It ain't the &*^%*ng caps!!!!!

[ecc83]

At least it is most unlikely...

There have been a couple of posts in the last month where people have gone blindly into equipment chasing a fault and immediately pounced on electrolytic capacitors as the source of all that is evil. IT JUST IS NOT SO!

MODERN (and by that I mean anything less than 20* years old) capacitors rarely fail. They DO go short if abused VERY badly by over voltage but not at all often. They DO loose a bit of capacitance over the years but tis MINUTE and in any case any decent design will use a capacitor of 20 even 50% bigger than the absolute value needed for any application.

So, If your amp/mixer/pre goes a bit hummy or fails altogher, DO NOT just swap out capacitors 'on spec' they are almost certainly NOT the culprit. MOST likely 'active' devices and in order of poor reliability..Discrete transistors &FETs, zener diodes, 78/9'regs', op amps, standard diodes, LEDs.

AND! MOST of ALL! ASK HERE before you get the Pozi #2 out!

*and imexp' even caps in 30yr old valve amps hold up in a very unkind place.
Dave.

 

[arcaxis]

Sort of agree, but for a novice that has absolutely no knowledge of electronics, troubleshooting, a lack of test gear, and lack of a schematic or ability to read one, caps are the obvious easy choice for hum problems sometimes for a novice. May or may not be the fix, but at least they tried and usually electrolytic caps won't break the bank and they learned a bit of soldering(maybe ).
Yup, asking here is a good place start if not sure.

Of problems I've had in recent years with my own gear.......
- Trace Elliott BLX80 bass amp about 1999 vintage. Developed low consistent hum regardless of volume settings. Confident it was a filter cap(s) so didn't bother troubleshooting and replaced both. Hum was gone.
- Yamaha DG Stomp effects box about 2000 vintage. Not hum, but a backup battery that would only last a few weeks rather than 3 or so years. Leaky cap was found to be draining battery prematurely.
- Yamaha QX3 MIDI sequencer with boot problems. Narrowed down to an electrolytic cap that delays the start of the processor until other logic circuits have stabilized. Replaced cap and boot problem fixed. Needed scope and logic probe to troubleshoot this one.
- Alesis and two pieces of Yamaha gear (early 2000 vintage) with encoders that got intermittent in data selection. You'd think at least Yamaha might use better reliability encoders.
- Korg Wavestation keyboard that had gotten flaky in operation. From what I could tell the main CPU chip had issues. The Korg service manual listed some test software and fixtures for troubleshooting so didn't bother to go further and sold for parts or repair.
- ART MPA II preamp, one channel intermittent. Ribbon cable connector making poor connection to header pins on circuit board.

Haven't had to do anything to a couple old 60's vintage Silvertone tube amps I have, other than upgrade the two wire AC cords and plugs and maybe a tube or two along the way and no hum from either amp

 

[Steenamaroo]

I tell people to look there first because it's one of the few things that a man without a meter might be able to see with their eyes.

Agreed, though - There's no a lot of point blindly swapping parts.

 

[ecc83]

Ok Mark you experience in the states has been different from mine. I have really found capacitors in even 'domestic' kit, TV's and VCRs to be remarkably reliable. Back in the day, early 'hi fi' was a bit feeble and transistors would die in Leak and Sony amps under even mild provocation but the caps were fine.

I understand that it only about NOW that Quad 303 and 405 amps need re-capping? But then they were always very compact designs and probably ran pretty warm.

But my point was really DON'T GUESS! A shorted cap is easily diagnosed. One that MIGHT be causing hum through loss of capacitance can easily be checked by tacking a new one across it. Anytime an inexperienced person attacks print to change a component they run the risk of damaging said print. The damage can usually be repaired but rarely looks good.

Dave.

 

[arcaxis]

I guess the few times I've had semiconductors bite the bullet is when the gear had taken a hit from a surge or spike of sorts and that hasn't happened much as of late. Otherwise most of my repairs involved what I noted above or similar. Yes caps are 'remarkably reliable', but then again the gear they are put in now days is pretty reliable overall as well.