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Old 14th March 2013, 01:03 PM   #1
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Location: Albufeira, Portugal
Default VERY LOUD cracks/pops but no sound !?

hi guys

i'm writing to you from Portugal because after a 15 year "rest", i started using my 30 year old Peavey Combo 300 bass amp again - after opening it, dusting, spraying it, checking for loose/broken wires & connections or noisy pots - it was all good !...

this went on for a month until it's gone nuts, please check the noise it makes when i switch it on, here :

https://soundcloud.com/nuno1959-1/cracks-pops - just click the ''Play'' orange button at the top left of window..

these noises happen regardless how i set the Pre & Post gain pots in it...

in a bass player's forum, someone suggested this is due to the caps being kaput… & indeed, when i removed the board they are attached to, i heard a rattling, glassy sound coming from inside them as if shaking a failed light bulb - surely this can't be right !?..
i recorded the sound on a short video, available here :

Clip #1 | Flickr - Photo Sharing!

because my local Peavey Service Centre is 200 miles away & my amp weighs a ton, shipping it to them would cost me 50€ up + 50€ to get it back. if the quote for the repair was too expensive & i decided not to go ahead, it would cost me a further 35€

this is all fair enough but all things considered, if someone would be able to determine it is either the caps or some other component that is shot, i wouldn't mind at all trying to replace them myself BEFORE committing to such expense - now, i know it's difficult/impossible to diagnose an amp via a post, a few pics & a sound file BUT...who knows i get lucky & someone here has come across the exact same symptoms on an amp of theirs ?


however, since i know NOTHING about electronics, i was wondering if you could have a look at the photos i took of my caps & tell me where could i get some ?

it's just that no matter what i type onto Google, i never get any worthy results - yes, i am clueless !!... :-b

perhaps even better quality ones at that : somebody suggested i could get bigger capacitance ones to get extra headroom, if true what would you recommend ? the very best quality possible please...


here are the photos :

1 - caps in their board
caps 2 | Flickr - Photo Sharing!


2 - their 6 prongs ( terminals ?.. ) that are soldered to the board
caps terminals/prongs | Flickr - Photo Sharing!


3 - a photo montage i made so you can clearly see what's printed on them ( their spec ?.. )
photo montage | Flickr - Photo Sharing!

if repairing the power amp proved impossible i even considered if i could get the preamp section out of the combo, house it in a 1 or 2 rack unit housing of it's own & go buy a nice, basic QSC or Crown power amp ? or is that REALLY difficult ?

sorry for the VERY long post, any help you could provide me with will be GREATLY APPRECIATED

many thanks for your patience & kind assistance

Nuno

Last edited by nuno1959; 14th March 2013 at 01:12 PM.
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Old 14th March 2013, 01:37 PM   #2
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That "15 year rest" means all Electrolytic capacitors are dried up.....replace them all ASAP
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Old 14th March 2013, 03:08 PM   #3
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Hi JRGuitarGuy

so i've been told but....do you have any idea WHERE can i get some & which ones do i have to look for ?
that's a big part of my problem if not the biggest... ;-)
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Old 14th March 2013, 09:35 PM   #4
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You live in Portugal, farnell.com has a service there. I use their US affiliate Newark.com. I like the fact that the hours service life are listed right in the cap selector table. That way you can buy nothing rated <3000 hours. Amazing how many service centers want to buy 500 hour life caps, everybody has a huge stock of those.
The electrolytic caps are the ones with a + on one end, or a minus in balls pointing at one lead, or marked ##WVNP where NP stands for non-polar. It is tricky getting non-polar from farnell but I usually just replace them with 50v ceramic caps up to 10 uf. If using a ceramic cap for audio you want to use more voltage than the old one is rated, so the non-linearity of ceramic doesn't sound. When replacing e-caps mark the PWB with + indelibly before removing, if you put the new one in backwards it pops and leaks.
You'll need a Weller WP35 iron with the accessory 7/32" screwdriver tip, or something more expensive. Needlenose pliers, slip joint pliers, small diagonal cutters from the fishing dept, small Miller or Klein wire strippers (1 mm - 3 mm), a 5 way screwdriver, a steel pick, safety glasses, rosin core solder .5 to .8 mm. Any amp with problems, I replace all electrolytic caps after 15 years since it left the factory. Check your power rectifier, shorted caps may have blown it, or resistors around it. I usually do 2 caps at a time and check my work by powering up to see if it is better or worse. Start with the big ones near the power transformer or in the switcher supply.
For more details, see this thread Could anyone please help me out with a Thomas Trianon?
It is about an organ, but they have transistor amps too. More connectors and corroded switches, though.
Work with the power unplugged and don't touch any metal that doesn't measure < 25VDC to speaker ground. Wear safety glasses unsoldering, solder splashes. I soak old solder up with old wire dipped in tin flux. If your amp doesn't work after recapping, or you have more than 0.2 vdc on the speaker, follow this thread vintage amplifier repair/upgrade manual
No use paying EEE to UPS if you can do it yourself for 6E freight on the parts. I taught myself before the internet out of the GE transistor manual 7th ed, but have learned a lot of useful things off diyaudio.com the last couple of years.
Good luck.
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Last edited by indianajo; 14th March 2013 at 09:49 PM.
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Old 15th March 2013, 04:41 AM   #5
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hi Indianajo

thanks for your input & the links to the other threads

i will definitely check out Farnell see what i can find & if in doubt, email them !
the tools you list if i haven't the exact same they are equivalent, so i'm good on that end, my problem is not knowing what most components are but i'll start with the large blue caps & take it from there - if that doesn't work someone gave me a contact of a local guy who seems to be good with amps & instead of 200 miles up + 200 down, he's 20 miles away from me & THAT i can live with, leet's see how it goes

much obliged !! ;-)
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Old 22nd March 2013, 11:37 AM   #6
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hi Indiannajo

just to say that FINALLY ! my Peavey Combo is sorted - a friend gave me the contact of this guy near where i live, he does mainly repair work on mixers, power amps/ PA maintenance & such so i sent him an email, we made an appointment & today i took just the Peavey's amp section leaving the cab at home....

got to his place, he had already sourced a schematic for it & started immediately working on it - right there in front of me !?

after checking & re-checking, measuring & re-measuring FINALLY he found what was causing havoc : one contact of a teeny weeny zener diode was badly oxidised so it ''de-soldered'' itself loose-ish & developed an intermittent contact with the board & a badly regulated current ( 23V instead of 15 i think he told me.. )

check the photo here :

http://www.flickr.com/photos/1370682...ream/lightbox/ - the faulty ''wire'' is the one facing down, towards those condensers

when i asked him how much i owed him, he charged me 50€ for 3 hours labour, 2 extra 4A fuses & a cleaning spray - how cool is that ?
as i was leaving, since he's worked w/ all sorts of Peavey gear over the years & knows most inside out, he guaranteed me my combo is ready for another 20 or 30 years !!...LOL...

plop, plop, fizz, fizz.....aahhhhh.....instant relief !! yes , life is good again ;-)

thanks a lot for you input
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Old 23rd March 2013, 09:35 PM   #7
JMFahey is offline JMFahey  Argentina
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Congratulations.
And you are another example that choosing the Pro way ends up being best, sometimes even cheapest too
Good luck.
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Old 23rd March 2013, 09:59 PM   #8
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many thanks ! ;-)
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Old 25th March 2013, 01:50 AM   #9
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Good luck. The repair was invaluable. You spent 50E, and you have a working amp packed with 30 year old electrolytic capacitors? Peavey bought a little higher quality capacitors than average, but still! If you use it much, I foresee a replacement amp in your future.
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Old 25th March 2013, 02:02 AM   #10
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yes, it might come to that but the guy measured everything & told me he had suitable replacement caps but the original ones were well within their tolerances & if the amp was his he wouldn't bother so i thought, let's try that out & see what happens !!
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