| Electronics > Repair |
| Vintage chip Programmer : " Micropross ROM 3000U " |
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| Vince:
Google found me this website about the board : https://www.thegeekpub.com/280079/gbs-8200-manual-cga-to-vga-converter/ Apparently I wired the thing properly, that's a good start. Says to use the SW button to switch from one input to the another.... did that, has zero effect on the screen not even a flicker.... suspicious. Says to use the AUTO to get the board to automatically detect what type of video signal is being fed to the board.... again this has zero effect that my human sense can witness. Not looking good. The menus don't let you specify manually what signals you are sending to the board, so if this AUTO button does nothing, I am screwed. Did a quick sanity check.... scoped the RGB and HV sync pins.... yes, all my signals are still there.... However I noticed that with the connector disconnected, I get TTL level signals, 5V, but once connected to the board the amplitude drops to 2V or so ?! Maybe that not normal and the boards fails to detect the SYNC signals because of that... |
| Vince:
Their website gives a couple suggestions in case like me you get no picture. 1) Modify the wiring harness to move the grey wire one notch, next to the yellow wire. Did that, no joy. So I put it back where it was. 2) Board can behave erratically if the power supply can't deliver 2 Amps at 5 Volts. Well I set my power supply to 9V and the board draws less than 200mA, it's not current limited, it seems happy. So it draws barely 2 Watts versus 10 Watts ?! Maybe the chip is half kaput in there.... After doing that... somehow the SW button now shows signs of life ! When I press it displays the name of the inpu at the top of the screen... woohoo ! So I set it to " RGBHV " but still no picture, monitor says " NO SIGNAL ", bummer. So now my two paths of investigation are 1) Can this board work with TTL level signals, and is it normal for it to drop the amplitude to 2V. 2) Does teh video signal of that EPROM programmer use some proprietary timing, in which case that board will probably never work as it appears to be designed for CGA/EGA only, to cater Arcade games. It's not a general purpose converter where one could program custom timings and voltage levels and polarity, and enable interlacing or not. Maybe such converters exist.... if they do I guess they would be out of my price range for sure.... The saga continues....not giving up just yet... |
| Robert763:
Hi Vince, see this manual too https://docplayer.net/42901042-Cga-ega-yuv-to-vga-converter-gbs-8200-ver-3-4-manual.html You have ver 4. Just connect ONE of the video pins of the progrmmer to the converter board, I suggest to the Green (G) input. Each input has a 75R load so 3 in parallel is likely to overload the single output driver in the programmer. Connect the 15kHz signal to Horizontal sync (HS) and the 50Hz one to Vertical sync (VS). Trouble is you have an unknown specification signal so hard to tell what is wrong. B.T.W when looking at the serial ports the data should be standard pin-out e.g. on pins 2 & 3. Robert. |
| Robert763:
--- Quote from: Vince on December 26, 2022, 10:09:57 pm ---Their website gives a couple suggestions in case like me you get no picture. 1) Modify the wiring harness to move the grey wire one notch, next to the yellow wire. Did that, no joy. So I put it back where it was. 2) Board can behave erratically if the power supply can't deliver 2 Amps at 5 Volts. Well I set my power supply to 9V and the board draws less than 200mA, it's not current limited, it seems happy. So it draws barely 2 Watts versus 10 Watts ?! Maybe the chip is half kaput in there.... After doing that... somehow the SW button now shows signs of life ! When I press it displays the name of the inpu at the top of the screen... woohoo ! So I set it to " RGBHV " but still no picture, monitor says " NO SIGNAL ", bummer. So now my two paths of investigation are 1) Can this board work with TTL level signals, and is it normal for it to drop the amplitude to 2V. 2) Does teh video signal of that EPROM programmer use some proprietary timing, in which case that board will probably never work as it appears to be designed for CGA/EGA only, to cater Arcade games. It's not a general purpose converter where one could program custom timings and voltage levels and polarity, and enable interlacing or not. Maybe such converters exist.... if they do I guess they would be out of my price range for sure.... The saga continues....not giving up just yet... --- End quote --- Posts crossed. Does the input selection have CGA? It is worth trying ALL the input selections. he main chip used on the 82x0 is capable of all modes but it needs to be "told" what to do. Different versions / clones of the GBS82x0 firmware have different capabilities / bugs. Robert. |
| Vince:
Fiddled with it some more.... was about to report that I did.... just what you suggested ! >:D Board has a VGA input connector, even though it's meant only for CGA/EGA. So as a sanity check I wanted to see if the board could read VGA and output VGA... So I plugged my Tek TDS544A scope to that board and.... it works fine, I have picture on the monitor ! 8) OK so that board is not dead, it is capable of reading video signals... just not MY video signals, grrr.... So I googled to double check what CGA signals should look like, especially voltage level-wise. Google served me that site out of the blue : https://gist.github.com/sigman78/706c5b8c7800e56aded87596fb5e75bb There it says that CGA is 15.7kHz, but the programmer outputs 15.4 or something. Maybe the video chip on the board is not very tolerant to frequency deviations. Again no documentation so I don't know. Anyway, that site says.. VERTICAL sync is 15.7kHz... vertical really, not horizontal ?! Strange... to me vertical is the slowest one, defining the frame rate, and the fastest clock is the horizontal that sweeps the lines :-// Anyway, nothing to lose, so entered humble mode thinking maybe I got it backwards somehow, and I swapped the H and V wires.... no joy. So I put them back to where they were. So looks like there is indeed something that board does not like in my video signal. Board has no documentation, but maybe I can find a datasheet for the chip itself, which would give me the tolerance on Sync signal frequencies, voltage level etc... |
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