Yet another simasimac SE/30 giving me grief

[mattsoft]

Started working on an SE/30 that won't start-up normally. Here are the symptoms:

• Simasimac-looking image on boot
• Death chimes immediately at power on
• Interrupt button does nothing
• Reset button will re-play the death chimes but not reset the image

I've done the following:

• Voltages tested at molex on logic board are good
• Recapped the SMD caps and cleaned the board
• No battery damage
• Tested RAM in another machine good
• Reseated and cleaned the video ROM and PALs
• Without ROM SIMM, no death chimes but same image -- guessing the ROM SIMM is OK
• CPU is not halted (F12), CPU clock (E1) is good, CPU /AS and /DS are active -- I think the CPU is good which is probably consistent with death chimes at startup
• Did the continuity test matrix from the last 2 pages of the schematics (that was labor intensive) and found no bad traces
• Tested the clock signals from the troubleshooting guide (pg. 38), all are good
• Performed the ROM address-walk from the troubleshooting guide (pg. 46), and other than the guide being slightly incorrect, the address-walk tested good

My next step is to continue through the troubleshooting guide (pg. 47+) and check the waves from the video ROM and multiplexing ICs.

Any other obvious ideas to check? I don't want to just start pulling chips, so any suggestions I can test with a multi or oscilloscope would be welcome. Thanks!

 

[GreenBar0n]

I have seen the simasimac pattern for the NEC, Ti, and Mt VRAM chips, yours doesn't look like the typical simasima pattern.

It's good that you get a chime of any type, as it means you can most likely use a serial cable to read your error code:

A lot of times a full simasimac condition SE/30 won't load the ROM, like yours seems to be doing.

Seems like testing the Video ROM chip is a good place to start.

EDIT: The Simasimac Repair Guide recommends to test continuity between the PDS slot and ROM slot, and not the CPU directly, because it's easier to access, but if you have a broken trace in between the CPU and ROM, that won't always show up by checking only the PDS slot. I learned that one the hard way.

 

[mattsoft]

Ya, I'm going to check out the video ROM on the scope tomorrow. To connect the SE/30 to a modern PC/Mac via USB, I'll need to figure out all the cables and adapters to make it work. Does someone have handy-dandy links to those?

 

[GreenBar0n]

I was given this link back when I was building a cable for PC to SE/30:

Products – RetroFloppy

retrofloppy.com

But my SE/30 simasima wouldn't chime and therefore load the diagnostic ROM.

Did buy a Techstep later to confirm everything was functioning correctly; a 4-pin mini DIN for the SE/30 serial port is what's necessary if you decide to build one.

 

[mattsoft]

Thanks! Cables ordered!