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Two EGA monitors, color pallette is different

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DennisDC

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I have two EGA monitors but they seem to produce slightly different colors, is this normal ?
The first is a Goldstar model:

IMG_0879.JPEG

This is the Unisys model:
IMG_0891.JPEG
 
The Goldstar one sorta looks like a problem in the signal path. Maybe with Secondary Green (pin 6), since the 2 colors in your photo which have that bit set look bright pink. But it's hard to tell without seeing all 16 default colors together.
 
I have that same unisys monitor! Good to see yours is somewhat dimmer as well, I thought maybe my crt was super worn. As far as the goldstar, I agree with the others, the image looks overdriven and overly bright. Sometimes necks on crts can short out , and cause that, but thats pretty rare, unless thats a sony trinitron crt, and that can be repaired (green gets shorted out, a lil extra voltage can burn off most shorts). Can we get a picture of the goldstar set at half brightness/contrast aka put both knobs in the middle. And display a picture with some green on the crt.
 
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Yeah seems the colors are out of adjustment on the tube or or one of the colors is missing. Color CRT's have many adjustments.
 
OK I managed to get an image of the EGA palette, first off this is the Goldstar monitor:
IMG_0903S.jpg

And the Unisys:
IMG_0896d.jpg

From what I can see the "reds" or oranges in the Goldstar are the most different.
 
Well the differences are unlikely to do with individual adjustments inside the VDUs. It is either the design of the processing circuits, but more likely a fault.

It pays trying to figure this sort of thing out to align the two images.

The missing brown is a big clue, because to generate that requires signals g & R, so clearly neither of these are being processed, or they are not being presented to the VDU inputs or the mixing matrix prior to the CRT gun amplifier/s. Possibly the g is there but too dark to see, so turn up the brightness and see if you can see it in the area that should be brown. Possibly the g and R signal lines are fractured in the cable (if its a different cable) or the initial logic gates processing these two signals at the monitor inputs have failed prior to the mixing matrix. The red you are seeing must be only r and with R missing it would explain the defective Magenta, but in theory it should look blue. But it would pay if you know to label what the colors are supposed to be on that color test pattern for their RrGgBb makeup to make it easier to work out. Cyan looks ok so probably G & B are ok, consistent also with G being ok.
 

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Red is off. It seems none or high intensity on the Unisys. I'll try to grab mine today if I can...
 
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twolazy said:
I have that same unisys monitor! Good to see yours is somewhat dimmer as well, I thought maybe my crt was super worn. As far as the goldstar, I agree with the others, the image looks overdriven and overly bright. Sometimes necks on crts can short out , and cause that, but thats pretty rare, unless thats a sony trinitron crt, and that can be repaired (green gets shorted out, a lil extra voltage can burn off most shorts). Can we get a picture of the goldstar set at half brightness/contrast aka put both knobs in the middle. And display a picture with some green on the crt.
Click to expand...
The last photo is with the Goldstar at half contrast.
 
Hugo Holden said:
Well the differences are unlikely to do with individual adjustments inside the VDUs. It is either the design of the processing circuits, but more likely a fault.

It pays trying to figure this sort of thing out to align the two images.

The missing brown is a big clue, because to generate that requires signals g & R, so clearly neither of these are being processed, or they are not being presented to the VDU inputs or the mixing matrix prior to the CRT gun amplifier/s. Possibly the g is there but too dark to see, so turn up the brightness and see if you can see it in the area that should be brown. Possibly the g and R signal lines are fractured in the cable (if its a different cable) or the initial logic gates processing these two signals at the monitor inputs have failed prior to the mixing matrix. The red you are seeing must be only r and with R missing it would explain the defective Magenta, but in theory it should look blue. But it would pay if you know to label what the colors are supposed to be on that color test pattern for their RrGgBb makeup to make it easier to work out. Cyan looks ok so probably G & B are ok, consistent also with G being ok.
Click to expand...
Thanks for putting the images together like that, do you think its just a cable issue?
 
I'd clean the cable and if that dont work, a lil deoxit on the red drive pot, free it up a lil...
 
It would help to have the schematic and a scope, then you could look at the signal after the initial set of buffers that buffer the cable signals and see if R or g is missing at that point then look at the inputs to those, if still missing probably the cable, but in any case you could follow the R and g signals as required through the circuit.
 
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