Atari 400 A/V mod

[jamm]

1 minute ago, flashjazzcat said:

SCCC's advantage is ease of installation, compatibility with 6502 and 6502C processors (by way of jumpers on the board), and improved audio output if required.

Ah, I didn't realize there was a potential incompatibility with UAV and the CPU in the older machines. That explains why the SCCC lists CPU compatibility as a primary feature!

 

Quote

UAV/SCCC video output is miles ahead of the KJMann mod, and you get composite and s-video in one mod

Thank you - that helps make up my mind.

 

[+DrVenkman]

1 minute ago, jamm said:

Ah, I didn't realize there was a potential incompatibility with UAV and the CPU in the older machines. That explains why the SCCC lists CPU compatibility as a primary feature!

Not at all. The SCCC needs the jumper because the CPU boards for early 400's and 800's for the standard 6502B is different from that of later models with the Atari-specific 6502C SALLY boards. The UAV itself makes no difference nor can it differentiate between the two - the UAV is strictly analog video circuitry. It has nothing whatsoever to do with any of the digital signal processing done by the rest of the system.

[jamm]

11 minutes ago, DrVenkman said:

Not at all. The SCCC needs the jumper because the CPU boards for early 400's and 800's for the standard 6502B is different from that of later models with the Atari-specific 6502C SALLY boards. The UAV itself makes no difference nor can it differentiate between the two - the UAV is strictly analog video circuitry. It has nothing whatsoever to do with any of the digital signal processing done by the rest of the system.

It did seem odd to me that the UAV installation would be dependent on the CPU type...  Ok, so the benefits of the SCCC over the UAV are simplified installation and inclusion of the audio upgrade (which is a separate, optional board in the case of the UAV).

 

Edited February 26, 2020 by jamm

[flashjazzcat]

1 hour ago, jamm said:

Ok, so the benefits of the SCCC over the UAV are simplified installation and inclusion of the audio upgrade

And the ability to use either a 6502B or 6502C in the same CPU board (by changing jumpers on the SCCC board).

Edited February 26, 2020 by flashjazzcat

[xrbrevin]

many thanks to you all - i think the Kjmann mod is the least intrusive and i will give it a go asap! i will have to root through my resistors & caps this eve.

i just got a laptop screen to replace, a TV inverter and a win8.1 black screen to sort first... (yawn) then i can do the 400 ?

 

 

[jamm]

4 hours ago, flashjazzcat said:

And the ability to use either a 6502B or 6502C in the same CPU board (by changing jumpers on the SCCC board).

Ok, I think I finally understand... a benefit of the SCCC is that it lets you use either the older or newer 6502.  I thought this was listed as a feature simply to indicate you didn't need to worry about which version your machine happened to have installed, but I assume it's really marked as a benefit since 6502C's are easier to find should you need a replacement, and all 400/800 machines come with 6502B's?

 

Have I finally go it straight? 

[flashjazzcat]

9 minutes ago, jamm said:

Have I finally go it straight?

Perfect!

[drpeter]

37 minutes ago, flashjazzcat said:

Perfect!

Except that I understood it's only the early 400/800s that came with 6502Bs, later ones had the 6502C?

[flashjazzcat]

6 minutes ago, drpeter said:

Except that I understood it's only the early 400/800s that came with 6502Bs, later ones had the 6502C?

I believe so, yes.

[jamm]

43 minutes ago, drpeter said:

Except that I understood it's only the early 400/800s that came with 6502Bs, later ones had the 6502C?

This thread confirms that some 800's came from the factory with 6502C's:

 

Edited February 26, 2020 by jamm

[+DrVenkman]

2 hours ago, jamm said:

This thread confirms that some 800's came from the factory with 6502C's:

 

All three of my 800's have SALLY's, if I recall correctly. They are all from '82-'83. This makes sense since the 5200 was released in 1982 and all of them have SALLY chips as well. 

[+tf_hh]

On 2/26/2020 at 3:51 PM, jamm said:

tf_hh originally says:

Ironically, the SCCC results in replacing the entire CPU PCB, which some might see as a pretty significant change relative to the UAV's addition of a tiny PCB.  Is the video improvement noticeably greater?

 

It´s meaned this way, that for installation of the SCCC there´s no need to drill extra holes in the case nor scratch any traces or so at the mainboard. Most owners of Atari 400 / 800 computers won´t do such destructive things. Changing the whole CPU card isn´t any kind of "destruction" - Atari wouldn´t design a changeable CPU card if they won´t have thoughts about new or better CPU cards for the system (specially with the also changeable personality card of the Atari 800) in the future.

 

In some rare cases the video quality of the SCCC might be a little bit better than using the seperate UAV rev.D Plugin-Board for example. I´m using a two-staged voltage regulation on the SCCC. First there´s a highend, very low drop (LDO) voltage regulator from the +12 volts rail to +5.0 volts down with max. 0.8 amps load. The "new" 5.0 volts are used for the video circuit involved chips needing 5.0 volts (NCS2563 video chip, the 74HCT74 for PAL color clock generator etc.). These clean 5.0 volts are again reducued to 4.5 volts using the exact same LDO voltage regulatur found on the UAV rev.D boards to meet Bryan´s specs. The difference is now, that the "new" 5.0 volts feed at the SCCC is absolute clean and free of any disturbances caused by CPU, ANTIC and GTIA (and at last all other chips using the standard 5.0 volts rail at the whole computer), so called independent from system load and capacitance. IMHO the picture is sometimes a little bit clearer and sharper than using UAV rev.D in an Atari 400 or 800.

 

[jamm]

14 hours ago, tf_hh said:

 

It´s meaned this way, that for installation of the SCCC there´s no need to drill extra holes in the case nor scratch any traces or so at the mainboard.

Thanks for your comments, @tf_hh!  In many cases it's difficult to determine what the details of functionality and benefits are of community-produced upgrades because the assumption is made that most people have been following along with the development on the forums.  I've spent hours the last few nights reading through the UAV threads and making notes just to get a better understanding of what design choices were made and how everything fits together.  It's understandable that many/most people will not be willing to invest that much time in their research.

 

I posted earlier that I wanted to understand the reason for the audio upgrade board.  For the benefit of anyone else reading this: the board was created simply to correctly mix the audio levels coming off the POKEY with the SIO sound.  In the case of the 7800, it also mixes audio with that from the POKEY that is found in some cartridges.  You could skip this and take audio straight from POKEY if you don't care about SIO, or you could create your own 'mixer' using some capacitors, but getting a good mix of the two levels isn't easy, and that's what the board simplifies for you.

 

@Bryan made an interesting, tiny version of this late in 2017, but only made a few a stopped making them.  The version currently for sale on The Brewing Company's site is different and designed by @MacRorie, but presumably has the same end-result.

 

 

[xrbrevin]

Kjmann mod completed and looking good! Here's the details:
I used this guidance:

But i couldnt get the exact values so i bought 20x 510ohm, 240ohm and 120ohm. I metered them all up and found ones that matched as close as poss.

I also decided to take the ground connection from an area nearby to these (see the black wire below), so as to keep all the wires as grouped up as poss. it also allows the power PCB to be removed without any fuss. I used an old USB cable as it is 4-core - its ideal and fits the cable guide castings with same tension as the original. i also added the 75ohm resistor (the one with red heatshrink tubing below) to the luma signal. i dont have any 22uf tantalum capacitors so i havent added anything to the chroma signal. anyhoo, here is my creation:

I didnt need to drill/file the EMF shield, the wires exit nicely just above the screw-hole when the base plate is screwed on.

I refitted my PAL power PCB as the RF modulator is removable via a pin header and it is now removed. this negated the requirement to cut the 2x tracks as stated in Kjmann's guide.

At the other end of the (now ex)USB cable, i soldered a female 5-pin DIN socket - like what is supplied with the Super Colour CPU Card from TF_HH.

Here are the results!

These photos don't do it full justice, i need a gimbal!!

The audio is nice and loud too - i never knew you could just tap the POKEY pin 37 directly. ?

So i'd recommend it to anyone, very cost effective and high quality results. the fiddliest bit was soldering the DIN plug! (pesky things...)

[+DrVenkman]

1 hour ago, xrbrevin said:

These photos don't do it full justice, i need a gimbal!!

 

You need to dump that 16:9 nonsense. ?

 

(But the mod looks good otherwise!)

[+Stephen]

27 minutes ago, DrVenkman said:

You need to dump that 16:9 nonsense. ?

 

(But the mod looks good otherwise!)

Fixing the world, one 16:9 screen and vertical video at a time   Apostrophe use when time permits, but my biggest pet peeve if dampen when what was meant (and proper), was DAMP.  One makes something wet (dampen), the other stops a ringing as in a bell (damp).

[Colleton]

That looks much better than I'd imagined it would.

[Colleton]

I have a couple of stock 400s sitting around, so I ordered the components needed from digikey today and will try the mod later this week when the parts arrive.

 

This is my 4th digikey order in the last 2 weeks.   Anything to stay busy.  lol

[xrbrevin]

1 hour ago, Colleton said:

I have a couple of stock 400s sitting around, so I ordered the components needed from digikey today and will try the mod later this week when the parts arrive.

 

This is my 4th digikey order in the last 2 weeks.   Anything to stay busy.  lol

nice one, i can highly recommend it.

its as good as my 800 on s-video

[xrbrevin]

some more pics of my mod

i did add the tantalum cap for what its worth but it didnt seem to make a noticeable difference

 

[Colleton]

Gave it a shot today, sadly my results aren't anything as nice as xrbrevin's were.

 

The Basic/Memo Pad background is zig-zag striped and is very washed out and pale.  Game graphics look correct, but are much paler than they should be. 

 

The resistors and the cap are installed correctly (I tried it with and without the cap), and I used an old USB cable as well.  I don't know what I'm doing wrong.  Only thing I can think is that I need more than 75 ohms at the luma pick-up point?

 

Any thoughts would be appreciated.

 

 

[_The Doctor__]

All things being equal, using an old USB cord isn't exactly a standard wire... I'd try using actual AV grade cables.... or at least some different USB cable.... I have seen a drastic difference from one to another in quality and wire thickness.

[Colleton]

Just now, _The Doctor__ said:

All things being equal, using an old USB cord isn't exactly a standard wire... I'd try using actual AV grade cables.... or at least some different USB cable.... I have seen a drastic difference from one to another in quality and wire thickness.

Okay, I have another cable I can try tomorrow.  I did try building a new cable using "dupont wires" (as FJC did in his video) but had the same result.  I really don't think it's the cable, and I tried a 120 ohm resister in place of the 75 at the luma pick-up point with no change either.

 

We'll see.

[xrbrevin]

can you test on another screen?

[xrbrevin]

can you post a pic of the mod?