IRIS 2400/ SMPSU questions
compoobah at valleyimplants.com
compoobah at valleyimplants.com
Sat Oct 22 00:36:08 CDT 2005
Turns out the second bit wasn't a varistor, but a disk cap (.1mfd/50v)
I'm now trying to figure out what happened. It seems rational that the paper cap blew first, but from there I'm not sure. It seems a bit bizarre that two caps blew at the same time.
The paper cap was wired between the primary of a transformer and a large power resistor that connected to (ground? the other side of the primary, anyway, and whatever that went to). The second problem area was from the secondary of the same transformer. 4 leads run to a stud rectifier bridge, and across each stud there is a .1mfd/50v disk cap dumping into a 3.3ohm 2-watt resistor connected to the other side of the rectifier. This resistor burnt up.
The only options I could think of was that the demise of the primary cap set up a oscillation of sufficiently high frequency that the reactance of the .1mfd cap was sufficiently low that enough current went through to overload the resistor, or (2) 2 capacitors went on the fritz, and on the second one the shorting whiskers burnt away without blowing the cap because of the load resistor, which smoked instead, or (c) some bizarre transient appeared on that winding that blew the 50v dielectric and was blocked by the final output choke so that it didn't blow the final 7.5v electrolytic filter caps.
And now for the question- I have new caps/resistor- should I look anywhere else for problems before I plug everything back together? None of my theories sound really convincing, and I don't want to blow anything else in this machine.
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