Filter Caps Going Bad? - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 9th January 2007, 03:50 PM   #1
Plundering the Planet From the Comfort of Home
diyAudio Member
 
DreadPirate's Avatar
 
Join Date: Jan 2006
Location: Northern Virginia, USA
Default Filter Caps Going Bad?

I have a Harman Kardon PM665 Integrated (dual powered) that I've cleaned up nicely with deoxit a few times. Got it used ($7). I cannot get rid of an intermittent static in the left channel. It does sound just like dirty volume controls (I'm very familiar with this issue), but occurs constantly regardless of button and knob use.

Are the filter capacitors the likely culprit? Is this a symptom of filter caps going bad?

Is there a way to quickly check if the filter cap is bad? Can I quick solder a capacitor in parallel of somewhat close uF (>voltage of course)? I will check with a voltmeter prior to messing with these, I understand they like to bite.

I do have an esr meter, but currently do not have a capacitance meter. Will this meter reveal the problem without disassembly?
  Reply With Quote
Old 10th January 2007, 04:33 AM   #2
diyAudio Member
 
unclejed613's Avatar
 
Join Date: Dec 2006
noise, like intermittant hissing or crackling is more likely caused by bad solder or a transistor junction breaking down (or sometimes a bad zener diode)....... i have seen some electrolytics go bad from time to time where they have an internal intermittant connection. the ones i have seen this happen to most often are Sprague caps with red epoxy on one end (if it's a radial cap, it's the end with the wires coming out of it). every single one i've seen fail like this, had either the red epoxy blackened around the positive lead (from the connection burning inside the epoxy) or the positive lead burnt to the extent that it actually fell out while removing the cap from the board. you could also have a dirty speaker relay (if the amp uses a speaker relay). try tapping on various components with a screwdriver handle and see if you can cause the static (or make it go away) (it's also possible to find bad solder this way). a bad transistor or zener will not usually respond to physical shock, but gets noisy (or quieter) with temperature only.

back to the Sprague caps, i once repaired an HP voltage standard that had 10 of those caps in parallel in the power supply, 8 of them had gone bad. i found the first one when i happened to bump it while trying to attach a scope probe. after replacing it i noticed that the problem had improved but not gone away, so i began removing the other 9, and found 7 of them bad. i replaced all 10 of them with nichicons, instead of taking the chance of replacing them with the same type and having the same failure happen later. since then i have seen many different types of equipment, audio, banking, radio transmitters, etc... with similar caps with exactly the same failure with that type of cap, so now if i see one, good or bad, i replace it.
__________________
Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net
spammer trap: spammers must die
  Reply With Quote
Old 10th January 2007, 11:34 AM   #3
Plundering the Planet From the Comfort of Home
diyAudio Member
 
DreadPirate's Avatar
 
Join Date: Jan 2006
Location: Northern Virginia, USA
Great reply! I need to get this unit going, seems the best one in the heap of vintage I own to power my recent purchase of Thiel c3.5s. This thing is "twin powered" with two massive transformers. Its calling card is an HICC of 60A, hoping that will do the trick until I get something better.

The crackling is coming through the headphone jack, I have not put speakers on it yet. It does NOT seem to be affected by the operation of any knob or button. Several posts here and there indicate these are problematic and I have found the rotary knobs on other older HKs to be noisy and get noisy again after 6 mos or so after cleaning. What I would really like is a lead on the pots for my HK730, they all have a loose feel to them since cleaning and are beginning to get crackly again.

Back to the PM665, I think you are on the right track with the cold solder or defective component call, I will tap around when I open her up this weekend. I have since looked into the failing leaky filter caps, seems these result in a hum, not crackling, when they are failing due to age.

Thanks again.
  Reply With Quote
Old 10th January 2007, 02:55 PM   #4
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
Noise on a 730 volume control can be DC leakage from the coupling caps.
__________________
Candidates for the Darwin Award should not read this author.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Do I Really Need Filter Caps? DreadPirate Solid State 6 21st August 2009 06:47 AM
Filter caps DeadSpeaker Solid State 5 11th June 2008 04:17 PM
B+ filter caps nhuwar Tubes / Valves 12 26th January 2007 09:33 AM
Just one big filter cap or more smaller filter caps ... beppe61 Power Supplies 2 18th July 2006 05:46 PM
PS filter caps mongiak Parts 4 19th March 2005 10:18 PM


New To Site? Need Help?

All times are GMT. The time now is 12:17 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2