What causes this type of Simasimac pattern?

[robin-fo]

Hi everyone

I‘m currently building my second SE/30 Reloaded board. Although my first one is fully socketed; I was too lazy to check all the donor ICs, but maybe I would have the same issue anyway…:

When I power up the board, I see this well known pattern of death on the screen:


The board is currently not fully populated, so I would expect horizontal stripes instead. What is the technical reason behind this pattern so I can concentrate my troubleshooting on the affected circuitry?

The board currently looks like this:

Yes, there is no ROM or Video ROM, but the circuitry should produce horizontal stripes even without the CPU

The CPU, GLUE, SONY ICs, PALs and Video RAM were all tested and should all work; except if they were damaged during the soldering or cleaning process.

 

[robin-fo]

Next steps would be desoldering and testing ICs.. Not really looking forward to that

 

[zigzagjoe]

Simiasimac pattern depends on the VRAM. It's whatever the VRAM contents tend to "settle" to when uninitialized.

TI VRAM does horizontal bars, NEC looks like that. So this is normal, nothing to worry about.

 

[robin-fo]

TI VRAM does horizontal bars, NEC looks like that. So this is normal, nothing to worry about.

Oh, that‘s really good to know!
Indeed, the current board has NEC VRAM and the other has TI..