Hitachi/Apple CRT No Color, Half Picture, Green Line

[coppercity]

Greetings, I started a new thread since the problem is diff from what I thought to start with. I will let the photos do the talking. It produces a loud high voltage buzzing noise, I heard a popping noise once and then the picture shrunk and then came back.

I would like to repair this Thanks for any and all help.

Model is M2943 15" Muilt-scan It's made in December of 1995 from a Mac 7200/100.

[Username1]

Found this stuff online:

QUESTION NO. P329-5: Apple Multiple Scan M2943 monitor, the customer said it
made a pop, then smoked. It was showing a line up the middle of the screen. I
found R410, R475, C416, and Q418 burned beyond recognition, I need the values.


A: R475-68 ohms, C416-514J mp250v, Q418 K1035. In the two chassis I have,
there is no R410.


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QUESTION NO. P327-10: Apple M2943 monitor. On the CRT board are two sets of
three resistors, white and orange. What do they do, how does one use them? I
assume that one set adjusts the base values of the three colors and the other set
adjusts the slopes. (I do have test patterns from Sonera Technologies which would be
helpful for adjustments.)



A: You may be referring to the two sets of trim-pots, on either side of the CRT
assembly. There are a couple versions of this Apple (different FCC numbers), so I
cannot know if yours will be the same as the one I will describe. Facing towards the
back of the CRT, on the left side are three closely-spaced trim-pots, towards the
bottom. Top to bottom, these are VR304 (Red Bias), VR305 (Green Bias), and VR306
(Sub Brightness). On the right side, there are two trim-pots above, VR301 (Red
Drive) and VR302 (Green Drive), and a third trim-pot, somewhat lower than those
two, VR303 (Sub Contrast). Typically, the red and green biases are adjusted, to give
a good grayscale; the drive controls are only adjusted if the bias control adjustments
are not sufficient to give neutral grays, and it may then need a screen pot adjustment
of the brightness, for the proper black level.


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Bottom half of screen has no hori sweep. LED lights both green & amber.

A: C001 470uf 16v on power saving dboard on right side of chassis.

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I have one of these, it came with my Performa 6200CD, they produce an outstanding
picture, with awesome grayscale. Sharper picture than their Sony screens! Mine also has
vertical issues. It works for the most part, but something in vert. is going as the
picture collapses now and then. I have not used it in 4 ? years, so I have no idea if
it's working at all now....

[coppercity]

Bottom half of screen has no hori sweep. LED lights both green & amber. A: C001 470uf 16v on power saving dboard on right side of chassis.
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Thanks, that sounds like what is going on with mine, let me check in to that cap. Humm sounds like a good display, I wonder if yours still works?

[Username1]

Well, if it's a cap drying out, or in some way mechanically failing, then who knows....

It did make a really nice picture....

[sweitzel]

I used to work on all flavors of Apple equipment from 1993 to 2000. Check all of the boards for cracked solder joints and re-flow as necessary. These monitors were prone to have them.

[coppercity]

Thanks man, that was the problem, I changed out the cap and it fired right up. I stole a 35v 470uf from an old LCD power supply ;-).

The color has a bad green tint until it warms up, and I can see the color change in waves like again until it warms up. Is that from other drying up caps or something more?

[Dreamsbeard]

Good job! Keep em running!

[Username1]

Those repair boards I found that stuff above on, has lots of "resolder" comments for lots
of problems on that model monitor. My monitor is a really low hour set, so its possible the
picture tubes are about the same high quality as the rest of the thing, yours might be getting weak.....
Or a buncha caps are going bad and whatever stupid pulse, star matter,
or internal windmill they get the heater voltage off of, might be getting weaker too...?

Anyway, I'm happy you got it working !

Good to see an old apple still put to good use.....

[zeno]

Originally Posted by coppercity

Thanks man, that was the problem, I changed out the cap and it fired right up. I stole a 35v 470uf from an old LCD power supply ;-).

The color has a bad green tint until it warms up, and I can see the color change in waves like again until it warms up. Is that from other drying up caps or something more?

Odds are its a weak CRT. The color changing dont add up unless the tube
has leakage. Does the problem suddenly or slowly get better ?? The screen
shot sure looks like a soft CRT. Also looks almost like a hum bar in the pix.

73 Zeno

[andy]

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