Emax

Hi all,

I have a 4MB Emax 2 and bought the ram chips to install. It appeared that I had all the PALs as I had the expansion board already running at 4MB without a problem. I then purchased an EEPROM programmer and managed to download the correct 8MB file for the EEPROM. 

I socketed the EEPROM and then programmed the necessary file to the EEPROM. All seemed well and it checked out as the 8MB version when I checked the memory. So far so good. Then it all went wrong. Once I switched off the unit it failed to boot up again. The firmware appeared to be confused. Fortunately I had kept the original 4MB EEPROM, however I had cut the legs in order to reduce chance of damaging the PCB whilst socketing this chip. I managed to solder it to a prototype chip holder and downloaded it's contents. I then copied this onto a brand new chip and inserted it into the socket. Much to my delight the unit came back to life although only finding the original 4MB even though the extra RAM was still installed. 

To me it appeared that what was happening here is that somewhere in the keyboard a record of what system was last booted was being held. I am not sure how or why this was possible, but it appeared that if the system was not updated via scrambled megs, it would know that the EEPROM was switched and refuse to boot. Maybe some sort of checksum was stored and this was detected on startup. Anyway it didn't work for me but was a lot of fun trying and I learnt quite a bit in the process. I hope this is useful to anyone else trying to do this. 

Regards

Tony

Sent from my iPad

On 27 Jan 2016, at 23:04, "Ted Summers djtbs1@... [emax]" <emax@yahoogroups.com> wrote:

> Per page 2- It looks like since you have 4MB you don’t need any PALs, just the scrambled megs or an eeprom programmed with 8MB stereo already detected to add more memory (and the memory itself of course).
> 
> The empty sockets on the main board are not used.
> The empty expansion board sockets (which are numbered ) should correspond to details in the memory guide page 6 and 7.
> in other words- those numbered sockets which are empty should match the instructions in the memory guide for what should be filled.
> 
> Per page 1, the memory per 2MB is
> Qty 16 of 44256 256K x 4 DRAM’s
> Whatever the memory speed of the chips -8, -10, or or faster.
> 
> For example, I would expect if you had some -8 on the expansion, you could put -8 or -7
> 
> Faster won’t cause you a problem, but slower could.
> 
> -T
> 
> On Jan 27, 2016, at 12:26 PM, schtom83318@... [emax] <emax@yahoogroups.com> wrote:
> 
> The PALs I have are:
> 
> IP431AEMU3593 in IC54
> IP432AEMU4393 in IC55
> IP433AEMU4193 in IC56
> IP430AEMU2294 in IC57
> 
> thanks,
> Tom
> 
> [Non-text portions of this message have been removed]
> 
>