Re: NEOTEK: Rebuilding a power supply; parts question

Sun, 16 May 2010 14:38:28 -0700 

Hi
I would tend to agree with Ike in that unless the transistors and rectifier (particularly) get more than a comfortable 'hand hot' then it is not worth installing a fan, which is itself more likely to fail than a 'moderately warm' piece of kit. Fuseholders are an interesting case in that their operation depends on them getting hot (to melt the wire inside during a fault) but that it does get warm in normal use which tends to encourage degradation of the terminals which in turn makes them hotter and prone to failure. Poor assembly and soldering is inexcusable although what I remember of the unit I worked on a while ago the mechanical assembly is a little 'strained' possibly encouraging failure unless carefully assembled. A bit like CSI, some interesting (yawn) effects come to light in gear left on for years on end which in turn suggests better ways of doing things. As a useful 'dodge', if you have a known stable mains supply you can investigate running the supply on a higher mains tapping (if possible) so that less power is wasted as heat in the supply. The only downside is that if your mains 'dips low' then you may get some mains 'ripple' appearing on the audio (120Hz in the USA). Certainly worth a thought and cheaper than a fan. 
Matt S

Ike wrote:

Guys,
It's been my experience that these supplies, at least the PS-3, do not run anywhere near hot enough to need fan cooling. 100% of the heat damage that I have seen has been due to bad solder joints on mainly the fuse holders and the pass transistors causing specific connections to heat up. All a fan will do in that case is possibly extend the MTBF. Some of the supplies I have rebuilt are in their 7th and 8th years of nearly constant use. Best 
Ike Zimbel
Zimbel Audio Ltd
416-720-0887
www.zimbelaudio.com <http://www.zimbelaudio.com>
Sent from my iPhone
On 2010-05-16, at 10:36 AM, Mike Thompson <[email protected] <mailto:[email protected]>> wrote: 


Awesome, thanks guys.
Would it be even better to go a step above and install a quiet fan into it? Either way this is going to be racked with at least 1U of space open top and bottom.
--- On *Wed, 5/12/10, Matt Syson /<[email protected] <mailto:[email protected]>>/* wrote: 


    From: Matt Syson <[email protected]
    <mailto:[email protected]>>
    Subject: Re: NEOTEK: Rebuilding a power supply; parts question
    To: [email protected] <mailto:[email protected]>
    Date: Wednesday, May 12, 2010, 4:39 AM

    Hi
    The main killer of power supplies in the long term is HEAT.
    Electronic parts are 'happiest' at around 20 - 25 Centigrade and
    the closer you can keep ALL the parts to this the better. Of
    course to achieve this involves decent airflow and intelligent
    placing of parts so that the ones that can tolerate a little more
    heat are placed in a suitable position.
    Overrating of particularly the 'pass' transistors and the main
    rectifier is 'cheap' insurance. In a 'power one' 13 Amp supply
    module they run 2N3055 transistors at about 2 Amps per device
    which is sensible and I have never seen any failures of these
    devices out of what must be over a thousand units. Rectifiers and
    occasionally transformers are a different issue.
    Remember that heatsink temperature is lower than the temperature
    the transistors (and rectifiers) get to so if the heatsink feels
    too hot to touch (or hold comfortably) then the transistors are
    probably being run a bit hard. Here, having multiple devices
    helps spread the strain as the interface between the transistor
    and the heatsink, using an insulating washer can allow
    significant difference. Make sure you have effective thermal
    compound in there and the screws are tight.
    With shortage of studio space and the fact these supplies are
    silent it is tempting to hide them away somewhere. They MUST have
    good cooling airflow.
    Matt S

    Ike wrote:
    > Hi David
    >       No daggers from this quarter! The only thing I would add
    is that what I have found with over a dozen PS-3's that I've
    known is that the failures are almost entirely due to assembly
    problems. IOW the parts that fail tend to do so because they
    weren't soldered and/or mounted properly at the factory. Once
    these things are corrected they can and do run for years without
    any trouble.
    > Best
    > Ike Zimbel
    > Zimbel Audio Ltd
    > 416-720-0887
    > www.zimbelaudio.com <http://www.zimbelaudio.com>
    > Sent from my iPhone
    >
    > On 2010-05-11, at 11:29 PM, David Butler <[email protected]
    <mailto:[email protected]>> wrote:
    >
    >> As a former power supply engineer I will weigh in here, all
    the while watching my back for daggers!
    >>
    >> :-)
    >>
    >> In general, PSU designers do NOT underrate components enough,
    IMNSHO. This is why so many power supplies dies early, untimely
    deaths. The capacitors in particular, tend to bake. If higher
    temperature caps can be found, so much the better. In general,
    going up a little in voltage rating on caps is OK, SOMETIMES
    going up in value is OK too, depends on the design. The idea all
    around is that heavier is GENERALLY better. You don't want to go
    extremely high on capacitor voltages: they are happiest on a diet
    of 50% or so of their nominal ratings.
    >>
    >> The power transistors can sometimes benefit from having higher
    voltage, power and current ratings, as long as everything else
    (gain especially) is the same. Personally I like rectifiers rated
    at at least double, if not triple, the PEAK voltage in the
    circuit. Again, rating for higher temperature handling rarely hurts.
    >>
    >> If the supply in question lasted a long time with no problems,
    there is no fault  to be placed on using exact replacements
    either. My own take is to be conservative by going for heavier
    parts if the costs are not excessive.
    >>
    >> Just my 50 cents...
    >>
    >> db
    >>
    >> --   David 'db' Butler
    >> AV Wizard, Audio Guru & Team Leader delivering exceptional
    >> on-time & under-budget results with cutting edge technologies.
    >>
    >>
    >> Quoting Mike Thompson <[email protected]
    <mailto:[email protected]>>:
    >>
    >>> I have a question regarding parts replacement -
    >>>
    >>> i have a tech who has looked at my Series 1E power supply and
    told  me he could rebuild it with no problem, but I wanted to
    make sure  before I handed it off to him if there were any parts
    that needed to  be specific values (equal to or greater),
    anything that should  specifically be improved upon when
    rebuilding, how to make it  compliant to the standard, or any
    other tips to make sure I get the  most out of it.  I know some
    of you guys had rebuilt them and I  figured this was the best
    place to ask.  Let me know.
    >>>
    >>
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