800XL, Lotharek 64K SRAM module, and U1MB

[+x=usr(1536)]

My daily-driver 800XL has, after some lengthy troubleshooting, what I believe to be a bad CO60472 delay line IC.

 

One of Lotharek's 64K SRAM modules is laying around, and I could use that - except that I intend to install a U1MB at some point, and my understanding is that both the MMU and delay line IC need to be functional in order for it to work.  Because the SRAM module effectively bypasses them and provides its own, I'm not certain that the U1MB will work with it.

 

Can anyone confirm if the above is correct?  I've looked but haven't run across a definitive answer.

 

Also, if anyone knows of a pre-built delay line replacement seller in the US, please let me know.  I'd like to have at least one on hand as a spare regardless.

[Beeblebrox]

@x=usr(1536)  I believe it will work if you install the 64k SDRAM first (which provides the delay line functionality and works - I believe - without the need for the MMU). Which will then let you install the U1MB which obviosuly replaces the MMU as part of the install.

 

See this thread:

 

 

 

[+scorpio_ny]

Hi @x=usr(1536),

 

Options to get this part is pretty limited. One option is to get one from Best Electronics.  Another option is to get another of Lotharek's 64K RAM module. The Brewinging academy sells them here in the states. Another option is to get it from EBay but, the seller is not based in the USA. I had ordered some from this seller on EBay. This is the modern replacement based off the project that you linked. It took a while, but I did get them. 

[+x=usr(1536)]

12 minutes ago, scorpio_ny said:

Options to get this part is pretty limited. One option is to get one from Best Electronics.

Yep, and they were my first port of call.  Problem is, I just don't need enough other stuff from them right now to make up a minimum order.

12 minutes ago, scorpio_ny said:

Another option is to get another of Lotharek's 64K RAM module. The Brewinging academy sells them here in the states.

This is the one I currently have   The situation I'm running into is that this machine has a 256K RAM expansion installed, and I don't believe that it will be compatible with the SRAM board because of its on-board 64K of RAM.  My thinking is that I can just pull the 256K DRAMS, install the SRAM module and U1MB, and call it done - maybe.  I'm not opposed to replacing and keeping the delay line in place, but that would be more for compatibility with the 256K expansion and / or U1MB than anything else.

12 minutes ago, scorpio_ny said:

Another option is to get it from EBay but, the seller is not based in the USA. I had ordered some from this seller on EBay. This is the modern replacement based off the project that you linked. It took a while, but I did get them. 

Good to know, and thanks.  I did see his auction and was thinking about that in lieu of ordering from Best, so may keep him in reserve as an option.

[+x=usr(1536)]

2 hours ago, Beeblebrox said:

@x=usr(1536)  I believe it will work if you install the 64k SDRAM first (which provides the delay line functionality and works - I believe - without the need for the MMU). Which will then let you install the U1MB which obviosuly replaces the MMU as part of the install.

That was my thinking - the U1MB shouldn't care about where the MMU or delay line are, as long as they're present.

2 hours ago, Beeblebrox said:

See this thread:

 

 

That was one of the ones I had run across in looking into all of this.  Knowing the differences between 600XL and 800XL memory management, it wasn't totally clear to me if that would apply to the 800XL or not.  I think it might; may as well give it a shot and see how it goes 

[Peri Noid]

SRAM and U1MB cooperate without any problem. Nothing to worry about. 

[Teapot]

I just installed the combo back in November. Works fine.

 

I needed the SRAM because there was a destructively failed install of a RamboXL in the machine by a previous owner. I removed the Rambo board and the DRAM ICs. U27 is now empty because the Rambo was plugged in there and the circuitry is no longer used. Connected the U1MB directly to the v3 SRAM board solder pads.

[+x=usr(1536)]

1 hour ago, Teapot said:

I just installed the combo back in November. Works fine.

 

I needed the SRAM because there was a destructively failed install of a RamboXL in the machine by a previous owner. I removed the Rambo board and the DRAM ICs. U27 is now empty because the Rambo was plugged in there and the circuitry is no longer used. Connected the U1MB directly to the v3 SRAM board solder pads.

 

Perfect, thanks.  This is the exact situation I'm facing (except that it's self-inflicted in my case), so good to know it'll work.  If you're interested in the full history of the problem (and there's plenty of it), check out this thread.