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PostPosted: Sat May 06, 2017 2:30 pm 
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You will need a NTSC PPU too, or else you'll get color only on some TVs, if any.


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PostPosted: Sat May 06, 2017 3:27 pm 
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You need a NTSC crystal and a NTSC PPU IC.


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PostPosted: Sat May 06, 2017 7:08 pm 
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Maybe the transcoding circuit built arount the 74LS74 could be modified to create a correct NTSC color subcarrier from a PAL-M PPU IC?
But the easier way definetelly is to change the PPU.
Can someone suggest a good place to get one NTSC PPU?
I couldn't find one, be it original or clone (the only NTSC clone I know is the UA6528), at least here in Brazil.

I really need to revisit this and the MegaDrive stuff, doing some tests with them.
An interesting fact on the MegaDrive's circuit is that the rainbow banding practically disappears if I use a crystal to generate the Color Subcarrier frequency.
It's becomes very visible if I connect the VDP's output to the encoder.
I really need to draw these schematics and get some pictures...
It will certanly help to show what I mean clearer.


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PostPosted: Sat May 06, 2017 8:47 pm 
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You're transforming the banding into dot crawl by using a crystal for color carrier frequency. The banding is fixed because it's generated by the same clock as the video (the color carrier coming from the VDP is synchronous to the horizontal sync). By switching to a free-running oscillator you have the interference drift around the screen, usually from left to right (may vary depending on the adjustment of the circuit, if there's any or the ambient temperature).

The NES has some measures on the PPU to diminish the effect of the banding/dot crawl artifacts. SEGA stuff not.


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PostPosted: Sat May 06, 2017 11:20 pm 
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Guys, thanks for the quick answers.

Luckily I have spare PPU(RP2C02G-0) here. Hopefully it is working.
I am planning to install the hidef nes mod in the Phantom. I already have the console and the mod kit. Just waiting for the desoldering gun to arrive so I can start the project.
Should I create a new thread or just post here?

Gonna need your help!!!


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PostPosted: Sat May 06, 2017 11:22 pm 
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Fisher wrote:
Can someone suggest a good place to get one NTSC PPU?


I have two NTSC PPU's here but since they are not tested I can't be sure both are working. In case they are I will have one for you.


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PostPosted: Sun May 07, 2017 7:59 am 
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l_oliveira wrote:
You're transforming the banding into dot crawl by using a crystal for color carrier frequency.

I think you're right, here are some pictures:
With Crystal:
Attachment:
File comment: Carrier with crystal
my_photo-1.jpg
my_photo-1.jpg [ 155.59 KiB | Viewed 908 times ]

With the VDP:
Attachment:
File comment: Carrier with VDP
my_photo-4.jpg
my_photo-4.jpg [ 141.83 KiB | Viewed 908 times ]

Would an S-Video mod eliminate the dot crawl?

The MegaDrive I'm using is a clone, it has jumpers to set many features, but unfortunately it hasn't an US/JP jumper.
I added a switch to do that, but looking at it today I see I totally goofed up back in the day :oops: .
It was being used without a top cover, wich I only could get several months later.
This is the MegaDrive in question:
Attachment:
File comment: MegaDrive Clone
20170507_102938.jpg
20170507_102938.jpg [ 860.37 KiB | Viewed 908 times ]

I found a switchless mod sometime ago and I'm willin to build it.
Any idea if it works fine?
melovictor wrote:
Should I create a new thread or just post here?

I think it's up to you to decide what is better, both options are fine, I think.
Anyway I really wish to see how this mod will be made.
So please, post as many pictures and videos as possible.
melovictor wrote:
In case they are I will have one for you.

Having an original CPU/PPU set would certanly help in this project I started a while ago but it is just stuck right now :cry: .
But I'm worried about the costs, specially the shipping.


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PostPosted: Sun May 07, 2017 9:12 am 
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Fisher wrote:
Would an S-Video mod eliminate the dot crawl?


No, but it will reduce the banding considerably if you return to using the VDP clock. The dot crawl is still noticeable even on S-Video, particularly because it has motion, while the banding is static.

The motion can be distracting for some people. That is the main reason why it's preferable to keep the banding than "upgrade" to dot. crawl...

To get rid of dot crawl AES NEO-GEO have a complex circuitry with a PLL feeding back clock fluctuations from the 3.57Mhz oscillator at the CXA1145 IC into the 24MHz oscillator which clocks the system. Any fluctuations on the color carrier frequency are compensated on the main VDC (Video Display Controller) making sure the clock which generates the horizontal sync keeps in phase with the chroma carrier.

Playstation (the first one) in addition to keep it's chroma carrier in phase with the horizontal, feeds a triangular wave to it's CXA1645 instead of a square wave, further reducing image artifacts on spots where colors change abruptly.


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PostPosted: Sun May 07, 2017 12:27 pm 
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HiDef board in place...
Attachment:
IMG-20170507-WA0115.jpg
IMG-20170507-WA0115.jpg [ 162.7 KiB | Viewed 884 times ]

HDMI connector
Attachment:
IMG-20170507-WA0109.jpg
IMG-20170507-WA0109.jpg [ 202.3 KiB | Viewed 884 times ]


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PostPosted: Mon May 08, 2017 5:12 am 
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Cool!!
Looks promising!!


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PostPosted: Sun Oct 15, 2017 4:53 pm 
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Ok, since it's the same clone I'm having trouble with I think it's a good Idea to ressurect this thread.

What happens is this:
I tried to do a repro, converting an SLROM to SGROM here.
The game I made (a retranslation of Rockman 2) ramdomly reseted / crashed.
At first I tought it was some problem in the repro, but I tried it on two other clones and it worked perfectly.

I tried some other games I have and find that oddly Gradius starts on the gray "Konami one Gradius ten" (wich means my CHR ROM is hacked) screen.
AFAIK, this screen is invoked by a combination of keys on the joystick.
It seems to stay sending some joystick commands to the console, because the title screen after being iddle for a while instead of showing a small demo gives a quick beep and comes back.
Both joysticks were disconnected when I did these tests.

I tried removing both joystick buffers (74'368) but I got the same results.
I disconected /OE2 and /OE1 from the CPU, same results.
I also changed it's CPU by other from a clone and again, got the same results.
Looks like it's some random component or even the PCB.
What else I can do to troubleshoot this? I'm out of ideas!

In case someonte wants it's schematics to take a look, they can be found here.


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PostPosted: Tue Oct 17, 2017 1:47 pm 
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Well, nothing new for now...
I'm trying to disassemble, clean the board, check components an tracks and them will assemble again.
This is what I've got for now:
Attachment:
IMG_2238.JPG
IMG_2238.JPG [ 1.73 MiB | Viewed 248 times ]

Attachment:
IMG_2239.JPG
IMG_2239.JPG [ 1.52 MiB | Viewed 248 times ]

In this clean I've given a eviction notice for a very small spider and other insects that seemed to live under the ICs. :P
I think that was kind of expected from a thing that was not cleaned thoroughly for at least 20 years.
Interestingly, most of the resistors were like this:
Attachment:
IMG_2240.JPG
IMG_2240.JPG [ 1.01 MiB | Viewed 248 times ]

Looks like they weren't properly placed on the board...

Maybe this test program by Tepples can help to figure out what / where to look.
I'll take my time to at least put the 74'139 back and the resistor (R4) + capacitor (C2) that plugs the clock generator on the CPU.
Interestingly it booted withouth these components (the resistor and the capacitor, not the IC). :shock:
Will the program work fine on a UNROM board?
Thanks in advance.


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PostPosted: Tue Oct 17, 2017 2:06 pm 
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Fisher wrote:
Maybe this test program by Tepples can help to figure out what / where to look.
[...]
Will the program work fine on a UNROM board?

Given its structure (CHR RAM based, only $C000-$FFFF used), I'm about 90 percent sure it will. You could try changing the mapper number in its header to 2 (UNROM) to see if it works in an emulator.


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PostPosted: Tue Oct 17, 2017 5:51 pm 
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Great!
I did as you said and tested on an emulator.
Worked like a charm! Thank you for the tip!! :beer:

I'm thinking in put sockets on all of this clone's ICs, would this be a good idea?
I'll try to reassemble at least the enough for it to boot tomorrow.
I'll try post new stuff as they're happening.
Just in case someone else is viewing this and is "cheering" for me. :mrgreen:

I don't know if it's visible in the pictures, but there's a lot of opaque stuff that gives this board a kind of "dirty" visual.
I removed a decent amount of it, but to fully remove it i think the only way is to take all the parts out, clean and them reassemble.
Would this be worth the effort?
I mean, it lasted more than 20 years, and a good amount of this time it was on a (very) less than ideal storage.
I know this sounds kind of a "generical retoric sentimental" question, but would this fix make this clone resist for about more 30 years (or even more) or it's really not necessary (would this be just a cosmetic fix)?

I really would love to show the stuff I'm fixing / building / transforming now to my grandsons in the future... :)
The experience of showing my kids the games and toys I used to play when I was at their age is being great!!
And they're enjoying each new cartridge I build, fix or mod. :D


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PostPosted: Wed Oct 18, 2017 5:22 am 
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It's some opaque 3M tape. They would put it on the board so during wave soldering assembly, solder would not climb through the component leads. They put it mostly at the points where ICs and sockets are soldered to. I suppose that helps out when you need to remove them from the board.


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