1450 XLD motherboard build, assorted questions

[AtariGeezer]

Just got done replacing the RF Modulator with a good one and the TV out now looks great

 

I'll have to set up a UTube account and borrow a cam with sound so you guys can see the 2nd 1450XL made in the last 25 years...

 

Now to get back to the case rework; I'm thinking I might make a "hot wire" cutter and carve out the rear of a 800xl in sections and re-glue them in the correct order to look more like a finished product. Also thought about trying a laser cutting diode too...

 

Jay

[AtariGeezer]

http://youtu.be/EvNYP4S3WFg

 

Proof she's a working

Edited December 19, 2011 by AtariGeezer

[Vandal968]

Did you build the modem daughtercard, or did you just use the other chip?

 

c

[AtariGeezer]

LOL, I cheated for now and just went with the National MM74HC942N modem...

I've got to practice my circuit etching before building the daughtercard, it's been many years since doing that

 

Jay

[Joey Z]

so now that I have the BOM, does anyone know where I can get a schematic (and how accurate it is)? only a cheapass like me would try to wirewrap this...

 

you all probably think I am joking, but you will be laughing your asses off when you see the front and back side of a working wire wrapped 1450xl...

Edited December 19, 2011 by Joey Z

[AtariGeezer]

The most accurate schematic is the Atari PDF in this thread, but is very unreadable. The one from Best and Jerzy Sobola have the the power inputs wrong and is missing the connections to the 34pin Floppy Board connector, plus U24 has a few different connections...

 

Jay

[mellis]

so now that I have the BOM, does anyone know where I can get a schematic (and how accurate it is)? only a cheapass like me would try to wirewrap this...

 

you all probably think I am joking, but you will be laughing your asses off when you see the front and back side of a working wire wrapped 1450xl...

 

Can't wait to see the case mods you make to accommodate a wire wrapped board .

[Joey Z]

thank you, I found them now... I read the entire thread and didn't see any, but I must have gone in skim mode instead of reading...

[Joey Z]

so now that I have the BOM, does anyone know where I can get a schematic (and how accurate it is)? only a cheapass like me would try to wirewrap this...

 

you all probably think I am joking, but you will be laughing your asses off when you see the front and back side of a working wire wrapped 1450xl...

 

Can't wait to see the case mods you make to accommodate a wire wrapped board .

case mods? nah. either custom case or no case...

[AtariGeezer]

thank you, I found them now... I read the entire thread and didn't see any, but I must have gone in skim mode instead of reading...

 

Check out this post for the Atari PDF

http://www.atariage.com/forums/index.php?app=forums&module=forums&section=findpost&pid=2371407

[Joey Z]

hmm. that's the problem with 25 year old schematics. they get smudged and impossible to read... maybe I should go with the 1400xl instead of the 1450xl

[AtariGeezer]

hmm. that's the problem with 25 year old schematics. they get smudged and impossible to read... maybe I should go with the 1400xl instead of the 1450xl

 

The schematic from Jerzy Sobola for the 1400 also has same errors with power...

[Joey Z]

what kind of errors with power are there? if they are pinout, it won't really matter since I will use an ATX supply. this wouldn't be meant to be just like the real thing, just compatible.

[Vandal968]

There is no 1450 schematic that I've seen, just the 1400XL. Fortunately, they are identical except for the power connector (7 or 8 pin) and the 34 pin connector for the floppy. The Atari schematic is more accurate than the Sobola one which was clearly made from the Atari version (since it contains ALL of the Atari errors and a few new ones). My BOM calls out the errors on both sets of schematics, so you should be able to accomplish this fairly easily. Keep us posted.

 

cheers,

c

[Joey Z]

There is no 1450 schematic that I've seen, just the 1400XL. Fortunately, they are identical except for the power connector (7 or 8 pin) and the 34 pin connector for the floppy. The Atari schematic is more accurate than the Sobola one which was clearly made from the Atari version (since it contains ALL of the Atari errors and a few new ones). My BOM calls out the errors on both sets of schematics, so you should be able to accomplish this fairly easily. Keep us posted.

 

cheers,

c

so are the errors only component values or are there mistakes in wiring?

 

EDIT: I guess my real question is, is it possible to use the schematics from Jerzy Sobola and Atari to construct this and not have wiring mistakes other than my own mistakes?

Edited December 19, 2011 by Joey Z

[Vandal968]

so are the errors only component values or are there mistakes in wiring?

Both. Although the errors in component values are FAR more prevalent than wiring errors, I only spotted a few of those and most of them are lazy errors. For example, the VCC line for each IC is supposed to have a small cap on it (.01uf IIRC), but these are only shown in the schematic for about a quarter of the IC's. I assumed (correctly) that all of the IC's would use the same value cap in the same manner regardless of what was shown in the schematic. Stuff like that.

 

Also, I'm suspicious of two of the transistors in the video circuit (Q3 & Q8?) I think that they may be shown incorrectly in the schematic, but I didn't need to find out for sure to complete my board, so I didn't dig too deep (I'm a mechanical guy, not electrical.) My BOM makes note of everything that I found suspicious. I also marked up my sets of prints as I worked through it, so if this project gets off the ground, I may be able to offer some insights.

 

I don't think that there should be any big obstacles, BOM & schematic in-hand you're probably 95% there already. If it were me, I'd probably start by drawing it up in Eagle.

 

cheers,

c

[Joey Z]

if you think I could do it with the schematics and your BOM, I might just go ahead and buy the parts.

[AtariGeezer]

Also, I'm suspicious of two of the transistors in the video circuit (Q3 & Q8?) I think that they may be shown incorrectly in the schematic, but I didn't need to find out for sure to complete my board, so I didn't dig too deep (I'm a mechanical guy, not electrical.) My BOM makes note of everything that I found suspicious. I also marked up my sets of prints as I worked through it, so if this project gets off the ground, I may be able to offer some insights.

 

I don't think that there should be any big obstacles, BOM & schematic in-hand you're probably 95% there already. If it were me, I'd probably start by drawing it up in Eagle.

 

cheers,

c

 

Q3 & Q8 are the switch circuit for the Neg 5 Volt line. Since only the +5VDC & +12VDC are controlled by the main switch, the -5VDC is controlled electronically. That's why I asked before if R140 & R141 get warm on yours, R141 may need to be changed to 1k?

 

Jay

[AtariGeezer]

There is no 1450 schematic that I've seen, just the 1400XL.

 

cheers,

c

 

Have you looked at the PDF in post #304 ? it's a 1450 schematic and even has U24 wired correctly, plus the wiring to the floppy board...

 

Jay

[Vandal968]

Have you looked at the PDF in post #304 ? it's a 1450 schematic and even has U24 wired correctly, plus the wiring to the floppy board...

 

Jay

I haven't looked at that one. My board was built and working by the time it was posted, and I was well into the "If I have to look at another goddamn Atari schematic I'm going to snap" stage.

 

c

[AtariGeezer]

LOL, understand that

[AtariGeezer]

Is there a schematic of this board around somewhere?

 

 

It would be nice to make use of the parallel floppy interface...

 

Jay

[Rybags]

But does the OS cater for it?

 

Or maybe it just sits on the PBI bus and utilizes the normal "takeover" aspect of SIO/PBI protocol.

 

ed - actually, that is probably the case, so then you'd need the ROM image with the handler that overrides the FP package.

Edited December 22, 2011 by Rybags

[AtariGeezer]

Yes, the handler for the floppy is in the same ROM as the Speech and Modem handlers.

Don't know if it uses the "takeover" aspect of SIO/PBI protocol, that's where a schematic would help to learn from

[Rybags]

You could probably work out fairly quickly by looking at the handler if it was using PBI - in all likelihood it'd map the registers into page $D1 or at least have some references to it.

 

If it didn't use PBI protocols then the OS ROM would need to be different, specifically within the disk handler or more likely SIO components.

 

Without the schematic, it might be possible to deduce what hardware is being used by reverse-engineering via the ROM - but not exactly easy.