SE/30 went from working to no video (does chime on startup)

[djc6]

I have an SE/30 that I recapped a couple weeks ago. Its worked fine and i've probably put 20-30 hours on it since recapping playing tetris and exploring HD images via my BlueSCSI v2. Its never once crashed or behaved strangely.

Earlier today I was looking at some old documents in ClarisWorks and properly shut down the system. Then later I went to turn it on and no video! I do hear the normal chime on startup.

Some things I have tried:

1. I have a CayMac Vintage "SE/30 Compact Analog & PSU Replacement Board". I've been exclusively using this for a few weeks now with the logic board on the bench. I'm using a Dell display, HDMI to DVI cable and a PicoPSU power supply and its been working fine. So its not the power supply or analog board as those aren't in use with this board. I do see the RGB2HDMI on screen display - it reports its getting no sync from the SE/30.
2. Same issue when I tried it with the stock CRT/analog board/power supply.
3. I was curious to see if I could access TechStep debug mode over serial. I don't see any output when I try TechStep serial commands using serial port closest to the headphone jack.
   1. My serial setup is a 2018 Mac Mini and a usb to db9 adapter, with a home made DB9 to mini-din serial cable. I built this cable for using ADTPro with my Apple IIGS. To confirm my cable and setup worked, I connected it to IIGS and successfully made a disk using ADTPro. Is this a valid test for using the same cable with TechStep on the SE/30?
   2. Pinout for my cable is shown here: https://adtpro.com/connectionsserial.html halfway down the page. Its wired as a NULL MODEM
4. I tried re-seating OEM ROM SIMM and putting some deoxit on the socket and the SIMM just grasping at straws at this point.
5. Removed socketed chips and put DeoxIT in the sockets, re-installed chips.
6. I have a Floppy Emu connected - I don't see the mac attempting to boot from it.

Any ideas what further troubleshooting I should do? I'm going to order an oscilliscope, probably this one below - so I can start poking around the board for clues:

https://www.aliexpress.us/item/3256806251266312.html

I did find this similar post mentioning chips UF8 and UG8 https://68kmla.org/bb/index.php?threads/se-30-chime-but-black-screen.4955/

Those chips (all the SOIC package ones) are a little crusty on my logic board due to leaking electrolyte from the old caps but nothing I would consider extreme. Weeks ago I tried to clean as much crust off with isopropyl alcohol and DeoxIT.

 

[chiptripper]

UE8, UF8, UG8, definitely start there.

Also check UE7 and UG7, if they’re socketed, pull, inspect, re-seat. I had one where UE7 had a bad socket. It produced the same symptoms you describe.

 

[djc6]

Some more troubleshooting... I was able to communicate with my SE/30 via TechStep debug mode!

I see the following when it turns on "*APPLE*00200000FF16*1*" and I'm able to run some of the tests described here:

Macintosh Diagnostics / Test Manager

docs.google.com

The issue was, I need to press the NMI / Non Maskable Interrupt / Programmer's switch (I see so many names for it) quickly after the machine starts up to get into debug mode. This is because my machine isn't booting into sad mac - I hear the normal boot chime.

I had been pressing this button and nothing would happen. The reset button worked fine - I would hear the normal boot chime. So I squirted some trusty DeoxIT D5 onto the programmer's switch while propping the logic board on its side so it drained into the switch. I let it sit like that for a while - and now the programmer's switch works! When I press it I hear the sad mac tone and that string above appears on the serial port. So no issues with my cabling.

 

[djc6]

I got my Oscilloscope - still learning how to use it.

To recap, I have no VSYNC or HSYNC. I'm trying to find something common between them that would keep both from working.

I've been focusing on UG8 (Binary Counter) and UG7 (Clock Generator PAL) because line TWOLINE output from UG7 is the pin 1 clock input for the binary counter UF8 used to generate VSYNC output on UG6. So I thought that maybe if UG7 doesn't work right, then UF8 won't work right, then UG6 won't generate VSYNC either.

I am seeing weird things on UG8 but again my first time using oscilloscope. This chip has four inputs and this is what I see:

Pin 1 "CK" on UG8 looks like a good clock - input is pin 15 "C2M" from UG7. I assume C2M means 2Mhz and thats what I see:



Pin 2 "CLR" and Pin 12 "CLR on UG8 - both inputs come from pin 19 "HCTRRST" from UG7 (Clock Generator PAL), and I see a 25-33Mhz (its all over the place) signal that is only in the 200 millivolt range? Single looks the same on all three pins involved.



Pin 13 Input "CK" on UG8 comes from output Pin 6 on same chip UG8 - and its always stuck high-ish around 1.7V as soon as machine is on. I tried resetting it a bunch of times, never see anything other than solid 1.7V:



Any ideas? Is UG8 bad or do I have a short somewhere? Thanks!

 

[djc6]

Replacing UG8 (LS393) fixed my video! Glad I was able to narrow down which chip was the problem versus throwing the parts cannon at it. I did buy all the ammo for the parts cannon to save on shipping costs, so now I have a lot of spare parts I bought some of the LS166 and 74F253 since they are also corroded from electrolyte.