Falcon Restoration Project

[rubber_jonnie]

Well, without a clock nothing will happen, guaranteed.

I agree. Have you checked for a clock signal on the CPU at all? a diagnostic cart won't mean a thing if the CPU has no clock signal.

Check the basics first.

[hunsra]

Well, without a clock nothing will happen, guaranteed.

I agree. Have you checked for a clock signal on the CPU at all? a diagnostic cart won't mean a thing if the CPU has no clock signal.

Check the basics first.

@stephen_usher and @rubber_jonnie, thanks. Yes, I had checked the clock signal to the CPU and it seems to be correct for boot (~8MHz).

I also just checked CLK32 (~32MHz), CLK25 (~25MHz), EXTCLK (~40MHz), and DOTCK (~8MHz) on VIDEL, DOTCK (~8MHz) on SGC DAC - U30, and CLK32 (~32MHz) and CLK4 (~4MHz) on COMBEL. All seem OK, and I assume to 40MHz EXTCLK on VIDEL is due to the 40MHz crystal on the 3-in-1 VGA adapter. However, the missing resistors are definitely not supplying a clock to U13, and U27 is missing, which are both required for the serial port to work, so that rules out using the serial port for diag until I get the resistors fitted and U27 replaced. The other missing resistor is part of the ECLK for U24, related to MIDI, so I don't think that's part of the initial boot issue. I'll fit the missing parts and try again.

Based on all of this, I wonder if my display is not able to properly sync with the output. It's an NEC MultiSync EA192M. I've successfully used it with other older systems, including a 520ST and a 1024 STFM, both with an ST2VGA adapter. I've also used it with an original MiST unit (not MiSTer) which also outputs at 15KHz, and the display can handle those signals. Is there something different about the Falcon's boot video signal that might be part of the reason I'm not seeing anything?

[Steve]

@hunsra your monitor will tell you if it's not syncing, there's no point in guessing.

[hunsra]

@hunsra your monitor will tell you if it's not syncing, there's no point in guessing.

Thanks. That seems reasonable. It seems to be detecting the proper frequencies, so I think it's OK.

[hunsra]

More progress:

I fitted all of the remaining missing parts and I was able to get the Falcon to boot! However, just powering up results in a blank display - I have to reset at least once before the boot sequence works. I'm not sure what to think of that. Maybe the auto reset circuit is faulty? Any suggestions? Also, the cartridge port doesn't seem to work. It boots to the desktop whether the diagnostic cartridge is inserted or not. Nothing on the serial port either. I'm going to try to troubleshoot the port to see if anything is broken.

desktop.jpg (373.59 KiB) Viewed 2010 times

Thanks again for all of the help and suggestions. It has been very helpful and educational!

[exxos]

Change the caps in the reset circuit or add larger ones. It's a known issue in the mandatory fixes section.

[hunsra]

Change the caps in the reset circuit or add larger ones. It's a known issue in the mandatory fixes section.

Thanks. I will do that and also review the rest of the mandatory fixes topic.

[stephen_usher]

Good to see it booting at last.

[DoG]

...Also, the cartridge port doesn't seem to work. It boots to the desktop whether the diagnostic cartridge is inserted or not...

Check 0.5A fuse.

[hunsra]

Good to see it booting at last.

Indeed. I was beginning to think it was a lost cause.