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juansolo

7800 Restoration

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17 minutes ago, DrVenkman said:

The RF on my NTSC 7800’s is terrible. Just rotten. The improvement from composite through the UAV is amazing, and the S-video is even better. Not sure how much difference it will make on your test systems but I’m looking forward to seeing your appraisal. 

 

The RF on my NTSC A1 is so good that I don't feel any pressing need to mod.  It's plugged into a DVD recorder, which then passes the video to my 60" UHD television via component video. Perhaps there is some signal processing going on in that mix, not sure.

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Posted (edited)
48 minutes ago, DrVenkman said:

The RF on my NTSC 7800’s is terrible. Just rotten. The improvement from composite through the UAV is amazing, and the S-video is even better. Not sure how much difference it will make on your test systems but I’m looking forward to seeing your appraisal. 

That was part of the reason I wanted to do this in the first place is to see what our mod does vs the UAV, vs the UAV plus chroma switching. Our mod is fairly basic but it's a lot better than the simple composite mods out there. The UAV does some really nice things and generally speaking does a better job at most things, but it's still blending the chroma so it'll be interesting if the switching makes it even better. We can't compare to RF because we don't have anything with an NTSC tuner in it sadly. But generally speaking, from the many different consoles we've modded, RF rarely looks good next to a decent composite mod.

 

I would say though that the NTSC 7800 is vastly better out of the box than the PAL one in terms of picture quality.

Edited by juansolo
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Posted (edited)

I make no appologies for the tarty piccs that are about to occur. All can be embiggend with much clickage.

 

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It's complete, for now, and I'm really happy with the results. The picture on it is better than my PAL machine that has a UAV with chroma switching, and there's just our AJM in the NTSC machine. Looking forward to seeing what changes the UAV then UAV plus switching might make.

 

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It's not the neatest install, but as it's only temporary and this things is likely to go through several iterations before I'm done with it, it'll do for now.

 

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I wouldn't normally do the outputs like this. Normally there'd be a case mounted 3.5mm stereo jack carrying both composite and audio, with the S-Video also just bolted into the case. As I'm planning to be taking this apart a bit, I thought I'd make that as easy as possible. There's no composite out and there is a board mounted phono carrying audio where the channel switch used to be. You need to drill some holes in your PCB to do this and cut two traces. Also I've grounded and anchored the S-Video jack using twisted solid core wire to the RF modulator mounting holes, this ended up being surprisingly rigid and the socket doesn't move. It's still bolted through the case when it's in, but that's super easy as it all just lines up when it's dropped in there. It's a bit of a faff to do, but in the long run it'll save me loads of time.

 

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the new socketry

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So that'll be it for a while, when the UAV lands the experiment will contine. But for now, we're done.

 

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Edited by juansolo
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Posted (edited)

Hit my first bit of oddness with the NTSC machine, seems it has the sticky fire button problem noticable on Rikki and Vikki resulting in your player auto picking up boxes in single player with only one gamepad plugged in.

Now this can be gotten around by plugging in a second controller. Which is fine, but I only have two controllers (a gamepad and a modified 7800 Zipstik) for both my machines so I'll probably end up making a dongle for the 2nd port. This does however potentialy scupper my internal Atarivox plans. I'll have to find out what lines the AVX actually uses and hope they're not the ones we need to add resistors to to negate this problem (if anyone knows this'd be VERY helpful as my two are buried inside machines). If they are, I can potentially negate the issue when running the AVX when it's switched in, and it'll just automatically negate it when it's switched out and I'm running two player with a second controller. It's a potential work around that depends on the planets aligning a little. That said the AVX itself might make the problem go away. I guess I'll be taking my 2600 apart and extracting that to test that.

 

First, of course, we're gonna swap some parts and see if we can't fix the problem. A job for Wednesday when I'm next over. Now you can see why I made it super easy to dismantle ;)

 

As for the colour fringing issue, this is interesting. Looks like a UAV equipped NTSC 7800 does this also (check out Dungeon Stalker):

 

 

Dungeon Stalker and Frenzy were the most apparent ones to us, but you can see it on certain colours in the palette picture. That'll be interesting because that looks awfully similar to my AJM equipped machine!

Edited by juansolo
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7 hours ago, juansolo said:

Hit my first bit of oddness with the NTSC machine, seems it has the sticky fire button problem noticable on Rikki and Vikki resulting in your player auto picking up boxes in single player with only one gamepad plugged in.

Now this can be gotten around by plugging in a second controller. Which is fine, but I only have two controllers (a gamepad and a modified 7800 Zipstik) for both my machines so I'll probably end up making a dongle for the 2nd port. This does however potentialy scupper my internal Atarivox plans. I'll have to find out what lines the AVX actually uses and hope they're not the ones we need to add resistors to to negate this problem (if anyone knows this'd be VERY helpful as my two are buried inside machines). If they are, I can potentially negate the issue when running the AVX when it's switched in, and it'll just automatically negate it when it's switched out and I'm running two player with a second controller. It's a potential work around that depends on the planets aligning a little. That said the AVX itself might make the problem go away. I guess I'll be taking my 2600 apart and extracting that to test that.

 

First, of course, we're gonna swap some parts and see if we can't fix the problem. A job for Wednesday when I'm next over. Now you can see why I made it super easy to dismantle ;)

 

As for the colour fringing issue, this is interesting. Looks like a UAV equipped NTSC 7800 does this also (check out Dungeon Stalker):

 

 

Dungeon Stalker and Frenzy were the most apparent ones to us, but you can see it on certain colours in the palette picture. That'll be interesting because that looks awfully similar to my AJM equipped machine!

Yes the color fringing is something I've seen on all 7800s I've put UAVs into. That is a lot of 7800s at this point. However, it doesn't seem to happen or show up as prominent with 2600 games so I suspect it is more of a MARIA issue vs the UAV? The issue with the stuck trigger is the TIA chip. I chose to live with mine doing it and haven't replaced the TIA to try and correct for this. I first noticed it when I was having a really good session of Xenophobe going and suddenly, without warning, the second player started up on the lower portion of the screen? I asked about it in these forums at the time and was advised the TIA was the issue. 

 

Anyway, I state this because I've plugged in and been able to use with my Avox without any issue. But, I did have to remove the PIC off it (Disabling Vectrex use) in order to do so as prior to that, it would reset itself and stopped working within a few minutes otherwise.

 

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I've got a later AVX so I shouldn't need to de-PIC it thankfully. But if it addresses the problem, it kills two birds with one stone for me. For the time being I'll make a ghost controller dongle for the P2 socket until I can get another AVX and fit it internally. Then when I'm single player and it's on, things should be ok, and when two player, I should also be ok. In the meantime if I end up with spare TIA at some point, I'll swap it out.

 

I didn't really see the fringing at all on the 2600 side. It's an exellent picture all-round other than that also. Really surprised by just how well our relatively simple mod worked on it!

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Assorted Wedge Hardware Tipz...

 

On 6/7/2021 at 12:24 PM, -^CrossBow^- said:

Made in late '87 and essentially uses the newer revision board with the extra timing circuit silkscreened but bypassed completely. 120ns Sony RAM with the standard resistor off the WE line as well. I think I've only seen that resistor installed on the 120 and 100ns variants.

This resistor messes with /WE's slew rate so it'll only be there for faster grade memory - to make it react slower.

 

 

On 6/11/2021 at 11:01 AM, juansolo said:

We can't compare to RF because we don't have anything with an NTSC tuner in it sadly. But generally speaking, from the many different consoles we've modded, RF rarely looks good next to a decent composite mod.

 

I would say though that the NTSC 7800 is vastly better out of the box than the PAL one in terms of picture quality.

From experience, the NTSC boards have marginally better signal integrity (including the digital junk) but both are kinda noisy and the layout isn't optimal. So the picture quality over RF is gonna be all over the place.

 

 

7 hours ago, juansolo said:

Now this can be gotten around by plugging in a second controller. Which is fine, but I only have two controllers (a gamepad and a modified 7800 Zipstik) for both my machines so I'll probably end up making a dongle for the 2nd port. This does however potentialy scupper my internal Atarivox plans. I'll have to find out what lines the AVX actually uses and hope they're not the ones we need to add resistors to to negate this problem (if anyone knows this'd be VERY helpful as my two are buried inside machines).

Going by this documentation, the AtariVox doesn't touch the Paddle / ProLine pins (5 + 9), so you should be able to add pulldowns to these without messing up the AtariVox's functionality.

 

What you might want to consider implementing is a circuit where these pulldowns are only enabled while in two-button mode. So gated through a transistor and using TIAEN and RIOT PB2 / PB4 to enable it - similar to the Q5, Q6, Q8 pullup network. This would (or moreso should) avoid interfering with the charge and discharge timing when using paddle controllers.

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33 minutes ago, TailChao said:

Going by this documentation, the AtariVox doesn't touch the Paddle / ProLine pins (5 + 9), so you should be able to add pulldowns to these without messing up the AtariVox's functionality.

 

What you might want to consider implementing is a circuit where these pulldowns are only enabled while in two-button mode. So gated through a transistor and using TIAEN and RIOT PB2 / PB4 to enable it - similar to the Q5, Q6, Q8 pullup network. This would (or moreso should) avoid interfering with the charge and discharge timing when using paddle controllers.

Very useful stuff, cheers!

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Thought we'd do a bit of due dilligence when I was over today. So with R&V the problem manifests when the pad is plugged into the left hand port. Plugged into the right hand port on it's own, it goes away. Likewise if you plug two controllers in, both work fine. So that's exactly the symptoms we expected from other's who've had the problem. Just to be absolutely sure we swapped out the associated 3 transistors and checked the associated resistors. All were fine.

 

So a TIA issue, I don't have an NTSC TIA so it's not something I can just swap out, so I'll be bodging the fix for this. What I'm going to do is put in the switching for the internal AtariVox (which will be happening on our next order when Al does the next cycle of new stuff). When I'm running the AVX I'll be running single player so it'll also switch in the resistors to make the left port play ball. When I'm playing two player, I have to switch the AVX off anyhow, but it'll also switch out the resistors. Nice and easy fix that is only two resistors more than what was already going into the machine regardless.

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Well the UAV arrived and somehow managed to avoid any additional charges, so my fears of a super expensive UAV, ended up making it the cheapest one I've bought in a long time at £30 or whatever it was. Nice.

 

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I had a spare terminal block from one of the many other UAVs that've ended up in things so dropped that on for the outputs. The other wires I solder kinda differently... There's one thing I really don't like about the UAV, I understand why it was done, it really is a marvel just how small it is, but the solder pads when you end up putting it into a 7800 are just too small and there's not enough pad around them. To the point that here I decided to solder to it as I would to a via. Which worked really nice and means that should I need to remove it, and re-attach it elsewhere it would be easy.

 

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I added some hot snot under the S-Video jack just to make it super rigid when testing out of the box

 

There is obviously something happening on the seperate chroma inputs that's specifically for the NTSC 7800. We tried to trace them to a point but couldn't work out where it went after hitting the IC on two seperate pins. I kinda lost interest and decided to put it in at that point and see. What's interesting is that the colour fringing, as seen on our AJM mod and the ZPH videos remains, but the picture is noticably sharper, which is what we expected. Thing is I don't think the NTSC machine has the issues with chroma blending that the PAL machine has, to the point that I'm fairly convinced that adding switching would make next to no difference. I may yet try it, for science, but I think that quite frankly until someone comes along with an RGB mod, if you've got an NTSC 7800, the UAV just does the job better than anything else out there currently.

 

Time for some test cards:

 

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UAV into 14" PVM via S-Video (7800)

 

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UAV into 14" LCD via S-Video (2600)

 

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Ballblazer into LCD

Edited by juansolo
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Some panel vs CRT comparison shots. Usual caveats apply when it comes to photographing such things:

 

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CRT above - LCD below

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CRT above - LCD below

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CRT above - LCD below

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FWIW, it looks really rather lovely on the CRT. The fringing appears to be here to stay on both so not a lot we can do there. The panel is fine, but wouldn't be my choice to plug this into.

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You know...the more I look at the color (colour) fringing issue. I wonder if it has to do with the timings on the 7800? The 2600 RGB mod will produce similar fringing in some games in some parts of the screen due to changes it makes in the timing of the video. Only in the case of the UAV (and other AV mods I've tried), it is coming from the maria side since the issue is less seen on the 2600 side. Could it just be a flaw in the maria design causing this?

 

Additionally you have confirmed that the issue isn't due to the RF modulator components either because you have all of that removed and yet it still remains. So I'm not sure how much cleaner a signal you can input in to the UAV beyond this.

 

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10 minutes ago, -^CrossBow^- said:

Additionally you have confirmed that the issue isn't due to the RF modulator components either because you have all of that removed and yet it still remains. So I'm not sure how much cleaner a signal you can input in to the UAV beyond this.

Totally aggree. We were debating the worth of the chroma switching given the results... Might do it at some point, but I seriously doubt there'd be any noticable benefits to it.

 

10 minutes ago, -^CrossBow^- said:

You know...the more I look at the color (colour) fringing issue. I wonder if it has to do with the timings on the 7800? The 2600 RGB mod will produce similar fringing in some games in some parts of the screen due to changes it makes in the timing of the video. Only in the case of the UAV (and other AV mods I've tried), it is coming from the maria side since the issue is less seen on the 2600 side. Could it just be a flaw in the maria design causing this?

Likely given we noticed that the colour fringing appears to be a static version of the aberations we get on PAL machines with the colour rolling, which we tracked to the MARIA because they're temperature sensitive!

Edited by juansolo

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5 minutes ago, juansolo said:

Totally aggree. We were debating the worth of the chroma switching given the results... Might do it at some point, but I seriously doubt there'd be any noticable benefits to it.

 

Likely given we noticed that the colour fringing appears to be a static version of the aberations we get on PAL machines with the colour rolling, which we tracked to the MARIA because they're temperature sensitive!

Not just the Maria. The TIA and GTIA chips also change their timings slightly depending on temperature and this can be seen in changes to the hues. @Trebor is the resident expert in this field.

But yeah, the right hand side color fringing on some of the colors looks nearly the same as what happens with timing issues on 2600s with the RGB mod in place. Also, using your CRT (Although you can't get it quite perfect), you can adjust that trimmer on the UAV to adjust the overall phasing and artifacting. I will sometimes mess with this using Tower Toppler on a CRT through composite output (Since s-video removes the artifacting completely). But the colors still won't be quite right compared to RF output. Not sure if anything on the UAV can be changed (Resistor values and the like) to affect it but just something else to play with since you have it all in place.

 

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