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7800 Restoration


juansolo

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I finally braved the heat and plumbed my NTSC 7800 into it's home on the 20" PVM. Just going straight in via S-Video. I'm utterly gobsmacked at just how good it looks now. Being super smug I thought I'd take a few pics to try and capture that and rather than give you our usual setup games (the ones we know how they should look) I thought I'd throw in something a little different for a change.

 

They've not come out half bad so here they are. Best viewed at their full res for scanline goodness.

 

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Edited by juansolo
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7 minutes ago, Muddyfunster said:

Looks excellent!

 

I don't think I've seen the Danger Zone title page look that good ever :D 

I do have a small run of the 4050 chroma fix boards being made up and will have them on hand for future 7800 installs as this pretty much should be required. Just correcting the timing for the chroma burst actually has improved the picture overall I think and made it that much more clear. And I thought the UAV on s-video form the 7800 was looking great to begin with! I've never seen the color screen test on the utility cart look as good as it does and that direct capture I posted above shows this.

 

I'm in the process of designing an SMD version of the board as well that eventually Console5 will have available to order for those that might want one. But until I get my initial boards in, I won't know if the sizes I've chosen are stupidly too small to actually be hand soldered onto etc.

 

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  • 2 weeks later...

Another update from @marauder666, both work. One has the expansion interface. I'll be over tomorrow to start the restoration with him. Sadly with The Brewing Academy being down for 6 weeks, it might be a while before these two get done due to lack of UAVs. I'll still use one to test an NTSC video mod. I've done the layout for it. I've not posted it yet because of the huge errors in the last one, once it's verified I will. It might prove useful to someone...

 

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Well they might be a little scruffy on the outside (they'll look better after a wash and what have you), inside these might be two of the best condition 7800's that have crossed our path!

 

The one that doesn't have the expansion appears to be about 5 months newer and has the logic chip and C64 cap that screws with Activision games. Neither have the bodge cap on the back that mine has (@-^CrossBow^- is it worth adding that?). It'll be nice not to have to spend half a day cleaning up corrosion and nastiness from a PCB for a change.

Edited by juansolo
Added pics and more details.
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2 hours ago, juansolo said:

The one that doesn't have the expansion appears to be about 5 months newer and has the logic chip and C64 cap that screws with Activision games. Neither have the bodge cap on the back that mine has (@-^CrossBow^- is it worth adding that?). It'll be nice not to have to spend half a day cleaning up corrosion and nastiness from a PCB for a change.

You need to check Ballblazer and Pole Position II for any graphical issues. That cap appears to have pretty much only be needed on a case by case basis. It was likely just a random 7800 that somehow skipped this testing with the one I ran into and had to add it. What I can tell you is that I have added that cap on systems that didn't have it and have had no issues with it present, and I've had at least one A3 unit that refused to display or show any games with that cap in place so... I would test BB and PP2 to see if you even need it first of all.

 

But I like seeing these two side by side as there are quite a lot of differences between them. The one on the left with the expansion actually has the silkscreen on the board for the extra timing but as you noted it isn't populated. It also has the second 3904 installed near the audio adj coil that has been bypassed on the slightly newer one. And, the one with the expansion port has all the components in place whereas there are caps that didn't get installed on the one on the right. 

 

Both have the same speed and brand of video RAM, but the one on the left has the preferred NCR 6502 in it as opposed to the Rockwell CPU on the right. Interesting that the Maria is in a socket though when nothing else is. And the BIOS are NOT in sockets either which is normal as I believe those were really only in sockets on earlier made units.

 

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3 minutes ago, john_q_atari said:

Could you take a close up picture of the front and back of the board section that is missing the ic chip for the timing circuit? I also would be interested in knowing what cap is soldered in where the timing IC would normally be.

 

Thanks

I can likey provide this later tonight as I've got semi stripped boards I use for reference. But that isn't a cap installed at the IC, it is a zero resistor that is being used to jumper across and bypass. Similar to what is also used in place of Q4 on the board that does have the extra timing circuit in place or in place of jumpers at W2 near the BIOS and video ram.

 

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47 minutes ago, marauder666 said:

Looks like Q4 is connecting the oscillator to the expansion port, probably to sync up an external device.  

The only known planned use for the expansion port was a laser disc player, and the port has a composite video in line; I expect they’d planned to synchronize playback and start/stop the video signal input as needed.

 

EDIT: Here’s that part of the 7800 schematic for anyone who might want to see what’s on the expansion port:

 

 

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I hadn't really paid that much attention to it before, but it looks like it provides direct taps to quite a lot actually! All of the Maria outputs are present including the color burst and sync. And I would guess that audio would have both external and TIA already mixed properly?

 

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4 hours ago, -^CrossBow^- said:

I hadn't really paid that much attention to it before, but it looks like it provides direct taps to quite a lot actually! All of the Maria outputs are present including the color burst and sync. And I would guess that audio would have both external and TIA already mixed properly?

 

I don't really know - I expect Curt Vendel would've known, alas.

 

As far as I thought I knew, the laser disc player would be controlled by and output through the Atari, but now I'm wondering if it was intended to be the other way around? In other words, would a/v overlay and mixing have occurred on the external side and then be output to the TV THROUGH the LD player? 

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19 minutes ago, DrVenkman said:

I don't really know - I expect Curt Vendel would've known, alas.

 

As far as I thought I knew, the laser disc player would be controlled by and output through the Atari, but now I'm wondering if it was intended to be the other way around? In other words, would a/v overlay and mixing have occurred on the external side and then be output to the TV THROUGH the LD player? 

It would make sense why there was a comp video line. Likely the LD attachment would have passed the graphics from the Maria through it and you would use an AV out on the LD player. Would make sense as I'm sure they would have wanted that LD player to be a standalone player as well to make it more marketable. 

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Long day today with some very interesting results. This is gonna be a big update.

 

So Cleggy's machine (he's claimed the expansion port one as it's the one most different to mine for testing) was on the receiving end of a long session of suckage.

 

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Caps, reg, buttons, BIOS (for future upgradage) and loads of video stuff pulled for the upgrade. I also reflowed all the mechanical connections (joystick ports, switches and cart slot), as if there's any bad joints they'll likely be there.

 

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All the basic service stuff swapped, new ports all fitted, socket in for BIOS etc. Really nice fit here. Didn't need much filing to get the phono for audio and S-Video socket in there. I've built this the same way I did mine in that it's done in such a way that it's really simple to take apart.

 

It was about at this point that I realised we were changing everything in one go and fitting an untested video mod... We were somewhat pessimistic about this all working first time and were expecting to be getting the scope out for fault finding.

 

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So what we have here is a DIY NTSC S-Video mod. It has the chroma shift built in and does chroma switching. It also now verified! Which is a bit of a giveaway as to where this is going.

 

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This is temporary. At least that was the idea when we just stuck it on top of the expansion port (despite being the smallest layout I could do, it's still quite a big board). With that done, time to plug in.

 

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It works, and it looks good. Shockingly good. Like amazingly good... I'll take this home and take some pics of it running on my 20" PVM tomorrow to compare it to mine directly. But on the 14" PVM it's looking VERY close to the UAV with shifter solution. We were both shocked at how good considering the video mod we did is a mish-mash of ideas we pulled out of our arses!

 

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One mostly done... The other will happen later. It's been a long day.

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You didnt spot the 74LS32,  the other has a 74AHCT32, as does John’s which will slighty affect luma/chroma timing.

 

Also the cartridge cup is molded with smooth non textured plastic, first i’ve seen like this.

So far all the NTSC machines we have modded require no dremelling to  fit the Dragonfly, unlike most PAL machines.

 

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19 minutes ago, marauder666 said:

You didnt spot the 74LS32,  the other has a 74AHCT32, as does John’s which will slighty affect luma/chroma timing.

I saw that it was a Samsung branded IC but didn't look much beyond that. What affect would it have with the 4050 chroma fix?

 

I know I've seen those Samsung ones installed before but I don't believe it is that common.

 

 

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55 minutes ago, marauder666 said:

its Motorola,  the batwing logo.  pal ones are always ls32
It won’t be noticeable, a timing difference of less than 5ns.

 

Can’t wait to see the pics on John’s PVM to compare with the previous ones.

I thought you were talking about the side by side he posted further up. That has the Moto chip and the Samsung. The Samsung is the AHCT32 chip...

 

The standard ls32 I actually see more commonly on the 7800s I'm pretty sure but I haven't really paid that much attention to it other than when I have to replace it out on very rare occasions. I've had 2 that were bad over the years in servicing them. I even had one just a few months back that would give slight graphic corruption and discoloration in most games until I swapped out the crystal. Strange thing was that it took me 3 donors to find one that would work without issue in that 7800. The others including the original worked just fine on another 7800.

 

Such a damn quirky beast the 7800 be.

 

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This one's gonna be picture heavy again. So this is the above machine on my 20" PVM. Usual excuses when it comes to photographing a CRT. In person, I'm struggling to see any real difference between this and my machine with the UAV plus chroma shift/switch. Kinda shocked by that.

 

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31 minutes ago, Muddyfunster said:

It could be the camera or environment or white balance or something but the colours look just slightly less saturated (I was comparing Danger Zone side by side), Otherwise that's a pretty amazing outcome.

I'd put most of it down to a crappy camera, variable room condition and me being a point'n'click photographer. In the flesh there's little to nothing in it.

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