I need some help with my troubleshooting.

[Reptile]

Ok guys. It's the first time I post here so hi! I'll list everything I use and after that I'll explain the problem.

Here's the hardware I use...

Consoles:
-NES with NESRGB v1.3 2015 (the version just before the J8 jumper for TTL or CSYNC 75ohm) modded with sync over composite (soldered on V) bought from a guy who modded it himself. I opened it personally to inspect the console and everything looks fine except some soldering that were a little loose that I resoldered and added the 3rd color palette.
-SNES 1CHIP that I bought from the same guy, I didn't opened it yet but he said he did a small modification (soldered a cable between 2 chips he said and that's it). Anyway, it work like a charm.
-N64 with N64 Advanced made by unmaker. That's guy is a true professional. The console works with both TTL and CSYNC if I'm not mistaken.

Upscaler
-OSSC

Display
-Sony Trinitron KV-32FV27
-Sony PVM-20M4U
-A 10 years old 55in LG LCD TV
-A cheap 55in HISENSE LCD smartTV
-65in LG OLED TV that is on the way

Cable
-DIN to SCART cable without resistor (I opened it to be sure) with an extra 3.5mm jack cable for the NES stereo mod that I bought from the same guy who had the NES
-2 Nintendo A/V MULTI-OUT to SCART one with and the other without resistors (I opened them to be sure)
-Female SCART to BNC adaptor with sync stripper that I bought last week from a guy on eBay (the cable arrived in an Amazon enveloppe, looked fishy at first but it works well with the SNES and N64)
-HD Retrovision Cable

Ok, I'm not an expert in everything RGB related but I spent at least 50 hours in the last 15 weeks learning how everything works but sorry in advance if I ask some noobish questions or make stupid mistakes.

Now, the problem. The SNES and N64 works perfectly with everything RGB related, either hooked up with the OSSC, HDR cables or to the PVM, everything is top notch in every configuration. I've got a problem with the NES.

The NES works fine on the OSSC, except I notice some grainy snow on flat colors (checkerboard?). I suppose the DIN-SCART cable's quality is poor and/or isn't properly shielded. This is a small detail for the moment. More importantly, I'm afraid that since the cable donc have resistors, it could potentially damage the OSSC.

The real problem is when I try to make it work with the PVM, I can play and I see the picture, but it's scrolling from top to bottom (or is it the other way around? anyway) and the monitor shows "NO SYNC", so the sync is definitely a problem too.

I made sure to buy a SCART-BNC cable with sync stripper to avoid that problem. I opened it and it indeed have a sync stripper and it works perfectly with the SNES and N64. So I wonder what could cause the sync problem...

I read over reddit that some sync stripper may have problems with the NESRGB so I told myself that it may be the SCART-BNC cable or maybe I could just change the NES "sync over component" to CSYNC by soldering to the CS# instead of V on the board and it could solve the problem... Maybe.

If I need another DIN-SCART cable with resistors, I think I'm a little out of luck since every NESRGB board 1.4 and above now have the J8 jumper to reduce CSYNC at 75ohm (0.7V if I'm not mistaken?) and nobody seems to sell those cables with resistors nowadays (because everyone juste use the J8 jumper) and even less with a premodded 3.5mm jack cable for stereo.

Or maybe I've got everything backward.

What would be the best solution? Thanks

[paulb_nl]

Maybe the Sync stripper is not getting (enough) power from the SCART connector. You need to try without the sync stripper.

For the checkerboard interference you can solder sync to Luma (Y) or CS#. CSYNC from the NESRGB does not output a high voltage so it doesn't need resistors unless the device really requires 0.3v sync. Composite video and Luma don't need resistors.

[BuckoA51]

The NES works fine on the OSSC, except I notice some grainy snow on flat colors (checkerboard?)

Is the interference like snow (random) or like a consistent pattern (checkerboard) ?

[Reptile]

The NES works fine on the OSSC, except I notice some grainy snow on flat colors (checkerboard?)

Is the interference like snow (random) or like a consistent pattern (checkerboard) ?

It isn't consistent, really like snow. It become worst or better when I move the SCART cable.

Maybe the Sync stripper is not getting (enough) power from the SCART connector. You need to try without the sync stripper.

For the checkerboard interference you can solder sync to Luma (Y) or CS#. CSYNC from the NESRGB does not output a high voltage so it doesn't need resistors unless the device really requires 0.3v sync. Composite video and Luma don't need resistors.

I contacted the seller and he told that maybe the +5V wasn't working properly. I opened the SCART head from both DIN and BNC cable, tested everything with my multimeter and everything is fine and is soldered correctly. The only way it can't work now is if the +5V cable isn't soldered in the NES console. That's what I suspect.

Thank you for the explanation about the resistors, I wasn't sure. I think I'll solder sync in CS# in that case.

I'll give an update once I've done that

[BuckoA51]

Try a new PSU, this kind of noise was cured 100% on my NES by moving to a linear PSU, though a good quality switched supply will probably work too.

[Reptile]

Try a new PSU, this kind of noise was cured 100% on my NES by moving to a linear PSU, though a good quality switched supply will probably work too.

Thank you for the advice. I'll try that!

For those interested, I soldered the NESRGB on composite sync instead of sync over composite. The problem was resolved but it still doesn't mean the sync stripper works.

I opened the head of the cable to make sure the soldering job was well made and everything was ok.

I made sure the +5v was soldered correctly on pin8. I used a multimeter and tested the voltage from the NESRGB board to the pin8 of my SCART cable and from the NESRGB board to the 5v power pin of the LM1881 chip. Everything looked fine. 7v was going trough pin8 and 2.9v was measured to the LM1881 chip that should be more than enough to power it.

I can't test the cable with something else so I don't know why it can't strip the sync.

I asked the seller if he tested the cable before sending it.

Thank you for your help group!