BOM for 800 PAL cpu boards to convert my ntsc cpu boards

[Beeblebrox]

I have a few NTSC cpu boards from NTSC 800's laying around. 

 

As I am UK based when I have converted said 800s from NTSC to PAL I have always just sourced a PAL cpu board (which among other things has the colourburst crystal on board).  So I've just swapped out the boards and put the NTSC cpu boards on the shelf. Then of course I do all the rest for the PAL conversion. 

 

However these discarded NTSC cpu board have just been gathering dust.

 

I never noticed before until today but the base pcb for the cpu boards are actually identical, it's just the NTSC board are missing the colourburst crystal, a 74ls74 chip and some other video circuit passive components. All the solder points and traces are present.

 

Therefore in theory I should be able to add the missing passive components, logic chip, colourburst to the pcb (and of course PAL Gtia and Antic chips), and these cpu boards will then be PAL cpu boards. 

 

So my thinking is aside the 74ls74 chip, and the colourburst crystals, (latter which I can source from donor A8's or atari 2600 Jr's) , it's the other passive components am not familiar with.

 

Does anyone have a modern equivalent BOM for these boards so I can identify and source the correct missing passive components?

 

A few pics 

 

In this first pic the top board is the NTSC and bottom one is the PAL, (which has a bad gtia btw):

Edited September 25, 2023 by Beeblebrox

[_The Doctor__]

The NTSC specific LSI' would need to be swapped for PAL, the rest of the components look very legible so you have all of the parts on that PAL board to simple write down. Not much to do really, just pull the parts that don't match and populate the empty holes, make sure you have the correct LSI, the correct crystal, verify the traces and PCB are the same configuration. It's a cake walk.

[xrbrevin]

beware of that polystyrene cap - they are easily melted..!

[Beeblebrox]

Thanks. However I am after the BOM for those pal components missing on the ntsc board. (I know the chip and crystal). Also just to clarify I am not wanting to remove and transfer the components from my pal board to the ntsc board. I want to source the modern replacement components that are missing on the ntsc board to populate it and convert it to a pal cpu board. I have no idea how to find out some of those old passive components, (for example the silver cap (just below the pot) named c308 - what value/rating is that?) see blown up pic below. 

 

And l303, not sure what that even is? 

 

So basically I figured I am after the detailed BOM for the pal board so I can work out what value/rating passive components they are and source modern equivalents for the missing components.

 

I can work out the resistors by their banding and assume 1/4w or 1/8w 5% carbon film ones of the same values will work. 

 

Edited September 25, 2023 by Beeblebrox
Errors

[reifsnyderb]

I'd compare the parts on this PAL board with the 800XL schematic.  While I've never seen an 800 PAL board, it's quite possible the components are the same and just have different component id's.  Here's the 800XL PAL circuitry:

 

[Beeblebrox]

7 hours ago, reifsnyderb said:

I'd compare the parts on this PAL board with the 800XL schematic.  While I've never seen an 800 PAL board, it's quite possible the components are the same and just have different component id's.  Here's the 800XL PAL circuitry:

 

Great, thanks. I have a link to a rev D 800xl BOM so I'll try. Any idea what type of component L303 is on the image of the pal cpu board? 

[xrbrevin]

L usually denotes an inductor

[reifsnyderb]

5 hours ago, Beeblebrox said:

Great, thanks. I have a link to a rev D 800xl BOM so I'll try. Any idea what type of component L303 is on the image of the pal cpu board? 

From what I can see of the board, L303 is probably the same as L8 on the 800XL board.  So I'd go with an 820 micro Henry inductor.

[Overange]

8 hours ago, Beeblebrox said:

Great, thanks. I have a link to a rev D 800xl BOM so I'll try. Any idea what type of component L303 is on the image of the pal cpu board? 

If you double check the track layout compared to the 800XL schematic, then using 800XL components should be good, however, it does all depend whether or not they did anything different else where that could affect the Colour burst signal. Without the original Schematics it does make it more challenging.  

 

So yeah just copy the Components of the 800XL circuit and you should be fine  

 

The values that compliment the Tank Circuit are:-

 

Inductor L303 would be L8 on the 800XL schematic = 1.5uH

Capacitor C308 would be C111 on the 800XL Schematic = 820pF

 

The components in the tank circuit that would be fitted on the original 800 Board may differ from the later 800XL board design. This could be partly due to the change from film-type capacitors to ceramic-type capacitors or, considering Atari's cost-saving practices at the time, driven by the cost of components.

 

If they are wrong, the tank circuit will not resonant at the desired frequency and therefore give problems.

 

Be prepared  

 

[Beeblebrox]

@Overange thanks for the input. I'll have a good look. I always have spare donor boards and have a few butchered 800xl rev D boards in a box somewhere so will have a go at populating the ntsc cpu board by salvaging from said boards and converting it to PAL.

 

I've a 74ls74 chip as well as a colourburst so sorted in that respect. I'll borrow the pal versions of antic and gtia from one of my socketed A8's. 

 

Will report back. 

 

I have also secured a VBXE carrier board so at some stage my test open board Incognito'D 800 setup will be getting VBXE.

Edited September 26, 2023 by Beeblebrox

[Beeblebrox]

Just as a quick observation it seems only the one ntsc cpu board I have is the same layout as the Pal version and thus is possible to convert. 

I just had a look at all my other ntsc cpu boards and they are very different with a different payout and no place for the colourburst crystal. 

 

So I can only convert the one ntsc board to PAL. That is fine as I'll just sell the others on, but good to know.

 

So top board in this pic is the ntsc one which has a very different layout to the ntsc board below, latter being the one I plan to convert to PAL by adding the missing components as mentioned in this thread. 

 

 

Edited September 26, 2023 by Beeblebrox

[ivop]

The upper board is one with a 6502B and two LS244's to separate the address bus for /HALT functionality. The lower board has a Sally CPU.

 

[Beeblebrox]

Quick update.

 

I managed to convert the NTSC CPU board to PAL over the weekend. (I also found another convertable NTSC CPU board as well so managed to convert two in the end).

 

Basically I followed some of your tips posted above, cross references the BOM for the 800XL, and used 4 x spare/redundant donor XL/XE boards for some of the missing components as well as a new modern Mouser replacement colourburst crystal. ( i hjave a big bag of these pal colourburst crystals if anyone needs one in the UK(?)).

 

I also used these online resistor and capacitor colour banding tools:

 

https://www.dcode.fr/capacitor-color-code

 

https://resistor.cherryjourney.pt/

 

.........both of which came in handy for getting the values of the resistors from the PAl CPU boards and double checking the capacitor values.

 

I used the original PAL CPU board below as a visual reference and managed to find all the components which I've mapped here:

 

 

 

Here is one of them. Excuse the shoddy solder work. The components got a little bend out of shap extracting them from the donor boards.

the C308 was an 820pf cap and I took this from C111 on a donor 800XL rev D donor board

the L303 was the same as the L8 on the 800XL and XE donor boards, even though they look nothing alike.

 

C310 was a a 56PF cap and I took this from C60 on and 130XE donor board:

 

C309 was a 22pf cap and I took this from C59 on a 130XE donor board

 

Not being a trained electrician, with the C308 cap I wasn't 100% sure of the orientation of it on the board so took a gamble and it worked.

 

Adding the 14pin socket for the 74ls74 chip was easy. I had a spare chip luckily. Also I found a 104 marked little turquiose cap from the 800XL donor board which went into the C301 on the cpu board. Plus I had a new 2N3904 transistor to pop in to Q301.

 

Hardest part in the absence of a BOM for the PAL cpu board was working out/double checking the colours on the resistors and some of the caps. So hard to make out the difference between some colours and it doesn't help some 40 year old components have dulled.

 

Anyways, both converted boards work with their PAL Antic and gtia chips in place.

 

Here's one of them again my incognito'd 800 bare board:

and here is the other, (where you'll see the C308 820pf cap sourced from C111 on another 800XL donor board is identical to the one on the original PAL CPU reference board:

 

  

 

 

Thanks everyone for your input.

 

 

Edited October 1, 2023 by Beeblebrox

[Panther]

I recommend cutting the legs of the crystal shorter so that it's as close as possible to the capacitors.

[Beeblebrox]

22 minutes ago, Panther said:

I recommend cutting the legs of the crystal shorter so that it's as close as possible to the capacitors.

Thanks for the tip. 

Just out of interest both boards are running fine with full length unclipped crystal legs, so what is the advantage of shortening them, aside looking neater?

[Peri Noid]

I once bought a 400 which was probably converted from NTSC to PAL since it had the following CPU board. It had a PAL Antic and a PAL GTIA mounted in the adapter as depicted. I still have this board. 

[Beeblebrox]

@Peri Noid thanks for sharing.

 

There are several PAL converters on the market/in the pipeline, (from memory ones from tf_hh, mytek(?) and a few years back from Dropcheck). Not seen this one before from PSU. Just looking at the colourburst crystal equivalent on this 2013 pcb that's a nice compact alternative to the one's I've sourced.

 

Going off on another related topic I so wish there were modern equivalents to pal antic and gtia chips. (I know the latter we have Sophia 2 as a drop in replacement with optional enhancements, and that someone had created an antic replacement as a proof of concept, but it's not available to buy). 

 

I've mentioned it before but finding Antic PAL chips especially is so hard in the UK. It's tough enough finding pal gtia's. 

 

Anyway, very happy I can convert my previously redundant ntsc personality boards.