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

T

thegenerallee86

Experienced Member
Joined
Feb 1, 2021
Messages
143
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.
 
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..)
 
kc8eyt said:
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..)
Click to expand...

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?
 
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.
 
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.
 
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thegenerallee86 said:
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
Click to expand...

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.
 
kc8eyt said:
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.
Click to expand...
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

Chuck(G) said:
Since you've got the case apart, can you see the heater glowing faintly in the CRT neck (with a signal applied)?
Click to expand...
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
 
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thegenerallee86 said:
What else could I check to see what it might be or look at?
Click to expand...

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.
 
Hugo Holden said:
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.
Click to expand...

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/11M2255OPMSd47izm0_YHO0iYsvAtHFT6/view?usp=sharing
You may have to zoom in to see it but it is there.
 
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.
 
Hugo Holden said:
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.
Click to expand...
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.
 
It wouldn't normally kill the flyback transformer but it could kill the Horizontal output transistor and its driver circuitry and possibly the gun driver transistors. But there is no absolute proof there is air in the CRT yet. Usually, if there is, the CRT heater reacts with the air and burns up leaving a white smoke like deposit on the inside of the neck , near the CRT's base.

So, if it were my monitor, despite finding that crack in the glass, I would proceed with the usual investigations, just in case the CRT has not let down to air yet.
 
It might be possible to put some glue over the crack to keep it from getting air. I'm not sure which I would use, but I think I would try that if it was me.
 
I have patched over a crack in a vintage TV CRT once 20 years ago, successfully, the CRT is still working. I used a product called TORR SEAL, made by Varian Vacuum. It is a white two part epoxy resin. But it is costly. It is a very low vapor pressure resin.

Edit: this is the product:

https://avtservices.com.au/shop/varian-torr-seal-v04990211/

Probably, a quick check would be the continuity of the CRT's heater. If that was ok, then the heater at least has not been running in air. Another check could be to power the heater with a power supply, most heaters, are 6.3V. If it behaved normally then likely the CRT is still under vacuum.

Probably though the best bet initially is to fault find the set in the usual manner.
 
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