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Model III CRT Issues

Yeah, I'll give it a shot, but I think it might be more involved than that.

I'm going to try and upload a video soon, so stay tuned!
 
Lets see some pics of the 2 pots. I am curious if maybe a wire is in the wrong place? On my Model III the center wire on the brightness is purple. And you mentioned in a PM to me it was orange? Could be the problem. Check the purple wire as chuck mentioned to ground and see if it is around 50v +.
Only place I see an orange wire is from the Power supply. Maybe they just changed colors??? Also with no Raster my center wire reads 6 volts

Pic is of what mine looks like

Then advise what you have.
 

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Now wait a minute.

Mine looks the same as yours except the middle wire on the top Pot (Brightness) is orange. And, the black wire on the lower Pot (Contrast) doesn't connect with the black wire on the top pot, it's grey on mine and goes to the video cable! Purple has no volts either.

What am I missing here?
 
Another pic of the edge connector to the display board. Maybe they just used a different wire color? Note where the purple wire is going! Is your center wire going to the same place? If so then maybe just used a different color. if it is then you need to check continuity.
 

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Mine looks nothing like yours!

The pinout on my plug is this, From left to right: Black, Blue, Orange, Purple, Red, nothing, Light purple (That's what is connected to the contrast knob), Grey, nothing, Brown.

What the heck? Mine has way to many wires compared to yours!
 
I think you are confusing the center wires away from the cable itself. That's why mine look clear.

Left to right on mine 1st hole nothing, 2nd hole blue, 3rd hole white, 4th hole orange 12 v,5th hole red, 6th hole nothing, 7th hole purple to wiper, 8th and 9th nothing. 10th and last hole black all ground leads.

Also 1st hole can be black it is also a ground connection same as last one on mine.

Only thing I can think of is yours is a different revision than mine is.

Ok continuity check to the light purple on yours. Make sure power is off! Touch a probe from a volt meter and set to ohms to Pin sticking up as seen in the picture should be 2nd one from right just below R301 right edge. That is the same point as the wiper. Touch the other side of meter probe to center of brightness pot should get zero ohms or a beeping sound. This means it is connected and have continuity. If not zero ohms or no beep than is open and could be your problem.
 

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Yep, there is continuity. Perhaps mine is a different version? Or, the previous owner rewired the pots, I can't remember if he did or not...
 
Basically, to rehash what Larry and I have said, there should be continuity between the wiper (center lug) of the brightness pot and pin 5 of the CRT socket. (you count CRT socket pins by looking for the gap in the circle they form and count from 1 clockwise from the gap, thus:
diag54.gif


Do this with power off!
 
Are you looking at the back of the socket or the front when removed from the CRT? I am seeing it on pin 1 and 5. Which makes sense according to SAMS
 
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Standard vacuum-bottle convention--looking at it from the bottom. The brightness pot shunts that pin to ground. When power's on, you'd read somewhere around 0-70 volts to ground, depending on the pot setting.
 
The video helps a lot. The first thing that I'd check for looking at that is heater-cathode shorts. Just pull the socket off and check the pins with a medium-range (200Kohm) setting on an ohmmeter. You should read infinity. Could be that you were sold a bad jug.
 
With the socket off, test (high ohms reading) between pin 3 and 2 and 4 and 2. If you get anything but infinity, you have the problem solved. If not, I'll have a look at some of my OEM monitor schematics and see what I can come up with.
 
Ehehe. Problem is, I don't think you can read "Infinity" on an analog multimeter. Which is all I have...

Is there anyway I can get an infinity on an analog meter?
 
ardsleytank said:
Ehehe. Problem is, I don't think you can read "Infinity" on an analog multimeter. Which is all I have...

Is there anyway I can get an infinity on an analog meter?
Click to expand...

Sure it does. Look at the far left of the scale. The needle will pin to the left on infinity.
 
Welp, when I have it set to Ohms, it pegs out to the right on both 2 and three, and 2 and 4.

What does that mean?
 
In other words, on your meter, it reads the same as if the probes aren't touching? Or reads the same as if the probes are touching each other?
 
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