Startup error on Commodore PC40-III

[rglenn]

I recently picked up PC40-III. Initially the error was a battery failure / CMOS checksum error. In researching I discovered this was a common issue and the Dallas time clock needed to be replaced. So, I removed the Dallas chip, installed a socket, and replaced with a NOS Dallas chip. Now I get an error when it tests the extended memory, illegal shutdown code in CMOS. Disabling extended memory testing via dip switch (4) has no effect. I have removed the NOS Dallas chip and socket. Planning to install a new socket and yet another NOS Dallas chip unless anyone has other ideas. Any help would be appreciated. I included pics from before the Dallas chip replacement and after.

 

[powerlot]

Don't buy a NOS Dallas chip and expect it to work.. the battery in these things is over 20 years old and might have gone bad already.

Did you replace it with the exact same type of Dallas chip? They have subtle differences which might make them not work in particular mainbaords. Best you dremel away the plastic on your existing Dallas and solder an external battery to it. There are several tutorials on the internet that show how to do it, example:

Out of curiosity, you could dremel the contacts on your NOS Dallas and check the voltages there as well

 

[rglenn]

I replaced a Dallas DS1287 with a Dallas DS14287. I though they were supposed to be equivalent.

Do you think this would work? https://www.ebay.com/itm/256115671181

 

[rglenn]

In the meantime, I'll watch the video you suggested.

 

[eight088]

I replaced a Dallas DS1287 with a Dallas DS14287. I though they were supposed to be equivalent.

Do you think this would work? https://www.ebay.com/itm/256115671181

The DS1287 and DS14287 have a small difference that might cause problems. Pin 1 on the 1287 is a bus selection pin, and the 14287 has ram power output. So going of that, I would think it won't work. The one you linked to ebay should work. The github for that replacement can be found here.

Out of curiosity, what happens with the original dallas chip when it is in the system? I always thought the system should still work, but you wont be able to save any cmos settings.

Cheers

 

[rglenn]

I found this -

The CMOS battery on this motherboard is integrated inside Dallas DS1287 real time clock controller. It can be replaced following these instructions. Without a working battery, the computer will loose its BIOS settings during reset and it will be not possible to boot it correctly.

 

[rglenn]

I installed the DS1287 replacement - https://www.ebay.com/itm/256115671181 and the "illegal shutdown" error is gone, however, now it gets stuck at "testing extended memory". No beep codes, continual flashing cursor.

 

[powerlot]

Is there some kind of memory expansion installed?

 

[Ruud]

I included pics from before the Dallas chip replacement and after.

I had exactly the same problem, added the external battery as suggested by @powerlot and things worked fine again. So at least try that as well.

 

[rglenn]

Thanks for the suggestions. I ended up removing the socket, soldering in a new one, dropping in the DS1287 replacement I got from eBay, and it was fully working.
An hour later, the hard drive died. Back to eBay I go.