NTC 5D-9 Thermistor?



My son's 3-month old desktop computer failed and upon troubleshooting it, I
found that the thermistor (TH1) that is in series with a 6.3A glass fuse and
located in the 120VAC input power feed inside the power supply module had
self-destructed. I tested the soldered in fuse and it was still good, so
assume that it did not fail due to an over current situation. To determine
conclusively that the failure did not result from a PSU secondary problem, I
temporarily bypassed (shorted) the blown device with a jumper. When I did
this the PSU and computer came up normally so I conclude that this is an
isolated failure, possibly due to an under-designed component in a cheap
imported PSU that came in the tower unit he built. (I believe it is a 600W
PSU and the computer is pretty lightly loaded without many peripherals, so
that is why I suspect it just being infant mortality, or possibly an
under-designed part in this design).

I know that the purpose of the device is to limit the start up inrush
current to the PSU and protect down stream devices, so I definitely ant to
replace it. Unfortunately, I'm not sure yet what the local Radio Shack will
stock and wanted to know in advance what generic substitutes I might be able
to use for this purpose.

Basically, what I am asking is how do I read the 5D-9 value that was stamped
on the old part? Is there a current rating and if so was the old part
consistent with the 6.3A fuse or was it undersized and that is why it failed
after just 3 months of use? Does the "5" in the first part of the rating
indicate the resistance in ohms and if so, is this the steady state value or
at the start up/inrush?

Knowledge on the part nomenclature, reliability, and use in a SMPS is
desired. Suggestions on suitable replacement parts that will prevent this
from occurring again are welcome. Thanks in advance.

Bob S.


.



Relevant Pages

  • Re: Yamaha R-50 receiver failed
    ... A shorted rectifier or main filter cap would blow the fuse every ... The receiver in question has a DC and current detect circuit, ... possible for a bridge or cap to have a short with the trickle charge ... protection is able to monitor both PSU and attached devices. ...
    (sci.electronics.repair)
  • Re: 3 blown Power supplys in 6 months.
    ... firecracker which I guess came out of the PSU. ... I am going to take Leythos's suggestion and investigate which fuse on ... The power leads have no fuses. ... >>> not use the proper screw size and will short a trace ...
    (microsoft.public.windowsxp.hardware)
  • Re: Yamaha R-50 receiver failed
    ... A shorted rectifier or main filter cap would blow the fuse every ... The receiver in question has a DC and current detect circuit, ... possible for a bridge or cap to have a short with the trickle charge ... protection is able to monitor both PSU and attached devices. ...
    (sci.electronics.repair)
  • Re: What have I done now?
    ... The PSU had a nowtput to the minotaur and somehow the ... > fuse in the 13A plug or in the PSU. ... Fan kicks when I connect 240v ac and switch on at the back. ... If the worsest cometh to the worsest and I've frazzled it, ...
    (uk.rec.sheds)
  • Re: How hot should an LCD TV transformer get?
    ... I wonder if they are made for a mains voltage ... run off 12 volt DC or 240 AC, with a supplied transformer. ... Look at the TV power rating - divide power by volts to get current ... then look at the rating of the PSU. ...
    (uk.tech.digital-tv)