Monochrome Computer CRT Brightness

[TinCanAlley]

I have an old 80s Canon green phosphorus monitor that wouldn't display an image. I have been unable to find a SM, but I dove in anyway.

Today I hooked it up and adjusted the contrast and brightness to max, but no image. I then advanced the sub bright control inside the unit and at max it produces a nice bright and focused image. I am sure this is not how it is supposed to be, so I am wondering what I should be looking into. I measured the G2 at 634VDC and the G1 at -1.83VDC. If I back off the sub bright pot, or the front panel control, the G2 stays the same and the G1 increases. I believe this is how it works, but I know I shouldn't have to max all controls to get an image.

Any suggestions as to where I should be looking? The only screen controls I could find is the sub bright and focus. All other pots are for H size, V size, H lin and V hold. No other pots.

Thanks

[zeno]

MOST of the times on SS sets the cathode is where the video comes in.
Voltages will stay about the same otherwise.
There is a video output transistor ( 3 on color CRT's). If the brightness
is increased the voltage on the C voltage goes down. If you turn the brite
all the way up the C voltage goes up to the B+ value. No raster results.
SO if you get a good pix after the sub brite adj either that pot has
a bad spot or something is "off".

For the SM if the set has an FCC ID number or "type acceptance"
number look it up at FCC.GOV That will list the MFG of the
actual builder & its model number. Take it from there.

73 Zeno
LFOD !

[TinCanAlley]

Originally Posted by zeno

MOST of the times on SS sets the cathode is where the video comes in.
Voltages will stay about the same otherwise.
There is a video output transistor ( 3 on color CRT's). If the brightness
is increased the voltage on the C voltage goes down. If you turn the brite
all the way up the C voltage goes up to the B+ value. No raster results.
SO if you get a good pix after the sub brite adj either that pot has
a bad spot or something is "off".

For the SM if the set has an FCC ID number or "type acceptance"
number look it up at FCC.GOV That will list the MFG of the
actual builder & its model number. Take it from there.

73 Zeno
LFOD !

This monitor is from '84. I noticed that turning the front brightness and internal sub bright affects the voltage of the cathode (I believe that is the negative value that controls the G2's emissions). Anyway, with all the brightness controls down, it put out roughly -130V. As they increase, the voltage drops to -2V or so and the screen illuminates. Never able to get a full raster, but bright enough to use and sharp focus.

So I am wondering that if the G2 is 628V at the socket, and G1 is -2V in order to produce an image, then the CRT is basically toast? If not, what else could account for the need to crank the G1 (brightness and sub bright) in order to get an image? I can easily use this monitor as is, but know there is something wrong and that drives me crazy.

I looked up the FCC stuff and it notes it as being a CRT type device, but goes no further. Doesn't provide enough to find a service manual or other usable specs.

[lnx64]

What's the model number of the monitor? I'm in a few vintage computing groups, I might be able to find some information for you.

[TinCanAlley]

Originally Posted by lnx64

What's the model number of the monitor? I'm in a few vintage computing groups, I might be able to find some information for you.

Here is the front and rear. I'm assuming it is just the Canon A-2001, but that brings up nothing in searches. I've also tried other numbers from the rear stickers. Funny thing is, some of those numbers are the part numbers for the stickers.

[lnx64]

Looks like it may be made by Panasonic. Chassis number 12Y08-4 seems to come up as such.

[TinCanAlley]

Originally Posted by lnx64

Looks like it may be made by Panasonic. Chassis number 12Y08-4 seems to come up as such.

Well I managed to find a factory setup manual, but it doesn't have the exact CRT. The manual covers a few different size CRTs as well as a couple different control board configurations (one for direct input and one for composite). So I went to the one that was the closest to the monitor I have. It has roughly the same voltages on the tube as I measured on mine. It states that with the panel brightness all the way up, adjust sub bright until raster shows up, then back it until it is almost gone.

Since this thing has 628V on the G2, and G1 has to go down to roughly -2V to bring up an image, the CRT must be toast. I tried to rejuvenate it, but for some reason my BK 470 will not setup properly. I set is as should be, but I can't get the needle to move setting up. I set up the G1 voltage @ 50, but can't set the G2 cutoff as it should show a movement in the needle on division. It doesn't move and it shows bad during the emissions test. Now when I do the same on another 12" monochrom CRT, using the same socket and settings, it also doesn't move setting the G2 cutoff and emissions test is bad. However, this monitor works perfectly and has a bright raster with the internal sub bright only half way and the front control at full. So there must be something wrong inside my tester. Will have to see how to diagnose it.

https://archive.org/details/manual_M...M_PANASONIC_EN

[TinCanAlley]

So I found a replacement CRT on ebay. It is new and exact replacement. However, it is 195 + 45 shipping. I like this monitor, but I'm not sure if it is worth the cost. Does the price for a new CRT sound reasonable?