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Peter Rabitt

520stm inside the cover

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OK, I went to the google way and found the answer on "best-electronics"...

The answer is:

CO26160       ST U.S. TOS 1.0 256K (H2) ROM       
CO26161       ST U.S. TOS 1.0 256K (H1) ROM       
CO26162       ST U.S. TOS 1.0 256K (H0) ROM       
CO26163       ST U.S. TOS 1.0 256K (L2) ROM   
CO26164       ST U.S. TOS 1.0 256K (L1) ROM       
CO26165       ST U.S. TOS 1.0 256K (L0) ROM  

I am assuming this is correct...

Does anyone want or need tos 1.0 roms???

I have read the best TOS for ST520 is TOS 1.04/1.4...

Now to try and make/get the second computer to run.. It comes up but does not display the desk top...Just sometimes different stuff with screen, colors, black screen etc... Also the power switch is bad and I would like to get the new one before jumping the switch...ON the way..




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O' boy more problems to solve..

After working on the 520 #2 ,got it to work and yes the TOS is 1985 So yes it must be TOS 1.0..

Re seated the chips(in sockets) on the mo and jumpered the power switch and it came up. Them I noted that the "F1" key was always down, not like the other ones...

What is the F1 key used for and does it mater if it does not work, If so then who knows where to get a new one??

If it does nothing then I will let it go...

The next problem is the mouse does not go down..OK other directions UP,Side to side but not down. Also always on the straight no diagonal movement...

I read some where that someone took the mouse apart and clean everything and put it back and it WORKED. So now I take it apart..Let you know what happens...

Do the problems ever stop so you can enjoy the ST's and even the A8's I have...?????




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On 11/28/2021 at 5:57 PM, Peter Rabitt said:

@bfollowell, Yes the switch you showed was a good switch for a power supply but not for the ST.. Ordered one from Digi-key...Little ex$$$ but ok with it..



Ah, yes, of course, 520, external PSU. I wasn't thinking.


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