omf Posted July 16, 2015 Share Posted July 16, 2015 so i have at long last with a lot of work got the French RGB colecovision board i have in my possession working once again. my question is does anyone know a fill pinout for the motherboard RGB connector. i have looked on http://www.colecovision.dk/technical.htm i have also looked on http://www.nightfallcrew.com/14/06/2009/cbs-colecovision-secam-rgb-hackcbs-colecovision-secam-rgb-hack/ they are both incorrect, and so my first attempt produced a pretty pants cable that was not fit to be used (wrong colours etc) I have finally got a rgb picture out of it using a combination of them both and my own judgement but the other pins in the connector provide voltage when measured against the board ground that is not documented on any site. do we know what the other pins do. also what are i would like to just put this out there for comments, the audio from the RGB connector is incredibly weak, i was thinking of using a transistor or maybe two paired together to increase the power of this so you don't have to have the tv on max to hear anything (hopefully will result in less interference buzz from whatever is causing that! i will post a completed pin out later that i know that is as good as i can get it. but the other pins i will need a bit of help maybe with someone with a proper French RGB cable any info greatly appreciated Quote Link to comment Share on other sites More sharing options...
CatPix Posted July 16, 2015 Share Posted July 16, 2015 I have one, but I'll probably won't have access to it before 2 weeks. Maybe your audio out is busted? I have those consoles, and on the one with working audio (I have one with fine graphics and dead audio, and one with garbled graphics and fine audio ) the sound come out of the TV at average sound level. The voltage if documented in the SCART pinout. There must be a 3V and a 5to12V. The 3V is used to switch the TV into RGB mode. The 5 to 12V is used for autocommutation (the TV goes into A/V mode when you power up the console; it's one reason why many 80's French TV doesn't have a proper A/V selection button). If there is one one voltage, well it's easy with a resistor to lower to 3V, it was a commong thing for consoles. I hope this helps! Quote Link to comment Share on other sites More sharing options...
GroovyBee Posted July 16, 2015 Share Posted July 16, 2015 so i have at long last with a lot of work got the French RGB colecovision board i have in my possession working once again. You've been battling that one for a while. the audio from the RGB connector is incredibly weak I've no idea whats on the PCB but is there a transistor or op-amp buffer between the connector pin and the sound chip? It could be the sound chip is dying or its gain stage or the electrolytic AC coupling cap has dried out. If they are all OK you might get more mileage from reducing the output impedance on the motherboard to the SCART pin. Then your TV will see more of the signal. Quote Link to comment Share on other sites More sharing options...
omf Posted July 16, 2015 Author Share Posted July 16, 2015 You've been battling that one for a while. I've no idea whats on the PCB but is there a transistor or op-amp buffer between the connector pin and the sound chip? It could be the sound chip is dying or its gain stage or the electrolytic AC coupling cap has dried out. If they are all OK you might get more mileage from reducing the output impedance on the motherboard to the SCART pin. Then your TV will see more of the signal. yes, indeed I have, in the end it was one of the TMM314APL static ram chips that was dead I doubt it is the sound chip as basically I replaced all the supporting chips (which are now all socketed), the only chip that is not socketed now is the z80, but i have changed this with the one on the pal board to see if it works or not, which I expected it would do due to my readings from the cheapo logic analyser (i was seeing activity) it could be the electrolytic caps however, I will look in to this there are a load of transistors on the French board near the back, which would be causing an issue, I would have to multimeter them all to see. probably wont be any chips, as they are all new Quote Link to comment Share on other sites More sharing options...
omf Posted July 16, 2015 Author Share Posted July 16, 2015 I have one, but I'll probably won't have access to it before 2 weeks. Maybe your audio out is busted? I have those consoles, and on the one with working audio (I have one with fine graphics and dead audio, and one with garbled graphics and fine audio ) the sound come out of the TV at average sound level. The voltage if documented in the SCART pinout. There must be a 3V and a 5to12V. The 3V is used to switch the TV into RGB mode. The 5 to 12V is used for autocommutation (the TV goes into A/V mode when you power up the console; it's one reason why many 80's French TV doesn't have a proper A/V selection button). If there is one one voltage, well it's easy with a resistor to lower to 3V, it was a commong thing for consoles. I hope this helps! yeah i managed to get both the voltage lines from the pinout, they are described on http://www.colecovision.dk/technical.htm although the pin numbers are incorrect, the website says 4 is blue out and 5 is +12volt, however these two pins are reversed Quote Link to comment Share on other sites More sharing options...
GroovyBee Posted July 16, 2015 Share Posted July 16, 2015 there are a load of transistors on the French board near the back, which would be causing an issue, They might be configured as emitter followers in order to drive the expected 75 ohm impedance. Quote Link to comment Share on other sites More sharing options...
ten-four Posted July 16, 2015 Share Posted July 16, 2015 The sound output via the RGB out on ColecoVision is low. I have taken the sound direct from the sound chip. I have two different RGB cables, both with different colors. The original Coleco RGB cable I have in use now Works fine. From DB 15 is my pin 4 a Black lead there goes to pin 7 on the Scart connector which is RGB Blue. As you can see on the Picture below, there are lots of color without error. Quote Link to comment Share on other sites More sharing options...
omf Posted July 16, 2015 Author Share Posted July 16, 2015 The sound output via the RGB out on ColecoVision is low. I have taken the sound direct from the sound chip. I have two different RGB cables, both with different colors. The original Coleco RGB cable I have in use now Works fine. From DB 15 is my pin 4 a Black lead there goes to pin 7 on the Scart connector which is RGB Blue. As you can see on the Picture below, there are lots of color without error. pac-hs.jpg ok, thats weird, as i understand it the rgb cables from the db15 are about 1.5volt when measured, on mine however, pin 4 (blue) is 12 volts also there appears to be a composite out (pin 7) when used at sync it produces bad colour. you instead need to use pin 13 which is csync output, well whatever it is it produces nice colour Quote Link to comment Share on other sites More sharing options...
omf Posted July 18, 2015 Author Share Posted July 18, 2015 ok, i have just done some testing and the audio circuit seems relatively basic, only using a few resistors and a few ceramic disc capacitors, i will attempt to draw it out and post here i would say i could use the schematics that are available, but low and behold, no where (that i have seen anyway) appears to have schematics for a French RGB colecovision! Quote Link to comment Share on other sites More sharing options...
omf Posted July 18, 2015 Author Share Posted July 18, 2015 of so i have attempted to draw up the colecovision audio circuit, and i make the attached so im thinking change the resistors and ceramic disc caps in this circuit and see if there is any improvement then possibly replace the 22kohm resistor with POT so i can adjust the resistance i have bypassed all of this and taken audio directly from the chip and it is all good, so its something to do with the circuit that's causing the issues what does everyone think? Quote Link to comment Share on other sites More sharing options...
GroovyBee Posted July 18, 2015 Share Posted July 18, 2015 What you've got there is effectively a potential divider that drops the input voltage to about 1/10 of its value. With a 0.5v/10K input impedance on SCART audio that would be correct if the audio chip output 0 to 5v audio e.g. rail to rail. I suspect that it doesn't do that hence the audio problems. My suggestion would be to replace the 22K with a 10 turn 10K pot and see what works. Quote Link to comment Share on other sites More sharing options...
omf Posted July 18, 2015 Author Share Posted July 18, 2015 (edited) What you've got there is effectively a potential divider that drops the input voltage to about 1/10 of its value. With a 0.5v/10K input impedance on SCART audio that would be correct if the audio chip output 0 to 5v audio e.g. rail to rail. I suspect that it doesn't do that hence the audio problems. My suggestion would be to replace the 22K with a 10 turn 10K pot and see what works. looks like 10 turn pots on ebay are very large, may have to make do with a 12 turn one, i am looking at: http://www.ebay.co.uk/itm/351357762655 i think that would do Edited July 18, 2015 by omf Quote Link to comment Share on other sites More sharing options...
GroovyBee Posted July 18, 2015 Share Posted July 18, 2015 Very pricey. This is a better deal :- eBay Auction -- Item Number: 251077394204 Quote Link to comment Share on other sites More sharing options...
omf Posted July 21, 2015 Author Share Posted July 21, 2015 OK, parts have arrived today to hopefully rectify this, i will install them tonight and post pack my results Quote Link to comment Share on other sites More sharing options...
omf Posted July 24, 2015 Author Share Posted July 24, 2015 I have installed all the parts to replace all of the audio circuit I replaced the 22k resistor with a 28 turn 20k potentiometer and adjusted it until the audio was what I deemed to be an acceptable level the reading i am getting from the pot in circuit is 3.6k ohms (obviously because it is in circuit the other components could be interfering with that reading) but its a good place to start. only thing left to do is convert a few jaguar controllers to colecovision then I can enjoy this beast rather than having a brick sat here gathering dust 1 Quote Link to comment Share on other sites More sharing options...
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