SuperVideo 21XL oraz errata.pdf

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1989, July 1990, and November 1990 issues ofthe SLCC

Jouraal , Bob went head-to-head with the 1200XL video beast.

A few times he came cloee to sla5nng the dragon, but he ran

out of gas just short of final

q .0c, Jooe/tlanl

"ictory. It muet have been oae of

the few times the Invincible Woolley tasted defeat (or at least,

something leee than total euccess). One of his articles got

posted to the 8-Bit Forum on CompuServe, where it oartinuee

lo befuddle Classic Atariang to this day. But the eheer

amount of guts and sweat Bob poured into the effort was im-

pressive even \r Alchemist etatdards.

An Old Pr.riect

I began inveetigating the 800XL's poor video performance

in 1986 and never really stopped. How do you condense eight

years of continuous reeearch on one topic into one short ar-

ticle? You don't. No way around it, this ie going to be one

Iong afticle! However, before we can roll up our sleeves and

start ehoveling up the video manure Atari dumped on ue, I

must first render homage to varioue publishers who par-

ticipated along the way.

SuperVideo 1.0 was published by Ed Dell in the February

1987 iesue of the now-defunct &mputerSmyth maga.zine. It

gave modest improvements in video performance but really

only repreeented a single-pass attempt to solve a problem that

went deeper than I realized.

My oontinued hackingat the problem led to the publication

by Joe Watere of Super Video 2.0 in the September 1991 issue

of Current Notes magazine. That article repreeented a real

breakthrough in my underetanding of 800)G video problems

and served as the epringboard for polishing up the mod and

applyrng the concept to similar upgradee for the 600XL and

the 1200XL. I'm grateful to Ed Dell and Joe Waters for releas-

ing my previously publiehed articlee. Had they not done so, I

probably wouldn't have continued the tinkering which

resulted in this final solution to all )G-series video defects.

Genesisof SuperVdeo2.1

Following the 1991 CN afticle I felt sure I had frnally

solved all the 800XL video defecte. In the elapeed two yeare,

however, with hun&ede of hours epent in front of my CBT, I

began to notice more subtle thingls. Color performane still

wasn't the best, and worgt of all the brightness of my video

display varied according to the electrical load on the power

bus of my 800XL. I've modified ay XEP80 go it draws power

from the joystick port: it sucks half an ampere. The addition

of stacked cartridges, a P:R:Connection, multiple operating

eystems and a 1088K RAM upgrade triplee the power drain

compared to the 700mA or so a stock 800Xt drawe (I run my

system offa monster IBM-type s,n'itching power supply). With

the addition of each new electrical load my CRT display grew

dimmer. I was dismayed to realize that after all that work

*rere were etill a f€,wgremlins I hadn't exterminated.

The culprit proved to be not the video circuit itself' but

components involved in supplying power to the entire video

circuit. The video circuit ie isolat€d from the rest of the Power

supply by an 820uH inductor, L5. The function of thie part ie

to pass clean DC voltage to the video circuit while euppressing

any video RF interference that could make its way via the

power bus into other pa.rts of the computer where supply-line

noise might disrupt the digital circuits. A prudent deeign*-on

PaPq, anyway.

In a perfect world, an inductor-which is nothing more

than a little coil of wire-paeees DC curlent perfectly but sup

pressea AC according to the inductance vdue (expreseed in

units called Henries). Well-made (but expensive) inductor'e

come very close to achieving this theoretical level ofperfor-

manc€. But a cheap one, wound with very thin wire, will er-

hibit the properties of a resistor as well as an inductor. In a

DC circuit, resistor€ waste electrical enerry by dissipating it

ae heat: the voltage coming out is ueually lower than the volt-

age you feed in. This is a desirable characteristic when

properly applied, but a diea.ster in the wrong environment. A

resistance in seriee with the power supply ie in this ingtance

very delinitely the wrong application.

So, did Atari use the nice expensive inductors that would

only squelch the AC noise but not eat up any of tlroee precious

DCvolts? Hah! Gueesagain! Ofcourseyou bow theyvsed

the cheap ones! This is, after all, Atari: a company where the

shaving of pennies was (and stil is) the ultimate erpreesion of

Corporate Culture. A clue to the crummy inductor uras provi'

ded by the low voltage on the collector ofoutput transistor Q5:

about 4.3V in most stock 800XL systems. Yet, the voltage on

my motherboard's main supply bus measured 5.1V. Atari's

cheapo inductor squandered L6% of the Power available to the

Flackers Vs" XLVideo

Like all good researchere, we Alchemists take a keen inter-

est in the efforts of others who work along similar lines, and I

must acknowledge their efforts. In the February 1986 isue of

Antic, John Borland described how to restore the miseing XL

chroma signal to the outputjack via a 220-ohm resistor. The

resistance value was wrong, and this mod did nothing to im-

prove basic video perfonnance. But he was on the right track.

Again in November L986, .4ntic published an article by

Jon Krahmer describing how to bring out the missing chroma

via a capacitor. While lGahmer deserves credit for pursuing

the subject in the facreof shamefully abusive treatment at the

hands ofAtari Corporation, his approach again did nothing to

solve basic video defects and was the poorest method for re-

storing mieeing chroma to the output jach.

In the July 1989 P,94JVMagazine , Rich Gratzer preeented

his fix for 1200)O video problems. It was strictly the work of

an amateur: basic video defects were again ignored, and color

shadows were aomewhat reduced at the expense of color

saturation performance. Moet of the parte employed serve no

real purpoee. He concocted his hack on the basis oftouching

his fingers to the video components (D and had a little difficul-

ty recalling detaile to rationalize his approach.

Finally, I must give special mention to AC's Bob \{oolley

for his efforts to remedy 1200XL video defects. Not because he

was successful, but because he tried eo hard. Bob did manage

to clean up some of the mono problems, but the color demons

held out frrmly against him. In the August 1987, September

Classlcc

Atarl

computers. Figure 1A is a simplified representation of the

digtal or TTL interface. This wae used mainly in early IBM

PC's, where it was implemented as CGA (Color Graphics

Adaptor) for color monitors or MDA (Monochrome Display

Adaptor) for text-only IBM monochrome displays. See Bob

Woolley's excellent article els€m'here in this issue for inforna-

tion on installing an lBM-sfyle MDA interface in your Classic

Atari.

Figures 1B-1D show the analog (NTSC or PAL) interfaccs

traditionally ueed in Atari 8-bit computers. The luma-chroma

interface in 18 offers the best overall performance but re-

quiree a more monitor that will aocomodate the var-

ious inputs. You'll want this type monitor/interface to obtain

best results with color monitors, and I consider it mandatory

for videogames.

Figure lC works well with monochrome compoeite moni-

tore, especially if you employ the Atari's luma output instead

of the standard compoeite output. This type of monitor/inter-

face provides the higheet screen reeolution and is ideal for

wordprocessors, spreadsheets, databases, or other text-

oriented work; it's also inexpensive. Color compoeite monitors

give a coarser display compa.red to luma-chroma, but at least

they ueually always have built-in sound. Mono composite

monitors often don't have an audio input, so to get audio you

have to run the audio line to a stand-alone audio amplifrer and

speaker. A mqjor disadvantage to both the luma-chroma and

composite video interfaces is a real scarcity of composite

analogmonitors in toda/e market.

I preeently know of only one model of composite monitor

still being manufactured: the Magnavox 1CM135. It's avail-

able from Midweet Micro (6910 U.S. Route 36E, Fletcher OH

45326 USA, orders 1-800-552-8080toll-free) for only $249. Its

performance is impreesive. It accepts CGA or MDA TTL in-

puts, luma-chroma or compaite video analog inputs, and even

has gtereo audio for all you GUMBY fans. This monitor

produces very decent color video for an IBM, Atari ST, any

Atari 8-bit except the 400, and your VCR. The Magnavox

1CM135 continuee a tradition eetablished by the Commodore

1902 and 1084 series monitors, which had similar characteris-

tics and were produced for Commodore by Philipe, the parent

company of Magnavox. The Commodore 1084 series monitor€

were still in production as recently as 1990. Fortunately,

analog monitore are popular items at electronic surplus out-

lets and turn up frequently at computer fairs, swap meets, and

even the Swap ads in the back of ,4d.

Figure lD shows the connection to a TV set. This is

probably what moet people use when they frrst bring the oom-

puter home. Very quickly, you discover how horible the TV

interface is: rippling herringbone patterns accompany the

usual grain, blur and smear, to the accompaniment of an an-

noying buzz from the T\Ps epeaker. Even under ideal condi-

tions the TV interface is at best poor, due to the limited video

bandwidth responee of moet T\Ps (4.5MHz w. 15MHz or more

for a monitor) and signal leakage into the computer video sig-

nal from adjacent broadcast channels in the T\ls tuner. A

guaranteed recipe for eyeetrain headachee!

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video circuit! I pulled theee inductors from several XL boards

and measured their DC reeietance: typically 10 ohms. Terr-

ible! (It shouldn't be more ttran an ohm or two.)

In Super Video 2.1. (which I'll call S-V from now on) wdll

replace this etupid inductor with a low-value reeistor, beef up

the associated filter capacitor to maintain a noise-free supply

line, and make a couple minor changee in the video circuit to

enhane color performance and signal strength a bit. S-V 2.1

will be "graftedn onto S-V 2.0, which I'll desqribe first. Before

deecribing S-V 2.0 I1l give you some background on various

video interfacee and provide a general deeaiption of the mqior

video flaws in the Xl,-seriee machines. Then I'll follow up with

instructions for installing S-V 2.1 in the 600XL and 1200XL.

The $rnnyvale &ltchers

Noboday at Atari Corporation erer underetood compoeite

video. And they etill don't. (Got an S?e? I\ry connecting it to

a high-qualit5r monochrome composite monitor in medium- or

lo-rez with a Monitor Master. The resulting display is a dis-

graceful abomination.)

The Video Butchers in Sunnyvale committed their most

grueaome atrocities on the XL machines. For starters, they

omitted bringing out the chroma signal to the rear jack on all

the XLs. They carried this concept a step further in the

Video Interfaces

Figure 1 outlineg various video interfaces used in home

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600)G by omitting the luma signal as well. A grces design er-

ror appeared in the form of mismatched signal impedance in

the video ou@ut: Atari ga.veit 100 ohme, but the standard im-

pedance for unbalanced video linee ie 75 ohms, resulting in a

weakened signal which is prone to interference from external

RF sources.

No matter, some blithering idiot at Atari'g Hong Kong fac-

tory installed 390 ohms, so that all Hong Kong-made 800XL

REVA2 and REVC motherboards were cursed with an output

mismatch erren worre than what was built into Atari's original

flawed deeign. When Atari later shilt€d production to Taiwan

some genius noticed the 390-ohm error and nconected" it back

to the original 100-ohm error, FK)video in the Taiwan 800XLs

improved somemrhat.

These scandalous incompetencies were bad enough, but

the Butchers weren't done yet. They hung bypass capacitors

on the XL video lines to suppress RFI. What they ac-

complished instead was to frlter offthe high-frequency content

of the video signal, where the resolution reeide6. Result: fuzzy

video that staye fuzzy no matter how much you twiddle the

focus control on your sronitor. This capacitance was omitted

in later production Taiwan models, which along with the im-

pedance "correction" previously mentioned helped improve

performance in later units. Circuit layouts in all models per-

mitted color elocking signale to leak into the monochrome cir-

cuits, so you get that wonderful grainy background on your

monitor wen when you u€rethe hi-rez luma output.

The 600XL preeents the saddest case. Atari's original de-

sign for 600XL video was essentially identical to that for the

800XL. Then Jim Morgan, pathetic master bean-counter from

Philip Monis Tobacco Co. (I worked at Philip Morris and met

Jim once, I was not impressed) came along just as the 600XL

was commencing production and tried to cure Atari's financial

follies by slaehing all the main video components from the

600XL, reducing it to a primitive T\I interfac'e. To add insult

to iqjury there'e a wrong-value coupling capacitor in the color

circuit in some units, causing washed-out color. Thus gutted,

the 600XL never eold well. Atari saved maybe 2?-cente worth

of parts from theee myopic blunders, in lfie process saddling

the user communit5r with a lega.cyworthy only of disgust.

The failure of so many hackers to cure the problems of the

1200XL is entirely understandable, for in that machine the

Butchers acoomplished their supreme achievement. In one of

his "Clearpicn articlee, Bob Woolley commented something to

the effect that "Atari engineers must have been paid by the

componentn. I quite agree. The 1200XL video circuits are the

most complex of all the XLD(E machines, and video perfor-

ulanoe is absolutely the wortt. Many of the extra parts don't

seem to serve any useful purpose, and quite a few ofthem

seem to have been placed there expressly to degrade perfor-

mance. The entire design incorporates virtually all the

blunders thus far mentioned, plus a frstfull of new ones: it's so

outrageously bad as to.approach the realm of the ineom-

prehensible. The irony ofit is, Atari intended the 1200XL to

be the anchor of an XL product line with improved video! As

we shall see, after a bit of Applied Alchemy the 1200XL indeed

has the best video performance of any 8-bit machine Atari

wer made.

Figure 2 demonstrates in actual screen photoe the various

stages of video quality. These photos lose much detail in

pnint, but even so you can see a big difference behrteen 2A and

2D. Study these photoe with a magnifying glase: the details

should stiU be visible (I hope!). Ifyour XL video lmke like 2A,

28, or 2C, and you'd like it to look like 2D, read on! (You

130X8 folks will have screens that look like 2C; see Charles

Cole's "Super Video for the XE" elsewhere in this issue if you

want to upgrade your XE video.)

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the bottom of the case and separate the case halves. Remove

the motherboard fastening-screws, and wiggle the board free

of the case. Make sure you discharge youreelf to some large

(preferably grounded) metal object before removing the

motherboard RF shields, and handle it only by the exposed

broad foil ground plane strip around the edges. Place the

board on a conductive eurface (damp newspaperr will su{ffce),

and orient it aeording to the diagram in Fig. 5.

ByThe Numbers...

Study Figwee 5-7 and refer to them for the followingstepe:

Step l. Locate reeistor R53. It will be either 390 ohms

(orange-white-brown-gold) or 100 ohms (brown-black-brown-

gold). Solder a resistor in parallel with R53 as follows: If R53

is 390 ohms, solder a 100-ohm resistor (brown-black-brown-

gold) on top of it in parallel (see Fig. 6); if R53 is 100 ohms,

solder a a 330ohm resistor (orange-roange-brown-gold) on top

of it in parallel. (This restores the mono output impedance to

the correct value.)

Step 2. Iocate the 180pF glase eapacitor C56 and snip it

offthe board with fine wirecuttere.

Figure2D.[snlnancooutpul ofSuperVldeomodfod

800xL:

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\Me'll do S-V 2.0 frret; it's the easiest of the upgrades and

yields spectacular reeults. You might elect to stop alter doing

S-V 2.0, eince going further with 2.1 brinp diminishing re-

ttrrns for more work. I gueeeI need to maLe a disclaimer f,ere:

ifyou try any of theee mods and botch it, tough krinkles. The

Alcheniet, Staffand Publisher of AC won't be responsible for

people who mangle their machinee (or themselvee) trying to do

thig stuff. Youll need reeistors, capacitors, heat-shrink tubing,

and a pa.nel-mount SPST mini toggle switch, all available at

Radio Shack. Buy the resistor assortment pack #27L-3t2: it

contains all the neeistore youll need in eractly the proper wat-

tage and phyeical size, with plent5r left over for future hacks.

Fignres 3 and 4 shos'the "befoie and after" schematics. The

schematic of Fig. 4 eeeentially represents the upgrade as it

will appear in all three XL machines. Only the component

deeignations will differ.

OK, lef,s get our hands dirty.

(This imprcves video high-

frequency response.)

Step S. Locate R116, a 5l-ohm resistor (green-brown-

black-gold). Solder a 2.2-ohm resistor (red-red-gold-gold) on

top of it in parallel. (Thie improves output current flow to Q3,

which is "starved" for cunent in Atari's original deeign.)

Step 4. Select a 10uF/16V tantalum capacitor and bend

the leads outrvard. Notice one lead is marked with a (+) eign.

Poeition this part above the board so the (+) lead touches the

bottom of the R116/2.2-ohm combination while the (-) lead

touches the top of R66. The leads are too long. Cut them off

right where the leads contact the respective resistors, then

solder the cap in place. (This improves Q3's transient

response and frlters noise from the supply line feeding the

video output.)

Step 5. Locate R66, a 100-ohm (brown-black-brorvn-gold)

resistor. Solder a 330-ohm resistor (orange-orange-brown-

Bold) on top of it in parallel. (This lowers the impedance of the

oolor signal output to the correct value.)

Step 6. Nowwe'll install the CVDisable switch. The pur-

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vldeoclrcuitafterSuperVideomodificailon.

pose of this sn'itch is to enable compoeite video for user€ who€e

color monitor accepts composite video only. Those who use

luma or luma-chroma interfaces should toggle the switch to

disable composite video. A cleaner signal, free of color clock-

ing interference that makes the ecreen background grainy,

will be obtained. Cut two 8" lengths of wire and strip 1/4" in-

sulation from one end ofeach. Solder the stripped ends of

each wire to the two lup on the switch. tWist these wires

lightly as shoqrn in Fig. 6. At the unattached ends, snip olf 1"

from one of the wiree, then etrip 1/4".insulation from the ends

of both wiree. Set the switch aeeembly aside temporarily.

Flgure4 S(X)XL

Now locate R56 on the motherboard, a 75-ohm resistor

(violet-green-black-gold). We want to desolder the left end of

this resistor (DONT cut it!). Get a good grrp on the left end

with needlenose pliers, then apply your soldering iron to the

joint at a 4Sdegree angle so it firmly contacts both the reeis-

tor lead and the golder pad. Allon' su{ficient time for thejoint

to heat up-about 10 eeaonds, the eolder will start to bubble.

lVith the iron still in place, pull up emoothly but firmly with

the pliers: the resistor should oome up eaeily. If it doesn't, al-

low.a good 5 minutes for ever5rthing to cool down, then try

agarn.

Once the left end of R56 ie free, use the needlenoee pliers

to form the free lead end into a loop. Then bend the resistor

into a vertical position supported by the end still eoldered to

, the board. Clear the vacated hole of sold€r. Now retrieve the

iprepared suritch aseembly and solder the longer wire to the va-

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