800 XL with Bad Memory -- Will U1MB upgrade fix this?

[BrainSlugs83]

Question is in the title -- I just came into possession of an 800 XL, and hacked together some video / power cables and the thing boots up to the self diagnostic, passing for ROM, failing for most of RAM.

 

I'm aware that I can desolder and replace the RAM chips; but is that necessary if I plan to install the U1MB upgrade? -- Does that disable the onboard memory anyway, or do I need working base memory for the U1MB to work?

 

Also, if I do need to replace the RAM -- in 2023, what is the most compatible / easiest to source RAM chips to replace it with?

 

Thanks!

[Peri Noid]

U1MB needs correctly working base RAM to operate. But you can mount a SRAM module instead of your regular DRAM, if you want. Or you can fix your 800XL's RAM first. 

Edited March 11 by Peri Noid

[_The Doctor__]

Most things need some base ram to start. That aside, it depends on the failure mode. Shorted ram chips can stress a machine and sometimes prevent this or that upgrade from working. In my humble opinion, it is always best to fix a machine fully before doing upgrades. Once that's done, it's up to the person if they want to remove stuff, but I add the caveat to keep the part in the case so when it needs parts you have them. Countless times people move upgrades to other machines or the upgrade fails and then they are screaming where can I find this hard to locate, unobtainium or expensive part.

Edited March 11 by _The Doctor__

[BrainSlugs83]

Quote

Shorted ram chips can stress a machine and sometimes prevent this or that upgrade from working.

 

Yeah, I mean... I was going to remove the bad chips... Just wasn't sure if I needed to replace them or not.

 

I see there is a module on Lotharek called SRAM 64Kb v3 -- that seems to be compatible with the U1MB, and is meant to "replace base ram of 64KB in all 8bit ATARI".  So maybe I'll go that route.

 

That way I can just remove the old chips, and install this modern 64kb SRAM instead.

(Is that crazy? -- Am I missing something important here?)

Edited March 11 by BrainSlugs83

[Beeblebrox]

As others have said, you need the base ram (64k) working before U1MB is installed.

 

Either remove old ram chips, socket and replace, or as mentioned by another, install the Sram 64k module, then install U1MB. (Also if installing the latter, you may as well socket 74LS08 and replace with 74F08 as a know stability fix generally for U1MB and - if considering a purchase, the SIDE3 cart).

 

Fyi the 64k sram (this is a UK reseller but their are other resellers stocking these):

 

https://retrolemon.co.uk/atari-8bit-upgrades/114-sram-64kb.html

 

 

 

 

Edited March 11 by Beeblebrox

[woj]

Regarding the SRAM module, there are at least two recent cases, one of them mine, where the SRAM module did more bad than good on an U1MB setup.

[Beeblebrox]

Personally if you have the skills, socketing and replaing the ram chips with (non Mt ram) chips is a preference, over the sram  option. 

[flashjazzcat]

1 hour ago, woj said:

Regarding the SRAM module, there are at least two recent cases, one of them mine, where the SRAM module did more bad than good on an U1MB setup.

Yes: there's a concerted drive from certain quarters to 'fix' the timing of the Atari motherboard for the benefit of 'certain upgrades' and peripherals, but what's generally being overlooked is the effect major changes to the memory bus and system clock have on components which already worked quite happily without any tweaks. 

[BrainSlugs83]

Dang, wish I had seen that yesterday.  I already ordered the SRAM module. -- I was honestly thinking of just proceeding with that for now without the U1MB...

 

I can socket and replace the chips instead if that makes more sense... but I will need to crack it open tonight and see what's inside, and do some cleaning on the device as a whole anyway...

 

I've read that some of the chips have a refresh of 128 or 256 cycles and that 256 cycle refresh chips are more compatible... Is that still considered true? -- What is the common wisdom around selecting replacement DRAM chips?

[woj]

2 minutes ago, BrainSlugs83 said:

Dang, wish I had seen that yesterday.  I already ordered the SRAM module. -- I was honestly thinking of just proceeding with that for now without the U1MB...

With no U1MB it should work just fine, I think?

[Beeblebrox]

3 minutes ago, woj said:

With no U1MB it should work just fine, I think?

yup. I think so.

 

I'd still go with the U1MB though.

 

[RodLightning]

26 minutes ago, BrainSlugs83 said:

I've read that some of the chips have a refresh of 128 or 256 cycles and that 256 cycle refresh chips are more compatible... Is that still considered true? -- What is the common wisdom around selecting replacement DRAM chips?

 

I would buy any brand of 4164 dram except Micron (MT) brand.  They have a reputation for high failure rate and were the cause of many premature deaths of Atari XL especially XE.

There are different stories of why, but I believe the one about Atari Corporation specifically being sold a large factory run of poorly constructed chips, which were installed in the second and third generation 8-bits.  If any of that bad batch was sold to and used by other companies, I have never seen any confirming evidence.  This topic has been discussed at length over the years. 

 

So yeah, avoid MT-ram.  Brands like NEC, OKI, TMS (Texas Instruments), etc. seem to have a good reputation for longevity.

 

Edit:  Oh, and as for ram refresh rate, faster chips generally coexist in 8-bits with no issues. They are just rated to tolerate higher refresh speeds.  They used to cost a little more back in the day.  I think 256 was the Atari 8-bit spec.

Edited March 12 by RodLightning

[ClausB]

5 hours ago, BrainSlugs83 said:

I've read that some of the chips have a refresh of 128 or 256 cycles and that 256 cycle refresh chips are more compatible... Is that still considered true?

128 cycle 64K DRAM chips are more compatible because some 800XLs have the older ANTIC with 7 bits refresh addressing.

[BrainSlugs83]

16 hours ago, ClausB said:

128 cycle 64K DRAM chips are more compatible because some 800XLs have the older ANTIC with 7 bits refresh addressing.

er... Wouldn't that make 256 cycle dram more compatible? -- i.e. a 256 cycle chip on a 7-bit refresh counter would just cause the dram to be refreshed twice as often as it needed (and that would be fine and in spec), but if you used a 128 cycle chip on a newer machine that happened to have an 8-bit refresh counter... it would be refreshed only half as often as it needed to be? (i.e. you could use a 256 cycle chip anywhere, but a 128 cycle chip would only work on a machine with a 7-bit counter?)

Edited March 13 by BrainSlugs83

[olix]

How do i know, if the ram is a 128 or a 265 cycle refresh type?

[ClausB]

9 hours ago, BrainSlugs83 said:

er... Wouldn't that make 256 cycle dram more compatible? -- i.e. a 256 cycle chip on a 7-bit refresh counter would just cause the dram to be refreshed twice as often as it needed (and that would be fine and in spec), but if you used a 128 cycle chip on a newer machine that happened to have an 8-bit refresh counter... it would be refreshed only half as often as it needed to be? (i.e. you could use a 256 cycle chip anywhere, but a 128 cycle chip would only work on a machine with a 7-bit counter?)

No, the 7-bit ANTIC would only refresh half of a 256 cycle DRAM, so the other half would fail.

[ClausB]

6 hours ago, olix said:

How do i know, if the ram is a 128 or a 265 cycle refresh type?

Gotta look at the data sheet.

[olix]

Did I understand correctly that the number of reresh cycles (128 or 256) only plays a role with DRAMs?

So if I use a 64K extension with SRAM, like the one from Lotharek, it shouldn't matter whether I use the older ANTIC with 7-bit refresh counter or the newer one with 8-bit refresh counter? Is that right?

[ClausB]

21 minutes ago, olix said:

Did I understand correctly that the number of reresh cycles (128 or 256) only plays a role with DRAMs?

So if I use a 64K extension with SRAM, like the one from Lotharek, it shouldn't matter whether I use the older ANTIC with 7-bit refresh counter or the newer one with 8-bit refresh counter? Is that right?

Yes. It doesn't matter unless you're replacing faulty DRAM chips.

[_The Doctor__]

be aware some s-ram mods don't play well with some upgrades now and possible new ones in the future.