Announcement

Collapse

Forum 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.


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.


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.



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.


"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.

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

Bought a Black G74 and it turns on and I hear it degausse like it should but no video

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

    Bought a Black G74 and it turns on and I hear it degausse like it should but no video

    IBM G74 Monitor Black Case Rare
    You can hear it degausse but no video or On Screen display at all and then a few seconds after I hear degausse I hear a click? It was a open box new old stock and the buyer said it worked when they shipped it and they tested it and everything inside looks brand new so I don't think it was ever used at all.

    #2
    Two things. 1. Something came loose inside in shipping. 2. The monitor doesn't support the video output of the system you have connected to it (refresh rate. resolution, etc..)

    Comment


      #3
      Originally posted by kc8eyt View Post
      Two things. 1. Something came loose inside in shipping. 2. The monitor doesn't support the video output of the system you have connected to it (refresh rate. resolution, etc..)
      I took it apart and nothing looks like it loosened up that I could see but I'll double check again and I know I am using it on a IBM PC series 350 P75 and I did try it on my IBM 8303-NUE and it did the same thing, so I'm pretty sure it is not the resolution cause I have a regular beige G74 as well that I use on my IBM 300PL and it worked no problem on the IBM 8303-NUE.

      What else could I check that might have come loose?

      Comment


        #4
        Since you've got the case apart, can you see the heater glowing faintly in the CRT neck (with a signal applied)?

        Comment


          #5
          I think I may have found the issue it looks like some fluid is leaking from the flyback transformer or something here is a picture https://drive.google.com/file/d/10bv...ew?usp=sharing

          Comment


            #6
            Is that definitely some liquid ? or could it be some resin like glue used when the transformer was assembled ? Test it by trying to wipe a little of it up. Flyback windings generally do not contain any fluid these days, but hard resin, though there were some oiled filled ones in vintage TV's back in the mid 1950's.

            Comment


              #7
              Are you sure that's a recent fluid leak, or perhaps some sort of adhesive that dried clearly during construction? I don't believe I've ever run across a flyback with leaking fluid, although I do know some transformers use an oil as a coolant, but usually in much, much larger applications.

              LOL, Hugo and I must have tapped into the same thought wave.
              Last edited by kc8eyt; May 8, 2021, 01:29 PM.

              Comment


                #8
                I am not sure if it was there before or not but it looks greenish and there is something on the side as well here is another picture from the side: https://drive.google.com/file/d/10mD...ew?usp=sharing

                Update:
                Here is a link to the folder with all the pics I have taken of this monitor: https://drive.google.com/drive/folde...pE?usp=sharing

                Comment


                  #9
                  Originally posted by thegenerallee86 View Post
                  I am not sure if it was there before or not but it looks greenish and there is something on the side as well here is another picture from the side: https://drive.google.com/file/d/10mD...ew?usp=sharing

                  Update:
                  Here is a link to the folder with all the pics I have taken of this monitor: https://drive.google.com/drive/folde...pE?usp=sharing
                  In that second picture that appears to be nothing more than resin from the manufacturing process. It even looks as though the QA mark (the pink line) has been written over top of it.

                  You know, it's also possible the person you bought it from "fibbed" when they said it was tested. Most of the "tested" stuff found on eBay has not been tested at all. Believe me, I know from experience.

                  Comment


                    #10
                    Originally posted by kc8eyt View Post

                    In that second picture that appears to be nothing more than resin from the manufacturing process. It even looks as though the QA mark (the pink line) has been written over top of it.

                    You know, it's also possible the person you bought it from "fibbed" when they said it was tested. Most of the "tested" stuff found on eBay has not been tested at all. Believe me, I know from experience.
                    I did touch the it and do believe you are right because it doesn't feel liquidy when I touch it or rub it with my fingernail

                    Originally posted by Chuck(G) View Post
                    Since you've got the case apart, can you see the heater glowing faintly in the CRT neck (with a signal applied)?
                    If you look in the links I posted above here in the photo's I don't beleive you'd be able to see the neck glow cause there is so much stuff on the neck of this CRT?

                    Update to everyone I wonder if the fuse could be causing this problem? I know it is a slow blow fuse
                    Last edited by thegenerallee86; May 8, 2021, 02:41 PM.

                    Comment


                      #11
                      What else could I check to see what it might be or look at?

                      Comment


                        #12
                        Originally posted by thegenerallee86 View Post
                        What else could I check to see what it might be or look at?
                        The usual thing if the monitor is not working is to check the fuses & power supply components first.

                        Ideally you would have a meter and scope. If the power supply is running normally then the H & V scan stages and CRT support circuitry is then checked after that, while making sure to be feeding the VDU with a known good signal. The conditions for the CRT are such that in some monitors the screen will be black without the correct input signal, even if the brightness control is fully advanced, but usually for many monitors the screen (raster) will be visible with the brightness on full.

                        There is really no guessing with this sort of thing as it only takes one component/part somewhere to fail to kill the monitor. So it usually needs a systematic approach working through the circuitry with meters & scopes to find the culprit if the obvious has been ruled out first by inspection and checking fuses. If the fault is on the line power side of the psu it can be risky for the less experienced making tests, it pays to have an isolating transformer or a special scope.

                        Comment


                          #13
                          Originally posted by Hugo Holden View Post

                          The usual thing if the monitor is not working is to check the fuses & power supply components first.

                          Ideally you would have a meter and scope. If the power supply is running normally then the H & V scan stages and CRT support circuitry is then checked after that, while making sure to be feeding the VDU with a known good signal. The conditions for the CRT are such that in some monitors the screen will be black without the correct input signal, even if the brightness control is fully advanced, but usually for many monitors the screen (raster) will be visible with the brightness on full.

                          There is really no guessing with this sort of thing as it only takes one component/part somewhere to fail to kill the monitor. So it usually needs a systematic approach working through the circuitry with meters & scopes to find the culprit if the obvious has been ruled out first by inspection and checking fuses. If the fault is on the line power side of the psu it can be risky for the less experienced making tests, it pays to have an isolating transformer or a special scope.
                          I think I found it and it looks like it is unrepairable which really sucks! The The Glass tube near the neck board has a crack in it and here is a picture of it: https://drive.google.com/file/d/11M2...ew?usp=sharing
                          You may have to zoom in to see it but it is there.

                          Comment


                            #14
                            That does not look good. Though I have seen cracks like that where air has not yet got into the CRT.

                            One interesting thing is, if air enters the CRT, and you power the monitor up, the final anode assembly in the CRT gun structure, connected to the EHT of over 20kV, arcs to the other gun electrodes with enormous blue flashes inside the CRT neck and puts on a spectacular light show. It is possible therefore that air has not entered the CRT.....yet, or if it has, it was left arcing for a while and that killed the Horizontal output stage & EHT generator.

                            Likely you can get a new CRT for it. NEWTUBES on ebay have a good selection of CRT's and many compatible types.

                            Comment


                              #15
                              Originally posted by Hugo Holden View Post
                              That does not look good. Though I have seen cracks like that where air has not yet got into the CRT.

                              One interesting thing is, if air enters the CRT, and you power the monitor up, the final anode assembly in the CRT gun structure, connected to the EHT of over 20kV, arcs to the other gun electrodes with enormous blue flashes inside the CRT neck and puts on a spectacular light show. It is possible therefore that air has not entered the CRT.....yet, or if it has, it was left arcing for a while and that killed the Horizontal output stage & EHT generator.

                              Likely you can get a new CRT for it. NEWTUBES on ebay have a good selection of CRT's and many compatible types.
                              Would that kill the flyback as well? I may not end up doing it anyways I'll probably just go back and try to fix my IBM G40 that I have that does not power on at all but have to figure out what I can use to get into the very small slit holes in the top I have a screwdriver small enough but definitely not long enough to reach the clips that are in there.

                              Comment

                              Working...
                              X