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Gents, I'm late to the party, but I agree with Trag and Uniserver that this is most likely a bad via or trace (I'm betting on the former). When my SE/30 went out I created a schematic tracing each of the SCSI pins back to at least one other chip. Eventually I discovered a bad via located near...

I replaced the two 100 microfarad, 6V capacitors on the logic board and voila! everything was good again. The bottom line was that the computer was locking up during the bootup sequence when it tried to wake up the Ethernet card. Those two caps are obviously crucial in supporting communications...

uniserver, I appreciate your prior input towards diagnosing my problem, but not your lack of tact in this last post. I type in a lot of information up front to save your time rather than waste it asking me a lot of background questions. And for someone who never assumes anything, you assumed...

I replaced the tantalums myself (see top of post) as I had them left over from an SE 30 recap, but I didn't have any 100 microfarad caps. I was hoping that the problem resided in one of the 47 microfarad caps. I also manage to consistently pick the slowest line at the supermarket, so I guess I...

Picture of logic board is attached. If you look close enough you'll see some streaks of white. I cleaned the board with both an electronic cleaner and rubbing alcohol, but the white marks remained. I believe they are corrosion (aluminum generates white corrosion). The internal RF shielding...

Okay, have isolated the problem a bit. beachycove wins the guessing game. I pulled the Ethernet card before reinserting the logic board this time and it started right up. I was sure I had already tried that, but apparently in all the excitement I had only fired 5 times, not six :-) The...

New hard drive arrived, but as feared it encountered the same problem on boot: system freeze at the Welcome to Macintosh screen. I'm now out of ideas and welcome any suggestions. Will need help posting an image of the logic board. I tried to upload a JPEG (2.73 MB) as an attachment but the...

Gents, Thanks for all the suggestions. Have not yet received the hard drive so can't confirm if a different drive fixes the problem, but can address some of your posts: 1. Original caps looked very good, but for giggles I did recap all but two of them (I didn't have tantalums in the right...

I forgot to add that in investigating this problem, I zapped the PRAM numerous times, including once in which I followed the Apple instructions of letting it bong 3 times before releasing the keys. I also replaced the PRAM battery (which needed replacing anyway). I didn't think the battery was...

I've had a Macintosh LC 575 for about a year that has always worked pretty well. However, after being on the shelf for about the last three months, I could no longer boot it up. Everything looked fine until the Welcome to Macintosh screen came up. At that point, the system simply froze. I...

The symptoms you describe for your SE/30 very closely match those I'm experiencing with a Mac LC 575. The system hangs shortly after displaying the "Welcom to Macintosh" screen. Unlike yours, booting from a floppy on my machine does work and the hard drive can be readily read and written to...

My SE/30 SCSi problem has been fixed!! The via connecting pin 25 of the SCSI chip to pin 9 of the SWIM chip was corroded by leaked capacitor fluids and was no longer conducting. I formed a solder bridge over the top of it after exposing the surfaces of the connecting traces and Voila! the...

TERMPWR checks out good (+5V) on both the internal and external SCSI connectors. I actually checked it at each of the inductors first and finally at the connectors themselves. I can't verify power at the IC due to the short cable connecting the logic board to the computer, but I'm beginning to...

techknight, If i did my research correctly, I should have seen +5V across pins 24 and 25 of the external DB25 connector if the SCSI bus were working correctly. Unfortunately, I measure no voltage differential between 24 and 25. So, if that's the problem, what's the cause? Is this a hard drive...

techknight, thanks for weighing in. Your videos were very helpful in getting me rolling, but I'm afraid I'm lacking background information to act on your current suggestion. What I have is a drawing of the 53C80 with connections to various pins on the internal and exernal connectors. What I...

ixnay on the ematicschay request. I just realized that zuiko21 gave me the logic board connections for the 53C80 in the link in his response. I thought it was a pix of his board and I hadn't gotten around to looking at it until just now. The drawing may be a little cryptic to interpret, but...

Cool. The symptoms were very similar to my problem, but on your board, the software at least detected that something was out there. On mine, SCSIProbe just blinks "SCSI Bus Not Terminated" and only shows the Mac itself at SCSI 0. I'm convinced it's nearly an identical failure, but also just...

JDW, I'm working on a MAC SE/30 and like your simple idea on discharging the CRT, but I'm a bit nervous trusting the technique since I don't understand how it discharges the CRT (and REALLY don't want to find out the hard way whether it's true). Did Dr. Lee explain why this works?

Gents, thanks for the quick update. Just got done watching about 4 of TheTechKnight's Youtube videos on resolving SE/30 problems to see if I could learn more. He also had a SCSi problem and traced it to a similar cause (bad connection, not bad chip). This gives me hope that my board can be...

zuiko21, Which connection was broken? The problem you encountered is VERY similar to what I'm trying to resolve on my newly recapped SE/30 (my system reports that the SCSI Bus is not terminated). Any receommendations regarding where on the MOBO you found the bad connection would be much...