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The IBM5153 monitor, with modification, displays a beautiful 9.5" diagonal EGA image.

Scali said:
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I've never understood why IBM didn't bother to put in a power button. Especially with monochrome, prone to burn-in, you'd want to turn off the monitor sometimes, while the system continues to run.
I think it's another case of poor decisions in cutting cost.
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Yet 30 years later we know it worked fine without a power button and kept everything simple.
It was normal at the time to just turn down the brightness to reduce burn-in.
 
Scali,
The Philips model is a fine example of a monitor with excellent discrete component circuitry. From the look of it the incoming sync is inverted and buffered by the 74LS86, and passes to TS341 which is a sync pulse amplifier, it then gets differentiated by C501 and passes to the phase detector circuit (sometimes called a flywheel circuit) composed of diodes D502 and D501. The output of this circuit is a partially filtered control voltage which represents the phase difference between the incoming H sync and a signal fed back from the horizontal output transformer. (it is pretty much exactly as in the block diagram I put in section 6 of the 5153 article) That signal is filtered by the RC network R505 and C506, but you will also notice the two extra filter components R506 and C507, this forms an "anti-Hunt" network. You will see this type of filter in many circuits that are essentially phased locked loops, so once its locked up it doesn't hunt around.The filtered signal passes to TS501 which is essentially a DC amplifier and controls the frequency of the horizontal oscillator composed of TS511 and TS512 which is an emitter coupled design. Then after that the signal from TS512 drives the horizontal output transistor.
So this circuit solves all the problems and its already designed and works. Therefore this sub circuit could be cloned into a small pcb to add into the 5151 or others. It would also run from 12v, might need a few resistor values altered a tad. It could be a good vintage computer forum project if someone would like to take it on. (unfortunately I don't have a 5151 or any monitor like that). In jest the article could be called "Philips saves IBM".
 
Hi Hugo,
Sounds like this Philips monitor honours the phrase "If it ain't Dutch, it ain't much" :)
Looks like this is the monitor I will be using for my experiments, seems to be the safest choice.
I also wonder what the prices were for this monitor and a 5151 at the time. Did IBM really save that much money on their design? (Or the Commodore for that matter).

Anyway, I like the idea of making it into a mod for the 5151. Aside from it being more robust, you also get control over horizontal size and position. Now that I think about it, it is actually quite silly if a monitor doesn't have these controls. Especially with all the clone cards around from Hercules and others, I doubt they will all get a nicely centered image automatically.
 
The H hold control does give some control over horizontal position, once the image is in lock, or you could alter the resistor in the reference pulse fed back to the diode phase detector to make a "H position control" too. H size on the other hand is normally done with a variable inductor in series with the H yoke coils.
Your Philips circuit has other good features, for example the two series diodes leading to the H hold control are for temperature compensation, to keep the H oscillator frequency stable with heating. Generally Philips always did a pretty good job and this monitor has obviously been designed by their TV engineering team and adapted for computer use. The H.Oscillator system is identical to standard TV technology. You could feed this circuit with all manner of incorrect sync signals and it won't harm it. Remember when analog TV's tuned into nothing and the video and sync signals were "snow" (noise) that is how tolerant this sort of design is to garbled syncs.
 
Chuck,

Yes the Synchroguide always sounded like some sort of auto transmission that belonged in a car. As shown in the link you attached, in that system the DC control of a blocking oscillator was mediated by half of a twin triode. The other half formed a blocking oscillator with an additional "ringing coil" in its grid. This added a sine waveform into the grid voltage, so instead of having a slow inverted exponential rise out of tube cut-off it was a sharp approach, improving the noise immunity.The synchroguide doesn't have an input from the H output transformer, it normally gets its reference signal from the blocking oscillator output directly.

Sync circuits with diode pairs, like the 6AL5 were generally called "sync discriminator" circuits and these types produce a DC output proportional to the phasing of the H sync and the reference pulse fed back from the H output transformer, often from the width coil in vintage tube TV's. Solid state TV's tended to copy this design idea.

There was also third variant called "Syncro lock" I think another RCA idea which used an oscillator controlled by a reactance tube but it really was similar because the twin diode phase discriminator controlled the reactance tube and therefore the oscillator.

Prior to all that in very early sets, the H sync just got directly coupled to the oscillator grid with something like a 50pF capacitor.
 
paul said:
Yet 30 years later we know it worked fine without a power button and kept everything simple.
It was normal at the time to just turn down the brightness to reduce burn-in.
Click to expand...

Speaking of burn-in, considering that there are 5151s, 5153s, etc. out there that do have certain images burnt-in, is there any screensaver program that is designed to be fed a manually composed "anti-picture", i.e. one where all the "non-burnt" pixels are on and all the burnt-in pixels are off? Because it occurs to me that getting your monitor to display that inverted picture whenever not otherwise in use might over time even out the damage, possibly even to the point where burn-in is no longer noticeable.

Does such a program exist?

I mean, in theory, any old screensaver program might do, so long as it allows you to specify a custom picture/text screen, and so long as it can be set to keep solidly displaying that custom picture instead of an ever-changing animation.

Or is this idea of "counter-damaging" the phosphor just crazy talk?
 
phosphor burn is strictly an area that has been exposed to excessive beam current for too long. once the damage has been done, it can't be undone.
 
retrogear said:
phosphor burn is strictly an area that has been exposed to excessive beam current for too long. once the damage has been done, it can't be undone.
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This is a total blast from the past, but that won't stop me from responding now:

You are correct that short of completely rebuilding the actual CRT, there is no way to put the burned-off phosphor back.
However, it should be possible to burn off an equal amount of phosphor in all other areas, thus evening out the damage, which may or may not yield an overall more pleasing result.

It depends on the severity of the burn-in I suppose. An equally small amount of phosphor removed everywhere may be fine. Most of the phosphor removed everywhere may make the screen no longer work at all, which would be worse than just a few severely burned-in pixels being non-functional.

Also, barring a fancy camera and feedback setup, our hypothetical counter-burn-in program has no way of knowing when to stop. Thankfully burn-in is a slow process, and a user might notice that sort of thing.
 
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