exxos's Atari, Amiga & retro forum

6 now in store

Will build up some more later in the year when I (hopefully) get a bit more time

https://www.exxosforum.co.uk/atari/store2/#0020

Hi Exxos

Have removed all 16 ram chips but my stfm was only a 512kb unit.

In my attached pic you can see I am missing those 3 resistors at r71 r72
and r73. What values are they exactly?

Have I connected pin 64 from surface mount mmu pin 64 correctly using that
via to make it easier?

The board is just sitting in the holes at the moment for show. Is it better
to solder the pins in directly? Would I be better off putting in 35 pin
sockets to the locations and cutting the pins to keep the board height down
just in case it doesn't power up properly? Is socketing the board more
trouble than its worth as I am sure you have tested the board?

I haven't installed the blitter socket yet with your socket as I just want
to perform one mod at a time just in case the unit doesn't post.

I HAVE successfully socketed the cpu and tested that b4 I attempt to
install the v2.3 accelerator and 1.04/2.06 bios board.

Anyway if you could be of help that would be great.

Thanks

There is detail on the resistors here: http://www.exxosforum.co.uk/atari/last/ram/index.htm

If you look at the 4th picture down it explains what you need. To save you some time they are 68 ohm.

I would suggest that soldering the pins indirectly is your best option, based on the install guide here: https://www.exxosforum.co.uk/atari/last/4mb/index.htm

Whilst sockets do make life easier if you want to take it apart, you will probably never want to, and sockets really can cause no end of problems and instability.

BTW I like your slow but steady approach, troubleshooting is so much harder if you have done lots of things!

As said above, 68R is normal, but I generally fit 33R. I never thought about these resistors when I did the new kits.

Socketing the board will make it to high to fit the PSU back.. and yes everyone is tested for a long time.

Pin 64 is actually for the PLCC chip, I never thought about the SMT... its actually pin 66 on the SMT MMU.

Hi

Thanks for your responses

I have fitted 3 x 38 ohm resistors as thats what I had in stock and sounds like it will be close enough if Exxos was using 33R.

I removed the 4 resistors and have now flush mounted the new 4mb mod right down to the lowest they will permit to get clearance from the psu plate which i covered anyway in plastic laminate just in case. Have left the 1mb/4mb open at 1mb for testing purposes.

Have used Kynar solid core wire and moved the MMU jumper as per photos below to pin 66 ONLY for the Surface Mount MMU as per photos. Exxos does this look right? Finally I havent tested it yet as I broke that damned fragile reset button and have to wait for the Araldite to cure. I enclosed a pic of that fix having to use 3 wire twists to hold back the spring to allow me to glue the button end of the reset button back.

Will let you know after all this if it posts Okay.

Looks OK to me

Yep and Okay it was.

Kludged it back together tonite and up came 1mb of ram and the ram test passed.

I will jumper it to 4mb and retest this weekend and then on to Install the 2.3 accelerator and matching 1.04 and 2.06 rom switcher.

Exxos I also want to solder in that crazy blitter socket in. Ive examined the socket and am assuming the solder bridges I see underneath make no difference as continuity is intentional or of no consequence anyway. You mention cutting out some cardboard to place under the socket to stop vias potentially shorting. Do I just cut out cardboard to fit under the square section butting up to but not going under the inner row of pins?

Well done on this design too so anybody wanting to build the ULTIMATE STFM(Accelerator 2.06TOS and Blitter) now can have 4mb altho I will confirm that amount of ram working soon.

Who needs to get a MEGA anyway

Yeah just keep it like 1mm above the motherboard just to make sure the blitter pcb isn't in contact with the motherboard. some thin card will do fine.

Not good news today.

I jumpered the board into 4mb mode and Sysinfo briefly displayed 4mb. Then the screen briefly displayed corrupt graphics and 4 bombs came up. I had no choice but to reset the machine and then after that all I could get was 1mb of ram to come up in Sysinfo.

Very strange. I have tested the 1024kb of ram that is all that comes up now and there seems to be no fault. What could be wrong with the xtra ram on the board as the 4 bombs and then corrupt gfx on screen occurred when I tried to run the 4mb ram test. Is 1024k the fall back safe mode?

Oh and the jumper on pin 66 on the MMU still seems to be in place okay and I am still on TOS 1. 02 and the original 68000 still sitting in its new socket.

Glad I am doing this VERY slowly. Whadya think I should do?