SE/30 video issue that has ME stumped!

[NE555]

I hear ya. I got a SE/30 that does exactly the same thing.

 

[bibilit]

Have you tried swapping PAL's as i did ? solved the issue for me.

 

[NE555]

I swapped the PAL (all of them) and cleaned the pins, I swapped the  PAL sockets, I swapped all the 8 bit shift registers, I swapped the ROM SIM socket and I swapped the memory SIM sockets.

I replaced the capacitors and some of the resistors underneath the PAL chips.

 

[NE555]

any more or other suggestions?

 

[BadGoldEagle]

Well, if you've swapped every suspect chip on that board, the only things that could be bad are traces... I know that's kind of a stupid suggestion, but I would go bad trace hunting with a schematic if I were you. 

https://www.macintoshrepository.org/875-macintosh-se-30-schematics-and-repair

 

[NE555]

I noticed that there is a slight difference between the OP's screen output vs mine. My lines seem to go through the mouse icon and the question mark disk.

 

[techknight]

yea thats commonly fixed. If you have already changed out UE8, then check the traces to it. 

But more importantly, check the VRAM I have seen those go bad as well. 

 

[NE555]

The LS166 is new. I am not 100% sure anymore if I changed out the VRAM. I'll check the UE8 traces again.

 

[NE555]

I think I found it Pin 5 on the ls166 (vid3) to UC7 pin 23 is OL. Pin 5 to via on the ls266 is OL. via to pin 23 on UC7 is .3ohm

a closer look reveals that the pad is disconnected from the Via



thank you for the help  techknight

 

[NE555]

and here is the result

 

[techknight]

Yeap, I figured as much. 

the board I have is way worse. lol. 

 

[redruM69]

Sorry to dig up a dead thread.
Techknight, did you ever find anything on this?  I have precisely the same video bug, but cant seem to figure it out.  Both VRAM's and UE8 have been replaced.  Tested all traces to and from VRAM.  I still get vertical stripes with a slightly abnormal disk icon.  Looks identical to your screenshot.

 

[redruM69]

Also, I have tried swapping all 5 PALs with known good.

 

[redruM69]

Bump?

 

[redruM69]

ISSUE RESOLVED!  Techknight, you may want to add this to your notes.

It appears that Texas Instruments SN74HC166DRG4 is NOT a valid replacement for the the 166 shift register @ UE8.  It causes the discussed artifacts.
I swapped it out again, but this time with a Toshiba 74HC166D, and the issue completely resolved!

 

[Bolle]

I would always use the appropriate 74LS166 instead of a 74HC. It’s supposed to act the same but as you see it might not always do.

 

[techknight]

You cant swap in an HC for an LS, because that is TTL vs CMOS, they have very different logic level High and Low thresholds. 

And yes, I checked for that, although its been a very long time, I can check again as if I recall, I dont know if I was the one who changed the IC. 

 

[techknight]

So, I pulled out that board, I had to remember where it was as its been a couple years. Sure enough, it has an HC166 in there. 

Didnt even think about it honestly. I checked my stashed that I was using and all of mine are LS166s like they are supposed to be. 

 

[error1]

Thanks everyone for sharing your repair experiences, it was an awesome help to finally get my SE/30 recapped and fixed. I was stumped by the black vertical lines but after inspecting the corrosion damage around the old caps under a microscope and thinking that maybe there's something I'm not seeing, I finally desoldered UE8 and found the broken trace. A bodge wire later and my SE/30 is good as new.

Now that I have a microscope it's making me really want a ultrasonic cleaner because the corrosion looks really disgusting up close and brushing with IPA apparently just smears it around   

 

[redruM69]

It's worth noting that although the Toshiba 74HC166D is a CMOS part, it appears to be TTL tolerant.  It worked fine as a replacement in my case.