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Investgating PAL 7800 picture issues (was 7800 RGB Musings)


juansolo

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This should be about right. I've taken the audio bits out as they'd be different for an NTSC machine also. The trigger you'd have do do some probing for. You can use pin 5 of the MARIA so worth having a probe around to find a nice via or resistor leg to solder it on to.

 

Once again, we're out of a few parts so we'll have to order some in so there might be a slight delay.

 

AntiJackModNTSC.thumb.jpg.595587a76f6abb663091eb546ac57d46.jpg

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3 hours ago, juansolo said:

@-^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.

I'm more than happy to check it out and see? I did change out the 10k trimmer in my MK to a 5k trimmer that allows for a little easier dialing in but again it can be touchy. Get it looking good on an LCD only to find out on a different TV the signal goes caddywampus and it goes out of sync. It is similar for a UAV as I have my personal daily driver 7800 with a UAV in it as well I can use for testing.

 

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For the UAV mod it's super simple as it's just the chroma switching. I'll send over both for you to experiment with. I'll get in touch when they're made. I wouldn't expect massive improvements, but you should get some...

 

AntiJackUAVModNTSC.thumb.jpg.74f885d5f5443db26612fc3adb0fff10.jpg

Edited by juansolo
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The 7800 video out is a very analogue affair and as such there is a degree of setup requried, especially as you're changing the video output stage from very poor RF to rather good S-Video. I've only set up 3 machines so far and I can't emphasise enough how badly set up they were out of the box. It didn't really matter as RF hides many sins whereas your new much cleaner output will not. But going through the setup of all the trimmers (including the Luma one on the all-in-one mod) is essential to getting a good picture out of the upgrade. Even with the UAV you'll still have to tweak the colour trimmers R42 (7800 colour, the one nearest the cart port) and R43 (2600 colour, beneath it). On all machines these were gooped with either hot glue (nice and easy to remove) or some horrible yellow glue (took some scraping). It's all in the setup section of the doc.

 

For what it's worth we have a starting point as all 3 of our machines ended up in the same sort of area:

 

Trimmers.thumb.jpg.21dfc7fff2b247d718356989c7ae448e.jpg

 

Updated the doc to add more detail to the setup section:

AntiJackModDoc_v1_2.pdf

 

Edited by juansolo
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You know when you're on the throne and you have a moment of clarity...

 

I suspect this is because the two colour pots no longer have an effect on each other and you're getting a clean 7800 or 2600 colour feed (or as clean as it can be). Where before you had to compromise one in favour of the other, you can now optimise both. It makes sense that they're set badly from the factory when you think about it.

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Presents for Mr @-^CrossBow^-  (bob me a PM with your postage details)

 

NTSCVEROAGE.thumb.jpg.1ac646073a9962a15b7e40fca4f8c0ce.jpg

 

Untested/Unverified but I can't see any reasons why they wouldn't work and give some improvement. As I've stated previously, it's doing less than the PAL mod in that it's only switching the chroma. Which is what the Longhorn mod does, but it's grounding the signal not in use. As I say, it's really just a nice DIY alternative for someone with the skills to do it. The little switch board should make an improvement to the UAV mod in that you should be able to get a good picture from both the 7800 and the 2600. As mentioned earlier, you will have to adjust the colour trimmers to optimise both mods regardless.

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  • 4 weeks later...

Finally received my new soldering station and got some time this weekend to install the AntiJack + UAV PAL into my 7800.  Picture on both the 7800 and 2600 is looking great and the both the Pokey and TIA sound is working beautifully.  Next up is spending to time tuning and enjoying the mod.

 

Thanks @juansolo and @marauder666 for spending quite some time analysing, putting this together and sending it to the other side of the world for me to try out.  I've started playing around and doing a udemy course in KiCad - once I get a bit further I might look to put together some PCBs unless you guys have already started looking at that ?

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Go for it dude. If you're thinking about PCB layout, the cap across the oscillator power wants to be as close to it as possible to the oscillator, and that whole section wants to be away from any other signal lines. Likewise you want to keep your chroma circuit away from the luma one as much as possible. All just trying to minimise interference. I've probably still got all the paper bits of schematic kicking around somewhere. Might want to go SMD for the Oscillator, I suspect they're easier to get your hands on.

Edited by juansolo
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Found a couple of bits. Essentially the complete mod is in four parts: Clock, Luma, Chroma and Sound.

 

The clock is simple. It has 4 pins, only 3 of them do anything. You've +5v, GND and clock out. That's it. Put a 100nf cap accross the power pins. Job done.

 

Likewise the sound, each line comes in through an 8K2 resistor. They then go together and go out through a 1Uf cap (it'd be very different on an NTSC machine, really easy here however).

 

Chroma is all switched by this IC (+5v is on pin16, that's not part of the scribblings, same as the buffer):

 

ChromaSwitching.thumb.jpg.fba974165bf4ff7851b5d11d3193bd3d.jpg

 

The out from this goes through a simple buffer:

 

ChromaBuffer.thumb.jpg.45540d1ec653d977795034c48a19e10a.jpg

 

They're all the bits in your mod. The all-in-one adds the Luma parts. They'll follow as I can't find the scribblings for that so Cleggy is re-drawing them up.

Edited by juansolo
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These should be good for people doing setup. Colour is about spot on here for the 7800.

 

Setting the luma is only required with the all-in-one mod and is easiest on the 2600 if you have a Harmony cart. Running the ChipHead demo, you should be able to see the grey bits on the picture below. If you can't, it's too low. You're trying to get it so that's visible and the bright white of the copyright on 7800 Asteroids isn't overblown.

 

Colour on the 2600 is a real PITA because it just doesn't photograph well with my camera. The first arena on Combat when the game is started should be green, with a sandy yellow border. The left tank light blue and the right pink. On mine it's a case of tweaking the pot to get that with as little interference as possible (I can't completely get rid of it, but it is at the stage where you wouldn't really see it if you didn't know it was there).

 

Setup.thumb.jpg.16ef505d05f19dd9e0054659543ee159.jpg

 

In the doc it shows the position of the trimmers for the 3 consoles we've set up as they're all in the same area so it could provide a good starting point.

 

Trimmers.thumb.jpg.9f568dd496590c946927c316fa44a9f4.jpg

 

Added more to the setup bit in the doc. I am trying to keep it all together in there so it's a one stop doc...

 

AntiJackModDoc1.4.pdf

Edited by juansolo
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On 8/4/2020 at 7:49 AM, juansolo said:

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.

Are you still looking for an NTSC console to test with? I'm happy to lend you mine but it does have a broken power connector. I'm in the UK. Just let me know by PM if you are still looking

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1 hour ago, mimo said:

Are you still looking for an NTSC console to test with? I'm happy to lend you mine but it does have a broken power connector. I'm in the UK. Just let me know by PM if you are still looking

@Jobf did get back in touch with us and may be sending his over for us to have a go at. However I don't think he gets on the internet much and we haven't heard back from him in a while. I'll give you a ping in a week or so if we've heard nothing back from him.

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1 hour ago, juansolo said:

@Jobf did get back in touch with us and may be sending his over for us to have a go at. However I don't think he gets on the internet much and we haven't heard back from him in a while. I'll give you a ping in a week or so if we've heard nothing back from him.

No worries 

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  • 3 weeks later...

Thanks to @mimo we now have this to play with:

 

Mimo1.thumb.jpg.1046ccbf3d3073d3de8f9685f5b37f2f.jpg

 

The power jack was broken so Cleggy has swapped that with one we took off one of our 7800's when we swapped it to a standard DC jack. It's also now been re-capped and has a new regulator.

 

Mimo3.thumb.jpg.28d5fa5c2909e20b59e286db33126ac0.jpg

 

The good news is that even then, the picture ain't great, so hopefully there will be some improvements to be had. I'll also use this to document up a DIY S-Video mod for NTSC machines.

 

Mimo2.thumb.jpg.990bbcbeec498a07954e8ca3a7850391.jpg

 

Starting tomorrow...

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Glad it arrived safe. 

The current video mod is the best electrics one, yep it's pretty crappy. My previous NTSC 7800 had the LHE mod which was much better but not without its problems.

I look forward to seeing your progress

 

Mike 

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2 hours ago, -^CrossBow^- said:

I still need to get to trying out the kit you sent me in my test unit. I've just not really had the time needed to try it and I do apologize for that.

 

Not a worry dude. If you want to hang fire a bit to see how it goes, and if it goes well, you'll have some instructions to go at also.

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I'll update the doc shortly, but it's been a fun day.

 

Pre1.thumb.JPG.99c87816c0e212c21a992905df2baecf.JPG

 

We noticed the buttons were a bit flakey. We had 3 left in the stash so replaced power, select and reset. Pause doesn't see much action so we left that one. We do the cap and regulator swap as a matter of course because while you're doing this it makes sense to. Also tidied up the wiring for the Asteroids OS mod. Finally removed the old mod and a selection of parts that are no longer needed.

 

Pre2.thumb.JPG.bd1ca39c5a9d20a95ff8027dcf8aec83.JPG

 

Until I get the doc updated, this can suffice. Thanks to Mr @-^CrossBow^- for the UAV doc saving us having to go hunting for these. Found a nice via to use for the trigger, and we've gone with the UAV stylie audio (6K8 from the cart audio, 18K from the TIA audio, then together and through a 10uf on the output). The reason being without having a copy of NTSC Commando, balancing the three channels in stereo would have been pretty much impossible. It's still nice and easy this way and can be done fairly neatly. Which brings us neatly onto that audio jack.

 

AudioJack.thumb.jpg.1e5ec7b48aaf4c3ca12ecbf1a9d56518.jpg

 

If you want to mount an audio jack where the old switch was, you'll need to drill the PCB (sadly this time it destroyed the pads, but there was enough around to make the thing super secure). Before doing so make sure you cut the two tracks above or all sorts of bad things will happen. The negative of the 10uf cap goes to the centre pin, the positive goes to the two resistors in R5 & R6. Make sure to file some of the solder mask away around the hole you drill towards the end of the board as you can't have too many places to secure this socket ;)

 

Fitted2.thumb.JPG.44b2065027d99f465ddf537d26ed8e7b.JPG

 

When you're done it should look something like this... The NTSC machine is so much easier to do than the PAL. Lovely short cable runs also. We used an unused S-Video socket from an VCS RGB kit. It's a glue in job which I'm not fond of to be fair, but it's neat enough... Hot snot and a very tight fit make it semi permenant should we need to get the board out. Needless to say, it was tested prior to fitting this socket.

 

Testing.thumb.JPG.3fa2efe9eb74a45e63a39912cc45def9.JPG

 

Talking of testing. Once again, easier on an NTSC box because we've got colour bars on the 2600 side for setting that, and we know what BallBlazer looks like on the 7800 side so dialing it in wasn't a big deal. Scope was there because I'd flubbed a capacitor on the vero and stuck it through the wrong hole. Typically the luma out cap... Did give us nice piece of mind when going through all the board that it was all doing what it should though.

 

Fitted1.thumb.JPG.a34c6ec1dc13a6e0606bc65f1486ac96.JPG

 

Job done.

 

Done.thumb.JPG.ce0d1aca7a6fb27e730778e92d6b89a5.JPG

 

So what's it like I hear you ask!

 

On the LCD you can still see jailbars. We're going to have a bit of an experiment there to see if we can't dial them back a bit. You can't really see them on a CRT. The picture is sharp however, and way better than the previous mod. Indeed I won't be too bothered if we can't fix them as I'm quite pleased with the results.

 

BallBlazerCRT.thumb.JPG.4615cdf9400126ea506fbea30b753263.JPG

 

Above: BallBlazer on a CRT

Below : Ballblazer on an LCD

 

BallBlazerLCD.thumb.JPG.2440921506de79850bf586cff507b96e.JPG

 

Ms PacMan on CRT, because it's one of the cart @mimo sent with his console.

 

MsPacManCRT.thumb.JPG.09d2de7aabcb9e9701deaf760d56d121.JPG

 

Finally some Pitfall 2 on a CRT for some 2600 action

 

Pitfall2CRT.thumb.JPG.18d6058b84fc8726a278f0f5c24ce5a6.JPG

 

I'll be over again on Wednesday to have a go at the jailbars and see if we can't do something about them. But other than that, jobs a good 'un.

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