Investgating PAL 7800 picture issues (was 7800 RGB Musings)

[juansolo]

You know when you've spent the last couple of days ironing out problems and then fine tuning... Layout is done and ready for tomorrow's build. Then this message arrives: "Your gonna hate me.  I’ll send a neat schematic soon."

 

 

So that's the bit that switching the chroma lines... IM'ing is ensuing...

[marauder666]

It worked first time, I won't look at the 7800 anymore, until tomorrow.

[juansolo]

LOL, it's no problem dude! I was just yanking your chain

[davyK]

On 7/15/2020 at 5:29 PM, RevEng said:

There's no PAL60 games in 7800 mode, just 2600 mode. In 7800 mode Maria does all of the sync signalling, and you don't have an option to override this as a programmer.

 

Games can be programmed to compensate (e.g. the Salvo homebrew increases enemy and player speeds if PAL is detected) but otherwise NTSC games run slower on PAL decks. Some of our PAL folks also have spare NTSC decks, for this exact reason.

Thought as much - I suspected that some 7800 games were adjusted for speed - i have played both versions of Asteroids and they feel similar in speed with the PAL one having a chopped play area and being not as smooth which is what one would expect.

 

I have no tolerance for sub-optimal PAL games any more. I am retrospectively angry at having been ripped off by game companies since the 80s and I have had enough. So if I want a proper 7800 experience in hardware I really need to be looking at getting a modded 7800 then since the RF won't work in the UK.

Edited July 17, 2020 by davyK

[juansolo]

RF works fine if you have an old CRT TV, or have a panel with an analogue tuner (nothing recent...). However it does look pants and in the long run you're gonna have to find another way. I've modded all my old RF only consoles over the years, there's ways and means for all of them, even the old Binatone Pong console I've got

 

The PAL/NTSC thing can be annoying. It actually doesn't bother me on the 7800 at all, I assume because of the measures Reveng talked about. I had no idea about that! But it does on the SNES (because it's slow enough to begin with), so when I snagged a PAL one-chip SNES we ended up swapping the crystal in that and running it as an NTSC machine.

Edited July 17, 2020 by juansolo

[juansolo]

This is now verified! Installed into Cleggy's poor, much buggered about with 7800. It is not the best option, but is it a nice all in one DIY option and it's better than any current option out there for PAL machines by a fair old margin. The best option will be coming shortly which is the best bits of this coupled to a UAV. That'll be going into mine on Wednesday hopefully. So here is the AntiJack Mod, so called because it fixes the cheapskatedness.

 

There's as little setup as possible here. The trimpot adjusts the luma level. Start fully clockwise and turn anti-clockwise which will bring the signal up. The text on the copyright logo of Asteroids is really bright white and a good thing to use. Turn it up so it's bright but not blooming. If you go too far you'll lose sync, so back it back off.

 

 

 

 

 

[juansolo]

A few examples playing with composite output and panels, usual caveats when it comes to photographing the CRTs.

 

Composite video via an S-Vid to Composite adapter on a 14" PVM

 

Composite video on a 20" BVM

 

S-Video on a 43" Toshiba LCD panel

Its right on the edge of shimmering, you can see it in the score circles.

 

Composite video on a 40" Samsung LCD

Got dot crawl on the horizon here.

 

No scalers or anything used here, all straight in. Bear with me, getting him to take a best case pic of S-Vid into the PVM (BVM doesn't support it).

 

UPDATE:

 

S-Video on 14" PVM

 

Edited July 19, 2020 by juansolo

[emmanuelf]

I've found 4.433619Mhz smd oscillators. They are on their way.

If they work well at 5v as advertised, it should be possible to do a highly integrated thing like a board to put between the maria and his socket.

[+mksmith]

Thanks again guys for being so open with your development - looking forward to seeing your UAV design as well.  Also thank you for more confirmation around the audio points - this has been less clear searching the forums for PAL users.

 

Such a great community!

[juansolo]

Cheers. I added the audio because I couldn't find on AA what it was supposed to be and thought it make life easier just to add it to these mods given it's only two resistors and a cap. The only thing the all-in-one doesn't do is composite out, the composite shots above show how compromised it is, but we thought we'd try it with an adapter as there are people who might want to use it.

 

The AJM-UAV mod is all ready to go, I just won't get over to Cleggy's until Weds to fit it and I just want to verify it before posting.

[juansolo]

10 hours ago, emmanuelf said:

I've found 4.433619Mhz smd oscillators. They are on their way.

If they work well at 5v as advertised, it should be possible to do a highly integrated thing like a board to put between the maria and his socket.

That would be pretty cool. That one simple mod gets rid of the dot crawl interference.

 

The chroma blending issues we're bypassing completely using essentially a dual pole switch that is selecting the active chroma signal and grounding the chroma out that is not in use so it can't cause issues. I really wish we could take decent pictures of the output as it look way better in person than it does in the photographs. Where you had to compromise one or the other as stock, you no longer have to compromise either. Again it's a really simple circuit now with no need for a transistor like the previous idea we had. Just an IC, a cap and a lot of links here and there.

 

[juansolo]

Verified!

 

This is the add-on board for UAV installs. What this gives is the seperate clock to run the Maria colourburst (the TIA remains running from the on-board colourburst), adds the chroma auto switching (rather than blending) and finally just puts the audio mixer. It gives a marginally better picture than the all-in-one board and it's easier to set up as there's no Luma pot to set. But otherwise, as with the other mod, you may still need to adjust the on-board colour pots to get the colours right. If you don't already have a UAV fitted, I don't think the minor improvement it gives is worth the £35 a UAV ends up costing. Also, for what it's worth, this mod like the other doesn't give a perfect picture, but it's really bloody good, and infinitely better than we've ever seen out of one without it.

 

 

 

When the colour is right on Ballblazer is right the rotofoil is C64 red, ie: it's red, but a bit brown... If it's intense red, the intro-screen Lucasfilm logo will be wrong and will be kind of rose gold rather than gold.

 

The colour here is actually good, just the camera can't pick it up. The left tank is light blue the right is pink, the backgound green and the border sandy yellow.

 

This picture just came out damn well!

Edited July 22, 2020 by juansolo

[juansolo]

That's the two upgrades pretty much nailed. The new 7800 is still on the way, that should be here by Saturday when I'm next over for a compare. That one will get the all-in-one. We've got more parts on the way also. What I'm planning on doing is making a couple of AJM-UAV kits for @Frank.Bullitt and @mksmith because both you guys are already running a UAV. Mainly because it'd be nice to get a 2nd opinion on things. Can both of you guys message me with your addresses and I'll get those on the way when the parts all arrive (again waiting for clocks from France and they took a while last time...).

[Jobf]

Just caught up on this thread. Great work. I've got a PAL and NTSC 7800 that have old (+10yrs) composite mods in. About time I looked to improve on that as they are better than RF but still leave a lot to be desired!

[juansolo]

There was a comment a couple of pages back about PAL slowdown and picture squishage. RevEng mentioned how the slowdown was compensated for in code. Frenzy is a bit slow on PAL so I'm not sure if it's implemented there, but I don't notice it on anything else and I've got a fair few 7800 titles both commercial and homebrew.

 

The other problem is PAL having 100 lines more resolution that usually results in the picture getting squished. Cleggy came up with a novel solution for PVM users yesterday that I've just implemented on mine. If you're lucky enough to have a monitor with a seperate set of settings for underscan (which the PVM has) or widescreen (if you're not actually using it for anamorphic content, I had 1 laserdisc that supported it...), you can use that setting as a PAL stretch mode to resize the screen so it's back the same sort of dimension it would be in NTSC where it stretches it (in comparison).

 

It's not a fix for all situations as there are PAL games that compensate for this. BallBlazer is one where it has a fatter score section to compensate. But most stuff benefits. One really noticable one is when you rotate your ship in Asteroids. On a PAL machine we're used to it going a bit flat as it rotates rather than keeping it's geometry... Doing this negates that.

 

It also gave me an excuse to have a mild fettle of my setting on the monitor while I was at it. My camera still can't deal with certain colours, so the ghosts in Pac-Man look wrong, but you get the idea. Also there's still dot crawl on certain colours, but it's very mild. You can see it on the maze in Pac-Man for example. But it's being nit-picky at this point as the picture is so much better than it was.

 

Anyhow, just an idea for the maybe one or two people out there with an appropriate monitor and a PAL setup. All the attached pics are in stretch mode apart from BallBlazer which is in squish mode

Edited July 23, 2020 by juansolo

[+mksmith]

I have Impossible Mission as well - the background (bricks) in the lift area sort of shimmers a little in my current configuration. Looking forward to seeing that cleaned up a little!

[juansolo]

The 7800 that I bought arrived. I spent quite a bit on it to be fair (£126) as it looked like a nice package. It came with 5 games, 4 of which it turns out are NOS, still shrink wrapped. Two control pads, also NOS sealed in their packaging. The console itself looks pretty mint. I can see a little corrosion through the vents in the bottom on the RFI shield, but that's super common. It still has the plastic seal on the metal strip which is nice. Indeed it's almost CIB and obviously has had very little use...

 

It's in moments like these that I question whether or not I'm a monster because I'm going to salvage the POKEY from the NOS Ballblazer, sell the other games and the controllers. I suppose when I'm done one of the consoles will get sold also. Which ever one is the least pretty (at this rate Cleggy's). All to recoup some of the costs...

[juansolo]

Behold the horror that is RF out on a PAL 7800 (straight into a 13" Trinitron portable). To be fair to it, BallBlazer is a worst case scenario given all the colour. The TV is actually really, really good, even on RF... It's not a good look.

 

It's also reminded me how bad the standard tact switches are on a 7800, where you have to push the buttons into the machine to get them to engage. I'll be swapping those methinks!

 

 

 

...and, FWIW, it looks worse in person, which I know is hard to believe!

 

EDIT: Almost forgot the 2600 test screen... As usual my camera doesn't pick up the colours well, but those jailbar patterns, yeah, they're as prominent IRL as they are in the pic.

 

Edited July 25, 2020 by juansolo

[juansolo]

The new 7800 has been really interesting. It's a much later machine than mine and Cleggy's and it's noticably not quite as nicely put together. The solder is actually quite horrible, I've no idea what they were using as this is pre-lead free, but it's still nasty stuff. The board was coated in flux and looked terrible for it. Components are thrown in there quite haphazardly and the set up it had was abysmal. Both colour pots were miles out. Indeed when we dropped the video board in there initially we wondered what the hell we'd done wrong as the picture was still pretty bad! Thankfully a bit of tweaking got it looking how it should. Just waiting for a phono jack for the audio out and it'll be done.

 

I did a fair bit of clean up. It's not totally thorough, but it's a lot better than it was. It's been educational doing the upgrade end to end. It's had a cap and regulator swap, and I've put new tact swtiches on it because I simply don't like the stock ones. What it has also allowed me to do is refine the install process and take some nicer pics to go along with it. I'll probably do a PDF for the upgrade then we can call this little adventure done and dusted.

 

We shoud probably look at an NTSC machine at some point. It doesn't have the shared oscillator that the PAL machine does which is why I suspect it's nowhere near as bad. However I do notice that people complain about the 2600 output and that's likely down to the fact it's still blending the chroma signals and they fight with each other. Just the auto switching thing above on it's own would solve that.

Edited July 29, 2020 by juansolo

[juansolo]

On 7/22/2020 at 4:16 PM, Jobf said:

Just caught up on this thread. Great work. I've got a PAL and NTSC 7800 that have old (+10yrs) composite mods in. About time I looked to improve on that as they are better than RF but still leave a lot to be desired!

Now we're just about done with the PAL upgrade (should be a final update on that tomorrow all being well), we're planning to look into the NTSC 7800. There's less to do there as it's not quite as compromised, but still, there's improvements to be had we reckon. So if you fancy a free upgrade and don't mind being without your NTSC 7800 for a bit, if you send it over we'll use yours as the dev machine. Wouldn't take too long as all the heavy lifting was done on our PAL boxes and the principles are the same even if they machines aren't. All we'd need is the machine and a couple of NTSC carts as we've not got any. BallBlazer and Asteroids would be best as we've stared at those two games for so long now, we know how they should look and BB has a POKEY so we can test the sound.

 

Bob me a message if you're interested.

Edited August 4, 2020 by juansolo

[juansolo]

Finally finished the new 7800, I used it as a basis for the doc attached. Hopefully it makes sense and proves useful to someone. @mksmith and @Frank.Bullitt, there are clearer instructions for the AJM-UAV mod within for when yours land.

 

AntiJackModDoc.pdf

Edited August 5, 2020 by juansolo

[+mksmith]

7 hours ago, juansolo said:

Finally finished the new 7800, I used it as a basis for the doc attached. Hopefully it makes sense and proves useful to someone. @mksmith and @Frank.Bullitt, there are clearer instructions for the AJM-UAV mod within for when yours land.

 

AntiJackModDoc.pdf 3.48 MB · 3 downloads

Thanks John - still awaiting arrival of the package. Hopefully not too much longer and very much looking forward to installing it ?

[Frank.Bullitt]

My mod kit has arrived, I'm going to look at installing it this week, with some before and after pictures of it running through the OSSC.

 

Super excited ?

[+-^CrossBow^-]

On 8/5/2020 at 11:45 AM, juansolo said:

Finally finished the new 7800, I used it as a basis for the doc attached. Hopefully it makes sense and proves useful to someone. @mksmith and @Frank.Bullitt, there are clearer instructions for the AJM-UAV mod within for when yours land.

 

AntiJackModDoc.pdf 3.48 MB · 12 downloads

If shipping weren't so crazy expensive, I'd be happy to send out my test NTSC unit that has a magic knight board in it currently, but I didn't actually wire any RCA jacks etc on it and it just has pin headers soldered to the ouputs to connect temporary RCAs/s-video jacks to it. However, the MK and UAV use the exact same video taps on NTSC machines. The only difference is that the extra resistors and filter caps for audio are included on the MK board so you don't have to add those in manually as we do on NTSC machines if we want to retain the RF modulator.

 

 

[juansolo]

@-^CrossBow^- if you want to be a guineapig as we're having no luck sourcing an NTSC box to play with, I can knock together a board for an NTSC machine to replace the MK for you to try. I don't think it'll make as massive a difference as the PAL mod does as the majority of the problems come from the clock on the PAL machine and the NTSC machine gets that differently, so should be a lot better. All this mod would be doing different is switching the active chroma then buffering the output, and changing the way luma is done slightly. Happy to bodge a board together and send it over the pond. The only thing out of the ordinary will be finding the trigger line, which shouldn't be a problem.

Edited August 10, 2020 by juansolo