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Hi Everyone,


Just entered the minefield of a faulty psu on my 475.


I removed a large electrolythic 5500UF c1452 seems damaged only 8.5uf on my capacitance meter.


I tried measuring others in circuit and was not sure how reliable my finding were. Some values were around 100uf some off scale (assuming good) some low uf (assuming bad)


I devised a test setup putting the capacitor c1452 across a half-rectifed (single in series rectifer diode) 32v ac signal I've rigged up to check its smoothing action. I got a noisey sawtooth (1v p-p ac) 6.3v dc voltage.


My questions are:


How reliable are my results ?
where is the best uk source of replacement capacitors ?
also is it likely that 2 or 3 capacitors are damaged ?


Regards


Alan

Jerry Massengale

Hi,
Your C1452 sure sounds bad. It would be good to have an ESR meter. You do not say what the expected capacitances were of the ones that were 100uf off but in circuit test with a capacitance meter can give you reading that are useless. A 475 is old enough to have several caps in poor condition. I would not trust a capacitance meter to judge the ability of an old cap. There are ESR meters available on Ebay for example. These meters are a much better indicator of cap performance.

Jerry Massengale

On 11/17/2014 9:37 AM, alan_w_global@... [TekScopes] wrote:

Hi Everyone,


Just entered the minefield of a faulty psu on my 475.


I removed a large electrolythic 5500UF c1452 seems damaged only 8.5uf
on my capacitance meter.


I tried measuring others in circuit and was not sure how reliable my
finding were. Some values were around 100uf some off scale (assuming
good) some low uf (assuming bad)


I devised a test setup putting the capacitor c1452 across a
half-rectifed (single in series rectifer diode) 32v ac signal I've
rigged up to check its smoothing action. I got a noisey sawtooth (1v
p-p ac) 6.3v dc voltage.

From this description the cap should charge up to about 40 volts and if
there is no load on the cap, there should be little if any ripple.
The basic rule of the thumb is that a 8000UF cap should filter to a one
volt ripple with a one amp load.
This is with a full wave supply and using a scope to measure the ripple.
It's best to get the AC from a variable transformer so that the DC level
can be brought up to about 80% of the capacitor rating.
Note that this is just to measure the capacitance or storage ability but
will also show leakage if you are careful.
Beyond this ESR a DF sometimes need to be considered.

My questions are:


How reliable are my results ?

See above

where is the best uk source of replacement capacitors ?

Mouser???

also is it likely that 2 or 3 capacitors are damaged ?

In my long term Tek experience, caps have proven to be either very good
or very bad
and if a dut scores poorly on any of the listed parameters, IMHO it is
bad on all of them.

My favorite in-circuit test is still to just insert a 20KHZ .2 volt
signal at a suspected trouble spot
with the scope connected and see what happens.
A good capacitor should "eat" just about all of it.


I personally don't believe in blanket replacement except in cases like
the underrated tantalum problem
that is so well covered on this list.
Other list member may differ ( strongly ) on this point.

Regards


Alan

[Non-text portions of this message have been removed]

Thanks Bert.

Would it be ok to use a similar value capacitor temporarily so that I can continue testing for other faults?


Regards


Alan

Alan,
Plus or minus 10 or 20 percent on the capacitance will make no
difference. The voltage rating needs to be at least 1.5 times the
operating voltage. So if you have a 4400mfd cap rated at 25 volts on a
12 volt line you could use a 3300 to 6600 mfd cap rated at 16 to 35
volts without any problems.
Thanks,
rich!

Thank Jerry,

I have ordered one of the meters with quite a flash screen from china, only a few pounds, and seems to test a whole lot of other components too.


Regards


Alan

great investment

Jerry Massengale

On Mon, 17 Nov 2014 13:33:18 -0500, you wrote:

In my long term Tek experience, caps have proven to be either very good
or very bad
and if a dut scores poorly on any of the listed parameters, IMHO it is
bad on all of them.

When I have found one bad aluminum electrolytic capacitors, often tests show
that the dissipation factor of the others has become several times the maximum
listed in the specifications. A couple of times I have found aluminum
electrolytic capacitors which tested good in all respects except at higher
frequencies. In decoupling applications this results in poor transient
response.

My favorite in-circuit test is still to just insert a 20KHZ .2 volt
signal at a suspected trouble spot
with the scope connected and see what happens.
A good capacitor should "eat" just about all of it.

I like testing for dissipation but I lack a dedicated ESR meter.

I personally don't believe in blanket replacement except in cases like
the underrated tantalum problem
that is so well covered on this list.
Other list member may differ ( strongly ) on this point.

I replace all of them depending on the details:

1. When accessing the area is difficult.
2. When it is better to order a whole set of replacements anyway to avoid
excessive shipping on multiple orders.
3. When one of a set of capacitors operating under similar conditions has gone
bad.
4. If I have to remove an aluminum electrolytic capacitor for testing, I usually
decide to replace it even if it tests good if it is old.

Regarding quick & convenient modern component testing. I suggest this item which I and several others I know (net 200 years electronic experience) have built and are full of praise for!


It tests FETs, Triacs, Bipolars, diodes, LEDs:all with Vf, Vth and Hfe as appropriate, resistors, Caps & ESR, inductors. Handles any pinout and identifies the pinout & polarity of semiconductors for you for unknown parts. It is small and handy enough to use anywhere. I built it in under an hour, no probs.

For me it's great when matching components for a build or reusing salvaged parts. Instant analysis of a pulled component for repair is great as well.

Thanks for the kit suggestion, I have ordered something similar already But this seems good too.

Cheers


Alan

Thanks David,

I like the 2khz test I'll try that.


Cheers


Alan

yes, I too thank you for the heads up, and have ordered the kit. Can
you tell me how it does as a ESR meter?

"Having sex is like playing bridge. If you don't have a good partner,
you'd better have a good hand"
--Woody Allen--

Alan,
What kit is this?
Thanks,
rich!

Hi Rich sorry for late reply I bought this:

Small 12864 LCD Transistor Tester Capacitance ESR Meter Diode Triode MOS LCR NPN



Small 12864 LCD Transistor Tester Capacitance ESR ... Small 12864 LCD Transistor Tester Capacitance ESR Meter Diode Triode MOS LCR NPN in Business, Office & Industrial, Electrical & Test Equipment,...



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Alan,

This looks like it would be very handy to have. When you have a chance to
use it we will all be interested in how well it works, and what, if any,
drawbacks it has.

Thanks, Dennis Tillman W7PF

On 11/18/14 9:02 AM, Ancel mosaicmerc@... [TekScopes] wrote:

Regarding quick & convenient modern component testing. I suggest this
item which I and several others I know (net 200 years electronic
experience) have built and are full of praise for!

I sprung for one of these on the strength of your report. I'd been
watching many auctions of similar things, but most ship from China. It's
inexpensive (below my what-the-heck threshhold) and can ship from US.
Got here yesterday.

Took me all afternoon (not an hour like some of you wizards) to build,
partly because my hands are not as steady as they used to be, partly
because these parts are getting smaller, and partly because the last kit
I built was a Heathkit.

Only one problem with the kit. The 28-pin DIP socket had lost three
pins. Two were loose in the bag and I put them back, but I didn't have
any like them and one pin short just won't do. I grabbed a 20-pin and
an 8-pin out of my thirty-year-old stock and used them.

Seems to work just fine (resistance reads a little high, somewhere
around 1%). I might want it to be a voltmeter and/or a frequency
counter as well, but it's just a device for passive parts. Even so, I
have one item for that wish list: If I stick a crystal in, tell me its
frequency.

Some fine-tuning I'd like someone else to do... Use the classic
triangle-wave symbol for a resistor. Curve one of the lines in the
capacitor symbol and indicate appropriate polarity.

I'm not sure how much I want to tighten and loosen those screws in the
test fixture. I suppose it would be simple enough to wire up an
outboard ZIF socket there.

--
Jeff Woolsey {woolsey,jlw}@jlw.com,first.last@{gmail,hp,jlw}.com
Nature abhors straight antennas, clean lenses, and empty storage.
"Delete! Delete! OK!" -Dr. Bronner on disk space management
Card-sorting, Joel. -Crow on solitaire

zif:
DIY Meter Tester Kit For Capacitance ESR Inductance Resistor NPN PNP Mosfet M168 images - LED Night Lights images





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