27 Jul
2007
27 Jul
'07
9:55 p.m.
Thanks again to everyone offering suggestions for fixing my Apple III's
power supply.
I opted to do a wholesale replacement of the electrolytics in the power
supply, since I was likely going to be removing all of them to test them
anyway and there's only a handful to take care of. $9 worth of parts
later, the issue seems to be resolved -- the system powers up and runs
diagnostics. (Though it keeps cycling, so I don't know yet if that's
another problem or normal behavior :)).
The only thing I have noticed is that there's a very noticeable "hiss"
noise coming from the power supply -- not sure where, exactly. Any
ideas if this is normal? At the moment I have only the motherboard &
256k RAM expansion running (no keyboard or floppy drive.)
Thanks again!
Josh
28 Jul
28 Jul
7:47 a.m.
From: Josh Dersch <derschjo at msu.edu>
---snip---
The only thing I have noticed is that there's a very noticeable "hiss"
noise coming from the power supply -- not sure where, exactly. Any ideas
if this is normal? At the moment I have only the motherboard & 256k RAM
expansion running (no keyboard or floppy drive.)
Hi
Many switchers will make such sounds. It is not too unusual.
Dwight
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12:59 p.m.
I opted to do a wholesale replacement of the
electrolytics in the power
supply, since I was likely going to be removing all of them to test them
anyway and there's only a handful to take care of. $9 worth of parts
later, the issue seems to be resolved -- the system powers up and runs
diagnostics. (Though it keeps cycling, so I don't know yet if that's
another problem or normal behavior :)).
In SPSUs it isn't always the wise way. Some of your old capacitors
surely are low-ESR types (you can spot them because they are 105? capacitors
and the high-esr ones are 88?) and it can mess the regulation of your power
supply. Have a multitester around? Know how to use it? Measure the voltage
of the outputs of the PSU and see if everything is ok. If you still have the
old capacitors, take a look if any of them has 105? written on that.
Greetz from Brazil
Alexandre
3:09 p.m.
On Jul 28, 2007, at 3:59 PM, Alexandre Souza wrote:
Whoa, hang on there Alexandre...I've seen no correlation
whatsoever between ESR and maximum operating temperature ratings.
It is definitely true that, in many parts of a switching regulator
circuit, low-ESR capacitors are essential...Not just a nicety, but
absolutely essential for the circuit to function. This is
particularly true of the output capacitor(s). It is also true that
many switching regulator circuits run hotter than some other types of
circuitry, so the use of high-temperature-rated capacitors is often
important in such designs.
However, I respectfully submit that low-ESR and high temperature
ratings of electrolytic capacitors for use in switching regulator
circuits is essentially a coincidence. While I've not specifically
researched this, I have designed quite a few switching regulators,
and during the component selection process I've not seen anything to
suggest that a high temperature rating implies low ESR.
Typical symptoms of excessive ESR in a switching regulator's
output capacitor is excessive ripple and poor line regulation. These
problems can be severe (up to and including SMOKE) if "ordinary"
capacitors are used without paying attention to their ESR.
-Dave
--
Dave McGuire
Port Charlotte, FL
Farewell Ophelia, 9/22/1991 - 7/25/2007
I opted to do
a wholesale replacement of the electrolytics in the
power supply, since I was likely going to be removing all of them
to test them anyway and there's only a handful to take care of.
$9 worth of parts later, the issue seems to be resolved -- the
system powers up and runs diagnostics. (Though it keeps cycling,
so I don't know yet if that's another problem or normal behavior :)).
In SPSUs it isn't always the wise way. Some of your old
capacitors surely are low-ESR types (you can spot them because they
are 105? capacitors and the high-esr ones are 88?) and it can mess
the regulation of your power supply. Have a multitester around?
Know how to use it? Measure the voltage of the outputs of the PSU
and see if everything is ok. If you still have the old capacitors,
take a look if any of them has 105? written on that. 
3:22 p.m.
On 28 Jul 2007 at 18:09, Dave McGuire wrote:
Whoa, hang on there Alexandre...I've seen no
correlation
whatsoever between ESR and maximum operating temperature ratings.
I can see one. If you try using a non-low-ESR cap in a SMPSU that
requires one, the temperature of said cap will rise very quickly.
Not exactly the correlation intended, but there IS one!
Sorry,
Chuck
5:04 p.m.
So... how do I tell whether the capacitors I've put in there are low or
high ESR? Are there particular markings I should be watching out for?
I just bought these from the local electronics shop, I had no idea there
was anything to look out for aside from voltage & capacitance. Guess I
shouldn't assume these things :).
Thanks,
Josh
Chuck Guzis wrote:
On 28 Jul 2007 at 18:09, Dave McGuire wrote:
Whoa, hang on there Alexandre...I've seen
no correlation
whatsoever between ESR and maximum operating temperature ratings.
I can see one. If you try using a non-low-ESR cap in a SMPSU that
requires one, the temperature of said cap will rise very quickly.
Not exactly the correlation intended, but there IS one!
Sorry,
Chuck
29 Jul
29 Jul
12:57 a.m.
Josh Dersch said:
So... how do I tell whether the capacitors I've
put in there are low or
high ESR? Are there particular markings I should be watching out for?
I just bought these from the local electronics shop, I had no idea there
was anything to look out for aside from voltage & capacitance. Guess I
shouldn't assume these things :).
Typically, you can't find this out from the stuff at a local shop, and in
some cases the sellers who occasionally even claim to have a BA in EE, do
not even know what ESR actually means :-(
Best choice is to pay the price for buying from larger distributors from a
catalogue, as they do specify what parameters the components have and
where they come from.
--
Holger
9:37 a.m.
From: Josh Dersch <derschjo at msu.edu>
So... how do I tell whether the capacitors I've put in there are low or
high ESR? Are there particular markings I should be watching out for? I
just bought these from the local electronics shop, I had no idea there was
anything to look out for aside from voltage & capacitance. Guess I
shouldn't assume these things :).
Thanks,
Josh
Hi
Not all the caps need to be low ESR or that would be the only type made.
The ones that filter the outputs of the secontary rectifiers should be
low ESR. The input rectifier filter caps should be low ESR types as well
but this isn't as critical.
Most others are low current filters and don't have the same requirement.
When used as bypass on boards, there are suppose to be high frequency
caps ( ceramics and such ) to deal with the high frequency currents.
Dwight
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alexandre-listas＠e-secure.com.br -
cclist＠sydex.com -
derschjo＠msu.edu -
dkelvey＠hotmail.com -
holger.veit＠iais.fraunhofer.de -
mcguire＠neurotica.com