottom of the thread to use diodes instead of the resistors on the monitor RGB lines.

Built it using break-out boards for the surface mount components and used a breadboard for testing. It works well apart from a few horizontal lines but if I clean up the circuit it should improve.

Below is a pic of the Atari TT connected to my makeshift circuit

IMG_2672.jpg

Running X on NetBSD at TT-High. See thread on running NetBSD https://www.exxosforum.co.uk/forum/viewt ... lit=NetBSD

IMG_2675.jpg

[Icky]

Even though I built the home-brew version of the TT ECL VGA Adaptor I thought I would give the one by Wolfgang at Inventronik a go.

It's a very compact design with the VGA connectors almost butted up against each other.

https://shop.inventronik.de/index.php?i ... &id_lang=2

The USB board on top is my modification to power up using USB phone charger

IMG_3222.png

IMG_3223.png

Doing some calibrations on screen phases / clock before posting a pic.

[Icky]

Doing some calibrations on screen phases / clock before posting a pic.

So using two monitors I get very different results from the adaptor. Am using the screen shot of NetBSD as this is similar to the capture I did with my home-brew adaptor.

IMG_3229.png

IMG_3230.png

[Icky]

Had an interesting event when swapping the monitors over.

When pulling out the first monitor cable I got a small shock from the shielding on the adaptor. Inspecting the adaptor I noticed the shielding is not connected to anything.

So the shock came from my monitor but still made me think why is this adaptor not all grounded.

Taking a look it seems both shields on the D-SUBs were not connected to GND.

A couple of soldered wires later I have a completely grounded adaptor. The image is slightly better (not so fuzzy vertically) but the best picture I can get still has the horizontal lines, just as my home brew version did.

[exxos]

Some monitors had "live chassis" IIRC... I never understood that, I always got shocks when plugging in RF cables. All metal should be grounded by law since long time ago.. I don't remember if it was part of the design or part of a bad design.. going back like 20 years now... But you could have like 100V - 2,000V on the chassis...

Also problems with "double isolated" mains supplies where nothing is referenced to gnd..I blew the audio chip up on my falcon by plugging in the audio cable while things were powered up. Basically one part is actually grounded, the other side isn't. Actually one of the main causes of audio hum in equipment because of voltage potentials across gnd connections. Also means that 2 equipments not referenced to gnd, you can end up with the chassis floating up to thousands of volts. Touch 2 such equipments and you know about it.

Its actually a pretty big topic, but never assume metalwork on old monitors is at 0volt, as it probably isn't.

[Icky]

Some monitors had "live chassis" IIRC... I never understood that, I always got shocks when plugging in RF cables. All metal should be grounded by law since long time ago.. I don't remember if it was part of the design or part of a bad design.. going back like 20 years now... But you could have like 100V - 2,000V on the chassis...

Also problems with "double isolated" mains supplies where nothing is referenced to gnd..I blew the audio chip up on my falcon by plugging in the audio cable while things were powered up. Basically one part is actually grounded, the other side isn't. Actually one of the main causes of audio hum in equipment because of voltage potentials across gnd connections. Also means that 2 equipments not referenced to gnd, you can end up with the chassis floating up to thousands of volts. Touch 2 such equipments and you know about it.

Its actually a pretty big topic, but never assume metalwork on old monitors is at 0volt, as it probably isn't.

I've lost count of the times I have had shocks. Most serious ones in my days in Electrical Engineering at college.

Yeah its crazy that the difference between devices can be large.

Even some of these aluminium based laptops sometimes have that electrical feeling on them when you rub your finger over them.

[exxos]

Even some of these aluminium based laptops sometimes have that electrical feeling on them when you rub your finger over them.

Wouldn't be surprised. I don't remember when the legislation came out, think late 90s sometime.. I was working on jukeboxes at the time, basically wooden boxes where the door lock had to have a metal strap to it connected to mains earth. The amount of shocks that caused over the years is unbelievable.. static carpets etc... that "all metalwork must be grounded" crap caused so many issues over the years its unreal. It was actually a order of magnitude safer not to gnd the stuff!

But to remain on topic a little bit here ... :lol: ... really never plug any equipment in with the power turned on... Plugging in a monitor into something while powered up could vaporize gnd tracks on what your connecting it to! :roll: That's happened on my falcon with the audio lead, nevermind the monitor.

[czietz]

Even some of these aluminium based laptops sometimes have that electrical feeling on them when you rub your finger over them.

Off Topic

When powered from a power supply with a two pole mains plug (i.e. no PE) this is perfectly normal. The metallic parts of the laptop will often be at half the mains voltage (i.e. ca. 115 V in Europe) with respect to earth. This is not dangerous (for humans) because the current is very limited. You might still be able to feel it especially on metallic edges or corners.