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repetto74

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Posts posted by repetto74

  1. Posted

    Hi Ksarul,

     

    Thanks for your answer which is confirming what I was thinking :-). I definitely assume that TMS9904 will not work as should the original TIM9904. TIM9904 are hard to find, I hear that there is apparently an alternative 74LS362 which can do the same job. Is that true?

  4. Posted

    HI Home Automation,

     

    Both IC's comes from the same reseller and I barely do not think tahat they mix good and bad IC's. I am somehow convinced that the TMS9904ANL is not the proper clock generator suitable for the TI99/4A.

  5. Posted

    Hi Guys,

     

    I am buying some spare parts of the TI99/4A to have them available for any repair needs. I have found some e-bay resellers in China with VDP chip, Clock generator, CPU and rams. I have tested successfully the VDP chip (does not look as a new old stock but a new manufacturing) but the clock generator fails (black screen and continuous tone on power up). Now I would like to be sure the one I purchase is the correct because the marking is different. The E-bay clock generator is marked TMS9904ANL while the original one is marked TIM9904ANL. Are they different then or is the e-bay clock generator a scam?

    Thanks,

    Rick

  7. Posted

    hi jhd,

     

    yes in basic mode I can display any of the 8 available colours without any problem for both machines and as per the pictures colours are displayed as they should be at the prompt. What is weird is that the LCD screen is not really displaying a B&W pictures as you can see in pictures. It is more like a mix of faded blue and green with a lot of striped patterns. weird ...

  8. Posted · Edited by repetto74

    Hi guys,

     

    I have both a PAL coco1 and a PAL coco2 the first being modded to composite and the second one using the RF output on a CTR monitor. Both will display a decent prompt screen (green and black). Today I received a CasDuino and tried to load some CAS images (Donkey King) but I have a weird result on screen for both. On the COCO 2 hooked to the RF output I do have a clear picture whenever the green and black display mode is shown but a scrambled picture with washed out colours when in High Res mode (pictures) as if the CRT Tv tuner goes out of sink when the high res video signal kicks in. On the COCO I through composite on a PC screen or the CRT TV I do have a stable picture but the colours are completely washed out with only a mix of blue and green on screen (this is barely unwatchable).

    What can be wrong? Is there any tweak to be done to the color circuitry potentiometer? :? :?

    Thanks

    post-37196-0-07503700-1522949870_thumb.jpg

    post-37196-0-44955300-1522949922_thumb.jpg

    post-37196-0-42208400-1522949943_thumb.jpg

    post-37196-0-37499700-1522949959_thumb.jpg

  9. Posted · Edited by repetto74

    Well difficult to read out this schematic image. Wondering just if the whole project was available to print out the circuit board. I do see also that this is apparently for NTSC COCO's while mine is a PAL version.Thanks anyway! :-)

  11. Posted

    Hi Guys,

     

    I have successfully built a fairly simple composite mod for the COCO 1 here :

     

    http://www.cocopedia.com/wiki/index.php/File:Trs80coco2compmod.gif

     

    This works pretty good and I can have a very decent composite picture over an LCD screen. Now I am wondering how to perform a composite mod on a COCO 2? As far as I read over the net this COCO1 mod is not compatible with the COCO 2 (a close look at the Coco2 MB reveals that there is no video encoder chip MC1372). Is there any DIY alternative?

    Here is a picture of the RF modulator on my COCO 2.

     

    Thanks

    Rick

     

    post-37196-0-00671100-1522075485_thumb.jpg

  14. Posted · Edited by repetto74

    hi guys,


    I have an issue with a TI99/4A. I had to open it to apply some thermal paste on some chips but when mounting back and testing I had a garbled image. I was suspecting the metal shielding was shorting the extra RAM chip piggybacked on top of the TMS9900 (Tursi mod) but the suddenly all went black and now I just do not have a video signal at all. No black or blue screen but just "no signal". the power led is turning on but that's all. That's really stupid from me and now I do have fried something for sure. I have soldering skills and tools but need maybe someone to point me out where to look at now.

    What can be the main cause of a total absence of video output ?

    The only check I did was to ensure that the main PSU and the modulator were ok by plugging them to a working Ti99 and they do work.

    thanks

    Rick


    PS : I gave a check at the power supply PCB and do have correct voltages of +5V, -5V and +12V.

    post-37196-0-01040200-1520118760_thumb.jpg

  15. Posted

    hi guys,

     

    I have an issue with a TI99/4A. I had to open it to apply some thermal paste on some chips but when mounting back and testing I had a garbled image. I was suspecting the metal shielding was shorting the extra RAM chip piggybacked on top of the TMS9900 (Tursi mod) but the suddenly all went black and now I just do not have a video signal at all. No black or blue screen but just "no signal". the power led is turning on but that's all. That's really stupid from me and now I do have fried something for sure. I have soldering skills and tools but need maybe someone to point me out where to look at now.

    What can be the main cause of a total absence of video output ?

    The only check I did was to ensure that the main PSU and the modulator were ok by plugging them to a working Ti99 and they do work.

    thanks

    Rick

  16. Posted

    Hi Combat Commando,

     

    You have a PM :-). Refer to the TI99/4A schematic to find out the ROM positions on the board. As far as I remember the U611 I changed is the one perpendicular to the TMS9900 CPU. I have sent both image files of U610 and U611 as they are different (Low byte ROM and High byte ROM). Good luck ! :thumbsup:

  23. Posted · Edited by repetto74

    OK so I mounted back the PCB into its metal case and mounted back the machine. On power up I was getting a garbled prompt screen with weird colors. After re-opening and testing all was fine again so I do have probably one or more shorts with the metal case. I suspect probably the piggybacked LS021 to have its legs touching the metal case. I will try to tape the whole area and check again ;-)

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