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Powertran Cortex

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    Originally posted by JEH View Post
    Have you modified your sync circuit as in http://www.quantums.info/cortex/Cort...Feb%201986.pdf ?

    Or are you using the video circuitry from http://www.quantums.info/cortex/Cort...Feb%201986.pdf - I can't find the 1k R26 in either circuit (well, the former has a 27k R26 between Q2 and the FF clock).

    OK, found R26 1k pullup in my printed CortexII schematics. Have you tried adjusting R37? It seems to be the voltage switched to Q5 by the sync pulse.
    Hi, I've not tried any of the various sync level mods as on my Cortex the sync pulses on the scope are pulling down to ground, the circuit is all standard Cortex 2.
    So I don't appear to have the problem these mods fix.
    The pot is adjusted to the only position that give a half stable picture, anything else just looses sync and the colours go haywire.
    Adjusting VC1 also causes all sorts of psychedelic colours and loss of sync.
    At it's best adjustments I am getting line tearing on any line with text on it.

    Interestingly all the problems remain, just in monochrome if I remove IC57,IC59 and IC60

    Many thanks for your thoughts,

    Jim

    Comment


      Not for the purist, but a simple solution with much improved picture quality is a RGB encoder. My favourite circuit is from the November 1988 Chicago TImes (probably on whtech), just 8 transistors and a few passive components. I have built 2 of those for my TI-99/4A and never want to go back to the modulator. Picture quality is superb with any RGB monitor, most current TVs can display RGB via the SCART input (my LCD TV can even take the YUV from the TI).
      Another circuit (10 transistors) from the MSX: http://www.msxarchive.nl/pub/msx/mir...lf/rgbmsx1.pdf

      Jens-Eike

      (just noticed, you already have the last circuit at http://www.quantums.info/cortex/rgbmsx1.pdf )

      Comment


        I have actually bought a F18A so I can run the Cortex with a LCD VGA monitor.
        I've just not yet found the box I put the small VGA monitor in !
        Also, I'd like to fix this problem before I fit it.

        I tried the simple ETI mod (added 560K resistor instead of pot) last night but it made no difference to picture quality.
        I've every RGB encoder circuit I could find on the net, I'm not sure about the one from Chicago times (sounds like a newspaper), do you have a link ?, I can only find a newspaper !
        Now I've the details from MPE I will probably reproduced the original Cortex RGB encoder though it seems massively complicated and an enormous PCB for what it does.

        I also looked at using the YUV from the unnamed connector on the Cortex but I believe the signals need buffering and matching to 75R before they can be feed to a TV.

        Jim

        Comment


          More Cortex bits on Ebay.

          PCB's
          http://www.ebay.co.uk/itm/POWERTRAN-...item5af36d9521

          Set of keyboard switches (no caps).
          http://www.ebay.co.uk/itm/POWERTRAN-...item5af36da6c3

          Jim

          Comment


            I was wondering what happened to you guys...

            Comment


              OK, it was me that bought the PCBs and switches on ebay. I am planning a modified build (SRAMs instead of 4500 + DRAMS, probably a ps2 keyboard). Reading previous threads, looks like I bought a duffer TMS9909 chip, but I do have a 2797 lying around. Let you know how I get on - just hope the 995 is not a duffer.

              Comment


                Originally posted by colbhaidh View Post
                OK, it was me that bought the PCBs and switches on ebay. I am planning a modified build (SRAMs instead of 4500 + DRAMS, probably a ps2 keyboard). Reading previous threads, looks like I bought a duffer TMS9909 chip, but I do have a 2797 lying around. Let you know how I get on - just hope the 995 is not a duffer.
                Welcome Colbhaidh. Did you make a deal on the switches, because I see there were no bids on ebay? Plenty of good 9995s around if you have a problem.

                Stuart.

                Comment


                  There's a Cortex II popped up on eBay, item 261297535704. I've sent a message asking for a photo of the PCB if possible so we can see which chips are fitted.

                  Comment


                    Originally posted by Stuart View Post
                    There's a Cortex II popped up on eBay, item 261297535704. I've sent a message asking for a photo of the PCB if possible so we can see which chips are fitted.
                    I just came here to post that..

                    Jim

                    Comment


                      Originally posted by Stuart View Post
                      There's a Cortex II popped up on eBay, item 261297535704. I've sent a message asking for a photo of the PCB if possible so we can see which chips are fitted.
                      Just sold for 227. From the photos, it's missing the 64K RAM chips, and one of the key tops is missing.

                      Comment


                        TMX9909 FDC chip on Ebay
                        http://www.ebay.co.uk/itm/RARE-VINTA...-/261303093183

                        Date code is 84 so it's feasible it's a real one not a fake from China which have much later date codes.

                        Update:
                        If you compare with my real one (top chip) in this picture it does look to be very close, certainly not like the fakes.
                        http://www.vintage-computer.com/vcfo...0&d=1351529006

                        Jim

                        Comment


                          F18a

                          6 months after I bought it I've actually tried the F18A in the Cortex.
                          http://codehackcreate.com/archives/30
                          And it works, just needed to lift it up slightly by putting an extra turned pin socket on the bottom of it.
                          It is available with longer pins but when I bought mine he only had the short version in stock.

                          If you use it you can remove the existing video memory and quite a few other chips for the video output if you want to save power.

                          Jim

                          Comment


                            I'm a bidding ...

                            Stuart.

                            Originally posted by Jim Hearne View Post
                            TMX9909 FDC chip on Ebay
                            http://www.ebay.co.uk/itm/RARE-VINTA...-/261303093183

                            Date code is 84 so it's feasible it's a real one not a fake from China which have much later date codes.

                            Update:
                            If you compare with my real one (top chip) in this picture it does look to be very close, certainly not like the fakes.
                            http://www.vintage-computer.com/vcfo...0&d=1351529006

                            Jim

                            Comment


                              Originally posted by Stuart View Post
                              I'm a bidding ...

                              Stuart.
                              I was as well but somebody just outbid me

                              Jim

                              Comment


                                Oops! I was trying to get it so I could send it to Stuart, since I have somehow misplaced the entire TUBE of them that I have and I'd promised him one. . .so it was me that outbid you. . .it does look like an original chip too--even the 5-digit lot number is in the right general range for that date code.
                                Enter My Mind At Your Own Risk!

                                Comment

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