MEGA ST 4 - blank screen boot

[macsonny]

Hi All,

So I've been working on getting aa TF534 working in my Megaa ST. So far now joy.,

However, last night I was doing some testing and had aa look at the 68000 CPU socket pings. They were looking a little rough so I reflowed each pin. From that point on - the machine will only startup to a blank screen was shown in photos.

Now let me walk you through the mods:

RD-50A power supply upgrade done
Entire board recapped
Internal UltraSATAN - removed in photo
Internal video mod to allow me to run via HDMI output
Internal wiring to external switch so I can change resolutions with switch

Machines has been solid for a few years.

Only real change is I did the reflow but as you can see from the photos - it's not too bad.

I've swapped in a different 68000 CPU that I know is good a now change. Also buzzed each pin from top to bottom of board and checked for shorts just in case I bridged a pin. Didn't find any issues.

Kinda stuck as not sure what to do next.

Any advice?

[PhilC]

That Mega ST never had the blitter patch, so no bodge wire required there.

I would remove all the solder from the CPU socket pins with solder wick and then resolder it. If all you've done is the soldering, then you've probably got a dry joint there somewhere.

[rubber_jonnie]

My first piece of advice is to roll it back to standard or at least use the original video out to see whats what.

The closer you can be to original the easier it is to try and figure out what's wrong.

If you have a diag cart then plug that in when booting.

[macsonny]

That Mega ST never had the blitter patch, so no bodge wire required there.

I would remove all the solder from the CPU socket pins with solder wick and then resolder it. If all you've done is the soldering, then you've probably got a dry joint there somewhere.

Good advice. Just desoldered each pin with my desolder station and then re-soldered each pin. Still a grey screen.

[macsonny]

My first piece of advice is to roll it back to standard or at least use the original video out to see whats what.

The closer you can be to original the easier it is to try and figure out what's wrong.

If you have a diag cart then plug that in when booting.

Getting late here in Sydney. I'll plan on using base video tomorrow and see if that helps.

I jusdst ordered a drag card and cable from Exxos but would be nice to get the Mega working prior to the cart getting here :-)

[HigashiJun]

Is your TOS chips replacement stuff OK ?

As @rubber_jonnie suggested, standard configuration would help, and this means original TOS chips too.

[rubber_jonnie]

Is your TOS chips replacement stuff OK ?

As @rubber_jonnie suggested, standard configuration would help, and this means original TOS chips too.

@macsonny I was also wondering this, but since we can't see the original display via the RGB2HDMI its hard to read. Typically bad/problem ROMs gives a white screen and RAM gives a black screen with a white border, but if you happen to be in Hi-RES both these usually present in white, so using the base video in LO-RES is a better option for troubleshooting.

[macsonny]

O)k. So managed to get some additional testing done this morning.

1. Removed RGB2HDMI and just tried to run from monitor port to VGA converter. Exact same image (blank) on the monitor so assume video converter is running ok.
2. Used a SideCart to see if it would boot form that. Whilst LEDs flash - same blank screen display.
3. Removed TOS emulator and replaced with original TOS 1.04 ROMs and moved jumpers and removed U12 chip - same blank screen.

Have made sure in all cases I'm trying to boot in LOW res mode.

I'm planning on going over the board later today with a fine tooth comb to look at each solder joint. When I touched up the 68000 solder joints I also touched up a few other joints that looked a bit questionable. Maybe I've caused a bridge.

Will report back.

EDIT: Also replaced the video IC socket.

[olivier.jan]

As you have a Sidecartridge, could you install DiagCart ROM image on it to check if you get some diag information?
Another question: is your machine running a US TOS ? I can see in your capture that the signal is 60hz, which means that you have a NTSC ROM or that the ROM is not even reaching the very early stage where it switches to PAL.

[macsonny]

As you have a Sidecartridge, could you install DiagCart ROM image on it to check if you get some diag information?
Another question: is your machine running a US TOS ? I can see in your capture that the signal is 60hz, which means that you have a NTSC ROM or that the ROM is not even reaching the very early stage where it switches to PAL.

I can put the DiagCart onto the SideCart and let you know. Where is the best place to get that file?

My machine is a PAL machine and the ROMs I’ve been successfully using in the past are all PAL.

Does that info help?