Maybe this person can help: http://www.tvmanrepairs.com. Never used him but appears to have been in business for a long time.
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IBM 5154 tube replacement/repair
- Thread starter jacobtohahn
- Start date
mrcity
Experienced Member
I happen to have a 5154 that lacks a power supply & neck board. As such, I can't vouch for the quality of my tube unless I decide to "sacrifice" my 5153 to test it. If you find out you need a new tube before I find those missing parts for myself, I could possibly send you the unit.
andy
Experienced Member
My 5154 had a bad HV multiplier which was causing erratic HV regulation. The result was that the brightness and focus varied (the image would dim, expand, and defocus simultaneously). I'm not sure how common this failure is, but I was able to find a replacement HV multiplier which fixed the problem. Even though it was a very high hours monitor, after fixing that and replacing a bunch of caps, it produces a good picture.
One thing is certain, if your monitor has been used enough for the CRT to go weak, it is definitely full of bad caps. I wouldn't judge the CRT until you've replaced most/all of the caps in the power supply, and video cage, and some on the main board. If it's not a high hours monitor (judge based on how dirty the HV components are, and how much heat damage you can see), then the CRT is probably fine. They used good quality CRTs that lasted a long time with a low premature failure rate.
My suspicion is that the HV is running a little low and causing the picture to be dim and to defocus when you turn up the brightness to compensate. Recap it it and then work from there.
In case it helps, this was the HV multiplier mine needed (I'm not sure if all 5154s use the same part):
https://www.tedss.com/2023000565
One thing is certain, if your monitor has been used enough for the CRT to go weak, it is definitely full of bad caps. I wouldn't judge the CRT until you've replaced most/all of the caps in the power supply, and video cage, and some on the main board. If it's not a high hours monitor (judge based on how dirty the HV components are, and how much heat damage you can see), then the CRT is probably fine. They used good quality CRTs that lasted a long time with a low premature failure rate.
My suspicion is that the HV is running a little low and causing the picture to be dim and to defocus when you turn up the brightness to compensate. Recap it it and then work from there.
In case it helps, this was the HV multiplier mine needed (I'm not sure if all 5154s use the same part):
https://www.tedss.com/2023000565
Stone
10k Member
The flyback transformer was suggested at the very beginning of this thread.
jacobtohahn
Experienced Member
I’ll definitely try adjusting the screen dial and see if that fixes it. If not, I’ll check in on the HV components and look for heat damage. I do think it’s a good idea to recap it anyway, so I’ll probably do that even if the screen dial is the solution.
MissArgent
Veteran Member
Outta curiosity, is the chassis on the 5154 as brittle as the 5151 and 5153 are?
modem7
10k Member
The unit in my 5154 is instead BG2097-642-505. Same for member IBM_User. I have not found anything online that indicates the difference between the BG2097-642-501 and BG2097-642-505.
jacobtohahn
Experienced Member
It’s pretty brittle. I’ve had some be completely destroyed in shipping. Two of them, to be exact. Luckily, this one arrived undamaged.
andy
Experienced Member
The flyback transformer was suggested at the very beginning of this thread.
The flyback was mentioned, but no one has suggested the HV multiplier. The is monitor is very unusual to have a separate flyback and HV multiplier. They're usually integrated into one unit.
Hugo Holden
Veteran Member
I agree, not the flyback transformer, or the EHT multiplier for that matter very unlikely for these reasons:
One thing to understand about the design of the 5154, unlike earlier monitors, it was designed for two scan rates (so it could support EGA).
In a typical monitor's line output scan stage, the line deflection scan amplitude (the peak yoke current at the end of line scan time) is proportional to the generated EHT (final CRT anode voltage) peak voltage. This is because the stored magnetic energy at the end of line scan is proportional to the square of the peak current, and the energy transferred to the tuning capacitance at the end of flyback is proportional to the square of the voltage developed across the tuning capacitor. So, to cut a longer story shorter, the picture width and the EHT generation in a typical CRT monitor are linked.
In the 5154 however (as noted above by andy), they are un-linked, in that the designers, to get stable a EHT, on the two different line scan frequency standards, had to go for a separate EHT generator, independent of the line scan generator. What does this mean? Since in a magnetically deflected CRT, for some amount of scan current (peak yoke current) if the EHT is varied, the picture width will be seen to vary. This is because the amount of deflection of the electron beam is inversely proportional to the square root of the EHT voltage all other things being equal.
So if you are viewing the raster image on the face of a 5154 CRT, and the width of the scanning raster is about correct, then you can assume that the EHT is in fact the correct value and not even bother to measure it. (This assumes the line scan stage is running from the correct DC HT potential). Also if the size of the raster scan doesn't alter much with alterations in CRT brightness and contrast, you can also assume the internal resistance of the EHT generator (multiplier circuits) is low and normal and that it the multiplier not faulty, as the EHT can then be concluded as stable in value over a range of CRT beam currents.
So in the case of a 5154, a lot can be deduced simply by looking at the CRT raster and manipulating the controls.
If the CRT fails to reach a sharp focus on some knee point of the focus control and not improved by adjusting the screen voltage, most likely then the CRT is responsible, possibly a combination of reduced cathode emission & gas (Not faulty circuits, EHT problems or capacitors). If the HT supply to the scan stages was low, you would also see inadequate width etc, but it is worth checking.
One thing to understand about the design of the 5154, unlike earlier monitors, it was designed for two scan rates (so it could support EGA).
In a typical monitor's line output scan stage, the line deflection scan amplitude (the peak yoke current at the end of line scan time) is proportional to the generated EHT (final CRT anode voltage) peak voltage. This is because the stored magnetic energy at the end of line scan is proportional to the square of the peak current, and the energy transferred to the tuning capacitance at the end of flyback is proportional to the square of the voltage developed across the tuning capacitor. So, to cut a longer story shorter, the picture width and the EHT generation in a typical CRT monitor are linked.
In the 5154 however (as noted above by andy), they are un-linked, in that the designers, to get stable a EHT, on the two different line scan frequency standards, had to go for a separate EHT generator, independent of the line scan generator. What does this mean? Since in a magnetically deflected CRT, for some amount of scan current (peak yoke current) if the EHT is varied, the picture width will be seen to vary. This is because the amount of deflection of the electron beam is inversely proportional to the square root of the EHT voltage all other things being equal.
So if you are viewing the raster image on the face of a 5154 CRT, and the width of the scanning raster is about correct, then you can assume that the EHT is in fact the correct value and not even bother to measure it. (This assumes the line scan stage is running from the correct DC HT potential). Also if the size of the raster scan doesn't alter much with alterations in CRT brightness and contrast, you can also assume the internal resistance of the EHT generator (multiplier circuits) is low and normal and that it the multiplier not faulty, as the EHT can then be concluded as stable in value over a range of CRT beam currents.
So in the case of a 5154, a lot can be deduced simply by looking at the CRT raster and manipulating the controls.
If the CRT fails to reach a sharp focus on some knee point of the focus control and not improved by adjusting the screen voltage, most likely then the CRT is responsible, possibly a combination of reduced cathode emission & gas (Not faulty circuits, EHT problems or capacitors). If the HT supply to the scan stages was low, you would also see inadequate width etc, but it is worth checking.
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jacobtohahn
Experienced Member
Oh wow, I only know the very basics of monitors, so the majority of this went right over my head, but it makes sense that it would be the tube and not the HV. I’m away from home right now, but tomorrow or Monday I will be adjusting the SCREEN voltage. Any advice for doing that while the monitor is on so I don’t kill myself? It seems like it would be very difficult to get to.
Hugo Holden
Veteran Member
That question makes me worried for your safety. An experienced technician would simply adjust it with an insulated tool. It might be risky for you to attempt it yourself. Obviously you could improve your chances of not getting a shock by using rubber gloves, keeping your other hand in your pocket and wearing good insulated shoes on an insulated mat. But, if you are not 100% confident to do it (as there are moderately high voltages on the tube base/pcb area) I would suggest don't attempt it and get an experienced monitor Tech to attempt the adjustment for you. The biggest risk in high voltage work is lack of experience.
(One trick used by experienced repairers is to set up a mirror so they can see the face of the CRT without bending around to look at it, as then often the hand with the probe or adjusting tool slips off when posture and attention is diverted from where they are, to the screen face, thereby encouraging accidental contact with circuits in the set. So there are of lot of safety tricks used by professionals that you might not be aware of).
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