Bad Caps !!!

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Some pics of bad caps or ones about to go bad !

And some tips on how to check your own caps in your consoles and gear...




First off, MOST caps do NOT need replacing!!

Caps last for years - and years - and years and - years
and actually your old caps may be one of the factors in your equipment's 'Vintage" sound!!


ONLY REPLACE CAPS WHEN YOU SEE SIGNS OF DETERIORATION

OR

if you find that a number of the same cap value and make needs replacement in various cards
(then replace all of that particular cap)


Note that there is NO Special "audiophile" Cap that is any better
then those you can buy off the shelf at the major electronics distrubutors...
 
The MYTH of a 'best audio cap' is just that - a myth and an 'old wives audio engineer' tale

Almost ALL caps manufactured today are excellent for audio use.     And all good caps
have just about the same specification - tight percentage of value, great temperature range,
extreemly low inductance and extreemly high 'self-inductance'.     Todays caps are Great,
and a 50 cent cap will perform JUST AS WELL as a 10 dollar one that some 'audiophile' store will try to
talk you into buying.     Don't believe that "Audiophile cap" crap!     Just buy GOOD normal caps
when you're replacing caps - Vishay/Sprague - Nichicon - Xicon and others all make great caps.

Also.... when replacing caps try to match the original value for capacitance or make small jumps
in value - it's usually ok to go from an original value of 10uf up to 22uf  (never in an EQ circuit !!!),
but NOT 100uf !!!
 
The piece of equipment was designed with those original values - these were are the ones
the designers chose
- and the ones you should keep the same to retain that original 'vintage' sound.
 
So if you find a bunch of 10uf caps have gone bad,
replacing them with the exact same value - 10uf - is the best thing to do
if you want to keep the gear sounding just like the original!!
 
Note you CAN bump up the VOLTAGE rating of any cap without changing the sound
of your gear - a 50 volt cap sounds exactly the same as the orignal 16 volt cap did.

Another NOTE:     You MUST keep the physical size of the Cap very close to the original size!!
Increasing the size of the cap makes the leads longer or makes you position the
replacement cap in a way it should not be.     Often you will cause
more problems by installing a much larger physical size cap because of the longer leads -
increasing the capitance, decreasing the self-inductance, creating new capitance
between board tracks and the new cap's leads, and so on.   Using the same
physical size cap eliminates these problems, so don't buy the wrong size cap!

 
What makes caps go bad?
Many things - heat, age, the voltages the cap 'sees', and so on...
Often it's because the machine sits unused for a few years...
some caps require that voltages actually appear on them every few months or so
and if they sit there without voltage (this is only once the caps have been
used for a long while in their circuit then sit un-powered for a long long time)
they can change their value or become leaky, or in rare cases just go bad completely.
 
Generally the most damaging thing to a cap is heat.
Using caps rated at 105 degrees Centigrade will help
insure a long life and stable operation, and only cost
a few more cents per cap... well worth the extra cost !!
 
Note that the 'normal' small physical size cap has a life of about 7 to 10
years, depending on the amount of heat and ripple currents it has.
But MANY caps are still functioning well after 25 years...
Life time depends on how the Cap was made, it's location in a
circuit, heat, ripple current, DC and AC voltage, and other factors.
 
Do NOT mass replace caps unless you KNOW they are loosing their
original values or failing...
 
 
So First let's look at what some bad caps look like!

Note that bad caps can look fine and still be going bad...
so not all 'bad caps' will look like these ones...
 











 
 

 
 

MORE PICS OF BAD CAPS SOON !!

If you see something like the above, where the rubber or plastic vent cap is puffed out
or if you see a gross gooey gunk coming from the cap - usually at the wire connections -
go ahead and replace it.... if a bunch of the same value and manufacturer of the cap are going
bad, then replace them all...


Note that all normal electrolytic and tantalum caps are polarized -
They have a positive side and a negative side, and they MUST be installed
in the correct way or they may explode or fail right away - so make SURE
that you replace your caps correctly !!!
If you are not sure what you're doing, hire a tech to come in and
replace your caps - or bring your cards over to your tech's shop
to get done right !


Caps to Replace on your Ampex AG 440 - MM1000 - MM1100 or MM1200 Tape Recorder !!

I'm finding that most 440's, MM1000's, MM1100's and MM1200's are now at the age
where a lot of the electrolyics in the Audio Cards are begining to leak
and go bad.

This may show up a a loss of over-all level, a loss of low frequency signals,
cards not working correctly and other probelms.

So in the older Ampex machines I recommend you replace the following caps:

RECORD CARD: C28     10uf 25 volts (replace with 10uf 50 volt caps)
REPRODUCE CARD: C13 and C8   50uf 50 volt (replace with 50uf or 47uf   50 volt caps)

Note these are AXIAL electrolytic caps - the leads are connected to each side of the cap!!

You MUST make sure to install these caps with the correct polarity   !!!!







You'll need the following tools:

++++++++++++++++++++++++++++++++++++
Soldering Iron and Solder



Jameco Electronics part # 229673 $ 59.95 each
get Solder at your local Radio Shack
++++++++++++++++++++++++++++++++++++
Solder "Sucker"



Jameco electronics part # 19166 $ 4.95 each

++++++++++++++++++++++++++++++++++++

Small cutters and small needle-nose plyers


 
How do you check to see if your console or other gear has caps going bad????
 
The best test is to first look at your caps in the various cards or channel strips
you have.... look for puffed out tops, corroded areas, a 'gunk' comming out of
the top or bottom of the cap.   This indicates that the cap is going bad - and it needs replacing.
 
But caps can go bad without showing any physical signs at all !
 
So here's a simple and easy way to check your caps:
 
First off you will need a good oscillator, so borrow one if you don't have one.
You can also go to the front page of the site and download the tones on the
alignment tones page, burn them to a CD, and use those tones to do this test.

It's important that the ocsillator does not change it's output level when
changing frequencies between low, mid and high frequency outputs!

first if you have a 2 buss insert patch point or input jack, send 1khz in at this point and move the
master fader up or down so the VU meters read '0'VU.
Next switch your oscillator to 50 or 40 or 30 hertz.... do NOT touch that Master fader!
The level should not change by more than .5db or less between 1k hz, 50 hertz and 15k Hz...
If it does then you need to replace the caps in the Master Section.
Also check the actual output by looking at external meters....on your tape recorder or whatever.

Next put all channel faders to the same level, no eq, no aux, no high or low cut.
Assign EVERY channel to let's say the Left buss only. Send 1khz to the first channel
(the oscillator gets patched into channel 1's line Input - do NOT put the oscillator into the Mic input!!!).
Bring the Master fader up or down so you see '0vu' on your Main Left Output Channel VU meter.
Make sure you're not overloading the channels of course! then do NOT touch anything!!!

Now send in 50 hertz (or 40 hertz or even as low as 30 hertz) to Channel #1 by changing the frequency at your oscillator.
If your caps are ok, then you should see no level difference (or maybe .5db or less) on that Left Main Output VU meter.
If the level drops by more than 1 db, you likely need to replace caps.
A great test is to go from 100 hertz to 50 hertz to 30 hertz and see if the levels drop lower each time you feed in
the lower frequency - if it does more than just a little you need to replace caps!  Check each channel this same way.
Reference the 1k hertz signal, then 50 hertz (or lower to about 30 hertz), and check the top end too at 10k hz or 15 khz.
You should have no changes in level between 30 hertz and 20khz!

Of course make sure your oscillator is sending out the same level signal at all these frequencies
or the above tests are worthless!!

You may need to move each channel fader just a little to get to '0vu' at the 1khz reference tone,
but if you find a channel that requires significant level changes, then that channel has something wrong with it!

Also you need to listen to the 'quality' of the tones.... each channel should 'sound' the same.

Of course there are more technical (and better) ways to analyize a console's caps,
but the above is a simple and easy way to find out the basic condition of your console without bringing in a lot of tech gear....
or hiring someone like me to do the check out...
 
You can do the very same thing with your tape recorder and any other piece of gear you have -
reference a 1k tone, then send in 50 hertz or lower - then send in 10khz and 15khz,
the levels should NOT drop by more than 1/2 db in a normal situation -
frequency responce MAY change in a compressor, and of course WILL change when you are using a tape
recorder in the record/reproduce mode.... so some gear you just can't always test as simply as the steps above.
 
It's also good to perform these tests every 3 months....
 

 


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