Video cable, DB23 to BNC.

[jimbob]

I'm after any tips on the correct way to wire up a cable from Amiga DB23 to 4x BNC for a Sony BVM monitor.

It was working great with the following connections but the connections to the solder buckets on the DB23 broke after too many unpluggings.

CSYNC - pin 10
R - 3
G - 4
B - 5

Only the CSYNC had the shield connected at the Amiga end.

Q1. What is the correct thing to do with the shields?
Q2. How do I prevent the connections breaking? It was properly secured in the shell before but even the slight wiggle eventually snapped the stranded core wire where it was soldered to the buckets.
Q3. Something else?

[dalek]

Some thoughts:

1. You mean grounds right? As far as I know all the individual colour signal grounds should be connected to the common grounds (pins 16-20 all connected together) at the DB23 end.
2. Maybe fill the shell with hot glue at the solder end? Make sure the cable is clamped in to the shell with the u-shaped bits of metal and screwed together to reduce wiggle at the cable end.

[Daedalus]

If wiggling the cable broke the connections to the solder buckets, it wasn't properly secured. A properly secured cable cannot be moved inside the plug - all the movement happens outside the cable clamp in the "neck" of the DB-23, and all connections inside the plug have slack. Perhaps the clamp wasn't tight enough, allowing individual internal strands to gradually pull out.

In video circuits, generally each signal has its own ground, which should be kept separate. So each of the colour signals (red, green and blue) would have their own separate, individually screened core in the cable from end to end. In reality though, the Amiga connects all the individual grounds internally near the connector so connecting them all to common in the plug probably won't make much (or any) difference. Do note however that they should all be connected to video ground, not digital ground.

For completeness though, I always connect the individual grounds to their assigned individual pins when I'm making RGB cables. It's not that difficult as they roughly match the signal positions on the other row.

[jimbob]

Thanks fellows. Yes, I should have said I "thought" it was properly secured!

I think I see what the problem was now. The U clamp was certainly tight enough on the outer cable but it can rotate slightly in the shell because I think the shell is supposed to be used with some kind of clip in strain relief grommet like the cable entry into a tank mouse. There is a slot in the shell to hold the inside section of one of these.

Also no slack inside, the cables are a pretty stiff coax with a heavy foil and braid shield. I had to have them point straight at the solder cups to fit meaning any movement was immediately working on the soldered wires.

I think the way I had the grounds wired before meant that the CSYNC shield was the ground path for all signals via the monitor chassis and BNC connectors. The coax shield on RGB should still be effective as they are grounded at the monitor end. Now, proper grounding and shielding is like black magic to me, but if the 4 signal grounds are all connected at the Amiga end and the monitor end, doesn't that create 4 ground loops which I gather are bad for some reason?

I don't think the grounding thing will make a huge difference either way so I'll connect them all up if the cable isn't too awkward. Though I think that's probably why I left them off before but I'll try to make a better job of it this time.

[idrougge]

Every VGA cable uses (at least) four ground connections. That's the way it's supposed to be and absolutely not a cause of ground loops.

[jimbob]

Originally Posted by idrougge

Every VGA cable uses (at least) four ground connections. That's the way it's supposed to be and absolutely not a cause of ground loops.

I'm sure your right, proper grounding and it's potential problems are a bit mysterious to me.

Anyway, I wired it up properly this time and it works fine. There is a some slack inside the shell now so it should be mechanically more sound, I may squirt in some hot glue instead of the proper strain relief gadget just to make sure.

I have another slight issue but it probably isn't the cable. Black seems to have a slight redness to it, quite noticeable when I switch to the B&W composite. Maybe just an issue with this particular A500, I'll try a different Amiga to check.