640k mod not working

[josephdaniel]

I did the 640k mod on my 5160 to expand it to 640k using intel p21256-10 RAM chips in banks 0-3. Fot the line selsctor.data multiplexer chip I used a Texas instruments SN74LS158N that I grabbed off eBay. My question is, where is the jumper supposed to go? E2-1 seems to be a square solder pad and I don't see any traces going to it. E2-2 actually is a hole and has a trace from the mother board going to it. If anyone could enlighten me ast o the placement of the jumper that would be great!

 

[Al Hartman]

Did you see this?

I might try this on my own board.

http://www.textfiles.com/computers/xt-640k.upd

 

[Stone]

Did you see this?

I might try this on my own board.

http://www.textfiles.com/computers/xt-640k.upd

I believe that's what he was using.

 

[modem7]

I did the 640k mod on my 5160 to expand it to 640k using intel p21256-10 RAM chips in banks 0-3.

Only two of the banks get upgraded to 256k bit chips.

 

[modem7]

If anyone could enlighten me ast o the placement of the jumper that would be great!

Photo of E2 of my 640K motherboard.

 

[Stone]

Only two of the banks get upgraded to 256k bit chips.

While that is basically correct he hasn't added the required jumper to jumper block E2 yet.

 

[modem7]

While that is basically correct he hasn't added the required jumper to jumper block E2 yet.

The OP had already upgraded all four banks of RAM: "I did the 640k mod on my 5160 to expand it to 640k using intel p21256-10 RAM chips in banks 0-3"

 

[Stone]

The OP had already upgraded all four banks of RAM: "I did the 640k mod on my 5160 to expand it to 640k using intel p21256-10 RAM chips in banks 0-3"

Yes, he added the necessary (and not necessary) chips but not the required jumper.

 

[SGTSQUID]

What they said. Only upgrade banks 0 and 1, and the jumper on E2. I did this on my XT around 10 years ago and I remember having to do some soldering. I think on mine there were no pins on E2 so I had to solder a jumper there.

 

[Stone]

.....there were no pins on E2 so I had to solder a jumper there.

...or a small piece of wire.

 

[modem7]

Only two of the banks get upgraded to 256k bit chips.

While that is basically correct he hasn't added the required jumper to jumper block E2 yet.

The OP had already upgraded all four banks of RAM: "I did the 640k mod on my 5160 to expand it to 640k using intel p21256-10 RAM chips in banks 0-3"

Yes, he added the necessary (and not necessary) chips but not the required jumper.

"Yes, it is true that Dr. Smith removed the wrong organ from the patient, but he has failed to suture the incision."

 

[Chromedome45]

256k in banks 0 and 1 64k in banks 2 & 3

 

[josephdaniel]

Will having 256k chips in all of the banks cause problems? I just put them all like that because I could and they would all match...

Thanks for clearing up the issue about where the jumper is to go...

 

[Chromedome45]

Well if you short J2 and it boots up then I guess not. But will only use 640k. Could use the 256k chips in something else? Good luck

 

[Stone]

Well if you short J2 and it boots up then I guess not. But will only use 640k. Could use the 256k chips in something else? Good luck

Actually it seems that there is a way to use all the ram, not just 640k. Of course it requires another mod.

http://www.vintage-computer.com/vcforum/showthread.php?28128-HIMEMV2-or-equivillent-PROM

 

[Chromedome45]

Of course there is! 640k is enough! That what Billy Gates said!

 

[Al Hartman]

I got the RAM today, and mt XT is now a 640k unit. Passes BIOS POST, and shows 640k from Norton SI. I also upgraded the unit to a NEC V20. Got 16 pin sockets for my two Lo Tech XT-IDE boards. Once the 20 pin socket arrive, I'll finish the two of them, and then test them in the XT. Hopefully by the weekend.