NESRGB board available now

[Link83]

From what I recall Tim stating in the past the NESRGB does not output 'true' TTL CSYNC, rather its high enough to be compatible with TTL whilst not causing any issues if connected to a device expecting 75ohm CSYNC.

I personally would prefer to configure the NESRGB for 75ohm CSYNC output if possible, but it shouldn't harm anything if its left as TTL CSYNC. Hopefully Tim can chime in and explain better.

[leonk]

From what I recall Tim stating in the past the NESRGB does not output 'true' TTL CSYNC, rather its high enough to be compatible with TTL whilst not causing any issues if connected to a device expecting 75ohm CSYNC.

I personally would prefer to configure the NESRGB for 75ohm CSYNC output if possible, but it shouldn't harm anything if its left as TTL CSYNC. Hopefully Tim can chime in and explain better.

Your understanding is correct. If you are using the 8 pin miniDIN that comes with the NESRGB kit as your AV port, then setting the NESRGB for 75ohm sync output is optimal (as all 8 pin miniDIN RGB cables have no components in them) But if you're using an SNES style multiAV port, then using "TTL" CSYNC makes more sense as most SNES RGB SCART cables have a resistor in the sync line.

The only problem I see with 75ohm vs TTL has to do with the R,G,B lines. The original NESRGB (1.x release) had 220uF capacitors on these lines to prevent signal reflection/shadows in the output. Because majority of installs were using SNES RGB cables with 220uF caps in the cable, installers were removing these capacitors and shorting the pads. For NESRGB 2.x, Tim removed these 3 capacitors as a cost saving measure.

This was all good for SNES style multiAV, but it means potential video quality degradation for those using the 8 pin miniDIN that still ships with NESRGB to this day.

[Link83]

The only problem I see with 75ohm vs TTL has to do with the R,G,B lines. The original NESRGB (1.x release) had 220uF capacitors on these lines to prevent signal reflection/shadows in the output. Because majority of installs were using SNES RGB cables with 220uF caps in the cable, installers were removing these capacitors and shorting the pads. For NESRGB 2.x, Tim removed these 3 capacitors as a cost saving measure.

This was all good for SNES style multiAV, but it means potential video quality degradation for those using the 8 pin miniDIN that still ships with NESRGB to this day.

I remember asking Tim about this at the time of the NESRGB V2.0 release, you are correct that the 220uF capacitors were removed for cost reasons, but it was my understanding that the THS7374 chip doesn't actually require the 220uF AC coupling capacitors (Although it can still work fine with them still in place inside the cable) whereas the older BH7236AF video encoder does require the 220uF capacitors on the RGB lines.

Since the RGB output is now all handled by the THS7374 and not the BH7236AF (Which now only handles S-Video and Composite outputs) the missing 220uF AC coupling capacitors when using the miniDIN connector shouldn't be a major problem?

<EDIT>Found my posts and Tim's replies here from 2019, although it doesn't 100% clarify that the THS7374 doesn't require caps:-
https://shmups.system11.org/viewtopic.p ... 2#p1352922

...It's the old fashioned video output drivers in the video encoder that need the coupling caps on the outputs...

https://shmups.system11.org/viewtopic.p ... 4#p1353184

I'm still curious about the switch to a THS7374 though, was it just a case of using a more modern video driver made sense? and have you tried comparing the THS7374 RGB output to the BH7236AF? I was just curious if there was any visable difference/improvement in the picture quality when compared to the NESRGB V1.X.

The main reason was to get rid of the coupling caps. The THS7374 is cheaper than the caps and their removal will reduce the amount of times I get questions about removing them to accommodate Nintendo SCART cables. The video quality is unaffected by the change.

[TooBeaucoup]

Great info all around. It would definitely be nice to get this all consolidated.

[Trevor spencer]

Hi

Im about half way through this install and all is going quite well but ive presumed something and i just want to check this is correct as i cant find it in the guide.

I installed the 47uf capactitor in the C12 position on the board , is this correct before i move forward ?

Thanks

https://ibb.co/VS8hBsw

[lordixidor]

mine is finally ok, i had problems with the audio and image, but with the support of GamesCare here in Brazil i managed to solve everything. follow photos of their work and the result.

Clock Buffer:


220pf cap:


result

[PsychicP]

deleted

[playa21]

Hello,
I installed a nesrgb v2 years ago.. not working well, and today came back in!

I fixed couple of things on the famicom av board and on the nesrgb board.. basically some tracks cuts..
To come up to this problem: Scrambled title screens on some games, not all but game perfectly playable...- On original cartridge. (Mario bros for example)
But also some games not starting at all on the everdrive with a grey screen at launch.
Like : castlevania 2, chip n dale, Mario 2,3.. But many others starting properly.

I have not this issue with famicom games original cartridges, just title screens or minor bugs.. but games playable almost perfectly!!

• when removing the nesrgb mod, the famicom works perfectly with all games! No glitch, no problem with everdrive, everything is working ! So, the problem is clearly on the nesrgb board.
• I checked continuity from the famicom Board till the end points on the nesrgb, all are bipping like schéma on etim.
• I see 5v on the nesrgb board and on the ppu.
• I doubt its an issue on ram, ppu or cpu because it works without the mod.
• The graphic problems are the same everytime, exactly even with another cartridge of the same title. If I launch from everdrive, pal or jap version - same.

Picture of Mario totle screen issue:
https://ibb.co/QjHhrfm

Somebody else could guide me to check something specific?.. That is touching these title screen from the nesRGB board ?

Thanks!!

[owen2a03]

Hey, I was directed to this post for support on an issue I've run into with my board. The post:

I had recently got a new nesrgb and installed it into my AV Famicom, and was excited to see it being the 4.1 revision.
It had been working fine, but suddenly when i had the famicom open to clean up the case a bit and reassembled it, the video signal became black with large gray stripes.
I felt around briefly and found one ic was greatly overheating. I put in my old 4.0 board that seemingly suffered a similar fate (it only outputted a black screen instead), and it too was heating up in that spot, but even faster.


The ic in question.

I tried the ppu directly in the chip socket with the stock video output and it behaved normally, so there shouldn't be any issue with the famicom itself.
I'm not sure if it's directly related to this chip or something else on the board that's been shorted somehow.
Given that a similar issue arose with my previous rgb board, my concern is for this to be a very easy issue to stumble into no matter what; i made minimal contact with the rgb board after its installation so i'm not sure what could be causing this.

Any help, even if it means somehow replacing this specific chip, would be greatly appreciated!!

Further elaboration, none of the LEDs turn on when powering up the system, and the effect is the same with the palette selection pin -> ground on or off, if that's helpful to identify the cause

[playa21]

Hey All,

Try to continue my investigation..
- I rechecked everything from the main board to the ram, cpu. Also from the ppu on the nesRGB board to the main board and to the first point of the nesRGB next component. - Everything seems to be ok.
- I changed the PPU, stil the same problem. So I can exclude PPU for sure.
- Tried another PSU and another RGB cable.
- Without the mod, the image is without artifact.
- The fact that some games are not starting from everdrive, but well from the original cartridge makes me think that something linked to CPU is not starting..
- on 90% on my original games, I have no problem!
- SMB title screen corrupted - game running too fast
- Double dragon 2 - screen black, grey, red, blue.. changing like that.
- Ice climber title screen corrupted
- Time lord , the game is blinking when playing
- Turtles mutant, I have the impression the game is not smooth..

From what I discovered/ question about :
- SMB having to read CHR-ROM to display the title screen properly. Do you know what can I check to verify this is well working from the NesRGB board?
- The EXT 0..3 are all connected together? Correct? so bridged?
- I have the impression it's an issue at the altera chip during the decoder palette rom process.. maybe faulty?.. :p Basic checks on that to advice?
- Problem of saccade or everdrive game not starting would be more related to cpu no?

I join additional pictures to see the problems I have.

https://ibb.co/4JK93zL
https://ibb.co/d0J0MqC

Thanks in advance for the help.

Hello,
I installed a nesrgb v2 years ago.. not working well, and today came back in!

I fixed couple of things on the famicom av board and on the nesrgb board.. basically some tracks cuts..
To come up to this problem: Scrambled title screens on some games, not all but game perfectly playable...- On original cartridge. (Mario bros for example)
But also some games not starting at all on the everdrive with a grey screen at launch.
Like : castlevania 2, chip n dale, Mario 2,3.. But many others starting properly.

I have not this issue with famicom games original cartridges, just title screens or minor bugs.. but games playable almost perfectly!!

• when removing the nesrgb mod, the famicom works perfectly with all games! No glitch, no problem with everdrive, everything is working ! So, the problem is clearly on the nesrgb board.
• I checked continuity from the famicom Board till the end points on the nesrgb, all are bipping like schéma on etim.
• I see 5v on the nesrgb board and on the ppu.
• I doubt its an issue on ram, ppu or cpu because it works without the mod.
• The graphic problems are the same everytime, exactly even with another cartridge of the same title. If I launch from everdrive, pal or jap version - same.

Picture of Mario totle screen issue:
https://ibb.co/QjHhrfm

Somebody else could guide me to check something specific?.. That is touching these title screen from the nesRGB board ?

Thanks!!

[OnoThRaL]

I need help with install. Color pallet not looking correct after install. the board is a v4 23.03. I am using valtairs qsb ffc kit. IGR and pallet switching working. i have since removed IGR and pallet select, just to make sure that wasn't an issue. I removed and soldering a different multi-out connecter, Checked and rechecked all jumper settings. tried the aux voltage regulator. re capped the whole NES. rechecked and re-soldered all joints multiple time. i even tried another ppu from another working console to no avail. The PPU came off a working NES and I got the same results. It appears that I am missing EXT2 line. verified by grounding Jumper D to ground. verified all connections with a multimeter. even the EXT2 under the PPU. I have a little scope i used to probe the EXT lines im getting the same "signal" wave length from the PPU and the level translator IC and at the FPGA chip. Its a little DSO Nano scope, i may not be using it properly. Is there anything im missing or maybe over looked. I have since ordered another rgb board and soldered that kit with one of the working PPU's on the same NES board and it work as expected. Ive been beating my head against the wall trying to figure this thing out. Any help would be greatly appreciated.
https://imgur.com/a/Sbgdul3
pictures of problem and install and scope

[TooBeaucoup]

I need help with install. Color pallet not looking correct after install. the board is a v4 23.03. I am using valtairs qsb ffc kit. IGR and pallet switching working. i have since removed IGR and pallet select, just to make sure that wasn't an issue. I removed and soldering a different multi-out connecter, Checked and rechecked all jumper settings. tried the aux voltage regulator. re capped the whole NES. rechecked and re-soldered all joints multiple time. i even tried another ppu from another working console to no avail. The PPU came off a working NES and I got the same results. It appears that I am missing EXT2 line. verified by grounding Jumper D to ground. verified all connections with a multimeter. even the EXT2 under the PPU. I have a little scope i used to probe the EXT lines im getting the same "signal" wave length from the PPU and the level translator IC and at the FPGA chip. Its a little DSO Nano scope, i may not be using it properly. Is there anything im missing or maybe over looked. I have since ordered another rgb board and soldered that kit with one of the working PPU's on the same NES board and it work as expected. Ive been beating my head against the wall trying to figure this thing out. Any help would be greatly appreciated.
https://imgur.com/a/Sbgdul3
pictures of problem and install and scope

Looks like you had the same problem that I did. My color symptoms and error LEDs were just like yours. Looking at your pics, it looks like you have the same faulty chip that I did from what I could see. You should email Tim with your order number and 'help' in the headline and tell him what's happening. He sent me out a replacement RGB kit free of charge.

Tim emailed me back and confirmed that I do have bad chips on my RGB board. If anyone is experiencing similar issues on one of their error LED lights, namely the EXT LEDs, check to see if you have this chip on your board. If you have this particular chip, it's faulty.

[BambooShadow]

So I left J8 open because I hadn't even looked to see what it was for. I've been using HD Retrovision component cables and also a Scart cable from Retro-Access terminated for 75ohm. Should I go back and close J8? What am I going to ruin either way?

Also, I'm confused about Tim's PDF. It says J8 appears on boards 1.4 and later. But it doesn't exist on 4.0, but then does on 4.1?

HD RV-cables take Sync from Pin 9, so maybe that's your standard composite video and it doesn't matter what you do with your CSYNC output.

If you put CSYNC on Pin 9, make sure it's 75ohm CSYNC. It's the best for the HD RV-cables and for all other equip.


I did some measurements with the NESRGB V4, regarding the CSNYC-levels. (the NESRGB-boards that are missing J8)
Without a resistor, my osci showed 0,58V
With a 470ohm resistor, it was 0,29V

So 0,58V isn't really TTL-CSYNC from what I understand .

I'm looking forward to test NESRGB v4.1 sync-levels, maybe I'll post my findings here again.

Don't know why Tim removed J8 on NESRGBV4 and then made it come back on NESRGBV4.1. Would be interesting to hear his thoughts/intentions on this

[tonyprzy]

I found that I now get no audio/video whatsoever from anything. Nothing from YPbPr, nothing from multi-out, nothing from composite.

- The power indicator light still behaves normally (blinks with no cart or bad connection, solid with cartridge and good connection)
- NESRGB board still powers on and selects a palette (LED1 illuminated).

I am seeing a similar failure mode to the above. It's the fact the LED 1 is lit, but I see a black screen on my TV that really concerns me. I also see that the palette selection with the controller does not work despite being wired up correctly.

My board is NESRGB4.1 23.03, so it's pretty new at the time of writing this. I have J1, J6, J10, and J5 closed. I have the extra voltage regulator that came with the board hooked up. I had J3 closed at first, but realized it was redundant, and now it is open.

My TV only takes composite, so I have tried that coming from V, and I have also tried S-Video (C and Y) converted to composite with an adapter. There is no change to the screen: always black. Actually, the screen turns brownish-orange if I hold the reset button...

Any help debugging would be much appreciated! As far as I can tell, everything is hooked up correctly, and I am out of ideas. Thanks!!

[thchardcore]

Just wanted to add an install note for anyone yet to do this. For the PPU socket on the top board of the NESRGB, toss the supplied machine socket and use a normal dual wipe. The machine one caused me all sorts of headaches with the chip not making good contact and created issues with the picture.

Since desoldering the supplied machine socket would be a major pain in the ass, I simply bent the solder legs of a dual wipe and popped it into the machine header.

There is enough vertical headroom with a toploader/AVFC that the shell still closes without issue. Solved my problem 100%.

[realm]

Spoiler

It's the Everdrive N8 causing the issue not the NESRGB. The original Everdrive N8 does not play FDS games on a Top Loader with an NESRGB 4.1 installed. The Everdrive N8 Pro plays FDS games flawlessly on the Top Loader with an NESRGB 4.1 installed.

I’m experiencing a weird glitch with the US Top Loader NES and the NESRGB v4.1 while running FDS games off my Everdrive N8. I get an error when I launch any FDS game and it will not play. I have done a few things to troubleshoot this glitch. Here is what I’ve done so far to troubleshoot.

• I first tried a different PPU and got the same error when launching FDS games.

• Then I tried multiple power supplies with the same result.

• I then thought it might be the voltage regulator and replaced the 7805 but that didn’t change anything.

• Next I upgraded the voltage regulator to a L78S05 but that didn’t make a difference.

• I tried another Everdrive N8 but got the same errors with that.

• I then installed the NESRGB into a spare Top Loader with the same results as the previous NES Top Loader, launching any FDS game results in an error.

• I decided to removed the NESRGB and restore composite video on the NES and all FDS games launched and played fine.

• I bought new SD cards formatted them using just windows disk management, also tried different rom versions all with the same result.

• I also tried it with the second voltage regulator board installed but that didn’t make a difference.

• Last I installed the NESRGB into a Front Loader and all FDS games launched and played without issue.

I don’t have an Everdrive N8 Pro to test with the newer version. Besides this issue the NESRGB 4.1 works perfectly fine. Launches other games without a problem.

Any help is appreciated.
Thanks

[bobrocks95]

What are my options for a front-loader no-cut install these days?

I found 2 RF box replacements- Borti had a board, but his Github is down and the site selling them will no longer stock them from what I've read. I found another with a Github, but it seems like the only option is to purchase the BOM and order some boards and hand assemble a bunch of SMD components to make my own, which is a bit much.

Can I cleverly mount the 3.5mm jack for the component add-on board or something like that? Are there any other options available that I've missed?

[owen2a03]

Hey,

Ive been planning and prepping a frontloader for an nesrgb and i personally took out the RF rca jack and channel switch and cut the case and metal shield a little to make room for a snes multiout, the other idea i contemplated was taking out the RF jack for a genesis mini din port,
for your case, i think id personally put in the aux jack for the component video in the spot your replacement rf board has for the RF jack (or genesis 9 pin, not sure which you got).
Just throwing out some ideas. If it works, i dont see any reason not to just modify the stock rf box to fit your nesrgb needs (assuming you dont intend to use the RF video hah)

[pixeltao]

What are my options for a front-loader no-cut install these days?

I found 2 RF box replacements- Borti had a board, but his Github is down and the site selling them will no longer stock them from what I've read. I found another with a Github, but it seems like the only option is to purchase the BOM and order some boards and hand assemble a bunch of SMD components to make my own, which is a bit much.

Can I cleverly mount the 3.5mm jack for the component add-on board or something like that? Are there any other options available that I've missed?

You can also take a look at the different power boards by Merlin Shaw. Most support no cut (or minimal cutting) options for NESRGB.
https://github.com/ShawMerlin/NES-Power-Module-Redesign

Also, you can normally upload the BOM with the PCB files and have all the SMD components soldered on in factory. Then you just have to solder the jacks and a few through holes caps by yourself.

[bobrocks95]

Hey,

Ive been planning and prepping a frontloader for an nesrgb and i personally took out the RF rca jack and channel switch and cut the case and metal shield a little to make room for a snes multiout, the other idea i contemplated was taking out the RF jack for a genesis mini din port,
for your case, i think id personally put in the aux jack for the component video in the spot your replacement rf board has for the RF jack (or genesis 9 pin, not sure which you got).
Just throwing out some ideas. If it works, i dont see any reason not to just modify the stock rf box to fit your nesrgb needs (assuming you dont intend to use the RF video hah)

Thanks, I feel like there's some way to mount the component jack in the RF jack's location. Might be a superglue thing instead of the proper panel mount nut.

What are my options for a front-loader no-cut install these days?

I found 2 RF box replacements- Borti had a board, but his Github is down and the site selling them will no longer stock them from what I've read. I found another with a Github, but it seems like the only option is to purchase the BOM and order some boards and hand assemble a bunch of SMD components to make my own, which is a bit much.

Can I cleverly mount the 3.5mm jack for the component add-on board or something like that? Are there any other options available that I've missed?

You can also take a look at the different power boards by Merlin Shaw. Most support no cut (or minimal cutting) options for NESRGB.
https://github.com/ShawMerlin/NES-Power-Module-Redesign

Also, you can normally upload the BOM with the PCB files and have all the SMD components soldered on in factory. Then you just have to solder the jacks and a few through holes caps by yourself.

Merlin Shaw's board was the second one I was referring to. I'll have to see what the BOM cost looks like from JLCPCB or something. You usually have to order 5 boards though so I wish I could do a group buy or something.

EDIT: Not too bad to hand-assemble and order the parts myself. JLCPCB + a Digikey order for the remaining parts was going to be like $60, which would be great if I had 2 other people interested in buying extras off me.

[susouke]

Hi all,

finally I had time to to install the NES mod 2.0 from (e)Tim. but I have only a black screen. Triple checked everything.
I found out that somehow a part got missing on the board (capacitor or resistor?). I think this was my fault

Do somebody know which is missing and which value the part has?

[bobrocks95]

Hi all,

finally I had time to to install the NES mod 2.0 from (e)Tim. but I have only a black screen. Triple checked everything.
I found out that somehow a part got missing on the board (capacitor or resistor?). I think this was my fault

Do somebody know which is missing and which value the part has?

You have a PAL board so you soldered jumpers J4 and J7 right? I can check that component tomorrow night when I finish up my Famicom install.

[susouke]

Hi all,

finally I had time to to install the NES mod 2.0 from (e)Tim. but I have only a black screen. Triple checked everything.
I found out that somehow a part got missing on the board (capacitor or resistor?). I think this was my fault

Do somebody know which is missing and which value the part has?

[...]

You have a PAL board so you soldered jumpers J4 and J7 right? I can check that component tomorrow night when I finish up my Famicom install.

Thanks! Yes, it is as PAL board! I soldered J4 and J7 (which seems to connect them to ground).
1. I cut a connector on the Lockout-Chip to play NTSC Games on my SNES. Does it make any difference? (does this make the NES to a NTSC variant?)
2. I did not use the Audio from the NESRGB Board, I had already a Stereo mod. Nevertheless, the Sound works fine.

[bobrocks95]

Anybody know what's going on with the latest Famicom power board? It has a capacitor spot C12 that isn't mentioned in the guide. I did get an extra capacitor in the kit, 22uF, but C12 is silkscreened as 47uF. Is the cap not meant for there and C12 is supposed to remain unpopulated, or are the silkscreen or cap value I received wrong?

Emailed Tim a few days ago asking about it and no response yet. My Famicom install currently has audio but no video whatsoever, so I'll have to open it back up and look over everything anyways.

EDIT: Tim replied back and said that cap is for muting audio on startup so you don't hear the typical "pop" sound, and apparently I just got the wrong value capacitor.

Hi all,

finally I had time to to install the NES mod 2.0 from (e)Tim. but I have only a black screen. Triple checked everything.
I found out that somehow a part got missing on the board (capacitor or resistor?). I think this was my fault

Do somebody know which is missing and which value the part has?

[...]

You have a PAL board so you soldered jumpers J4 and J7 right? I can check that component tomorrow night when I finish up my Famicom install.

Thanks! Yes, it is as PAL board! I soldered J4 and J7 (which seems to connect them to ground).
1. I cut a connector on the Lockout-Chip to play NTSC Games on my SNES. Does it make any difference? (does this make the NES to a NTSC variant?)
2. I did not use the Audio from the NESRGB Board, I had already a Stereo mod. Nevertheless, the Sound works fine.

It's a small capacitor on my board revision, but it seems to just go to the J5 jumper from what I can tell. If you're not using J5 I wouldn't think it would matter. You can try checking for continuity between the closer component pad and the closer pad for J5 to confirm it's the same on your revision.

[Link83]

Hi all,

finally I had time to to install the NES mod 2.0 from (e)Tim. but I have only a black screen. Triple checked everything.
I found out that somehow a part got missing on the board (capacitor or resistor?). I think this was my fault

Do somebody know which is missing and which value the part has?

Somebody else recently ended up with the exact same missing component:-
viewtopic.php?t=72144
Based on the last post in that thread it should be a 5pF capacitor, but it likely isn't needed if your using the NESRGB on a PAL system and have not shorted the J5 jumper for NTSC systems.

Unfortunately your problem likely lies elsewhere

[bobrocks95]

Yeah so it's effectively unused on a PAL install. Do you have a blank screen like I do, no flicker or anything on video when you power on, but audio working fine? I'll be troubleshooting tonight myself.

Also anyone know anything about that Retro Game Restore acrylic eject? Someone earlier was saying it's a lower profile and lets you install it on an NESRGB Famicom. RGR's website barely even tells you what it is, much less explaining how it fits with an NESRGB.

[susouke]

Yeah so it's effectively unused on a PAL install. Do you have a blank screen like I do, no flicker or anything on video when you power on, but audio working fine? I'll be troubleshooting tonight myself.

Yes, no flicker, just a black screen. Audio works! I also have OSSC Converter which seems to have sync. If I use the standard composite output there is a white/grey picture which seems to be on purpose.
From my understanding the Output device does not switch to "RGB mode". I have checked the signals on my scart connector which all seem to be fine.
Also tried V and CS sync.

[amd20x6]

Hey guys.

Is there a way to flash the "Digital Prime (FBX)" palette, into a NES RGB 1.X?

I just tried it on a Mister FPGA and now I kinda want it in my top loader

I have the same question. Is there any hope of updated palettes for 1.x owners?

[LaC]

Hi everyone,

I recently switched from a Sony PVM-1954Q to a PVM-2030 and am now experiencing sync issues, but only with my NES RGB setup. I did the NESRGB mod myself back in 2014 and I believe I have one of the original revisions of the board. I’ve been using a SNES SCART cable made by Retro Console Accessories. The issue I’m encountering is that the screen goes black randomly every now and then. Has anyone else experienced similar issues with this setup or have any advice on what might be causing this and how to fix it?

[Konsolkongen]

Hi everyone,

I recently switched from a Sony PVM-1954Q to a PVM-2030 and am now experiencing sync issues, but only with my NES RGB setup. I did the NESRGB mod myself back in 2014 and I believe I have one of the original revisions of the board. I’ve been using a SNES SCART cable made by Retro Console Accessories. The issue I’m encountering is that the screen goes black randomly every now and then. Has anyone else experienced similar issues with this setup or have any advice on what might be causing this and how to fix it?

Tim released a firmware 1.9 for the original boards that fixes jitter on the sync line. You loose the palette switch though.

This fixed the sync issue for me with the OSSC.

https://www.etim.net.au/nesrgb/background_fault/