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7800 Restoration


juansolo

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  • 4 weeks later...

Well I didn't manage to score the one with the broken case, but I did get this one for sensible money. It's made it's way from Florida, and it looks as rough as it did in the pictures. This one is going to need a fairly deep clean I suspect! I think I shall call this one Crusty.

 

Crusty-1.thumb.jpg.dd903b7b964ad7b87043dd57e3ffbe92.jpg

 

Crusty-2.thumb.jpg.e742cc46ba83bd9b89f0aed3f34fbc74.jpg

 

As usual, at this point. No idea if it works or not.

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Crusty-3.thumb.jpg.7ed8fb303a5ef6b286a533702ca9a942.jpg

 

No C64 or LS02. That coupled with an NCR CPU bodes well for it playing nice with a Dragonfly. Interesting switches, definitely not the usual ones. If they work ok, I'll likely leave them be. Solder looks nice and shiny, unlike the last one where we had to take out, thoroughly clean then re solder every IC and socket on the board because it was so bad that touching chips or the cart could crash the machine.

 

So it's manky, but promising at this point.

 

Case is being washed, as will the cart cup...

Edited by juansolo
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This is as good as we can get out of NTSC RF through a PAL tuner. We've got one TV that we can force to a particular frequency and we can just about get a picture. Obv there's no colour information there, so it's black and white, no sound either. But we can see if the console is alive or not, and in this case it is! Yay.

 

Buttons are buggered, so we'll be swapping them as usual.

 

Also forgot to mention, dead things inside (thankfully, have had a cart full of cockroaches before...). Though other than a clean up, I suspect this one might actually just need a refurb (caps, switches, reg, video mod, power jack, etc).

 

Crusty-4.thumb.jpg.2fd021911ab80fd2336305cd2044f97f.jpg

Edited by juansolo
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Very interesting. Those look to be the same Alps branded switches I offer as a premium switch over the OEM. I've seen knock offs of these installed into later made 7800s but what really sticks out to me is the way the switches are oriented. 

 

That is exactly how I orient them when I install those?! You didn't see one of my stickers on that think anywhere did you? Although, I don't recall anyone sending me a 7800 to repair and leave stock either. Looks to have the original caps and VR still in it. I wonder if whichever factory made these that was using similar switches to the ones I use just happen to orient in them in this manner on this particular one? 

 

Also, yes it would seem that at some point in very late '87 into '88 timeframe, Atari stopped adding the extra timing circuit in the systems and just installed 0 Ω resistors to bridge the signal traces across that part of the circuit. It also has 120ns Sony RAM but without the extra resistor. I've not been to quite figure out a pattern on these on what needed what and it leads me to believe that they had to be tested individually at the factory to determine what bodges were needed on a console by console basis. Does it have the extra cap off pin 15 from the CPU on the bottom of the PCB? I've seen that installed on both Rockwell and NCR CPUs.

 

Speaking of DF... I was using mine pretty much exclusively with the last 7800 I put a UAV into and it had a Rockwell CPU in it. Ballblazer seemed to work fine as well, although it did have some minor flickering here and there during the actual matches but it never crashed. I added the extra cap to the A15 line to see if it would help with the flickering in BB and it actually made it worse in that 7800's case so I removed it back off. But, I was able to play a lot of E.X.O. on that 7800 without any issues at all. So it might not be the Rockwell CPUs themselves but something else in combo with the Rockwells perhaps?

 

 

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Swapping the CPU for another doesn't help. Tried it on the last one we were having bother with. Infact we were getting on screen corruption with a different CPU. We suspect the selection of bodges and timings are all based around which CPU and memory they're built with. That particular system was most stable with the A15 bodge in place (it was from the factory) and C64. Indeed removing C64 caused way more issues. So we've got Muddy's coming back for a quick looksee (should land today). Got to fix an error I made and we're going to try putting C64 back in.

 

This machine is like the others we've had with an NCR CPU in that it hasn't got the bodge.

 

This is the first one we've ever had with these buttons. Seems completely stock otherwise, so just might have been a supply thing during assembly. They've gone bad though, so we'll be swapping them out for our usual ones.

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1 hour ago, -^CrossBow^- said:

Very interesting. Those look to be the same Alps branded switches I offer as a premium switch over the OEM. I've seen knock offs of these installed into later made 7800s but what really sticks out to me is the way the switches are oriented. 

 

That is exactly how I orient them when I install those?! You didn't see one of my stickers on that think anywhere did you? Although, I don't recall anyone sending me a 7800 to repair and leave stock either. Looks to have the original caps and VR still in it. I wonder if whichever factory made these that was using similar switches to the ones I use just happen to orient in them in this manner on this particular one? 

 

Also, yes it would seem that at some point in very late '87 into '88 timeframe, Atari stopped adding the extra timing circuit in the systems and just installed 0 Ω resistors to bridge the signal traces across that part of the circuit. It also has 120ns Sony RAM but without the extra resistor. I've not been to quite figure out a pattern on these on what needed what and it leads me to believe that they had to be tested individually at the factory to determine what bodges were needed on a console by console basis. Does it have the extra cap off pin 15 from the CPU on the bottom of the PCB? I've seen that installed on both Rockwell and NCR CPUs.

 

Speaking of DF... I was using mine pretty much exclusively with the last 7800 I put a UAV into and it had a Rockwell CPU in it. Ballblazer seemed to work fine as well, although it did have some minor flickering here and there during the actual matches but it never crashed. I added the extra cap to the A15 line to see if it would help with the flickering in BB and it actually made it worse in that 7800's case so I removed it back off. But, I was able to play a lot of E.X.O. on that 7800 without any issues at all. So it might not be the Rockwell CPUs themselves but something else in combo with the Rockwells perhaps?

 

 

It does have the 1k resistor on the RAM, the pcb has the space for it on this revision, next to the Maria trimmer.  Last one had it also, but a 220 ohm  and the MHS?? RAM.

 

Seems like depending on CPU and RAM manufacturers Atari were tweeking parts to alter timings?

 

Edited by marauder666
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Crusty is as good as done. A couple of issues. It wasn't behaving from fully cold. But that might have been a couple of other things we've addressed so we'll only know tomorrow if that's still a problem or not. Otherwise, it's had the usual. On top of that, just reflowing the cart slot wasn't enough. Still when you touched the cart when it was running it could crash. So ended up pulling the slot out, cleaning everything and completely re-fitting it which fixed that. Had to Dremel the cart cup (I absolutely hate doing this) as some carts were super tight. Did my own while I was at it. They're both still tight, but they're a lot better than they were.

 

Crusty-5.thumb.jpg.e764eebb3b5bcc7a9f478e937f58c898.jpg

 

Board on this one had lovely solder. Still nice and shiny, so that was something. Everything else was the usual, got our S-Video mod with on-board chroma shift. Has a lovely picture on both 7800 and 2600. Overall, a nice little machine.

 

Crusty-6.thumb.jpg.d3f80867fe354f5ec3e24b2e3e1e6ad5.jpg

 

Other than the band, which is rough, the machine itself was in really nice nick when cleaned.

Edited by juansolo
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  • 1 year later...

In the words of Aaron Lewis, it's been a while since I updated this thread. But then we're used to doing much weirder old consoles and computers these days. Anyhow @Jetboot Jack was chatting away to us and turns out he liked the idea of a 7800. Being in the UK like us I steered him towards a US machine and said we'd be up for repairing one that looked promising on eBay. As usual this was a spares/repair machine (only way for it to be economical really) and this one was specifically advertised as having issues in that when you powered it on it did this:

 

s-l1600.thumb.jpg.4cb0f7152e060e1d346c67862f965fbd.jpg

Followed by this:

s-l1600-1.thumb.jpg.e8959a19348720dc5ab983a2cd5e3ec2.jpg

Now the fact it gets the Atari logo then craps out loading the cart points toward the issues being with the cart or the cart slot most likely. Otherwise the machine looked pretty good. It was boxed (the the box does have two bullet holes in it, thankfully it seems the console wasn't in it at the time of it's attempted murder) and complete.

s-l1600-3.thumb.jpg.0e506fc8b0c3012d16aa4fd9f12b3881.jpg

Well it landed here a couple of days ago and it's actually mint. Like NOS mint. The plastic protection is on the console itself and the two painline controllers, which are tight as a tiger.

 

So the first thing to do was see what the problem is. Plug in a known working cart and we're away (B&W because our TVs don't support NTSC over RF).

P1090235.thumb.jpeg.2a474bff7e0f8a12c607f71a351325fe.jpeg

Plugging the Pole Position II cart into a known working 7800 and the problem is the cart. It's deed. Taking the 7800 apart it was as insanely good on the inside as out. This is easily the best console in terms of condition we've ever had pass through our mitts. The solder is like new, all the switches work and feel good so we don't even need to swap them. We've only swapped the caps because there's three of them and while we're in there doing what we're doing there's no reason not to. We're not bothering with the regulator though, it's all just so unused it's highly unlikely there's anything wrong with it.

 

It's an '88 machine, and interestingly has a socketted TIA, which I'm not sure I've seen before. Anyhow I made a start on it today. We're still waiting for bits but I've pulled the modulator (useless in the UK), caps (swapped the two I had, the other will get dropped in latter), swapped the ferrite bead for a diode, swapped the bespoke power jack for a 2.1mm DC jack (again, the US PSU is of no use here) and added the audio out jack (phono for this installation, amusingly from a 2600 Jr). Bit of fileing of the case so everything fit and that's the first couple of hours work done. Mainly fiddly stuff, the actual fitting of the video mod will be simple really.

JBJ-7800-1.thumb.jpg.4424bac91960b55116a682fa0c1b399e.jpg

This machine's getting a UAV, which is on it's way from The Brewing Academy and will be wired for S-Video only. We're waiting for a few bits to land to be able to continue, but I thought I'd get started. I oddly enjoy working on 7800s, not sure why... Though it is going to need it's cart cup dremelling as it's super tight which I don't really enjoy doing.

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On the cart sleeves I've found a method that takes more work, but looks better as a result. What I do is use a drill to just drill out the bottom portion of the sleeve on the sides. I then use a rounded small file and file away at the corners of the sleeve. Most of these, the issue is the corners on the lower half of the sleeve that prevents the carts from seating in fully. So after some time of filing away, you can remove enough material without actually going all the way through the plastic. You end up with a pretty stock looking sleeve when done but again, it is much more time consuming vs a dremel wheel to take out the corners.

 

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I tend to use a small grinding ball bit in the Dremel that can get deep into the cup. It's a pain and it takes a long time, but you can barely tell that I've been in there usually (save for a few scratches that are hard to avoid).

Edited by juansolo
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  • 2 weeks later...

JBJ's machine done, just running it for sanity testing now. Easily the best condition machine we've ever worked on. Possibly down to the impossibly tight cart slot it was probably hardly used. I've never had one that tight before and it was horrific. I've taken a shocking amount of material away and it's still snug, but most things fit ok now.

JBJ-7800-4.thumb.jpg.c1a83a6a3b2f97f3ef54043d99e7e14e.jpg

Haven't bothered with chroma switching as it doesn't really make much difference on an NTSC machine all said and done. Put a chroma shifter on there though which cuts back on the ghosting on the 7800 side of things.

JBJ-7800-2.thumb.jpg.bebdc2e47a9791b10244c513f3b92222.jpg

New jacks work really well. Need to make a metal template to make drilling the PCB easier (this was the first so used a plastic one that was destroyed in the process). Considering we've got another 99 of the things, this seems to be the way forward ;)

JBJ-7800-3.thumb.jpg.f809a4d592133a83674f2256ca7beea2.jpg

Though I get points deducted for forgetting to clean the flux off before taking this photo. But it shows how we mounted it.

JBJ-7800-5.thumb.jpg.45dd51dcc32b17b08356069976d47252.jpg

I think it looks pretty good considering it's all board mount.

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7 hours ago, juansolo said:

JBJ's machine done, just running it for sanity testing now. Easily the best condition machine we've ever worked on. Possibly down to the impossibly tight cart slot it was probably hardly used. I've never had one that tight before and it was horrific. I've taken a shocking amount of material away and it's still snug, but most things fit ok now.

JBJ-7800-4.thumb.jpg.c1a83a6a3b2f97f3ef54043d99e7e14e.jpg

Haven't bothered with chroma switching as it doesn't really make much difference on an NTSC machine all said and done. Put a chroma shifter on there though which cuts back on the ghosting on the 7800 side of things.

JBJ-7800-2.thumb.jpg.bebdc2e47a9791b10244c513f3b92222.jpg

New jacks work really well. Need to make a metal template to make drilling the PCB easier (this was the first so used a plastic one that was destroyed in the process). Considering we've got another 99 of the things, this seems to be the way forward ;)

JBJ-7800-3.thumb.jpg.f809a4d592133a83674f2256ca7beea2.jpg

Though I get points deducted for forgetting to clean the flux off before taking this photo. But it shows how we mounted it.

JBJ-7800-5.thumb.jpg.45dd51dcc32b17b08356069976d47252.jpg

I think it looks pretty good considering it's all board mount.

That looks awesome. What about your chroma shifter board. You've got a TI chip with one input one output, power and ground. But what is needed on the north side of that PCB, I couldn't see exactly what is needed.

 

Thanks,

Ray

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1 hour ago, raymondjiii said:

That looks awesome. What about your chroma shifter board. You've got a TI chip with one input one output, power and ground. But what is needed on the north side of that PCB, I couldn't see exactly what is needed.

 

Thanks,

Ray

Chroma shifter is what I've been calling the Chroma Fix or C-fix for short. It is a 4050 IC along with a 100nf capacitor.

 

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7 hours ago, -^CrossBow^- said:

@juansolo & @marauder666, did I ever send you guys the gerbers and BOM for the 7800 mount PCBs? Course they can only be used on NTSC models, but... as there isn't a UK distro for things like this?

I'm fairly certain we've got the one for the add-on board but not the new one that board mounts everything.

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7 hours ago, raymondjiii said:

That looks awesome. What about your chroma shifter board. You've got a TI chip with one input one output, power and ground. But what is needed on the north side of that PCB, I couldn't see exactly what is needed.

There's a timing offset on the NTSC machines with the 7800 chroma being slightly ahead of the luma. What we're doing is running it through the gates of the 4050 to slow it down and bring it more into sync. Now the offset and the 4050's all vary in the amount it will correct this, so a degree of suck it and see is required. Helps to have a few chips and to socket it to get it as accurate as possible. Or of you want to be super accurate you can go as far as I did on my machine using two 4050's (one with fast propogation timings and the other with slow), with jumpers on each to chose the number of gates to pass the signal through. With mine it's fine tuned to the point that the drift is virtually imperceptable. With the single IC going through all six gates there might be some drift still, but usually it's greatly reduced. It makes a big difference to the picture quality.

 

We go into it in detail on page 3 of this thread:

 

Edited by juansolo
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