circuit board smelling like toxic waste

I have an Onkyo A919- circa 1992. so it's not exactly a vintage. It's a mosfet/bjt hybrid amp and the tubiest SS sound I've ever come across. It also smells like burning styrofoam. From sticking my nose to the components, I'm certain that it's coming from the circuit boards. I already had one bad experience with a vintage Sansui au-D907 that was stinking from the circuit boards due to it's age. (phenolic boards smelling like roses... and ***) But to have the same symptom from an amp that's only 8 years old is a surprise to me. Is my situation unusual? Could this 100V only amp being operated on 115V stepdown by the previous owner have accelerated the degradation of the pcbs? and what exactly do you think is contributing to this burnt styrofoam/industrial solvent-like smell?
 

jmmartins

Member
2005-05-24 3:46 pm
I have a sansui AU-D11 that is the best amplifier that I ever heard and I heard lot´s of them, including some very expensive ones like Krell etc. Nothing compares to that sound. And nothing compares to the smell coming from those PCB’s. I tried everything: Sun exposure, cleaning products … nothing works. I had to take it out of home. I’m thinking of taking out the phono PCB’s, wich i don't use, and making some PCB cloning of the amp and power source and transferring the parts to new PCB’s. I refuse to let it go.
 

ramiro77

Member
2010-06-07 3:09 am
I have an Onkyo A919- circa 1992. so it's not exactly a vintage. It's a mosfet/bjt hybrid amp and the tubiest SS sound I've ever come across. It also smells like burning styrofoam. From sticking my nose to the components, I'm certain that it's coming from the circuit boards. I already had one bad experience with a vintage Sansui au-D907 that was stinking from the circuit boards due to it's age. (phenolic boards smelling like roses... and ***) But to have the same symptom from an amp that's only 8 years old is a surprise to me. Is my situation unusual? Could this 100V only amp being operated on 115V stepdown by the previous owner have accelerated the degradation of the pcbs? and what exactly do you think is contributing to this burnt styrofoam/industrial solvent-like smell?

I have a Sansui A80 and I never had a problem like yours. Have you tried to clean it? Perhaps there is hidden dirt that is heated by the use of the amplifier
 
I have a sansui AU-D11 that is the best amplifier that I ever heard and I heard lot´s of them, including some very expensive ones like Krell etc. Nothing compares to that sound. And nothing compares to the smell coming from those PCB’s. I tried everything: Sun exposure, cleaning products … nothing works. I had to take it out of home. I’m thinking of taking out the phono PCB’s, wich i don't use, and making some PCB cloning of the amp and power source and transferring the parts to new PCB’s. I refuse to let it go.

I know what you mean. my sansui AU-D907Limited was ungodly when I had it hooked up. I auditioned some high end exotics during that period and nothing impressed me, not even the flagship macintosh. but according to the vintage fanatics at audiokarma, sansui's later alpha models should sound even better than their vintage ancestors, although their build quality might suggest otherwise.
 

Alex79

Member
2018-01-25 2:16 pm
Usually the smell of old vintage gear is from electrolytic capacitors. Electrolite is already leaking, and it has little acidic "vintage" smell.



Sometimes the elctrolyt can be already soaked into PCB, however it is not often.



Changing electrolytic capacitors and clean PCB in alcohol - best is Isopropyl Alcohol IPA, as it doesnt include any water. Throw whole PCB with all components to alcohol, keep it there as long as needed (IPA cannot do any damage to electronics)...10-30min shoud be ok... clean it with nylon brush and here you go...
 
Sounds like the resin in the pcb didn't fully cure or was mis-mixed, and its leaching out monomers or actually breaking down. It could be the flame retarding chemicals leaching I suppose, FR4 stands for "flame retardent type 4". If phenolic type board it would breakdown to phenol derivatives and aldehydes, aldehydes smell pretty bad/off, phenol derivatives very "chemical".


Long term prognosis isn't good if this is happening.
 

Alex79

Member
2018-01-25 2:16 pm
Hello, thank you for excelent answer. Everyday is school day. Didnt noticed, phenolic typt boards were largely used in some era.

More info I found is that Phenolic resin boards were FR1 and FR2 types of PCBs. FR3 and FR4 are strictly Epoxy resin.
Seriously, if that is the case, that phenolic resin degrade over time, and smell going out is actually formaldehyde, I cannot imagine what to do with it. Maybe try to encapsulate PCB from all sides with some lacquer should more or less help.
 
Hello, thank you for excelent answer. Everyday is school day. Didnt noticed, phenolic typt boards were largely used in some era.

More info I found is that Phenolic resin boards were FR1 and FR2 types of PCBs. FR3 and FR4 are strictly Epoxy resin.
Seriously, if that is the case, that phenolic resin degrade over time, and smell going out is actually formaldehyde, I cannot imagine what to do with it. Maybe try to encapsulate PCB from all sides with some lacquer should more or less help.


Formaldehyde is highly noxious and being a small molecule it will diffuse through most organics - time to retire the unit? Clone a PCB?
 
If there is room inside, try putting small brown paper lunch bags with new charcoal from for BBQ grill. Not the type with starter fluid already impregnated. Just basic cheapest charcoal briquettes. It does a great job of absorbing odor. Cover the amp with a air tight plastic sheet when not in use with the charcoal bags. You have to change the charcoal when it wears out.

Anyone who has used outdoor gear like tents or tarps coated with polyurethane will be familiar with a rotting stench from the polyurethane decomposition after 20yrs. The stuff gets sticky and peels off and smells like rotting vomit.

If the PCB has a sprayed on conformal coating made of polyurethane - that might be the culprit.

The alcohol bath and toothbrush should take all that off. But it’s a lot of work.

Try making a new DIY amp. Check out some of the SE Class A designs that have a dominant H2 harmonic profile with descending higher orders. It will sound good and warm and sweet. Not harsh and fatiguing like some ultra low distortion amps that may have dominant H3 and existence of higher order harmonics. There’s lots of amps here that will blow away most commercial amps.
 
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Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
Actually, light buff coloured PCBs are based on Kraft paper and urea formaldehyde resin, often blended with melamine formaldehyde resin when a higher quality substrate is needed. Though they are all phenolic type resins, phenol formaldehyde hasn't been used for circuit boards in a long time, probably because of cost and its characteristic dark red-brown to black colour. It's the urea formaldehyde resin type which breaks down over time and smells of stale cat's pee and formaldehyde, as the name suggests.

I guess that to maintain their cost advantages, Japanese manufacturers always built their electronic PCBs assemblies on paper/phenolic boards and the stench was quite pronounced with the budget models of just a few brands of audio and video gear from the 1980s until the end of the product lines.

There are a few threads about the problem here and though I have read some replies suggesting it works, the boards need to be cleaned thoroughly first. Perhaps scrubbed hot water, detergent and finally a sparing rinse with alcohol or IPA, then spraying both sides with a solvent based clear lacquer. That should at least reduce the stench. However, since the PCB is actually breaking down, its only a matter of time before the lacquer loses its sealing quality too and the smell slowly returns.