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pspring

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About pspring

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    Combat Commando
  1. More scope poking revealed that my CV is "flaky". LOL Pressing reset will eventually make different pieces partially operate like white bars on the TV or a steady tone. Things that didnt seem to be working(in previous posts) will work if I press the reset enough times. It's like it wants to start but hangs up part way while booting. I think I've seen all chip selects work. Seem like RAM? Kinda hard to debug without a data analyzer. : )
  2. Thanks for the help! I brought the CV board to work where I have much better equipment. Both clocks were spot on. Maybe the 9928 is not getting initialized. I read there are registers needing setup at boot time, one of them controlling INT. Hooked up the mixed signal scope(16 digital + 2 analog) and tried to trigger on U6 addr x01 or x02 pattern while watching the read and write lines controlling the VDP. Neither line went low. The only output line that wasn't always high was the CTRL_EN_1(pin 11). So I went home and swapped U5 and U6 thinking bad decoder. But, no joy... Unless maybe both are bad(I only had time to check U6).
  3. Thanks! I'm slowly learning pieces. : ) No output on 35, 36, 38. Level is steady 2-3v. Found the Coleco troubleshooting guide so I poked around with the scope comparing it to the pictures in the guide and found no NMI. Not sure how it works. VDP CSW(couldn't get to trigger after reset release). Followed flow chart to where U9:17-24 are good(data) but couldn't fond where it is supposed to pick up on sheet 6...
  4. Cleaned with distilled alcohol around crystal and supporting chips. AUD_CLK and VID_CLK are signwave. I think this correct? CPU_CLK is square.
  5. Soldered all the chips back in. Caps on main board measured a bit over 10uF(with cheap meter). Measured current draw with no cartridge or controllers connected: 5v = 460mA -5 = 9mA 12v = 225mA Hooked up composite video and line level audio per these instructions. https://www.benheck.com/bens-colecovision-composite-video-mod/ Still no video or audio on TV. Scope also shows no activity at either output. Don't have Arduino but can maybe dig up an STK600 or some other demo board. Or maybe I can figure out how to use my Coco 2 or TI99/4a!? Might be quicker to replace the ram chips. We have an old DIP memory programmer at work. I check if it can check RAM.
  6. Ok thanks! Good to hear 3.3v is ok. I was chasing a non-problem. Never done that before... lol The insert cartridge message is not shown. The most video I've even gotten was some vertical white bars. Video is mostly a squiggly snowy mess. Both channel 3 and 4 were tried. I don't have Frogger to easily check the audio but have tried waiting 15secs then press 1 to start Donkey Kong but get no output on sound chip pin 7. I've read that the 2 ram chips can cause black screen / dead unit so I'm trying to figure out how to test them. From reading here it seems like getting sound working is a good first step? I'm also going to do the video line out mod to bypass the rf module for now, in case that ain't working. The -5v does not go through the switch, that I have jumpered. Is it ok to just plug the power supply into the wall or does that cause issues?
  7. ACK! I misread the schematic! Video ram ain't connected to the Z80. Maybe I'll hold off removing more chips till someone pipes in on 3.3v on the CPU address pins.
  8. No picture or sound, sometimes steady tone or very garbled pic. I shorted the power switch for now. Power supply is 12.2v, 4.9v, -5.1v. Sound IC pin 7(output) is normally quite so BIOS seems to be loading most of the time. CPU seems to be partially running. Reset cap uF measured ok. Using an oscilloscope I found the CPU address line signals to be 3.3v p-p. Shouldn't they be 5v p-p like other CPU lines? CPU Vcc is 4.9v. Some of the 4116 IC's where nearly too hot to touch so I just removed them all, will probably replace them with 5v, to check if one or more were loading down the Z80. It made no difference. I'm an electronic/software technician but have no experience with CV. Unit is in fair shape and untouched, till now. Doing a lot of reading here. Wondering what makes sense to do next. Appreciate any help.
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