Recently I was given a NeXTstation turbo with some custom software installed that I need for a project. The NeXTstation had not been booted up for two years, but had worked well back then. Unfortunately, when I turned it on, the NeXT fried a surge protector. Now I'm looking for some advice. Has anyone else experienced this sort of failure? I'd like to provide some further details:
When I first I turned on my NeXTstation, it didn't fry the surge protector immediately. The NeXT actually began booting up -- I could see the sequence on the monitor -- but then my surge protector went off before the boot-sequence was completed. My surge protector didn't just turn off, it had been fried. I might mention that I was also using a generator for power. We are off the grid here, but I didn't want to use my inverters because they are not of the true sine wave variety. I've tested the generator and it seems to be working okay, and not frying surge protectors on its own. In fact I've been using it since with two different computers and a large screen tv with no mishaps.
Anyway, after the surge protector malfunctioned, I was a little concerned, but decided to try to boot up the NeXT again. So, I hooked up another surge protector, which was of a different brand and type. This time, as the NeXTstation booted up, I saw smoke rising from the new surge protector. So, I quickly turned off the power strip in mid-boot. The second surge protector was also fried.
I disassembled both surge protectors to inspect the circuitry. The mode of failure in both cases was a high voltage between the hot wire and the ground that had fried the varistors. The fault began in both instances shortly after I turned on the NeXTstation. It's as if a very high voltage had been injected back into the power line.
Does anyone have some insight into how this could have happened? I am a bit of a hardware guy, but I know nothing about the design of the self-adjusting power supplies used by the NeXT.
After thinking about it all and doing some internet searching, my hunch is that some capacitors in the power supply have failed. Electrolytics dry out over time, and will cause all kinds of problems. Also, I'm aware that NeXTstations are notorious for power supply failure.
I think there is a high probability that the computer itself will still function if the power supply is replaced or repaired, and I'm up to the task. This sort of thing is not unusual in old electronics. I've had to rebuild old power supplies before. In this case it will be well worth the effort. Just trying at this point to gather any relevant information before proceeding.
Quote from: "seedpress"After thinking about it all and doing some internet searching, my hunch is that some capacitors in the power supply have failed.
Interesting story. I doubt this is the problem though as the NeXT components tended to be of better quality than what comes out of Guangdong today. Stations are fused, if I recall (mine are in storage), and if yours are intact while the varistors are not, then you have a reactive load problem (or reactive source problem). The design is almost 20 years old and is not a modern switched power supply. If it is anything like the cube's, there's an isolation transformer feeding a bridge going to a capacitor producing high-voltage DC to feed the downstream regulation. This will probably not be happy with high frequency events on the power line. (Going from memory here, traced the cube's supply a long time ago...)
What, exactly, does your generator output if you consider your inverter's output too dirty?
Quote from: "cubist"
What, exactly, does your generator output if you consider your inverter's output too dirty?
I'll have to dig my scope out and take a look at my generators output to see how clean it is. I know that my inverter is one that approximates a sine wave by using a staircase waveform, which inherently contains harmonics. My understanding is that such inverters can sometimes cause problems with reactive loads. That's why I used my generator. I've always been able to run reactive loads with it, such as power tools, washing machines, etc.
I called Rob at Black Hole and he suggested that I try to plug it into regular mains power, which I plan to do at when I can get to some.Quote from: "cubist"
Stations are fused, ...if yours are intact while the varistors are not, then you have a reactive load problem (or reactive source problem).
Maybe my generator and the NeXTstation's isolation transformer/capacitor combination interacted in some way that combined to generate peak voltages that burnt out the varistors.
I'm going to have to mull all this over. I don't want to damage the NeXTstation anymore than I may have already.
Thanks for input: it gives me some grist to chew on.