If you damage the pads, traces or through holes while working on U8 it's more than likely the board will not start correctly. Check all the pin connections / continuity between the 28 pins of U8 both upstream and downstream. A break in the address or data bus will result in the board not starting correctly.

The software performs some form of diagnostic check. The problem is that if the address or data bus are not correctly wired then the diagnostic check cannot pass to even display anything. The first sign of any successful pass of the diagnostics is the blinking diagnostic LED. If you don't get that then everything else beyond that does not matter. The display is scrambled because there's no software programming the display output (it's just displaying whatever the power-on RAM state is). The "bong" happens entirely on the sound board and is not under CPU control.

The pin numbering system you used is not consistent with standard order. It's really hard for people used to standard order to see what's wrong. Reverse your 1-14 and 1-16 order and try using the information below.

The address bus stretches from the ASIC to the I/O connector through the main CPU ICs (U4/U6/U8/U9).

The data bus stretches across the board with the address bus but also connects down through the buffers and flip-flop (U7/U11/U12/U13/U14/U15).

bus_address_00_07.jpg

bus_address_08_15.jpg

bus_data_00_07.jpg

u8.jpg

It sounds to me that you've pulled the through hole at U08-12. This is where the D1 signal goes from the bottom of the board to the top of the board. The connection with U09-32 is at the bottom of the board (but goes back to the top through the via). I agree with what zaza wrote. You need to verify where the continuity is broken between the connections going "up" from U8. If there's no continuity between U08-12 and U06-14 then you can probably put a jumper wire between the pins and test that the board boots. See picture for better detail. It's the yellow/red signal.

Continuity is continuity. For my DMM it appears to be defined as less than 50 Ohms resistance. I typically don't diode test between pins. I only check for continuity to make sure that digital signals are correct.

VBATT is the voltage source for the battery backup for the SRAM. It's labeled on the schematic. It can be selected as deriving from the battery (B1/B2/B3) or the power source (VCC) through W6 or W7.

Thanks. That's a copy/paste error from the U06 entry. I've fixed it. See picture for correction.

u8_corrections.jpg

u8_traces.png