What kind of RAM upgrade is this?

[flashjazzcat]

I've just taken apart a 130XE I recently received and discovered this wiring on the underside of the board:

 

 

The second bank of RAM is socketed, and if this wasn't originally a 65XE (it's in a 130XE case), the chip removal and socketing has been expertly done. Only half the extended bank is populated (with drams marked D4164C), but I think I have suitable chips to fill the other four sockets. The motherboard is also missing some major ICs, but fortunately all the vacant slots are socketed and I have suitable replacements for those too. I'm just not sure how much RAM this thing will have when I power it up!

 

Note also the various jumpers, such as the ones between the OS ROM and BASIC.

Edited March 27, 2010 by flashjazzcat

[Rybags]

On an 8 or 16 chip board, you must have the first, or both columns populated with RAM chips, otherwise it won't work.

 

Each chip in a column supplies 1 bit of each byte, so all chips in a column are always active for a relevant RAM access, ie normal 64K or extended.

 

The 65XE on a 130XE board upgrade to 128K isn't just plug & play - fairly sure some extra work is required.

That work looks... strange. I thought the only thing needed for the extra RAM was patching in an extra CAS line or something similar.

[flashjazzcat]

Well, on closer inspection it was obvious that these were 64kbit DRAMs, so I just took out the four that were in the sockets and replaced them with eight DRAMs from an old 65XE to 130XE upgrade kit. I also fitted FREDDIE, GTIA and OS ROM. When powered up, the machine displays a white screen with yellow bars running down it. I've tried a different OS ROM and reseated the RAM. I can't see what the two jumpers between the OS and BASIC are for, but temporarily disconnecting them made no difference. I noticed the BASIC ROM's socket is pretty crooked. All the ancilliary wiring around the RAM... I can't understand why that's there, unless this machine had a 512K upgrade fitted once upon a time, and chips were removed.

 

65XE to 130XE requires the EXTMMU and a couple of other bits of soldering apart from the RAM and caps IIRC. I'm inclined to wonder if simply removing all the extra wiring will yield a working 130XE. Surely the cabling isn't patching broken traces: the jumpers are profuse, and the original socketing for the most part looks reasonably competent.

Edited March 27, 2010 by flashjazzcat

[Rybags]

Jumpering OS to Basic just sounds wierd and wrong... unless somehow a bus line is bad on one of them.

 

Maybe your best course would be to get it working as a 65XE first, then work up from there.

 

I'm fairly sure that regardless of OS, it doesn't know or care if the extra 64K is present or not... it's only in the later OS version that the Self-Test will detect and test the full 128K.

 

Of course, having a system wired for 128K but not having the chips present or properly wired might cause problems in itself.

 

The other consideration is that the 128K system needs the later Antic "E", to provide the extra refresh row selects. Some upgrades implement that functionality with extra logic chips.

 

 

ed - it might also be worth a shot seeing if you have a Diagnostic type game cartridge (Star Raiders comes to mind).

These are run directly by the OS, and on problem machines can often still work even if a ROM is corrupt or the machine has other problems.

Edited March 27, 2010 by Rybags

[ClausB]

Surely the cabling isn't patching broken traces: the jumpers are profuse, and the original socketing for the most part looks reasonably competent.

All those short jumpers under the RAM sockets are connections that were already printed on the component side of the board. My guess is that someone damaged quite a few traces while pulling the old chips out and then tried to repair them with those jumpers. Possibly the same case with the other sockets. Take a close look under the sockets on the component side. Are there broken or missing traces? Maybe he missed a few and that is why it won't work.

[MEtalGuy66]

Claus is right.. ALL of those wires are "repairs" to correct broken/lifted traces on the top side of the board where someone did a totally crappy desoldering job..

 

The ones on the OS/BASIC ROMS are as well.. remember that most of the adress & data lines are shared between those 2 roms..

 

That all you got there.. a board that's been repaired after someone did a totally shitty job removing the chips.. I hope to god aftar all that they had the sense to install sockets...

 

Heres one that I am almost finished repairing for someone who THOUGHT he knew how to socket his own board.

 

Folks.. I can't stress this enough... THERE ARE NO MORE ATARIS BEING MANUFACTURED...

 

PLEASE PLEASE PLEASE.... Learn how to solder by practicing on SOMETHING ELSE!!!

Edited March 27, 2010 by MEtalGuy66

[flashjazzcat]

Folks.. I can't stress this enough... THERE ARE NO MORE ATARIS BEING MANUFACTURED...

 

PLEASE PLEASE PLEASE.... Learn how to solder by practicing on SOMETHING ELSE!!!

Hear, Hear!

 

Closer inspection reveals that your analyses are correct: what looked at first like a fairly nifty socketing job actually conceals a mess of missing barelling and lifted traces. A couple of the sockets are pretty crooked, and you can easily see the damage. It's a real shame: I received this Atari for free as a very kind donation, and although I can hardly complain (and I'm sure the donor knew nothing of the mess on the underside of the board), it pains me to see this kind of amateurish work on what is otherwise a pretty good-looking board. Hopefully I'll be able to do the donor justice and get it up and running again (the case is already fifty per cent Retr0Brited!). I now have the choice of stripping out all the sockets and starting again or trying to trace the remaining bad connections with a multimeter and finishing the job someone else started...

 

The overriding question here is why would someone socket the second bank of RAM in a 130XE only to put the same RAM back in the sockets. My theory is that someone was attempting a 320 or 576K upgrade and at the point in the instructions where it says "Power on your Atari now: it should work as normal" - it didn't. The RAM upgrade was at that point abandoned. Presumably the major IC socketing (GTIA, FREDDIE, OS and BASIC) was (ill advisedly) carried out coinstantaneously with the RAM upgrade. Whether the machine ever worked after being patched up, I'm unsure at the moment.

 

My inclination is to replace all the sockets when I have time. It's painful to hear all the de-soldering and chip-removal horror stories: I remember several machines which apparently bit the dust after the VBXE boards shipped out. Even the best of us have been faced with non-working machines after a simple socketing job, but if you proceed one step at a time, at least you know what caused the machine to stop functioning.

[MEtalGuy66]

 

The overriding question here is why would someone socket the second bank of RAM in a 130XE only to put the same RAM back in the sockets. My theory is that someone was attempting a 320 or 576K upgrade and at the point in the instructions where it says "Power on your Atari now: it should work as normal" - it didn't. The RAM upgrade was at that point abandoned. Presumably the major IC socketing (GTIA, FREDDIE, OS and BASIC) was (ill advisedly) carried out coinstantaneously with the RAM upgrade. Whether the machine ever worked after being patched up, I'm unsure at the moment.

 

My inclination is to replace all the sockets when I have time. It's painful to hear all the de-soldering and chip-removal horror stories: I remember several machines which apparently bit the dust after the VBXE boards shipped out. Even the best of us have been faced with non-working machines after a simple socketing job, but if you proceed one step at a time, at least you know what caused the machine to stop functioning.

 

The answer is that the RAM in those machines is GARBAGE and is notorious for going bad..

 

Dont bother fixing that mess.. Its real easy to replace the entire "bank" of all that ram with a 30 pin SIMM. and it will come out with less wiring and much neater. If you desolder those sockets a second time, chances are that even more traces will delaminate and youll end up rewiring the entire extended ram address bus at a minimum. USe a 30 pin simm. all you have to do is hook up ONE set of connections, rather than 8 sets.. and the SIMM will lay flat, taking up no more space than the original chips did.. Just my advice..

Edited March 27, 2010 by MEtalGuy66

[flashjazzcat]

The answer is that the RAM in those machines is GARBAGE and is notorious for going bad..

 

Dont bother fixing that mess.. Its real easy to replace the entire "bank" of all that ram with a 30 pin SIMM. and it will come out with less wiring and much neater. If you desolder those sockets a second time, chances are that even more traces will delaminate and youll end up rewiring the entire extended ram address bus at a minimum. USe a 30 pin simm. all you have to do is hook up ONE set of connections, rather than 8 sets.. and the SIMM will lay flat, taking up no more space than the original chips did.. Just my advice..

I tend to agree. Lotharek has some nice inexpensive SIMM adapters...