Just destroyed my SE/30

Good morning all. This is heartbreaking to report. I've owned a Mac SE/30 for the last 8 years or so. When I bought it, the motherboard (MB) had been recapped, the CRT was bright and sharp and still is. For the past year, I've been sprucing it up, like replacing the Sony power supply with modern ones that have crowbar circuits (Thank goodness for them! They protected the MB from even more catastrophic damage) and a higher current rating. I replaced the fan with a quieter one and replaced the hard drive with a BlueSCSI desktop that also got the SE/30 on-line. I also added an 68030 accelerator card and replaced the Rominator II with a GW-4402B ROM Card. It was really shaping up and the last thing I wanted to do was re-cap it.

So, I bought replacement capacitor kits for both the Analog board and MB and tonight I sat down and installed the new capacitors. Now the MB had it's capacitors replaced when I bought it but whomever did it, did a really ugly job. So I was going to clean it up with Tantalum and electrolytic caps. I replaced all the caps being careful to observe polarity and properly installed with new solder.

I reassembled and powered up and it bonged! Great! But then the Mac shutdown. Weird. I looked around and checked things but couldn't find the problem. Powered it back up while monitoring the 5v rail. The 5v rail was oscillating between 0 and 5v at about a 2 second period and I saw some magic smoke escaping so I powered off immediately and pulled out the MB. C2 had burned up and was looking terrible. I went through the schematics for the SE/30 and found C2 was a decoupling cap for the 5v rail. After cleaning the board up, I rechecked the 5v rail and it's still shorted to ground.

I am so bummed out. The only way to find where the short is to put the 5v rail on a variable power supply and slowly bring the current up and use a thermal camera to identify where it's getting hot. I don't have those resources so there's little I can do. Also, this is a 5 or 6 layer board and if the short is inside the board between the layers, then it's toast. It could be a great candidate to repopulate a new MB but that's beyond my resources as well.

If anyone has any ideas I'm all ears. My wife is already upset with me that I've spent money to rebuild a 35 year old Mac that's only good to play games with. I just downloaded A/UX because I wanted to explore how that worked. Anyway, if you have a possible solution, I look forward to hearing from you.

A very sad Classic Mac owner,
Gerry

Great point Elemenoh! I found a set of schematics for the SE/30 MB and have identified 5 caps that are used to decouple 5 volts around the board that I replaced. C1, C7(blew up), C11, C12 and C13. I know where they are on the board so I can check them.

Phipli, I asked the exact same question the night I changed these caps. I've not worked with SMD caps, so I googled what the stripe meant. It came back and identified it as negative. According to your pictures, the stripe means positive. Crap, if you're right, I installed them all backwards. I bought the kit from Console5. I'll email them.

Jmacz, I did check the voltage rating on the replacement capacitors and they were 25 volts. So I'm good there. I also prefer 105 degree rated caps over 85 degree rated caps depending upon how warm the interior gets. These caps were all 85 degrees but I had to use a magnifying glass to read them.

Thank you for your responses and I'll get to the bottom of this.

Here's my final question, If C7 was backwards and shorted, causing it to blow up (it's totally gone) why is the 5v rail still shorted? That bothers me.

Gerry

Thank you, jmacz. I've emailed Console5 for replacement capacitors and suggested the metal can types.