N64 RGB Relacement Dac - Faint Jailbars

N64 RGB Replacement Dac - Faint Jailbars

Hey everyone,

I'm having a slight issue with a n64 i just modded with the Replacement DAC using my PCB design and I'm noticing faint jailbars in the picture. I dont see the jail bars when in game or when the theres black boxes on screen (For example: Mario Kart 64 score board), but when i go into loading zones (Plain grey screens or white screens) i notice them or when i boot up wave race 64, i notice the jail bars around the Nintendo 64 logo that pops up just when the games loading. Is this normal with RGB modded n64's or is it my PCB design?, ground points or 3.3v points im using?. Help is much appreciated.

*Edit* Posting pics, may take some time.

 

Did you add the 100nf decoupling cap between VCC and GND like the schematic says?

 

Yup, i even added 2 more to the other 2 pairs of VCC and GND points. Still jail bars. The only thing i can think of right now is where im getting GND and 3.3V.

This is where im getting my 3.3v



This is where im getting GND.



My install, its not the greatest, im just doing testing . I added the caps after taking the picture

 

What are you using for a display?

 

Im using a Sanyo CRT with component inputs and a RGB Scart To Component Adapter you see on ebay for 60$. I also tested it with my Bravia HDTV just to be sure but i still see them.

 

I'd be tempted to see what it does on a PVM/BVM.

 

I made a new design trying to space out the 3.3v and GND traces, added a footprint for J-Tagging and added copper planes so ill try to give it another go once it comes in and see if those things helps any, if it doesnt work i dont what to do after but would you be up to giving it a go? i'll assemble it and all if you want, i know those R-2R ladders are a pain to solder.

Here is my new design. It was just shipped today.


*Edit* I wish i could give it a try on the PVM/BVM's but they're expensive and rare around here and the ones around here are the 8" to 13" PVM/BVM's.

 

If you send me something I can give it a test on my two PVMs. The 20" seems to produce a better picture than the 13".

Be willing to pay for it too.

 

Ok, soon i get the new PCB's in and some more of the CPLDs, ill assemble them and shoot you a PM. Im off to order some more parts from digikey.

 

What are you using to program the CPLDs?

 

I use a Xeltek Superpro 600p with a PLCC44 Adapter.

 

What is the reason of the Jtag? can you program the chip in circuit using a jtag?

 

yes.

You could reprogram it when its already soldered to the board (in the unlikely case of improvements to the code). Or you could get them preassembled in China and program once they arrive.

 

What would be a good programmer to use with the jtag connector? or could my GQ-3X work without the proper adapter?

 

Probably find one of those Xbox LPT programmers will work with it (they just use a LPT cable and Impact after all). The proper USB cable, like http://www.ebay.com/itm/New-Platform-USB-Programmer-FPGA-JTAG-Cable-For-Xilinx-/200539866123 and I think the GQ-4X has support for Xilinx devices via jtag - but dont quote me on that.

High end programmers like mine also support it via jtag.

Edit:

Googling suggests might work with GQ-3X too, with the jtag adapter.

 

If I remember correctly there was a similar problem in a german forum.

The things that helped were:
- recap the power suppy and adjust the voltage perfectly to 3.3V, there are some variable resistors inside the power supply.
- add a 220uf electrolytic capacitor to the VCC pin of the RGB replacement dac
- get the power directly from the power switch since the signal is cleanest there.

 

Thanks Bad, I will have to save up and get a good programmer that handles more chips but I will look into using the one I have to see how much work it will be.

 

Why would a PVM be any different? It's still a CRT.

My 9 incher (lol) showed very visible jailbars with my PCE Core Grafx II.

 

1) In viletim's logic the color components aren't synchronized, so if you have a reasonably high resolution display you'll always see artifacts.

2) The DAC isn't impedance matched so some signal reflection over a coax cable is inevitable. Whether the reflections are visible or not will depend on the coax length and characteristics.

3) There isn't a reconstruction filter of any sort on the DAC which exacerbates #2

4) Your new planes are useless if they aren't connected to a supply... Also the current decoupling scheme isn't very effective; route the VDD tracks *through* the pads, and terminate on the other side with a decoupling cap (through vias is OK).

Adding a large electrolytic would be pointless unless you had 50/60 Hz noise, which would be due to poor grounding and should be eliminated with proper grounding. You should probably be using lower gauge/thicker power wires however.

 

So far what im getting from your post is and if you can confirm:

1.) Link the planes that i have added to Ground.

2.) Instead of connecting the caps to the tracks in the middle, connect them the VCC and GND Pads directly. Though this didn't help regardless because I've add the extra caps directly to the pins of my old design and it still didn't fix it

I have RGB modded my main unit with a CPU-04 board (THS7314, 75 ohm resistors, Coupling Cap, Sync-On-Luma, etc) and can confirm the jail bars aren't there on that board with my same cabling and setup that i was using with the jailbar'd CPU-05 board (with the AVDC-NUS) and the Viletim DAC.