Wg 4915

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I have a Paperboy with a 4915 Med. Res. monitor. I just repaired the power brick and got the machine up and everything was blue.

I recapped the monitor. Everything still blue. Removed the input connector turned the brightness up and the blue cutoff down and have a blue screen -no white. When in bookkeeping you can see a little bit of red and white writing is blue.

Anyone seen this problem before?

I'm thinking. Pull blue drive transistor on neckboard. See if Red & Green are OK. If OK look at Q205 , Q208 and D209.
 
Pull the blue transistor for sure. If it's still blue, then it's the tube...
 
Looks like it is the tube. Removed the blue drive transistor (Q403) still had a blue screen. Checked R410-R415 all good. Turned all the drive and cutoff pots down and checked the voltage at pin 6(R) , 8(G) , 11(B) of the CRT socket all around 40 volt. There is very little Red no Green and a ton of blue. I wonder if someone tried to Rejuve it and fried it.

So. Will a regular K4900 series tube work in this Med. Res. monitor?
 

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Looks like it is the tube. Removed the blue drive transistor (Q403) still had a blue screen. Checked R410-R415 all good. Turned all the drive and cutoff pots down and checked the voltage at pin 6(R) , 8(G) , 11(B) of the CRT socket all around 40 volt. There is very little Red no Green and a ton of blue. I wonder if someone tried to Rejuve it and fried it.

So. Will a regular K4900 series tube work in this Med. Res. monitor?

It is most likely NOT the tube. Had the exact same problem after a cap kit on a Paperboy with a 4915. Haven't had a chance to diagnose what is wrong with the CHASSIS. Do know for a fact that it isn't the tube, as a different chassis colors up fine.

I pulled all of the color trans, with no change as you have stated.

I would almost guarantee that you have an issue with your chassis.
 
yeah, now that you've posted pics, it's not the tube. If it was, you wouldn't have the black edges...
 
Swap the blue input to the neckboard with the red input to the neckboard and see if it changes on the screen...
 
Swap the blue input to the neckboard with the red input to the neckboard and see if it changes on the screen...

Actually I removed the RGB connector going to the neckboard turned up the brightness and still had blue.

What I can't understand is I have consistant voltage between all 3 guns at the CRT socket. Also still have blue with Q403 removed.

Socket Pin 1 is Focus and Pin 7 is Screen - Both have full control so I doubt the problem is there.

Pin 5 is -39V

Pin 9 & 10 is heater. I need to check voltage. Should be 6.3V.


I think I'll pull R413-R415 right at the socket and see if I have any blue then.
 
Measure the voltage of each color as it comes into the neckboard. All three should be the same (about 6vdc). ...
 
If thats what the pic looks like and you can't get any red or green, that could be the tube. I have a 7203 with a thin neck tube on the shelf right now that has no red. Everything is good to the tube socket - voltages are even when doing a test pattern, just no red.

Maybe a rejuv would fix, or see if you can find another tube to try?
 
If thats what the pic looks like and you can't get any red or green, that could be the tube. I have a 7203 with a thin neck tube on the shelf right now that has no red. Everything is good to the tube socket - voltages are even when doing a test pattern, just no red.

Maybe a rejuv would fix, or see if you can find another tube to try?

It is NOT the Tube, it is a chassis issue.
 
BTW - if you ever go find my weird G07 thread, voltages can be even at the neck socket and still have colors missing. My fix turned out to be something completely out of the color circuitry, and yours might also...
 
Anybody know what the tube model # would be on the 4915 in a paperboy? I'm doing a rejuv and can't find it on the tube anywhere (suspect a sticker fell off). I want to make sure I adjust the G1 properly and not just assume it's 50v.
 
Ok. I looked at this again today.

I lifted R413 (Red) , R414 (Green) and R415 (Blue) at the CRT socket. I turned the screen control up and powered it up. I had very light blue raster lines and light blue jailbars on the left side of the screen. No White raster.

I then connected R413. I had very dim red

I swapped Red & Blue inputs to the neck board. Still had dim Red

Connected R414 and I could see very little green with the lights out and the dim red.

Connected R415 and I had a screen full of blue. (still have Red and Blue inputs swapped)

Then I lifted R415 & R414 again and jumpered the output of R415(blue) to socket pin 8 (Red Gun) and had dim Red.

So this tells me with the final output of the blue jumpered to the Red Gun the problem can't be in the color side of the Chassis/Neckboard.

I then tested the Heater voltage and only have 2.9V AC (should be 6.3) This was tested with the blue gun still disconnected.

Could the tube have a short between the heater and blue gun? (I still have dim blue raster with no input to any gun)

What would cause the low heater voltage? (flyback?)
 
Could the tube have a short between the heater and blue gun? (I still have dim blue raster with no input to any gun)

If you suspect a H to K short you can pull the neckboard off and meter the H and KB pins on the tube itself and check for a short like you would anything else.

Sounds to me like you need to have the tube checked.
What you may have going on is a good blue gun but a weak red and green gun.

As for the heater voltage - Measure the resistance on the resistor in line with the heater pins, think it's R416 glancing at hes schematic. Make sure it's to spec.
Sometimes it's hard to get a true reading on the heater voltage (honestly forget what the term is) but generally if you have decent noticeable heater glow then I wouldn't worry about it. And from the looks of the screen brightness even though it's "blue" I wouldn't worry about it.
 
If you suspect a H to K short you can pull the neckboard off and meter the H and KB pins on the tube itself and check for a short like you would anything else.

Sounds to me like you need to have the tube checked.
What you may have going on is a good blue gun but a weak red and green gun.

As for the heater voltage - Measure the resistance on the resistor in line with the heater pins, think it's R416 glancing at hes schematic. Make sure it's to spec.
Sometimes it's hard to get a true reading on the heater voltage (honestly forget what the term is) but generally if you have decent noticeable heater glow then I wouldn't worry about it. And from the looks of the screen brightness even though it's "blue" I wouldn't worry about it.

Checked R416 -It's good - Checked voltage going in 4V going out 3.1V Compaired it to another k4900 it had 4.6V in 3.6V out.

Checked the heater pins on tube - 2 ohms. Checked another tube it was the same.

Checked heater to R,G,B - No short.
 
Ken Layton has told me the only way to accurately measure the heater voltage is with a meter with true RMS (or something like that). I had a monitor I thought was having heater issues because it was reading similar to what you're saying, and he posted about that.

IMO, if your heater is on nice and bright I doubt you have a voltage issue.
 
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