800xl wire question continues to baffle.

[seastalker]

Just got my second consecutive 800xl socketed ntsc board which has 2 soldered wires in it which are identically placed. Can anyone identify the function of (pix attached)

 

solder joint between C27 and L10 going to one just beneath L12

 

and

 

solder joint between C79 and L10 going to one just next to C69

[+kheller2]

I think those are power lines. Later versions of the board incorporated them as traces down the right side there by the shield ground.

[Rybags]

It's a common thing in many models though not sure 400/800 or 1200XL ever had it. Fixes devised for problems or omissions done by jumper wires before later incorporation into the next board revision.

I guess the assembly line at the time was a pretty hands-on process. The other common attribute is otherwise unsocketed later machines like late XL, all XE where some chips are socketed, the theory on that one being that failed ICs are replaced with a socket put in place first.

[1050]

Just my opinion, but these two jumpers fix nothing that

was broke in the first place. Done at Atari by the

board repair team and the shear number of them indicate

to me that this was a secondary task assigned to them

because without this extra work assignment they were

reading novels on company time and having food fights.

 

I can say this because I've checked the schematic and

board and see no valid reason for bypassing both L10

and L12 with +5 buss directly. It's a pointless fix

but in large volume while NOT being on every single

board and all of that at the same time.

 

Other wire mods have this aspect in common with them

too and there were many of those -- ALL unneeded,

and yet there they are just the same. There was no

revision to the motherboard to include these jumpers

or a bare wire jumper used instead of L10, just as

there is no second version of the schematic.

 

I always remove these two 'power fix' jumpers to

restore full function to both L10 and L12 on all

mine. SIO cable wire can't possibly handle a short

to ground if it's fed straight off the buss. Because

it just doesn't happen isn't an excuse here. I see

no reason for them and they are gone.

[+DrVenkman]

I'm with 1050 here ... My Rev A 800XL does not have these wires, while both of my later machines with Rev C boards do have them. Someone thought it was a fix for something that wasn't broken to begin with.

[+kheller2]

Without getting out a bunch of boards, the changes certainly were incorporated into the XL boards.

Whether or not they serve a good purpose, I haven't investigated.

 

here I think those power lines are replaced with traces:

post-40814-0-88437000-1416450010.jpg

 

Later, the XLF boards had additional (omissions) and fixes added. Actually, there are several changes to that area of the board from the 4051s over to the joystick ports over the years.

 

post-6732-0-86231200-1314844223.jpg

 

Which is very close to this version:

 

post-4566-0-36563600-1314889643.jpg But this board has some additional stability fixes.

 

This topic was covered slightly before: http://atariage.com/forums/topic/200894-wires-on-my-800xl-pcb/?p=2568596

[1050]

Bob is quite right in that other thread, jumpers like these can make

a great improvement in the area of video signals notably. In some

video upgrades it's the central theme. Perhaps this issue is even

that issue?

 

The jumpers are not fixing traces that don't exist in the first place,

they can be removed and zero penalty(?) is paid for the offense. The

jumpers are not universally applied to earlier versions.

Which of course begs the question - why not?

 

But they did monkey around with the traces on that side, and like you,

I haven't looked into what the improvements might have been. I wouldn't

know where to start that process either.

 

And I've done some incorrect assuming - I assumed Atari printed

an accurate schematic, foolish me.

 

L10 was never meant to power the READY line of the SIO as

depicted in the schematic here

http://www.atarimania.com/documents/Atari%20800XL%20Service%20manual.pdf

800XL service manual 40 megs

 

I assumed that was it's purpose, but after looking around some I've now

decided that L10 originally was supposed to supply filtered power to the

OS and BASIC rom. Which NO schematic shows. Not even this one

http://www.atarimania.com/documents/Atari_800XL_Sams_Computerfacts_Technical_Service.pdf

Sams Photofact 16 megs

 

Interesting to see yet a different version of motherboard with the jumpers

in the Sams version. That makes three at least and they all have changes

along that right side. I had noticed the changes, this was not the core

issue for me, thanks to some incorrect assuming and misguidance from the

master keeper of the flame, I assumed they were powering the READY line

incorrectly and that didn't set well with me. Turns out they always have

pumped the buss out there and I own that mistake alone.

 

I at least have some crow to eat for supper, what to make of it taken

in it's entirety, I'm not even sure of right now. It does appear one

board revision was not enough though.

 

Would sure be nice to know how the decision was made to NOT install

the jumpers, early and late models included. I'm leaning toward they

finally just gave up. Perhaps it was as simple as 'Oh this one has

a horribly noisy picture - take it back and do something to it'? And

these jumpers to the OS/POKEY power source was their video mod? When

the XE showed up they just said fugetabout the video - it can't be

fixed.

 

Oh, and thank you Atari for the mistake on the schematic. I did

automatically assume L12 was a similar victim in the jumper deal.

After I digest some, I might look into the L12 issue with a calmer

frame of mind, all in good time of course.

[seastalker]

Thank you everyone for having the same investigative interest as me in this regard. In the grand scheme of life, this topic is such a tiny blip, but I was that child that always had to know "why".

[+kheller2]

Having tinkered with the 1400/1450 boards and XLF boards it always seemed Atari was trying to provide filtered power to different areas. It would be wonderful to build a "definitive" schematic of the Atari 8bits, even incorporating some of the overly used components from the 400/800 days. Of course, no one is going to agree on exactly what is and is not necessary in said definitive schematic, but creating an accurate schematic of just one board might be useful at times LOL. I only focused on those jumpers when doing some research on the 128K 800XL board and then noticed they have been re-routing traces a lot in that area with each revision of the board (everything from location, quantity and even thickness of some traces were changed especially on the solder side). I think even the CHELCO boards are slightly different than the above pics.

 

I had always assumed those wires were part of the manufacturing process because things were missed on the original trace work. It would be interesting to find a board made before ones with the jumpers just to investigate -- for no other reason than to investigate history and progression of the design.

 

Let's not even get into the silkscreen errors. Oh how many duplicate IDs there are ...

[Almerian]

 

 

The other common attribute is otherwise unsocketed later machines like late XL, all XE where some chips are socketed, the theory on that one being that failed ICs are replaced with a socket put in place first.

 

Another theory is that there was a temporary shortage of IC's, or a (suspected) bad batch of IC's and instead a socket was put in. Time is money, so better to put out populated boards with sockets than having to wait or having to solder in IC's at a later time.