Hey, especially thanks for the link. I've also had to deal with the adapters issue. An adapter I bought came with no documentation, and 10 slide switches. The manufacturer suggested trying all combinations, and that even they did not have a schematic. (And that was a well known adapter and cable manufacturer!) Can you imagine trying 1024 combinations and rebooting each time?
Here is a pinout of the VGA side: http://www.diyha.co.uk/electronics/vga.html This shows which are the R, G, & B ground returns. And this one (sorry for spamming popups!) http://www.epanorama.net/documents/pc/vga_bd15.html gives a little better information. And even BETTER: http://www.monitorworld.com/faq_pages/q17_page.html That MAC adapter schematic definitely has it wrong. The R,G,B grounds are indeed on their own ground area, though I still insist they are connected _together_ at the source D/A in the computer. The worst offence in that diagram is to connect the case ground directly to the analog RGB groundplane there at the video output! (I warned about that in my original post). That will put all the noise of the computer circuit board in a loop through the video D/A circuit, passing over the RGB signals. And it would probably do horrible things to the RF interference as well. D-shell of the MAC side should only be connected to the video cable shield and drain wire and the on VGA side D-Shell shield of the connector, and the drain wire. Metallic connectors can account for that with mechanical connections, even if not soldered. I don't see any case grounds to connect into the drain wire on either end. Then they grouped the sync grounds (Mac side 11 and 14) with the analog ground. These are indeed separated on the computer side by probably an inch or so, though having a common internal ground node or plane connection. These would probably not introduce much noise, but could couple in a little bit of logic circuit noise. Certainly when doing a _cable_ as opposed to an adapter, the grounds should be kept separate. Here is what I see as the ground pin connections, let me know how that compares to your cable? (I want to get this figured out, even if I wind up making my own adapter.) And unless one is doing a printed circuit board, using the separate wires for hand wiring is the best. First the raw data, then my cable or adapter pinout. I just realized I need to make _cables_ as well, to run from MAC to KVM switch. Macintosh pinout: 1 RED GND red video ground 2 RED VID red video 3 CYSNC composite sync 4 MON ID 1 monitor ID, bit 1 (also known as SENSE0) 5 GRN VID green video 6 GRN GND green video ground 7 MON ID 2 monitor ID, bit 2 (also known as SENSE1) 8 nc no connection 9 BLU VID blue video 10 MON ID 3 monitor ID, bit 3 (also known as SENSE2) 11 C&VSYNC GND CSYNC and VSYNC ground 12 VSYNC vertical sync 13 BLU GND blue video ground 14 HSYNC GND horizontal sync ground 15 HSYNC horizontal sync Shell Chassis CHASSIS GND chassis ground VGA (2nd ref) pinout: Pinout 1 Red out * 2 Green out * 3 Blue out * 4 Monitor ID 2 in 5 Ground 6 Red return 7 Green return 8 Blue return 9 no pin 10 Sync return 11 Monitor ID 0 in 12 Monitor ID 1 in 13 Horizontal Sync out 14 Vertical Sync out 15 reserved (monitor ID 3) VGA (3rd ref) pinout: Pin # Description 1 Red Video 2 Green Video 3 Blue Video 4 Sense 2 (Monitor ID bit 2) 5 Self Test (TTL Ground) 6 Red Ground 7 Green Ground 8 Blue Ground 9 Key - reserved, no pin 10 Logic Ground (Sync Ground) 11 Sense 0 (Monitor ID bit 0) 12 Sense 1 (Monitor ID bit 1) 13 Horizontal Sync 14 Vertical Sync 15 Sense 3 - often not used So PARTIAL pin mapping for cable or adapter -- get the rest from diagrams, in MAC pin order but on the right to agree with diagram: VGA MAC Signal name 6 1 RED GND red video ground 1 2 RED VID red video NC 3 CYSNC composite sync ? 4 MON ID 1 monitor ID, bit 1 (also known as SENSE0) 2 5 GRN VID green video 7 6 GRN GND green video ground ? 7 MON ID 2 monitor ID, bit 2 (also known as SENSE1) NC 8 nc no connection 3 9 BLU VID blue video ? 10 MON ID 3 monitor ID, bit 3 (also known as SENSE2) 10 (See below) 11 C&VSYNC GND CSYNC and VSYNC ground 14 12 VSYNC vertical sync 8 13 BLU GND blue video ground 10 (tied together at VGA) 14 HSYNC GND horizontal sync ground 13 15 HSYNC horizontal sync D-shell D-Shell Chassis CHASSIS GND chassis ground Additional notes: 9 should have no pin on VGA side, as it is a "key", if this is a cable with a connector at VGA side. 5 "ground" on VGA--no this is some kind of "test" ground, don't use. AH, this agrees with their "simple" cable pinout, except for sense lines. ----- Original Message ----- From: "Artur Yelchishchev" <[EMAIL PROTECTED]> To: "Quadlist" <[EMAIL PROTECTED]> Sent: Monday, September 29, 2003 9:21 AM Subject: Re: Apple Multiple Scan 1705 Display > Gordon Elliott <[EMAIL PROTECTED]> wrote: > > > > Hi, Arthur, > > Hi Gordon, > > Please excuse me for delayed answer. > > > I don't think we disagree on much except for a particular > > detail, so I'll only respond to that. > > Ok. > > > The circuitry to do the subtraction is expensive, especially at video > > frequencies. But I don't deny that the monitor might have such a > > circuit--since neither of us have the schematics we can't determine that for > > certain for a given monitor. > > Giving the absence of schematic diagram for this particular display, I > don't know exact details either, but many expensive monitors are > designed with true separate grounding of signal lines. Please note that > I'm using the word "differential" in double quotes; just to put the > whole idea simpler. BTW, Apple prefers to use real differential > technology in another place - the Mac's serial ports are an example of > that, so I suppose the monitor circuitry is also made with good > design... > > > However, whether the monitor uses a differential receiver is not > > particularly relevant to our problem here. The reason is that any "adapter" > > would be applied at the transmitting end (the computer), not at the > > receiving end. As long as the transmitter side (such as our "adapter") does > > not add noise to the signal return grounds, even if the receiver has a > > differential circuit it will work without newly created noise. > > Hmm, I'm still thinking that the ground lines should be kept separate on > both ends of cable. Properly designed transmitter must use the signal > return ground to ensure normal operation of particular line, and > connecting the grounds together will block 'current loop' there. > > > if you do separate the grounds in a WIRED adapter or > > cable, that is also entirely appropriate. The currents do indeed flow > > "differentially" whether or not the receiver uses differential circuits, and > > improperly wired can introduce noise. > -snip- > > You're on the right track, and method will work--I only disagree on some of > > the details of your comments. Improper grounding can most certainly > > introduce unwanted signal distortion. > > It's my understanding as well. Anyhow, after several days of searching > and soldering, I've made my own cable. In case it's useful for others, > I've found good page: > http://www.saragossa.net/intfcing.html > > Unfortunately, the suggested schematic is not perfect - the ground lines > on the VGA side are tied together, but main advantage of that article > is, a good information about Mac's monitor detection technique. I wasn't > aware that there's diode involved! :-) > > My variant is very close to the one shown on that page, with two > exceptions: I've inverted the diode, and connected all the ground lines > separately. In addition, the cable I've used, does have cylindrical > ferrite inductive filters on the both ends. > > Now I can proudly report, that I have excellent picture quality - crisp > & clear! > > > (PS I have designed a lot of equipment that has to meet better than 100 dB > > analog signal/noise standards, which are levels that can only be dreamed > > about by video designers. And also equipment with both differential and > > single ended signals approaching gigahertz frequencies.) > > You know, my job was a electromagnetic liquid flowmeter's development - > very weak signals in presence of high-level noises (both electrical & > magnetic), with strong requirements for the accuracy and stability... > > Best wishes, > Artur -- Quadlist is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Enter To Win A | -- Canon PowerShot Digital Cameras start at $299 | Free iBook! | Support Low End Mac <http://lowendmac.com/lists/support.html> Quadlist info: <http://lowendmac.com/lists/quadlist.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/quadlist%40mail.maclaunch.com/> Using a Mac? 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