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techknight

68LC040
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Everything posted by techknight

  1. techknight

    Color Classic Analog Board

    another thing that invokes my curiosity, i wonder why the LC550/575, etc etc doesnt have these. maybe something to do with the higher resolution. its kind of gutsy, but whta happens if you run the color classic without them? wont sync the res?
  2. techknight

    Color Classic Analog Board

    most likely are in my humbile opinion, since they are in parallel.
  3. techknight

    Mac Color Classic CRT/Analog board problem

    Since you brought up convergence deflector plates that i seemed to have overlooked in december, the thing that comes to mind is the old 40s electrostatic TV sets. if the design is anything like that, the V and H sweep signals are coupled to the boost voltage to the convergence deflectors via a high voltage mylar cap. or something like that i think. Those caps could be open....
  4. I dont know if the problem is in the CRT, or the analog board. but the horizontal convergence is gone. vertical convergence is A OK. the ALPS white pot on the CRT neck/video board does nothing to the picture. has no effect. the pots on the top of the yoke change the vertical and horizontal convergence a little bit. there is a E/W coil with a ferrite adjustment screw off to the right and i broke the ferrite into many peices to try to adjust it. (didnt affect the convergence hardly at all). i tried using the convergence rings on the back of the neck, and if i play witht hose i can bring the picture in ALMOST, but not enough where it wouldnt drive me nuts. so something is wrong somewhere, so i returned the adjustment rings back to thier original positions. i ESR tested all the electrolytics and they are fine. any ideas? i dont have another machine to swap yoke, CRT, analog boards to figure out where the problem lies.
  5. techknight

    Mac Color Classic CRT/Analog board problem

    You also mention the plates in the trinitron CRT that has an AC sweep-synced signal that goes to the CRT. that might be whats missing, But im unsure of to what pins these are. Do you know? Thanks.
  6. techknight

    Mac Color Classic CRT/Analog board problem

    I know this thread seems a little old now, But i never did get this thing working. I got down to replacing the entire neck board, and went through all the resistors in the main circuit for any out of tolerance values or opens. Nothing. Checked all the transistors for opens and shorts, all seem good. I tested all the electrolytic capacitors with an ESR/DCR check, and found a couple of weak ones in the video circuit, but the rest are good. Swapped the two in the video circuit, it made the image a little bit more crisp, but the convergence issue still resides. So that eliminated the convergence adj pot, and the neck socket, becuase i swapped the CRT boards between the LC550 and the CC. and no difference. I'm at a standstill. I need to figure out what in that little analog circuit generates the dynamic convergence waveform that the tube uses for that adjustment to even work. thats where the fault is going to be.
  7. techknight

    broken 512k on ebay

    I have a logic board for this unit that im going to toss. it works fine. pulled from a 512k with a shattered CRT. (kids).
  8. techknight

    Mac Color Classic CRT/Analog board problem

    do you happen to have a pinout of the CRT? so i can trace the electrostatic convergence driver circuit?
  9. techknight

    Mac Color Classic CRT/Analog board problem

    Hey, I'm just trying to help. The manual shows the location and function of all of the convergence controls. Your post seemed to express surprise at the function/discovery of one ("there is a pot on the back of the video board if i adjust it, it causes the horizontal convergence to adjust left to right"), so it was completely natural to think that you had not read the manual, ok? Plus, you gave much too serious consideration to the "crt is at fault" hypothesis, which told me that you are relatively inexperienced in these matters. Don't get defensive when someone's trying to help. After all, you were the one asking for assistance. Sheesh! Now on to more technical topics. Abandon the mysterious "grid voltage" fault theory. A trinitron has a very simple crt structure. Its convergence circuitry is also very simple. All grids are common to all guns, so you cannot have a failure in a grid that selectively affects convergence of only one color. There are, however, trinitron crt elements called deflectors. Convergence is achieved in part by applying sweep-synchronous ac voltages to these (electrostatic) deflectors. When you say that the pot "reads the same" as the pot on the 550, are you referring to a pair of resistance readings (you need to measure a pair for one pot), or to a measurement of the tap voltage? If the latter, does it vary as you rotate the pot? And if so, how does the voltage control range compare with that on the 550? I agree that a schematic would be nice to have, but you do have the 550 to use for comparison, which is almost as good. Just hang in there, work logically, and you will crack this nut. only "one" color? all colors are affected bro.
  10. techknight

    Mac Color Classic CRT/Analog board problem

    yes i read the manual. so don't mis-judge me would ya please? i hate that... anyway, the convergence control pot on the back of the video CRT neck board (assuming you know what that is, remember the part about mis-judging) does not function. this pot is electrically connected to one of the CRTs grids to ground. the pot reads the same as the pot on the LC 550 analog board. so it isnt the pot. only thing i can figure its a low or missing CRT grid voltage somewhere. has to be. there are NO other bad parts on the analog board itself. i tested all the resistors, they are within tolerance, caps are good, even the ceramics and mylars. Diodes statically check fine, but that dont mean they arnt breaking down under load. there was 2 buldged looking electrolytic capacitors that were under the shield near the video output IC, they ESR and LSR check fine, but i replaced them anyway. no difference. so the only possible thing that can be wrong in the analog board is a bad fly, or a bad IC somewhere since i cant physically test those without a USEFUL service manual...
  11. techknight

    Mac Color Classic CRT/Analog board problem

    well i just found out it IS the analog board. i have an LC/performa 550 model with the SAME board in it, but its wider. there is a pot on the back of the video board if i adjust it, it causes the horizontal convergence to adjust left to right but on the classic analog board, that pot does NOTHING. the only thign i can figure, is because im missing a grid voltage somewhere.. but anyway, i took the 13" 550 CRT out, and stuck my 9" CC CRT in place of it, and boom, perfect convergence after adjusting the pot. i put the 13" CRT back in, and stuck my color classic analog board in and bam my 13" cRT is out of convergence and pot does nothing. so something is wrong right there... either im missing an anode voltage, or something.
  12. techknight

    Mac Color Classic CRT/Analog board problem

    yea i got it all back to its original position. ive done this before, but i dont see anywhere on the circuit that would have anything to do with convergence aside from the yoke itself?? all the capacitors ESR test comes out good. so i can rule out caps. only thing left is diodes and resistors and transistors. i have full deflection, no pincushion distortion, or insufficient vertical sweep. all that is fine. would be nice to have a schematic diagram of this damn thing.
  13. techknight

    Mac Color Classic CRT/Analog board problem

    as far as the yoke, theres only one plug that goes from it to the analog board. the horiz/horiz return, and vert/vert return wires. 4 wire plug. thats it. no extra wires. so all the controls on the yoke affect whats within the yoke.
  14. techknight

    Mac Color Classic CRT/Analog board problem

    ive already played with the yoke position. the yoke can only be in one position to maintain proper purity. and it has very little affect on convergence where the yoke is placed. there is a coil on the right side of the yoke. not the left, but it dont do anything to the picture. i shattered the adjustment ferrite core trying. so that yoke is either bad, or the analog board is bad.
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