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I have found a Macintosh Quadra 700 recently, together with an Apple High-Resolution RGB Monitor and want to try out if they are functional.

Since both came out slightly before my generation, I am severely confused about the whole D-Sub ecosystem - when I had first contact with computers, VGA was already a widely accepted standard.

Basically I want to buy a cable to plug the monitor into the computer (duh), but not sure about what cable I actually need and what I could break if I just try it out.

Both devices have a DB15 slot according to the documentation, so I am looking for DB15 M/M cables online, which apparently do not exist, since the naming convention does not technically allow for DB15 (which somehow comprises of DA15 and DE15?), because the letter "B" actually implies for it to be a 25-pin socket?

I am completely lost here, can I go with my gut feeling and just pick out any 15-pin D-sub cable (e.g. a cable with no further specification than that, because these do exist) which simply fits the shape I expect (2 rows of pins instead of 3 rows) or are there any different pin mappings I should be aware of?

And what exactly could I break in case of connecting a wrong (yet physically fitting) cable, would there be any irreversible damage to e.g. the monitor by receiving a too strong signal for a parameter it does not expect this kind of signals for?

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    Best to use the cable that comes with the Apple monitor. It's not a one size fits all as with PC-VGA. The Apple-cable does usually also carry configuration information telling the Mac what kind of screen is connected.
    – Raffzahn
    Dec 13, 2023 at 1:53
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    Fixing typos: DB-15 is a mistaken but common term for either DA-15 or DE-15. DA-15 is two rows, DE-15 is three. Link.
    – dave
    Dec 13, 2023 at 13:48
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    Do yourself a favor, don't plug in anything you are unsure of. I don't know if there are any 5 or 12 volt rails exposed on that connector, but the last thing you want to do is short one of them to ground and fry something. Take your time, find the pinouts, test your cable with an ohm meter to be sure - then do it all over again to double check.
    – Geo...
    Dec 13, 2023 at 14:53
  • @Raffzahn There was none, I found both devices on the street as giveaway. That's why I am looking to find the right cable to plug those in, but original Apple cables are hard to find in Germany, I only found US-based resellers that do not ship (or for immense costs).
    – kopaka
    Dec 13, 2023 at 20:37
  • @Geo... Thanks for that warning, I was not so sure if my caution is justified, but apparently it is!
    – kopaka
    Dec 13, 2023 at 20:38

4 Answers 4

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The second letter of a D-Sub connector indicates the size of the shell. Apple tended to use the DA-15 connector: a larger one than VGA, with a lower pin density and only two rows of pins. There's one shown on this picture of a Rear view of a Quadra 700 at Wikipedia.

Not just any DA-15 cable will work: Apple used several incompatible cables with the same connector for the Apple IIc and Apple IIgs. You'll have to use the right cable for your Mac monitor.

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  • Do you know if there is any "label" or standard identifier I can look for in a regular DA-15 cable that makes it compatible for my use case or do I specifically need to look for original Apple DA-15 (online and in the manual referred to as DB-15) cables to be sure? The other alternative suggested by Geo... would be to find the pinouts and test cable candidates but frankly, I do neither have the knowledge or the tools for procedure.
    – kopaka
    Dec 13, 2023 at 20:45
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    Raffzahn's suggestion to Get a Mac-to-VGA Dongle is probably better than trying to find the right 15-pin cable.
    – scruss
    Dec 14, 2023 at 20:38
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"DB" doesn't mean that it has 25 pins, but that the connector is as wide as the DB-25 you're familiar with (which is actually correctly named).

A DB-15 could sort of exist, but it would have empty spaces: 25 is the smallest ("normal density") number of pins usually used for that shell size. On the other hand, there are things like DB13W3, which has 13 regular pins and three coaxial jacks in that space.

As already well answered by scruss, the connector on the Mac is properly a DA-15, it's just that people (from the 80s right up to today) have a bad habit of calling any D-sub connector "DB", because DB-25 was the first to make a big appearance in the home. So they'll call a DE-9 (common for serial ports and mice in the 90s) a "DB-9", and a VGA connector (properly DE-15) a "DB-15" or "DB-15HD".

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    Yeah, nobody can remember what the shell size codes are, so "DB" has become a colloquial abbreviation for "D subminiature". In that use, it generally refers to the original common 100 mil two row 9-37 pin configurations and the three row 50.
    – John Doty
    Dec 13, 2023 at 14:42
  • A DB13W3 has 13 pins, 10 of which are regular, 3 are coaxial.
    – bodgit
    Dec 13, 2023 at 17:20
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    The truly odd one is the 23-pin Amiga connector as there isn't an official D-sub shell size for that so it gets called DB-23 as there isn't anything more appropriate.
    – bodgit
    Dec 13, 2023 at 17:23
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    @bodgit AIUI on a 13W3 there are three special positions which can be populated with any combination of coaxial or high current contacts (though I'm not aware of any products which populate them with a mixture). Dec 14, 2023 at 13:53
  • @PeterGreen I'm not sure about that exact combination, but a mix of high current, coax, and normal pins on a D-sub is something I've seen on lasers, between the power supply and the laser head
    – Chris H
    Dec 15, 2023 at 10:10
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TL;DR: Get a Mac-to-VGA Dongle

The Quadra can be easy connectet to a contemporary multi-sync screen using a DA15 to DE15 dongle. They still show up with vendors as well as on Ebay. Keywords Mac to VGA, Mac to PC or Mac to NEC adaptor (*1).

enter image description here

With one of those the only cable needed is a standard VGA cable.

Make sure to get the manual describing all settings with your dongle.

Also, Big Mess o' Wires is in the process of creating a modern version which will allow an even wider range of Macs to connect to VGA.

enter image description here

Maybe the least effort solution - as soon as it's done.

Otherwise you may need to fire up your trustworthy soldering iron :))


Connector Details:

Note: TheQuadra700 has two (?) NUBUS slots which may carry additional video card(s). This is only about build in video.

Quadra 700 Video Conector

A good part of the early 1990s Macs used the same female D-Sub DA15 connector, especially LC, LC II, Performa 400, IIci, IIsi, Quadra 700, 900/950 as well as some of the docks.

Mac-Pin Signal Description VGA-Pin
1 RED.GND RED GROUND 6
2 RED.VID RED Video Signal 1
3 /CSYNC Composite Sync -
4 ID1 Monitor Sense Bit 2^0 -?-
5 GRN.VID GREEN Video Signal 2
6 GRN.GND GREEN Ground 7
7 ID2 Monitor Sense Bit 2^1 -?-
8 nc -
9 BLU.VID BLUE Video Signal 3
10 ID3 Monitor Sense Bit 2^2 -?-
11 C_VSYNC_GND Common Ground for CSYNC & VSYNC 10
12 /VSYNC Vertical-Sync 14
13 BLU_GND BLUE GROUND 8
14 HSYNC_GND Ground for HSYNC 5
15 /HSYNC Horizontal-Sync 13
Shell GROUND Common Ground Shell

Sense Signals

Those strange "Sense" signals (*2), marked with -?-, are what helped a Mac to detect what screen is connected and only offer valid resolutions.

(Note, these are the values I know)

ID3/2/1 Signal
0/0/0 ???
0/0/1 15" B&W Portrait
0/1/0 12" RGB
0/1/1 ???
1/0/0 ???
1/0/1 ???
1/1/0 12" Mono or 13" RGB
1/1/1 ???

The 13" RGB might be the best match for VGA.

So the rest is easy, right? No.

More Pitfalls

It should have been telling that the dongle features a lot of DIP switches. No manufacturer would add them without real need. The main reason is about the way sync signals are transported and encoded. Monitors had different ways where they expected those signal. Either fixed, or selectable (*3), so one needs a way to configure according to the screen used.

The Mac simplified this by detecting the screen using above sync signals and moving the sync signals accordingly. Cool, isn't it? No, not for our issue, as we now may have to move the signal assignment according to which Apple Monitor we wan to simulate (see above).

Long Story Short: Either get one of those adaptors or you need to dig very deep into pin assignment.

Here's a nice write-up of one who took the challenge with his IIci. Note that the IIci uses a different video logic and different monitor IDs, so the values mentioned may not be the same.

Quadra 700 Screen Resolutions

What the build in video can display depends on the amount of VRAM (*4) which can be of 512 KiB, 1 MiB or 2 MiB:

video: 512 KB VRAM, expandable to 1 MB or 2 MB; vinternal video does not support 16-bit mode

512 KiB:

  • 512 x 384 @ 16-bit
  • 640 x 480 @ 8-bit
  • 832 x 624 @ 8-bit
  • 1152 x 870 @ 4-bit

1 MiB:

  • 512 x 384 @ 24-bit
  • 1152 x 870 @ 8-bit

2 MiB:

  • 640 x 480 @ 24-bit
  • 832 x 624 @ 24-bit

*1 - NEC and their Multisync-series was, at the time,- synonymous with high quality screens.

*2 - VGA also supported a similar way to distinguish between Monochrome and colour and two resolution types (800 × 600 or 1024 × 768), but most drivers/OS simply ignored that. Later a more versatile DCC system was developed, but again support was rather lame.

*3 - Today almost forgotten, but screens, especially higher end models had their own set of DIP switches (aka Mäuseklavier) as well as multiple connectors.

*4 - Video RAM, in most Macs a dedicated SIM board and thus often missing in second hand Macs. The 700 being a lucky exception as the minimum 512 KiB is soldered in.

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which apparently do not exist, since the naming convention does not technically allow for DB15

In the original naming scheme from the original manufacturer of the connectors, there was/is no such thing as a DB15.

The thing is manufacturers can come up with naming schemes all they like, they don't get to define the English language. The English language is defined by custom and practice among it's users, and yes this means that in some cases the English language becomes ambiguous or that you need to distinguish between different dialects.

Sometimes the "technically incorrect" usage becomes more common than the "technically correct" usage. Certainly growing up I remember it being the norm to use "DB" as a shorthand for regular D connectors regardless of the pin count. I don't remember encountering the "technically correct" nomenclature until Wikipedia started pushing it*.

Some people even use DB for the 15 way high density connector** I have personally always regarded this as wrong, but I may be in the minority here.

To check this wasn't just me, I went to the Farnell (a major electronics distributor in the UK). In the "D Sub Connectors" category I get 430 results for DB15 compared to only 42 results for DA15. Similarly I get 95 search results for HD15 and none at all for DE15.

can I go with my gut feeling and just pick out any 15-pin D-sub cable

In general you can't assume a cable is correct just because it uses the same connectors. The DA15 was used for many incompatible applications including the PC joystick port, the BBC micro's analogue input connector, the AUI Ethernet transceiver connection and the classic macintosh video output port.

Often hardware would have documentation of the pinouts in the user manual, so you could determine what cable was appropriate and buy or make one.

D sub cables were often, but not always, wired straight through connecting the same pin at each end of the cable. Some wires may be disconnected. Sometimes miniature coaxial cables may be used for better signal integrity.

https://68kmla.org/bb/index.php?threads/has-someone-the-db15-db15-video-cable-pinout.31010/ claims the apple high resoloution color monitor needs a cable that is straight through wired with all 15 pins present but I have no way to validate this information.

* Wikipedia similarly pushes the use of the term 8P8C for what everyone calls RJ45.

** The 15 way being the only high density connector that is widely used.

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  • As far as serial cables are concerned, D sub cables tend not to be wired straight through.
    – scruss
    Dec 13, 2023 at 16:58
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    AIUI serial modems usually used straight through male to female cables. Connecting two PCs without required a female to female "null modem" cable. but I'm sure I've also come across hardware combinations that needed a male to female crossover cable or a female to female straight through. Dec 13, 2023 at 17:09
  • Actually, 8P8C modular jack is the real and correct name of the connector used for Ethernet. The RJ refers to telecom wiring standards of Registered Jacks, such as RJ11 used for telephones. The only problem is, there is no such thing as RJ45 in the standard.
    – Justme
    Dec 13, 2023 at 17:45
  • I know that argument, I could equally argue back that 8P8C just says the number of positions and contacts and tells us nothing about what family of connectors is in use (I've certainly seen the xPxC terminology used in reference to BT style connectors as well). Dec 13, 2023 at 17:49
  • @PeterGreen for serial applications over DB-25 connectors, even simple connections that were mostly straight-through often needed some tweaks to work properly. Patch boxes were popular for a reason. Dec 13, 2023 at 20:08

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