Jump to content


  • Content Count

  • Joined

  • Last visited

Community Reputation

166 Excellent

1 Follower

About ChildOfCv

  • Rank

Recent Profile Visitors

2,280 profile views
  1. So, I'm going to make an educated guess about how the SECAM mod works. 1) Pin 8 is connected to ground. 2) The 4.53MHz crystal is the oscillator source for an FM modulator for the color. 3) The "luma" output is instead used as the color and goes to a DAC resistor ladder as usual, but the output of that feeds the FM modulator's input. 4) The crystal's weird frequency is probably chosen because there's some genius circuit that can use it to hit both of the required subcarrier frequencies for the red and blue lines. It should be possible to covert this to PAL, but you may need to add a daughter-board to complete the required signal paths.
  2. That's okay. You could use the PAL schematic as a crutch anyway. That may give you a style guide, if nothing else, and some or all of the circuit may be the same.
  3. Hmmm, well 0 is definitely not a good number. There are a couple of possibilities: 1) The SECAM mod jumpers pin 8 to ground and this circuit goes elsewhere. 2) The TIA is dead. 3) Q203 (the transistor that should be amplifying that RC tank) is beyond dead.
  4. Yeah, I gather that your goal is to convert to PAL? Anyway, the crystal can be replaced with the correct value but that circuit seems to be failing. What's the resistance to ground at the point that has 4.45MHz? (Power disconnected for this measurement of course)
  5. Looking at the 2600 PAL schematic, PAL-S is for synchronization. Apparently they want the PAL signal to be synchronized with something, at least on occasion. This feeds the PAL-I which should be oscillating at 4.453MHz every time PAL-S "rings the bell". But yes, for PAL it should be 4.43MHz. But until you figure out why the oscillator isn't outputting anything useful at the moment, that's a moot point. Are you using an auto-timing mode? You should make sure it's doing about 100ns per division in order to see whether there's anything at the level you're interested in. What does the signal look like at the common node that connects R237, Y201, C241, and L204?
  6. Just noticed this quote since someone else quoted it. On PC, there's a routine that searches the line pointers for a line number. If the target line is greater than the current line number, it will start at the current line number pointer. Otherwise it starts at the beginning of the program and fast-searches the line pointers. I know there is at least one circumstance where it looks for the end of THIS line, though. Well, I think that has to do with handling the ELSE case, and it's actually searching for the end of the current statement (its search also stops at ELSE tokens). I guess if other platforms don't do the line pointer search, it's probably because that special routine was axed for space.
  7. I wonder if all of this was caused by the Power Brick of Death? That's a lot of dead chips.
  8. Well, first check continuity of pin 6 to 8 on the joystick input while holding the fire button. If that passes, make sure pin 6 (player 1) reaches pin 35 of the TIA chip, and pin 6 (player 2) reaches pin 36.
  9. I'm not sure about documentation, but I looked at the TIA schematics. They're posted in some threads on this board. You may also find them at the Atari Museum.
  10. The 25Hz frame rate is for a total of 625 lines. Some of those lines will be vertical blanking, and it will also be interlaced. So that's 15625 lines per second (visible or not). Horizontal resolution is 160, so that's roughly 2.5M pixels per second, not counting sync time.
  11. The internals of the TIA color circuit are a delayed-shift register which is around 14 bits long (however many hues the Atari is capable of). PAL may be slightly different but that's basically what it is. The input is fed a 4.43MHz clock. If the color delay is set correctly, it will propagate halfway down the row of registers before a state change on the input. Color output is selected by sampling at the point of the color index you want. Except that on color burst, the clock itself is sent out. Black is special because it leaves the color output disabled. So yeah, color is just square waves that get sent through a bandpass filter before mixing with the luma DAC output.
  12. Exactly, which is why they should have just fed it a self-contradictory statement on its own, rather than beginning with all the irrational theatrics and ending with it. And actually, (this is from memory, so I could be wrong...), what finally broke the machine was when Mudd simply stated "I am lying."
  13. Really, the "This statement is a lie" part should be sufficient on its own, because if the statement is true then it is false. But still, the fact that it caused the robot's head to explode just revealed how much the 60's generation trusted computers.
  14. Do you know if other RF-type devices work on that TV? Because if so, then all signs point to the RF modulator on the Atari not working. There would be a couple easy checks to make there too, but first we need to know, how many pins connect it to the board? If it's 5 pins, check voltage between ground and pin 3 (the middle one). If it's 4 pins, check between ground and pin 2. If the voltage is near 5V there, but you get no signal, then something in the RF box is dead. Could be a broken inductor wire or a dead LM3086.
  15. Make sure there is continuity between the outside contacts on both ends. Then again with the inside contacts. Now make sure there is no continuity between inner and outer. Now plug it into the Atari. You should now see around 100 ohms between the outer and inner contacts on the other end.
  • Create New...