A500 and Baseboard 4mb. not seeing all ram

[cypher007]

i have an A500 rev 5 with a baseboard 4mb fully populated in the trapdoor and 512k onboard.

back in the day i had to fit a 8372A to get 1mb chip and i remember having to bend one pin up on that. i also had to run the wire from the Gary adaptor to the middle pad 2 of JP2 and cut the trace between 2-3.

now reading the manual again after 30 years it seems i should have linked pad 1-2 as well?

is this why when i run avail, after running cram, i see 1mb chip and 3mb fast? i would have thought it should read 1mb chip and 3.5mb fast?

its as if its not seeing the 512k chip onboard or maybe the 512k chip on the card?

[psoma]

Hey, I can help here as I've gone through a very similar scenario.

The wire from the Gary adaptor to the middle pad of JP2 is only required if you are using the "B PAL" which from what I understand in the manual, is only for Rev 6 motherboards. I'd ditch that.

As per https://i.ibb.co/RT4wHr4/Baseboard.png, your config is on the second line (sorry, mine is highlighted) and you should only need the FTR Agnus installed, and JP2 set to 1-2. Bank 0 basically becomes the additional 512KB chip mem and banks 1-7 add 512KB each.

As for the 3MB Fast you're seeing, I had the same thing because there was a bad memory chip in one of the banks (remembering it adds mem in banks of 512KB). To isolate this, I removed the leftmost chip out of each bank one by one (except bank 0) - each time, the output of cram should drop 512KB. If it does, replace the chip and try the next bank. When you get to a bank that doesn't affect the 3MB, you've found the one that's not working.

Now, you need to know which of the 4 chips in the bank is bad. To do this, I returned all chips back into their original positions and then emptied the bad bank. I now swapped one chip at a time into the leftmost slot of a "good" bank and when cram came back with 2.5MB, I knew I'd found my bad chip. Note: you may have more than one bad chip in the bank, so check all 4.

As for the bent chip on the 8372A, I think that's to switch between PAL and NTSC.

Hope that helps?

Cheers,

Tom

[cypher007]

solved.

needed to read the rest of the manual. i had the jumper set correctly what i needed to do was run cram with the command contig not fatter.

now have 1mb chip and 3.5mb fast.

thanks for replying psoma it seems the gary wire works with the rev 5 board also. i knew i had fitted it for a reason 30 years ago just forgot about the contig setting. the original harddrive a 20mb one has failed so needed to reinstall workbench.

[psoma]

Ah, cool! Even easier solution

Nice one.

Tom

[cmorley]

Originally Posted by cypher007

solved.
it seems the gary wire works with the rev 5 board also. i knew i had fitted it for a reason 30 years ago just forgot about the contig setting.

As you had upgraded to an 8372A Agnus so you've got the key bit from a 6A which is the 1MB Agnus - so I'd expect the chip RAM wire to work on your rev 5. The Amiga would probably crash with a stock rev.5 board and the Gary wire fitted.

[Jope]

Originally Posted by cypher007

solved.

needed to read the rest of the manual. i had the jumper set correctly what i needed to do was run cram with the command contig not fatter.

So you have the fabled B pal in yours then? :-)

[psoma]

Originally Posted by Jope

So you have the fabled B pal in yours then? :-)

Funny - just a day after I said "What are the chances of finding someone who actually has a B PAL?!?"