Jump to content
IGNORED

7800 Dev Units...


-^CrossBow^-

Recommended Posts

Anybody out there who maybe has undertaken this procedure. To those people...I have a few questions.

 

I recently received a new Bios for my 7800 containing the DevOS burned into. I then took it upon myself to make the other needed modifications to my 7800

 

However, of course it didn't work. All I would get when turning the unit on was multi colored bars...same thing that happens when you remove the bios chip out of the unit and turn it on. I rechecked all my connections...etc. and all seemed just as the PDF documents. But now a few questions.

 

On the SRAM 74SL04 that has to be piggybacked onto the SL08...what do we do with pin 14? The PDF mentions to soldier down pins 1 and 7 to the SL08..bend up pin but that is all. It does state to bend up the other pins of course...but never mentions 14??? Anyone know?

 

Also..on the bios chip itself...is all that needs to be burned in the last 4k of the chip..just the DevOS file...or do you burn the DeVOS bin in to the chip...and then burn a copy of the 7800 bios itself into the last 4k? I believe that the chip I have may only have just the DevOS burned into it. Even then, I am not sure if it is at the first of the chip segments...or actually in the last 4k. Without access to an eprom burner myself...I cannot verify the chip.

 

My suspicions are that the chip wasn't burned proper or that it all has something to do with that stupid pin 14.

 

Anybody enlighten me as to what could be wrong?

 

 

 

CB_Sig.gif

Link to comment
Share on other sites

I haven't done this modification myself since I own a PAL console, but maybe I can help you anyway.

 

In step 5 it should read "Solder down pins 1, 7 and 14. Now bend up pin 8."

 

DEVOS02.BIN should be burned into the last 4K of an 8K, 16K or 32K EPROM. What's in the lower parts of this chip doesn't matter at all. Remember to follow step 4 of the instructions if you are using a 4K EPROM chip.

 

 

Ciao, Eckhard Stolberg

Link to comment
Share on other sites

Eckhard,

 

Thank you for clarifying Pin 14 for me. I might try and do it again tonight...although I already repaired the broken trace..etc. But it wouldn't take me as long now that i don't have to map out the exact pin locations anymore. BTW...I would not only add that missing step about the pin 14...but also..add that after removing the "Resistor-like" jumper from the W2 location...that it is much easier to add it to the bottom of the console board..rather than mess with the everything else in your way.

 

BTW...ever heard of a 7800 that has all the ICs in sockets already?! mine does...

 

it already had the socket in there for a 28 pin chip...but nothing else had been done.

 

also my 7800 is a Rev A 001 unit...hehe...I love it..

 

 

 

PS...where do I get the DevOS02.bin file? It isn't in the devkit.zip I grabbed from Dan a while back...

 

Thanks

Link to comment
Share on other sites

Yes, I think we really should update the documentation sometime.

 

BTW, a good deal of the PAL 7800s have most of their ICs socketed. They also were designed to work with the BIOS on an EPROM right from the start. If your PAL 7800 comes with a normal ROM, you just have to move one of those resistor like jumpers and it would take an EPROM instead.

 

I think you meant that you got the first version of the devkit from one of John's sites, right? Anyway, the second version can be found on my site atbuerger.metropolis.de/estolberg/

But it could use an update too.

 

 

Ciao, Eckhard Stolberg

Link to comment
Share on other sites

  • 3 weeks later...

Hi,

 

My PAL 7800 has the ROM chip in a socket (With build-in Asteroids).

Unfortunately the SRAM chips are not in a socket but are placed on some kind of riser board containing the SRAM chips and some resistors. The problem is that the riser board hangs above the ROM chip. Thus to replace the ROM chip, I have to desolder the SRAM riser board .

 

Has anyone an idea why the ram is placed on a riser board instead directly on the board?

 

Regards,

 

Robert

Link to comment
Share on other sites

These boards came near the end of the 7800's production life. I suppose it was just cheaper to use RAM chips in the small packaging and put them on a riser board, than it was to use RAM chips in the normal packaging or to design a new board.

 

BTW, your BIOS chip is probably a normal ROM instead of an EPROM, which means that you'd have to move a jumper to turn your PAL 7800 into a dev system.

 

In the lower right corner of the board are some resistors. Among them are the jumpers W5 and W6. One of them should be empty while the other is bridged with a resistor like component that only has a black ring. To make the PAL 7800 work with an EPROM BIOS chip, W6 has to be open and W5 must be closed. If this isn't the case, you have to solder out the black ring component from W6 and put it into W5.

 

 

Ciao, Eckhard Stolberg

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...