Announcement

Collapse

Forum Rules and Etiquette

Our mission ...

This forum is part of our mission to promote the preservation of vintage computers through education and outreach. (In real life we also run events and have a museum.) We encourage you to join us, participate, share your knowledge, and enjoy.

This forum has been around in this format for over 15 years. These rules and guidelines help us maintain a healthy and active community, and we moderate the forum to keep things on track. Please familiarize yourself with these rules and guidelines.


Rule 1: Remain civil and respectful

There are several hundred people who actively participate here. People come from all different backgrounds and will have different ways of seeing things. You will not agree with everything you read here. Back-and-forth discussions are fine but do not cross the line into rude or disrespectful behavior.

Conduct yourself as you would at any other place where people come together in person to discuss their hobby. If you wouldn't say something to somebody in person, then you probably should not be writing it here.

This should be obvious but, just in case: profanity, threats, slurs against any group (sexual, racial, gender, etc.) will not be tolerated.


Rule 2: Stay close to the original topic being discussed
  • If you are starting a new thread choose a reasonable sub-forum to start your thread. (If you choose incorrectly don't worry, we can fix that.)
  • If you are responding to a thread, stay on topic - the original poster was trying to achieve something. You can always start a new thread instead of potentially "hijacking" an existing thread.



Rule 3: Contribute something meaningful

To put things in engineering terms, we value a high signal to noise ratio. Coming here should not be a waste of time.
  • This is not a chat room. If you are taking less than 30 seconds to make a post then you are probably doing something wrong. A post should be on topic, clear, and contribute something meaningful to the discussion. If people read your posts and feel that their time as been wasted, they will stop reading your posts. Worse yet, they will stop visiting and we'll lose their experience and contributions.
  • Do not bump threads.
  • Do not "necro-post" unless you are following up to a specific person on a specific thread. And even then, that person may have moved on. Just start a new thread for your related topic.
  • Use the Private Message system for posts that are targeted at a specific person.


Rule 4: "PM Sent!" messages (or, how to use the Private Message system)

This forum has a private message feature that we want people to use for messages that are not of general interest to other members.

In short, if you are going to reply to a thread and that reply is targeted to a specific individual and not of interest to anybody else (either now or in the future) then send a private message instead.

Here are some obvious examples of when you should not reply to a thread and use the PM system instead:
  • "PM Sent!": Do not tell the rest of us that you sent a PM ... the forum software will tell the other person that they have a PM waiting.
  • "How much is shipping to ....": This is a very specific and directed question that is not of interest to anybody else.


Why do we have this policy? Sending a "PM Sent!" type message basically wastes everybody else's time by making them having to scroll past a post in a thread that looks to be updated, when the update is not meaningful. And the person you are sending the PM to will be notified by the forum software that they have a message waiting for them. Look up at the top near the right edge where it says 'Notifications' ... if you have a PM waiting, it will tell you there.

Rule 5: Copyright and other legal issues

We are here to discuss vintage computing, so discussing software, books, and other intellectual property that is on-topic is fine. We don't want people using these forums to discuss or enable copyright violations or other things that are against the law; whether you agree with the law or not is irrelevant. Do not use our resources for something that is legally or morally questionable.

Our discussions here generally fall under "fair use." Telling people how to pirate a software title is an example of something that is not allowable here.


Reporting problematic posts

If you see spam, a wildly off-topic post, or something abusive or illegal please report the thread by clicking on the "Report Post" icon. (It looks like an exclamation point in a triangle and it is available under every post.) This send a notification to all of the moderators, so somebody will see it and deal with it.

If you are unsure you may consider sending a private message to a moderator instead.


New user moderation

New users are directly moderated so that we can weed spammers out early. This means that for your first 10 posts you will have some delay before they are seen. We understand this can be disruptive to the flow of conversation and we try to keep up with our new user moderation duties to avoid undue inconvenience. Please do not make duplicate posts, extra posts to bump your post count, or ask the moderators to expedite this process; 10 moderated posts will go by quickly.

New users also have a smaller personal message inbox limit and are rate limited when sending PMs to other users.


Other suggestions
  • Use Google, books, or other definitive sources. There is a lot of information out there.
  • Don't make people guess at what you are trying to say; we are not mind readers. Be clear and concise.
  • Spelling and grammar are not rated, but they do make a post easier to read.
See more
See less

Why AT PSUs have 4 wires connecting to the on-off switch

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Why AT PSUs have 4 wires connecting to the on-off switch

    I need to replace the regular AT PSU switch with a round 16mm latching switch, preferably illuminated (hole already there). From what I have seen those are single pole single throw. Why does the AT PSU has 4 terminals going to the switch? Will I have to concoct something with a relay?

    Well the other solution is to use an ATX PSU. Since the cables that convert one to the other take a SPST switch, but I would prefer to use an AT PSU. Thoughts?

    Thanks!!

    #2
    AT power switches are DPST because they switch both mains line and neutral

    Comment


      #3
      Phase, your location is unknown, so we can't draw any conclusions about what your power distribution is. However, if you're in North America and have 120VAC power, then you need only switch the "hot" side of the line. Electrical codes in other countries (240V ones) may insist that both line connections be switched.
      Reach me: vcfblackhole _at_ protonmail dot com.

      Comment


        #4
        Awesome. I’m int the US. So, if I understood you correctly, I need only to switch the “line” side of the wire. Correct?

        Comment


          #5
          That's correct. There's no connect (other than via the line filter caps) between the neutral side and power/chassis ground in these switching PSUs, so they're effectively isolated.
          Reach me: vcfblackhole _at_ protonmail dot com.

          Comment


            #6
            Perfect. Thank you very much!!

            Comment


              #7
              I'll add that on my 240VAC shop machinery, both sides of the line are switched, since both sides are "hot" with respect to neutral/ground in North American power distribution. On 3 phase equipment, all three phase lines are switched, since all are "hot" with respect to neutral.
              Reach me: vcfblackhole _at_ protonmail dot com.

              Comment


                #8
                Off topic perhaps but I owned a Thomson DVR at one point that was fused (internally) on the neutral. I thought that was a tremendously bad idea!

                Comment


                  #9
                  Originally posted by pearce_jj View Post
                  Off topic perhaps but I owned a Thomson DVR at one point that was fused (internally) on the neutral. I thought that was a tremendously bad idea!
                  Why? The fuse is triggered by overcurrent from a short. It doesn't matter where it sits. A fuse it not there to protect people from getting a shock!

                  In Germany and many other European countries, you can't even tell what neutral and what live is from the equipment side, as mains plugs are not keyed and also go in when rotated 180.
                  Last edited by Timo W.; September 27, 2021, 11:54 PM.

                  Comment


                    #10
                    See, for example, the Schuko (CEE 7) receptacle and plug family. That one always baffled me--usually German-origin stuff is pretty decent with respect to safety.

                    Hence, my answer regarding non-North American systems. Although it's possible that a receptacle will be wired incorrectly (a code violation), it's less likely nowadays. As usual, a short story...

                    When we moved into our current home more than 30 years ago, I couldn't understand why a Toshiba microwave oven refused to power on in the kitchen. Plugged into other outlets, it was fine, but not in its intended spot. A quick check with a lamp indicated that power was indeed present at the subject outlet, but still the oven refused to operate. Eventually, I got out the multimeter and checked the outlet--backwards. Apparently the oven was smart enough to figure that one out (and no, the ground line wasn't being used as a power return). Checking around the house I found about 8 outlets that were similarly wired.

                    Back then, there was still a fair proportion of "hot chassis" equipment around. That could lead to unpleasant surprises down the line...

                    But Timo's response is why DPST power switches are common on most electronic gear today.
                    Last edited by Chuck(G); September 28, 2021, 07:45 AM.
                    Reach me: vcfblackhole _at_ protonmail dot com.

                    Comment


                      #11
                      Originally posted by Chuck(G) View Post
                      See, for example, the Schuko (CEE 7) receptacle and plug family. That one always baffled me--usually German-origin stuff is pretty decent with respect to safety.
                      I believe it was because originally the German supply was centre tapped so it really didn't matter which way round you plugged it in

                      It must be said, the UK 13A plug is the most dangerous of all.

                      Not when in use, but when left on the floor. The pins inevitably point upwards and really really hurt when stood on with bare feet.
                      Current fleet
                      TRS80 Model 4 - BBC B - Tatung Einstein - PCW9512 - PET 3032 - C64 - ZX81 - Spectrum 48K - Amiga A500 - Apple II europlus - Apple iMAC G3. Sharp MZ-80K. - IBM 5160 XT - Multibus 286/10 - Micro PDP 11/73 - Rainbow PC100A - MicroVax II - MicroVAX 3100, 3300, VAX 4000 VLC & 4000 Model 96 - AlphaStation 225 Apricot PC - Apple Performa 6200 - Apple Mac IIcx - Osborne 1 - ACT Sirius 1

                      Comment


                        #12
                        Originally posted by Gary C View Post
                        Not when in use, but when left on the floor. The pins inevitably point upwards and really really hurt when stood on with bare feet.
                        Hah! I can believe that!
                        Reach me: vcfblackhole _at_ protonmail dot com.

                        Comment

                        Working...
                        X