XEGS Memory Upgrade Extra RAM Check

[gilsaluki]

Performed the Innovative Concepts-developed 128K upgrade to the XEGS using the custom chip and off-the-self parts (chips and sockets). All went fairly well. It loads all the 64K (and below stuff) okay. Carts work, Missile Command fires up without the keyboard, etc. It will start to load Extended RAM programs, but will simply hang up and free towards the end of the loading process. I ran a Memory Check holding option. All the Basic (48 blocks) check out. Then it very quickly runs through the four large RAM Blocks on the lower row (telling me it is behaving like a 130XE), but they are RED. So, I have a computer that is behaving like a 130XE, but the 4 RAM Banks are RED. One thing I forgot to do, which the late Mathew Ratcliff suggested, is test my new RAM chips out prior to using them. Do you guys think I have installed or damaged the RAM chipped I have piggy-backed on. By the way, I used (from the same lot) four new RAM chips (41464s). It was easier to cut out the old RAM chips that to try and desolder them. So close, yet so far on this upgrade.

[Mathy]

Hello gilsaluki

 

If all 4 RAM banks of the memory expansion are red, there's probably something else wrong. You used four new RAM chips. Of those, the two used for main memory would be OK, but those two used for extended memory would be damaged. That's possible, but highly unlikely. You probably made an error somewhere while installing the upgrade.

 

Sincerely

 

Mathy

[gilsaluki]

Thanks Mathy. I agree think you are right. The Custom Chip (130 GATE ARRAY) is probably telling the OS it is a 130XE, which is detected by a 130XE specific program I have--but something down stream is wrong, preventing access to the extended RAM. Probably some solder connection somewhere.

[Rybags]

Maybe a bad connection to chip select. Generally ext Ram detection writes a set of values to different banks then readback will confirm what's available.

If you have an EMMU or equivalent setup then you'll either get the extra Ram or an empty hole which could be interpreted as being 130XE compatible.

[gilsaluki]

It's looking for extended RAM, but they show RED (4 large blocks at the bottom) when the memory check is performed. Not sure where to start looking.

[Mathy]

Hello Rybags

 

IIRC the Innovative Concepts upgrades used the CO25953 that Atari used in the 130XE.

 

Sincerely

 

Mathy

[Mathy]

Hello gilsaluki

 

You're best bet would be to check out all the connections between the CO25953 and all it is connected to.

 

Sincerely

 

Mathy

[gilsaluki]

Whew! Found the issue. Using a jeweler's loop (magnification device) I found (1) one leg of a piggy-backed RAM chip which did not make good contact with the lower chip. I carefully checked the rest of my installation, this is all I found to be wrong. It check out! All four RAM banks turned Green and Atariwriter Plus (130XE version booted) as well as my 130XE GigaBlast game. Success. Now for the lessons-learned for this upgrade. First; NOT for the faint of heart. The only reason I risked it is, I had a spare XEGS board. I used fairly stiff hook-up wire, maybe too stiff. I broke the #23 pin on the Freddie chip after I was done (moving other wires around). Luckily there was a slight nub which I was able to solder the required wire onto. Take your time, this is critical. Use a good soldering iron and desolder device. I could not get the old RAM chips free from the board. I know I damaged the VERY THIN circuit pads on a few. I would always suggest buying (4) four new RAM chips (41464), and cut the old chips off the board. This greatly simplifies the removal stage. Use heat shrink between the pins on the Custom Chip (available from BEST and B&C for about $10). Solder all the wires on the Custom Chip first, before piggy-backing it on to the boarded chip; this will greatly simply your task. It is very close quarters. Did I mention to use a very fine soldering tip. Again, very close proximity to other components and pins. I would also take Matt Ratcliff's suggestion to test your RAM chips prior to piggy-backing them. The instructions here on this site are good, a few typos. Matt's diagram does not show Pins 7&8 soldered together, they are. It took me 8 hours to do this upgrade. Much more than others have reported. I am a fairly novice solder jockey, which may explain the time. Would I do it again. NO! It is nerve-racking even though I knew I had a backup XEGS Board. I just hate trashing what is now getting hard to find, good XEGS'. I think I am done with self-improvement projects. From now on, I will pay a professional--where ever they are.

[gilsaluki]

Thanks, Checking the Custom Chip (C025953) and the RAM chips themselves helped me find my issue. Thanks to everyone here for the advice. A great upgrade, but skill and patience is needed.