exxos's Atari, Amiga & retro forum

LarryL wrote: 30 Jan 2026 15:32 Thanks for the photo
I immediately found (at least) one mistake I have made: rotated the OSC by 90 degrees :oops:
So JP4 - the solder jumper - is not set at all, right?

JP4 is left at whatever the default is, I honestly can't remember :lol:

PhilC wrote: 30 Jan 2026 15:36

LarryL wrote: 30 Jan 2026 15:32 Thanks for the photo
I immediately found (at least) one mistake I have made: rotated the OSC by 90 degrees :oops:
So JP4 - the solder jumper - is not set at all, right?

JP4 is left at whatever the default is, I honestly can't remember :lol:

Right - according to the schematics 1-2 should be bridged by default. Will check

Hi
Not really progressing…
Rotated the OSC and re-checked Jumpers - seems Ok
Tried several BIOS versions - no luck
Realised from your photo that you have populated R1
From the datasheet I see that this enables a 3C3 mode - did not fully understand this from the description. No difference on my board with or without R1

@PhilC did you populate this intentionally for some reason?

Also changed R4 to R3 because I have slower RAMs - no difference

But now after all this rework the VGA BIOS is not detected anymore

Need to sleep about it and maybe populate a second Board…

@LarryL. Those four resistors configure ram selection for the bios but the bios must match otherwise you'll get screen corruption.

Does your rom have two bios images on it or one? Mi e has two images. So if you're using a different rom size or image then that will have an effect on the rom jumpers.

PhilC wrote: 31 Jan 2026 12:16 @LarryL. Those four resistors configure ram selection for the bios but the bios must match otherwise you'll get screen corruption.

Does your rom have two bios images on it or one? Mi e has two images. So if you're using a different rom size or image then that will have an effect on the rom jumpers.

Yes, right - R2,3,4 is for selecting the right RAM (MCLK and whether it is 2xCAS or 2xWE), R5 is to enable 64k ROM and R1 for this 3C3 mode which I do not understand.
So far quite understood.
I flashed the 32k BIOS two times in the lower and the upper segment of the 39SF010 to be on the safe side
I think that JP3 selected the lower/upper segment of the 64k Flash

When I started testing, a VGA BIOS got detected - interestingly the Raven reported a 42k size BIOS but no start message and then only 8bit VRAM - so something was wrong there…
After my testing and changing R1,3,4 and flashing different versions of BIOS files, now the BIOS is not detected anymore

Will double check the soldering again - I have already checked continuity of all control signals and the data bus between the RAMs and the GD5434, as well as 25% of the address lines (is an annoying kind of expertise…)

@LarryL id go over the gd5434 pins again if you're not getting anything detected as they are a big pain in the arse to solder due to the pin pitch.

PhilC wrote: 31 Jan 2026 13:15 @LarryL id go over the gd5434 pins again if you're not getting anything detected as they are a big pain in the arse to solder due to the pin pitch.

Yes, that’s right!
Usually I fail with the SOJ40 RAMs but they look good this time…