64KB SRAM updrade 800XL

[deffroe]

Tonight I am Confucius's lesser relative. Confused!  I've purchased a couple of these and have had a go at installing one tonight.  The Step-by-step guide is as follows,

 

• remove old RAM chips (hint: this is actually not necessary; if your RAM chips do not get hot, you can remove resistors on data lines to RAM and keep chips intact) 
• install SRAM module under main CPU
• insert CPU to SRAM module
• Please refer to VBXE fitting manual to locate following signals on your motherboard:
  • EXTSEL (EXT solder point on the SRAM module)
  • CasInh (CI solder point on the SRAM module)
• Make at least one connection between CI point on the SRAM module  to  CAS_INHIBIT signal on Atari motherboard
• EXT / Extension Select - EXTSEL signal is not needed to boot up the Atari, but some upgrades may needed it, especially all PBIs connected expansions: Rapidus, VBXE with RAM cores, etc
• Pin 1 of the SRAM module is below IRQ_VBXE hole; bottom left on the picture.

 

Following point 4, refer to VBXE to locate EXTSEL and CasInh,

 

According to the table for 800XL(NOT XLF) they are located on U18 pins 9 and 10.

I have followed this but get no video signal, I've checked for voltages around the board and get 4.9V which is acceptable.  Now looking around the web which has mainly shown 600XL's and the sample image of an 800XL from the sellers website, which is the same on Brerwing Academy and Lothoraks, it shows only CI but going up to the MMU.  Which on is correct? Image or instructions?

 

 

[BillC]

44 minutes ago, deffroe said:

Now looking around the web which has mainly shown 600XL's and the sample image of an 800XL from the sellers website, which is the same on Brerwing Academy and Lothoraks, it shows only CI but going up to the MMU.  Which on is correct? Image or instructions?

EXT / Extension Select - EXTSEL signal is not needed to boot up the Atari, but some upgrades may needed it, especially all PBIs connected expansions: Rapidus, VBXE with RAM cores, etc

[deffroe]

1 minute ago, BillC said:

EXT / Extension Select - EXTSEL signal is not needed to boot up the Atari, but some upgrades may needed it, especially all PBIs connected expansions: Rapidus, VBXE with RAM cores, etc

Hi BillC, I did see this, I am planning to add VBXL and U1MB at a later date so am connecting EXTSEL while I'm at it.   But regarding CI, does it go to U18(74LS08) or U3(MMU)?🤯

[BillC]

12 minutes ago, deffroe said:

Hi BillC, I did see this, I am planning to add VBXL and U1MB at a later date so am connecting EXTSEL while I'm at it.   But regarding CI, does it go to U18(74LS08) or U3(MMU)?🤯

According to the table included in your post both EXTSEL and CASINH connect to pins 9 and 10 of U18 respectively.

[deffroe]

Had a little time to play about with this a bit more.  In my case, following the instructions to follow the instructions in the VBXE fitting manual🤯, where it...instructs that CASHINH is on pin 10 of U18 did not work.  

Success is achieved by connecting to pin16 if the mmu chip.

[svhovater]

I installed it this weekend in a 65XE. Machine has U1MB and SophiaII - and Side3. Prior to the installation, I kept getting machine lockups and garbage on the screen.

I removed all the RAM chips, their resistors, and connected the EXTSEL and CASINH to Freddie pins 3 and 4.

This resolved the lockup and garbage (I'm assuming it was a RAM issue), but trying to enter the Side3 loader (updated to latest firmware), I get black screen.

The PBI disk functionality via U1MB is working.

 

One thing at a time, I guess. 

 

[Peri Noid]

Replace the 74LS08 with a 74F08. There's only one such chip on a notherboard, you cannot make a mistake.

 

[Beeblebrox]

2 hours ago, svhovater said:

I installed it this weekend in a 65XE. Machine has U1MB and SophiaII - and Side3. Prior to the installation, I kept getting machine lockups and garbage on the screen.

I removed all the RAM chips, their resistors, and connected the EXTSEL and CASINH to Freddie pins 3 and 4.

This resolved the lockup and garbage (I'm assuming it was a RAM issue), but trying to enter the Side3 loader (updated to latest firmware), I get black screen.

The PBI disk functionality via U1MB is working.

 

One thing at a time, I guess. 

 

where are you based?

 

Yup, as Peri Noid advises defo install the 74F08 in place of the 74LS08 and see how ya go. They are diret cheap. I always carry a stash of them.

[svhovater]

already have a 74F08 installed.. I'm in New Hampshire, near Manchester.

[Beeblebrox]

25 minutes ago, svhovater said:

already have a 74F08 installed.. I'm in New Hampshire, near Manchester.

Sure. OK next is the cpu. I had a 65xe the other day with various issues of instability with side3. I swapped out the existing cpu and tried 2 x different cpus which seems OK in other machines and whilst the first of these still showed instability, the second worked. Also worth checking your gtia chip isn't failing. Had this as cause of so much instability in many machines. 

 

Unfortunately XE's are not socketed so it's not so straightforward with chip swapping. 

 

Watch some of Flashjazzcat's recent videos as he covers troubleshooting an XE. 

 

 

Edited July 24, 2023 by Beeblebrox

[svhovater]

It appears that EXTSEL on Freddie is tied to +5 - which makes sense, since there's no expansion port.

 

Odd thing is that the Side3 worked as both "disk" and loader, before this upgrade. I'm concluding that EXTSEL isn't needed to support Side3.

(snip) EXTSEL from Freddie to the 64KB SRAM unit removed. Behavior remains.

I'll be looking at CPU's next, per Beeblebrox's suggestion.

[flashjazzcat]

1 hour ago, svhovater said:

Odd thing is that the Side3 worked as both "disk" and loader, before this upgrade.

I read above that you were initially experiencing lock-ups, garbage on the screen, and the loader plunging you into total darkness. By 'this upgrade', do you mean the 64K SRAM board? The symptoms you described, anyway, aren't symptomatic of RAM problems, but of timing issues normally rectified by 74F08 (progressing then to the CPU, etc, as previously advised, if problems persist) when the original base RAM is still present.

 

The 64K SRAM board (along with the '02 Fixer', an example of which I was promised for evaluation some weeks ago, but which hasn't showed up yet) was supposed to - among other things - rectify SIDE3 stability issues, but it seems that hasn't been the case here (unless I'm reading the situation wrongly).

17 hours ago, Beeblebrox said:

Watch some of Flashjazzcat's recent videos as he covers troubleshooting an XE. 

Follow-up on that one: the machine went back to the owner he confirmed (as per my experience) that only the original SIDE3 (not SIDE 3.1) worked, even after the usual stability fixes were implemented. In addition, he encountered issues flashing U1MB (which were entirely un-reproducible here, since I flashed the entire 512KB of the U1MB ROM on camera without any issues at all). That was quite the challenging XE, then.

Edited July 25, 2023 by flashjazzcat

[Beeblebrox]

@svhovater  Could you perhaps upload an image of the 64k Sram board with the CI wire hooked up. Are you soldering a wire both ends, (one from the 64K solder point to the Freddie pin 4), or have you installed a dupont header connector on the Sram pcb?

 

I am not sure if it could be a factor or not but just asking to ensure the CI connection is 100%

 

Also are you 100% happy with any sockets you have needed to install on the XE PCB?

[svhovater]

Well.. pulled out the jeweler's loupe and inspected the soldering job I did on the CPU socket. Apparently, using my old bulb-solder sucker, I had nicked a trace.

Repaired. Side3 loader working now.

 

Egads. What a klutz. 

Thanks all for the suggestions.

[Beeblebrox]

glad it's sorted.