Testing chips in circuit with an Oscilloscope

[Steve Rieck]

(for idiots perhaps...). I've got a Simasimac reloaded SE/30 board and I suspect the GLU chip is at fault. It cleaned up well but was kinda rough when I got it off the bombed board.

I have checked all pin continuity several times and everything checks out to destinations. No bridges also. Assuming that side of things is good, what would you specifically be looking for with the Oscilloscope to see if the GLU was alive and functioning correctly?

Walking the ROM bus? How is this done? Are there other aspects of the GLU that can be checked? Sorry I'm new to this side of things.

Thank you very much for any help!

 

[GreenBar0n]

The Simasimac Repair guide gives an excellent breakdown of what to look for and how to proceed - I'm so glad they made this:

https://tinkerdifferent.com/threads/macintosh-se-30-vertical-horizontal-bars-on-display-simasima-repair-guide.4705/

Specifically regarding the GLUE chip, you'll be looking for voltage, Reset condition, and with the O-scope for the clock signals, I remember there being (2) different clock values on the GLUE chip, might be (3). That GLUE chip is hard to kill, unless you see the corrosion wicking past the legs and in to the body of the chip, it's probably fine.

The one thing the Simasimac Repair Guide fails to mention, is that if you check all of the continuity to the PDS slot from the ROM slot, and to the surrounding chips, the ROM slot can still be missing one of the signals from the CPU. Best to check all of the signals to the PDS and CPU from the ROM slot.

The walking the Bus test confused me for quite a while, there were different clock speed values I was getting, than the Simasimac Repair Guide said to look for. This is what I got for the clocks:

In the end, my problem was the trace D1 from the CPU to the ROM slot was missing, I had to go back and check all of my Address and Data lines from the CPU directly to the ROM slot to locate the problem. One missing trace will cause the SImasimac condition.

From: https://wiki.retrotechcollection.com/Macintosh_SE/30_Troubleshooting (CPU Bottom of the logic board)

Let us know if you have any questions.