Hi,

I am working on placing a 1 mb simm into a nms 8250 according to instructions posted on Hans Oranje and Hans Ottens website.
First thing I did was taking out the ram chips and after that I tested the machine if it still worked. Replaced the ram chips with sockets and the machine is still in perfect shape.
Then I placed the extra ttl logic ICs into the machine and connected the simm.
When switching it on it gives the relais click so something is wrong.
I then tried to start with external memory which did not work.
Removed the simm and booted with external memory and everything works.
Even with 2 ram chips placed in the sockets with the mapper circuit still intact the machine boots.
What could be wrong? I don't know of the simm is working, purchased 4 cheap ones and according to seller they should work ....
Can try another one but don't think it will work. Is there any way to test the mapper circuit for the simm without placing one?

If necessary I can show a picture of the used simm.

Erik

i tried making that thing once too (last year)
also a klick

of course im not sure but i wouldnt be surprised if that schematic isnt right/oomplete/errorenous

I know, I have read your post.
My click only comes with the simm connected. Without the simm but with the rest of extra ICs and internal or external (512Kb cartridge) it works fine.
I want to try to get a 30 pin simm connector so I can try easily with multiple simms. Saves me the pain of soldering the wires over and over again
But I have difficulty finding a 30 pin simm connector. Is there anyone who has such a connector?

are you sure you have connect the Simm with the good pin direction and don't reverse it

can you post the schematic that you use or a link

in a 8250 you can use 70ns 80ns and 100ns with a Simm 3 , 8 or 9 chips

Quote:

I know, I have read your post. My click only comes with the simm connected. Without the simm but with the rest of extra ICs and internal or external (512Kb cartridge) it works fine. I want to try to get a 30 pin simm connector so I can try easily with multiple simms. Saves me the pain of soldering the wires over and over again But I have difficulty finding a 30 pin simm connector. Is there anyone who has such a connector?

the width of the pins on a 30 pin memory stick are the same as a regular ISA slot

find an old mobo with isa slot at take it out?

you can desold it on a very old PC
30 pin is easy with a desolder pump

I used this a source: http://www.hansoranje.nl/downloads/1mbnms8250.pdf but it is in dutch.
Over here is an english translation: http://msx.retro8bits.com/msxdocs/1mbnms8250e.pdf

Well the 1 and pin 32! is marked on the simm (don't know why it has 32 pins though ...)
I know I can desold it from an old pc, but I do not have one around. I might have a 30 pin simm slot at work I can try

if you have 32 pin is not a standard Simm memory !!

which is the marked reference on your pseudo Simm ?

I know, never seen a 32 pins simm and do not believe it is a real 32 pins.
What do you mean with marked reference?
I can post a picture of both sides if that helps

yes post a picture

boy I feel stupid. I purchased 4 simms thinking they were all 30 pins. Guess what. 2 are 32 and 2 are 30 pins. I just took one out of the bag and that was the 32 one.
Now I installed a 30 pins and the computer starts again!!
I wish my problems were now solved but another one came around the corner.
I cannot boot with my sunrise CF adapter. Could this be due to the fact that only 64Kb is recognized?
I am trying to start testram.com to see how much memory is installed but I cannot start msx-dos ...
Also tried with a floppy, does not work either. Must confess that I only tried with boot floppy from 2.40.

At least the computer now works with the simm so the schematic does work

NICE!!!!


shit
now im am compelled to try and make it again


hehe
it got the remains of my first try still sitting under me bed
hehehe

Update, I got testram working and it finds 1024 Kb. When doing the mem test option it hangs at page 55.
Now I need to find out what is not working properly....

maybe memory stick is faulty ?
tried another one?

I have not tried another one, hope to have a socket for the simm tomorrow so I can swap easily.
Have only one more simm left...
Still looking into the schematic to see if I made an error somewhere