Icelvlan Posted August 14, 2023 Share Posted August 14, 2023 (edited) What’s the voltage coming off of the fpga? possible to sketch a small diagram for how to wire? Edited August 14, 2023 by Icelvlan Quote Link to comment Share on other sites More sharing options...
SainT Posted August 15, 2023 Share Posted August 15, 2023 15 hours ago, Icelvlan said: What’s the voltage coming off of the fpga? possible to sketch a small diagram for how to wire? There may be a simpler option, which would remove the composite video sync and provide a 3.3V CSYNC. This may be enough to keep the framemeister happy, I have a 3.3V to 5V translator on this output now. Remove R82, cut the trace from U12 to pins 4/5 on the mini DIN on the back of the PCB. Cut the trace running between pins 4&5. Connect a wire from the FPGA side of the removed R82 resistor pad and connect to pin 5 on the mini DIN. This is a direct connect of the 3.3V sync output to the CSYNC, you ideally want 5V here. I don't like connecting FPGA outputs to outside facing ports as you have no additional static protection and can burn out the driver on the FPGA if you short the connection, but it's your choice if you want to try it. Quote Link to comment Share on other sites More sharing options...
Icelvlan Posted August 15, 2023 Share Posted August 15, 2023 Is there a reason why I can't lower the value of R82 and maybe R48 instead? Not sure what it is at the moment as I have to take off to measure. I thought I saw that the THS7374 can take a pretty wide range of voltage. I can also cut the trace going to pin 4/5. Quote Link to comment Share on other sites More sharing options...
SainT Posted August 16, 2023 Share Posted August 16, 2023 18 hours ago, Icelvlan said: Is there a reason why I can't lower the value of R82 and maybe R48 instead? Not sure what it is at the moment as I have to take off to measure. I thought I saw that the THS7374 can take a pretty wide range of voltage. I can also cut the trace going to pin 4/5. If you want to feed 3.3V through the THS7374 then remove R48 and put a 0R link at place of R82. The output trace goes to the composite video pin first, however, so to avoid 3.3V on the composite video output you'd still need to cut the trace between 4/5 and also 4 and the THS then run a jumper from the output of the THS for the sync to pin 5. I definitely do not recommend leaving the cart in a state where it could damage anything (ie. 3.3V on the composite video output) should the wrong cable be used. Plus of course, this is also feeding 3.3V to the CSYNC pin, not 5V. This is not a proper fix regardless. Note: I don't recommend or endorse any of this when the simple option is to buy a cheap RGB cable and change a resistor. 1 Quote Link to comment Share on other sites More sharing options...
Icelvlan Posted August 17, 2023 Share Posted August 17, 2023 I might just keep a spare cable for now. Once you have the a proper fix tested is it possible to release a small schematic so I can put a fix in? Quote Link to comment Share on other sites More sharing options...
SainT Posted August 17, 2023 Share Posted August 17, 2023 3 hours ago, Icelvlan said: I might just keep a spare cable for now. Once you have the a proper fix tested is it possible to release a small schematic so I can put a fix in? No schematic is needed, just do as I’ve stated above regarding the 3.3V to 5V level shifter. This is the fix and it results in the same voltage output as the megadrive. If this is an issue, when I have the rev2 pcb’s, I can swap it for you. Quote Link to comment Share on other sites More sharing options...
Icelvlan Posted August 17, 2023 Share Posted August 17, 2023 Shouldn’t be a problem. Where do you recommend the trace be cut? Right before the connector? In this case I would remove the first resistor and use the pad. Can you recommend a part #for the shifter? Just curious are the level shifters that are on the PCB all filled up or can one be used? Quote Link to comment Share on other sites More sharing options...
SainT Posted August 17, 2023 Share Posted August 17, 2023 (edited) Remove R82, cut the trace from U12 to pins 4/5 on the mini DIN on the back of the PCB. Cut the trace running between pins 4&5 on the mini DIN. Connect a wire from the FPGA side of the removed R82 resistor pad and connect to the input pin of the 3.3V to 5V level shifter. Connect a wire from the output of the level shifter (5V side) to pin 5 on the mini DIN. Wire up the rest of the level shifter -- OE / 5V rail / 3.3V rail and decoupling caps. This will give you TTL sync on the CSYNC pin, which is what is required for around a 600mv sync signal. I use a TXU0101 to do this job, and no, there are no spare pins on any level shifters on the board. This is my proof of concept bodge for these changes (plus composite video sync mod, open drain audio driver and external audio low pass filter) -- Edited August 17, 2023 by SainT 1 Quote Link to comment Share on other sites More sharing options...
Icelvlan Posted August 17, 2023 Share Posted August 17, 2023 Thanks for summary! Quote Link to comment Share on other sites More sharing options...
Icelvlan Posted August 17, 2023 Share Posted August 17, 2023 What are you doing on the other side for comp sync? I see the THS is still in use Quote Link to comment Share on other sites More sharing options...
SainT Posted August 17, 2023 Share Posted August 17, 2023 You don't need it, don't worry about it. Adding bodges in here is not pretty due to the lack of space. Quote Link to comment Share on other sites More sharing options...
Icelvlan Posted August 19, 2023 Share Posted August 19, 2023 (edited) Which sku? My guess is the fixed and not unidirectional? Edited August 19, 2023 by Icelvlan Quote Link to comment Share on other sites More sharing options...
Ouzy Posted August 22, 2023 Share Posted August 22, 2023 Just so someone does not make the same mistake as myself. This device from Aliexpress does not provide a compatible hdmi supply from the 7800GD. See photos The image shows on screen but is bent at the edges and the screen is not static. 1 Quote Link to comment Share on other sites More sharing options...
SainT Posted August 22, 2023 Share Posted August 22, 2023 25 minutes ago, Ouzy said: Just so someone does not make the same mistake as myself. This device from Aliexpress does not provide a compatible hdmi supply from the 7800GD. See photos The image shows on screen but is bent at the edges and the screen is not static. There will be a couple of changes to sync signal on the next revision of the PCB, these may help with this device. I'm happy to swap your PCB for a new revision when I have them (will be a few weeks yet) if you want to see if this helps. Quote Link to comment Share on other sites More sharing options...
Ouzy Posted August 22, 2023 Share Posted August 22, 2023 33 minutes ago, SainT said: There will be a couple of changes to sync signal on the next revision of the PCB, these may help with this device. I'm happy to swap your PCB for a new revision when I have them (will be a few weeks yet) if you want to see if this helps. That would be very kind @SainT. If you think it would make any difference. Luckily I'm UK so not to difficult for a swap out. Thank you 1 Quote Link to comment Share on other sites More sharing options...
SainT Posted August 22, 2023 Share Posted August 22, 2023 4 minutes ago, Ouzy said: That would be very kind @SainT. If you think it would make any difference. Luckily I'm UK so not to difficult for a swap out. Thank you I'll let you know when I have something you can try. 1 Quote Link to comment Share on other sites More sharing options...
Icelvlan Posted August 25, 2023 Share Posted August 25, 2023 Hi @SainT, I did the bodge you recommended and it worked instantly! I ordered the smaller component, so it took an extra minute to solder in but worked. As per the other mods, you mentioned composite...wouldn't mind adding that. I'm assuming you connected the resistor back on the other side of the board an added a cap and resistor? what values are they? As per the audio mod, what improvements would I see? I ordered an extra level shifter incase. 1 Quote Link to comment Share on other sites More sharing options...
SainT Posted August 25, 2023 Share Posted August 25, 2023 The composite video sync mod is just a 75R resistor and a polarised cap added to the signal path on the output side of the THS. If you don't use composite video for sync, which you are not, this makes no difference. If you did, it would have a similar effect to the CSYNC mod you did -- ie. it will improve sync compatibility with some devices. The audio mod is for internal audio only, so unless you use an AV mod in your 7800 and use composite video, then it will make no odds. This changes the audio driver to an open drain driver rather than push / pull to help alleviate issues where people have just shorted the output of the internal and external audio together in the audio side of some AV mods. While shorting two open drain drivers together is not a problem (although in this case it doesn't give good results either) it's a very bad idea when using push / pull drivers. So this mod is less about improving quality but more about working around some of the bad mods out there such that people don't have to modify them to avoid damaging the cart or console. Quote Link to comment Share on other sites More sharing options...
Icelvlan Posted August 25, 2023 Share Posted August 25, 2023 (edited) Not sure why I was thinking composite it wouldn’t come from sync. Edited August 25, 2023 by Icelvlan Quote Link to comment Share on other sites More sharing options...
+-^CrossBow^- Posted November 3, 2023 Author Share Posted November 3, 2023 I wanted to add another cable option that isn't too expensive that also works quite well with the 7800GD and even seems to be okay through my OSSC! That cable is the Genesis 2 / Megadrive 2 component cables from Retro Gaming Cables. They are basically RGC's version of the HDRetrovision cables but use Tink2x tech to convert the RGB to component output. But yeah, they seem to work just fine on my 7800GD and provide another method of using the the AV out port from the cartridge to provide excellent output for playing the games! Here is a link directly on where to get the cables: https://www.retrogamingcables.co.uk/sega/mega-drive-2/Sega-Mega-Drive-2-Genesis-2-32X-Component-YPbPr-cable-240p 4 Quote Link to comment Share on other sites More sharing options...
+evg2000 Posted November 12, 2023 Share Posted November 12, 2023 The hyperkin cable mentioned in the first post is current on sale for $20 on amazon https://www.amazon.com/dp/B07RW8R3QF?th=1&psc=1 3 Quote Link to comment Share on other sites More sharing options...
Trebor Posted November 18, 2023 Share Posted November 18, 2023 On 11/12/2023 at 1:47 PM, evg2000 said: The hyperkin cable mentioned in the first post is current on sale for $20 on amazon https://www.amazon.com/dp/B07RW8R3QF?th=1&psc=1 Currently on sale for $17.99: 3 Quote Link to comment Share on other sites More sharing options...
Trebor Posted November 22, 2023 Share Posted November 22, 2023 Kaico SEGA SATURN 2x HDMI Converter works per this post. Quote Link to comment Share on other sites More sharing options...
+-^CrossBow^- Posted November 22, 2023 Author Share Posted November 22, 2023 @Albert is it possible to give me edit ability on my 1st post? Be nice to take all of these cable options and consolidate them into the first post and add links...change links as needed over time? 1 Quote Link to comment Share on other sites More sharing options...
Albert Posted November 22, 2023 Share Posted November 22, 2023 2 minutes ago, -^CrossBow^- said: @Albert is it possible to give me edit ability on my 1st post? Be need to take all of these cable options and consolidate them into the first post and add links...change links as needed over time? Done. 1 Quote Link to comment Share on other sites More sharing options...
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