when to re-cap

[kambo]

i have couple of Meyer Sound CP-10 EQs. i bought them used 6-7- years ago... they must be at least
15-20 years old by now... they seem to be working just fine...
is there a specific indication/hint for recap time ?

 

[Brian Roth]

"Caps" in this context would be electrolytics (and tantalums) as used for signal coupling  and PSU rail bypassing.

Bad caps in the signal path can be seen with failing frequency response in the low end of the device's response.

Caps on power supply rails which fail often create "smoke" and Bad Fails.  Tants usually fail as a short circuit.

Bri

 

[JohnRoberts]

Path frequency response measurement is your friend. The typical fault in old electrolytic capacitors is loss of electrolyte. These will exhibit low capacitance. In typical DC blocking applications this will express as higher LF cut off frequencies. Another metric to review is AC ripple on power supply reservoir capacitors.

If you have a few similar units, measure the frequency response and look for differences in LF cut off. If one measures worse than the others, look at capacitors to replace with new. Then repeat the measurements. If/when you measure an improvement in lower LF cut off frequency, replace all the similar capacitors that are from the same production lot.

JR

 

[pvision]

The Meyers use very high-quality parts and none of them I have have seen has shown signs of needing recapping

I have had problems with the bypass relays, though, and it seems the part is NLA. It uses two 4p2t relays

 

[kambo]

sounds good,than you all!
i am only using couple of mid frequencies and a high boost from each for room and hearing correction. no bass frequencies used.
but i will hook them up to sound card and see what they are doing...

 

[Scodiddly]

An ESR (equivalent series resistance) meter is probably the best tool for figuring out when to re-cap.  I don't use mine every day or even week, but probably once a month and when I do it always finds the culprit.

 

[pucho812]

An ESR (equivalent series resistance) meter is probably the best tool for figuring out when to re-cap.  I don't use mine every day or even week, but probably once a month and when I do it always finds the culprit.

I got mine from peak atlas. A great investment and time saver for sure.

https://www.peakelec.co.uk/acatalog/esr70-capacitor-esr-meter.html

 

[Brian Roth]

I built one of these years ago:

https://anatekinstruments.com/collections/anatek-blue-esr-accessories/products/anatek-blue-esr-meter-full-kit-for-self-assembly-besr_kit

(They also sell that fully assembled.)

One unusual application for many (all?) ESR meters is tracking down a shorted bypass cap on a power supply rail. 

Bri

 

[kambo]

An ESR (equivalent series resistance) meter is probably the best tool for figuring out when to re-cap. 

do you still need to take one leg off the board/connection of a cap to use ESR meter ?

 

[warpie]

do you still need to take one leg off the board/connection of a cap to use ESR meter ?

I am wondering the same. Also does the cap need to be discharged before the measurement?

 

[Scodiddly]

do you still need to take one leg off the board/connection of a cap to use ESR meter ?

I can't speak for all ESR meter products, but mine works in-circuit.  You do have to discharge the capacitor first.
https://www.midwestdevices.com/index.php

 

[kambo]

I can't speak for all ESR meter products, but mine works in-circuit.  You do have to discharge the capacitor first.
https://www.midwestdevices.com/index.php

that is a nice tool,

i have couple of Atlas tools, they do work well, but i hate their test wires...
every other month i have to re-open and solder/repair the broken/snapped off test wire(s)!

 

[warpie]

that is a nice tool,

i have couple of Atlas tools, they do work well, but i hate their test wires...
every other month i have to re-open and solder/repair the broken/snapped off test wire(s)!

Same here. Really annoying.

 

[fazer]

I have a b/k. It works well also but the clamshell clamp broke after using it extensively on circuit cards.  Still works if you have a chopstick type grip.

 

[Brian Roth]

do you still need to take one leg off the board/connection of a cap to use ESR meter ?

A problem arises when poking around with PSU rail bypass caps.

In many devices there are many/dozens hanging (all in parallel) from a rail down to 0V.  Which cap is being measured with the ESR meter?  Only way I know to measure is to lift one end of each cap.

Caps in series with the audio path are less problematic.

Bri

 

[JohnRoberts]

I still think it's easier to measure frequency response, while that is indirectly measuring the capacitance, so maybe use a capacitance meter to check capacitance. 

JR

 

[kambo]

I still think it's easier to measure frequency response, while that is indirectly measuring the capacitance, so maybe use a capacitance meter to check capacitance. 

JR

makes sense! no plans to spend ex money for ESR meter!

 

[Brian Roth]

I still think it's easier to measure frequency response, while that is indirectly measuring the capacitance, so maybe use a capacitance meter to check capacitance. 

JR

Amen.  For years I learned to look for sagging LF response on the LF end of an errant console module, then trace it down to a crappy 'lytic in the signal path.  But sometimes a REALLY crappy lytic would act almost like a wideband attenuator in the signal path....but with some additional LF response droop.

Crap lytics can also add THD (IM?) distortion and the results after replacing the junk caps can be amazing to hear.  Older MCI desks  seem to have better "sonics" especially after the lytics around the summing buses are replaced.

Bri

 

[Brian Roth]

makes sense! no plans to spend ex money for ESR meter!

Foo....an ESR meter is worthwhile to add to the Tool Kit.  My fave Fluke multimeter cost me hundreds but the ESR meter was under $100.

Bri

 

[Scodiddly]

My main use for the ESR meter these days is troubleshooting switching power supplies.