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IBM 5154 tube replacement/repair

J

jacobtohahn

Experienced Member
Joined
May 1, 2018
Messages
79
Location
North Carolina, USA
Hello,
I have an IBM 5154 EGA monitor that’s in great condition, but the picture is dim and out of focus, no matter how much I adjust the flyback transformer. I was wondering if there’s a way that I could repair the monitor, or, if not, see if I could find a replacement tube to put into the enclosure.
Thanks!
 
Find a local electronics repair shop locally. There may be some old timers out there yet that used to service CRTs. They will have the answer.
 
Finding a replacement tube is going to be rather difficult.

More likely than not it's the flyback, itself, and that's much easier to obtain and wayyyyyyy easier to replace.
 
NeXT said:
Second this. Low brightness and focus issues (bloom on bright images?) can indicate a low anode voltage.
Click to expand...

There’s definitely some bloom on bright images, but it’s hard to tell as I can’t get it very bright. My brightness is always at max. I’ll attach some images at various brightness and contrast settings. The one with the 2 monitors shows both at max brightness. The image starts to noticeably blur when the contrast gets bright enough to tell the difference between red and brown. It’s definitely much dimmer than when it was new. Sometimes, (but not always for some reason) it seems like the convergence is off only on white text.

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As for the flyback transformer, do you know where I could pick one up that would be compatible? Are there any other steps I could take to increase the life of the tube itself?
 
1) When you turn the focus control, is there a crossover point? In other words, focus gets better but then worse or does it just get better as moved all the way to the end?
2) If you have the best focus somewhere in the middle (even though not good) then does the focus get better when dim and worse when brighter?

If both those are true, I'd lean toward a bad tube. If focus is best all the way to one end, more likely a bad HV tripler or HV drive circuit problem (or power to it)
I see the 5154 has a HV drive separate from the horizontal drive. Does the size of the raster (width and height) change with brightness? If the dimming is due to low HV then the raster would change size (bloom bigger) with more brightness and not be a fault
of the tube. I hope this makes sense. I serviced CRT's for like 20 years.

Larry G
 
retrogear said:
1) When you turn the focus control, is there a crossover point? In other words, focus gets better but then worse or does it just get better as moved all the way to the end?
2) If you have the best focus somewhere in the middle (even though not good) then does the focus get better when dim and worse when brighter?

If both those are true, I'd lean toward a bad tube. If focus is best all the way to one end, more likely a bad HV tripler or HV drive circuit problem (or power to it)
I see the 5154 has a HV drive separate from the horizontal drive. Does the size of the raster (width and height) change with brightness? If the dimming is due to low HV then the raster would change size (bloom bigger) with more brightness and not be a fault
of the tube. I hope this makes sense. I serviced CRT's for like 20 years.

Larry G
Click to expand...

Well, shoot, it’s most definitely the tube then. Does anyone know where I can find a compatible tube to put in the monitor? I thought I saw a few sites selling compatible tubes once, but I could be wrong.
 
Almost no CRT cross references exist for computer monitors in comparison to people who collect and restore old television sets. Just a lot of word-of-mouth tube changes where the make and model are not really given.
I hope that one day changes before the remaining stock of CRT's are either recycled or completely worn out.
 
NeXT said:
Almost no CRT cross references exist for computer monitors in comparison to people who collect and restore old television sets. Just a lot of word-of-mouth tube changes where the make and model are not really given.
I hope that one day changes before the remaining stock of CRT's are either recycled or completely worn out.
Click to expand...

So, basically, there’s no hope of replacement?
 
Has any other work been performed on this 5154 ? Have the power supply capacitors been replaced ?
You should add your location to your profile, maybe someone local to you has a non working 5154
that the tube could be removed from.
 
mikey99 said:
Has any other work been performed on this 5154 ? Have the power supply capacitors been replaced ?
You should add your location to your profile, maybe someone local to you has a non working 5154
that the tube could be removed from.
Click to expand...

I’ve opened the monitor before and adjusted the focus, but I haven’t done anything else myself. I got it on eBay, but the screws were so bonded to the plastic my first time opening it that it seems like it never had been opened before. Once I get a new tube I might have a repair shop adjust the pot values for me, as they could do better than I could.
I’m located in the Triangle area in NC, if anyone has a working, bright tube to donate or sell locally. Otherwise, I’ll try to buy one.
 
I had a look at the screen images you posted. Your CRT may well still be ok. The EHT is about correct, if it is significantly off, the size of the scanning raster is too big or too small, because the amount of deflection is inversely proportional to the square root of the EHT voltage.

Normally as well as the CRT's focus control, there is the control for the CRT gun's screen voltage. This may simply be set a little low and adjusting that may produce a very good improvement. Over the years as the CRT ages, this often requires a small adjustment.

I have only looked inside a 5154 once, as I recall it used a Japanese manufactured CRT. The part number will be on a large sticker, I just looked at a schematic, it is a M34JDU30X15. Probably best to try for exactly that part if you need a replacement as substitute type often do not have other qualities like the exact phosphor pitch, faceplate curvature or faceplate tinting, even if the guns are similar.

Also, the Screen adjustment in the 5154 appears to be on the CRT's socket/circuit board, so if you do adjust it be mindful of the high voltages in that area. (There is also a sub brightness and sub contrast control on the rear panel, also you will need to re-tweak the focus adjustment too)
 
Last edited:
As Hugo said, here's the location of the screen control. You could try using it to brighten up the tube some to see if it looks better when focused.5154-3.JPG
 
I'm not an expert, but when I looked at the screenshots, it looked like regular bloom due to the brightness being jacked up too high. Does sharpness improve if you reduce brightness?
 
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