Computer PSU Schematic ATX-250GTA

  • Thread starter Thread starter rubenz1967
  • Start date Start date
Thanks to all for the help, I've got plenty to chew on. I'll post some
pics and results after I get the repair finished.
 
I ordered both metal film and metal oxide resistors for the replacement
resistors. Which would be best for this application, or would there be
no difference:

Metal Film Flameproof:

http://www.vishay.com/docs/31021/cpf.pdf

Metal Oxide Power Resistor:

http://www.mouser.com/catalog/specsheets/XC-600043.pdf
Click to expand...

You don't have to be very picky about resistors used, since you have
silver solder you might even be able to solder a new end (lead) on each
old resistor. The idea with the silver solder is that using a solder
with a melting point high enough above that of 60/40, you can prep the
resistor with the new lead before stuffing it on the PCB, then solder
it to the PCB with lower heat and 60/40 without melting the silver
solder again.

Flameproof would be fine, I'd tend to buy whichever is cheaper or since
there is typically savings in buying bulk, whichever you might find a
use for other than this PSU repair then buy 10 or 24 or whatevever the
quantity for the price break... but I have no idea if you'd ever have
use for more. Generally the best choice is one I'd mentioned
previously, the highest wattage rating (and physical size to the extent
that a larger resistor surface area helps to cool it, in some designs
the leads 'sink away some heat to the copper but given the trace repair
on this PSU, it would be ideal to have radiation of heat from the
resistor as much as possible instead of through the leads). Also, just
because the one resistor wasn't tombstoned, doesn't mean you can't
tombstone it's replacement... but this is another detail you can judge
best since you have the board in front of you.

However, the more significant part of the repair is fixing the torn
trace and making sure the resistors are immobile, buying the cheapest
resistor (was it Mouser you used?) carries would be fine. If they
weren't high tolerance or were inductive they'd still meet the basic
requirement, only that they can sustain contast current (heating).
 
You mentioned epoxy to fix the resistors in the tomb-stoned position,
what other alternatives are there? Would hot melt glue work? I ended
up having to get the 12.5mm 3300uf caps, as 10mm seems to be rare. As
a result, some lead will be exposed, as the tight fit will mean the
caps will sit up high. Should I just shoot some silicon under there?
Slide some heat shrink to cover the exposed lead?
 
You mentioned epoxy to fix the resistors in the tomb-stoned position,
what other alternatives are there? Would hot melt glue work?
Click to expand...

No, it is a very bad choice because it has a low melting point.
Further, it's not very solid even when set, the ideal fixation method
does not allow any movement, particularly on the resistor leg soldered
to the makeshift-repaired trace as it is bound to be fragile (unless
completely covered in epoxy on the bottom as suggested previously.

Keep in mind that it "could" only be the caps and resistors that need
replaced, but supposing the possibility that some other parts are bad
too, it would be best to keep the epoxy on in the near vicinity of the
parts being replaced. ie- not covering too many leads for other parts
further away.


I ended
up having to get the 12.5mm 3300uf caps, as 10mm seems to be rare.
Click to expand...

As already mentioned, you did not need 3300uF, necessarily. Many other
supplies have same basic requirements and don't use 3300uF. Even so,
within same family of cap, jumping up to a larger size will tend to
increase it's lifespan and reduce ripple some due to the inherantly
lower ESR of the larger physically sized cap.
As
a result, some lead will be exposed, as the tight fit will mean the
caps will sit up high. Should I just shoot some silicon under there?
Click to expand...

No, you do not want anything that will have the potential to
permanently seal it. You could put a bead around the perimeter but the
goal should not be to cover entire bottom of the cap. I would do as
suggested previously (if I were trying to fit a 12.5mm in a 10mm
space), take a block of plastic and drill a couple holes for the leads
(typically 5mm or 0.2" apart is the lead spacing for 12.5mm diameter
caps).

Slide some heat shrink to cover the exposed lead?
Click to expand...

How far off the board is this cap going to be? You can't just
indefinitely extend the lead because it negates the benefit of having a
low ESR cap if the cap isn't close to a wide trace. If it's going to
be sitting pretty far away, you might want to put a 0.1uF mono ceramic
cap parallel to it, close to the board.

If the leads are long enough that it looks possible that they could
short against something else, yes definitely do put heat shrink or
other heat resistant tubing over the exposed area... or if sitting on
the plastic block, that would be enough.

If you come across this issue again, I suggest simply using the 10mm
diameter part. My prior recommendation still stands, to use the 6.3V
rated and tallest available. In many brands that would be about 2200uF.
 
You mentioned epoxy to fix the resistors in the tomb-stoned position,
what other alternatives are there? Would hot melt glue work?
Click to expand...

I use silicone rubber sealer because it can stand 500 deg. F. but is
soft enough to cut up or tear off if I ever have to remove the
component.
I ended up having to get the 12.5mm 3300uf caps, as 10mm seems
to be rare. As a result, some lead will be exposed, as the tight fit
will mean the caps will sit up high. Should I just shoot some silicon
under there? Slide some heat shrink to cover the exposed lead?
Click to expand...

I had to do that recently with a PSU and used heatshrink. A blob of
silicone rubber under the cap should help hold it, but I also bent the
leads into an "N" or "L" right above the circuit board, before
soldering, for extra mechanical strength. I was told that extending
the leads an inch would be OK for caps on the output side. However I
soldered #16 solid wire right up to the caps (wrapped thin wire around
each pair of wires for reinforcement), hoping this would reduce any
inductance.
 
I do not think any of the caps are going to sit up more than about a
1/4", I'll use heat shrink and secure with a blob of something. I have
since looked at several PSUs, some as high as 450W and indeed all had
smaller caps, 2200uf/6.3V. I received a new PSU yesterday so was able
to test it on the board this damaged PSU used to power, an MSI 6337
815ET Pro. The new PSU will not power up, the board is quite possibly
damaged, but this board is known to have cap problems. They are not
leaking, but they are TEAPO, which some feel had issues on this model.
Any ideas what to check on the board?

I ended up getting a COOLER MASTER eXtreme Power RS-430-PMSR/P for
replacement (was $23 shipped on Newegg recently). It has HiPro branded
compenents inside and some print on the case makes it out to be their
450W model. It too has TEAPO caps, but one thing I do not like about
this unit is that there is no plastic bushing where the cable harness
exits the house, the metal is just folded over. First time I have seen
that. I noticed there is quite a bit of epoxy fixing down the caps,
resistors, coils, and other standing devices.

I also opened up an Enhance 230W PSU that must be 5 years old and has
been powering a 1.3Ghz (Tualatin), looked brand new inside, well made
unit apparently.
 
I do not think any of the caps are going to sit up more than about a
1/4", I'll use heat shrink and secure with a blob of something. I have
since looked at several PSUs, some as high as 450W and indeed all had
smaller caps, 2200uf/6.3V. I received a new PSU yesterday so was able
to test it on the board this damaged PSU used to power, an MSI 6337
815ET Pro. The new PSU will not power up, the board is quite possibly
damaged, but this board is known to have cap problems. They are not
leaking, but they are TEAPO, which some feel had issues on this model.
Any ideas what to check on the board?
Click to expand...

Check that the new PSU has it's AC voltage switch set
correctly per your location. Clear the CMOS on the
motherboard. The old power supply might've damaged the
motherboard, if you had the two load resistors shorting out
against each other and it sent a higher voltage on one of
the lower voltage rails, there is a fair chance of damage to
the board.

I ended up getting a COOLER MASTER eXtreme Power RS-430-PMSR/P for
replacement (was $23 shipped on Newegg recently). It has HiPro branded
compenents inside and some print on the case makes it out to be their
450W model. It too has TEAPO caps, but one thing I do not like about
this unit is that there is no plastic bushing where the cable harness
exits the house, the metal is just folded over. First time I have seen
that. I noticed there is quite a bit of epoxy fixing down the caps,
resistors, coils, and other standing devices.
Click to expand...

Teapo makes decent caps. Perhaps some of their older ones
were problematic but they weren't one of the most notorious
brands with constant failures. Why would you like that a
PSU has no plastic bushing? It's actually slightly better
with the bushing because it keeps the wiring harness from
being pushed in or out while dealing with it, so the wire
connections to the PCB are less stressed. However, when
it's only a folded metal hole that can work equally well if
there is also a strong/tight nylon wire tie securing all the
wires to the case (not just bundling all the wires together,
but at least that is better than nothing).

The power supply you bought is probably a good value for the
aging system (if the system had worked still?) but in
general Cooler Master is not as good as SPI's 400W models.
As much as wattage rating on 3rd party units (Cooler Master
doesn't actually make PSU, they relabel them) you can get an
indicator of quality based on regular retail pricing... a
decent PSU just costs more, corner-cutting is required to
achieve the lower price points.

I also opened up an Enhance 230W PSU that must be 5 years old and has
been powering a 1.3Ghz (Tualatin), looked brand new inside, well made
unit apparently.
Click to expand...


How new they look can have a lot to do with the environment.
Dusty room or moderate to heavy smokers can make even a few
months old PSU look old inside. The PSU isn't so picky
though, it merely needs cleaned out before the buildup gets
too bad. Such residue is usually more problematic on other
mechanical connectors, particularly those that had remained
unused then later system changes cause them to be used after
exposed to accumulate the *dirt* buildup.
 
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