SE/30 with Serial Port Issues - Fails Snooper "Handshake Test"

[Garrett]

Hi all, I am working on an SE/30 that works with the exception of the serial ports. Snooper 2 is my go-to for testing, as it seems to be reliable in picking up problems.

The issue is, the entire system crashes when I run the serial port tests. With loopbacks connected, it'll give me the "handshake test - OK" and then lock up. With no loopbacks connected, I get the "handshake test - BAD" message followed by a freeze. This seems to indicate that there is some functionality here, just not 100%.

I have recapped the board and checked traces between the serial ports, the serial controller itself, and everything in between. I did have one intermittent connection between UC12 and UG12, so I removed UC12 for cleaning and then replaced it.

This didn't solve the issue, so I went ahead and removed the UG12 chip hoping to find bad corrosion under it. Nothing found though - it looks really really nice and clean. Argh! How often do these chips fail? I have repaired many of these boards and have never had Snooper actually lock up. Most of the time it'll just fail and move onto the next test if there's a problem.

Any thoughts or ideas? Going to swap in another UG12 I had saved for a reloaded board, but I'm really doubting that's the problem.

 

[eric]

Are there any pull up/down resistors on the serial ports lines? maybe something to check (spitballing)

 

[Garrett]

Only thing I can see in schematics are the Bournes RP2 and RP3, which I checked out as part of my initial probing. Other resistors include R40-R43, but I'd doubt that's the cause because they're going to the edge connector on the front of the board. Thanks for the idea though, keep them coming!

 

[Garrett]

All fixed!

A replacement SCC did the trick. I actually used the chip I had saved for my sleek black reloaded board, but seeing Snooper run without issue was worth the sacrifice. That new board is socketed, so I'll give the old chip a test at some point.

If the old controller chip was bad, it was only partially bad, because System 7 would still startup with it. Without the chip installed, it would hang up at boot. Either way I'm happy to have another working SE/30!