Repairing corroded PCB

[ivan747]

Hello guys,

I've rediscovered an old tube amp kit from my father. He passed away some years ago, so it's got some sentimental value for me. Please don't let the valves madden you, there's no audiophoolery going on here, we're just reviving old stuff.

The kit is a K12G stereo tube amplifier, with 8W per channel. I believe the kit was purchased about 10 years ago. The kit was never mounted in an enclosure, since it didn't come with one and my dad never got round to building one for it.

As a result of having no enclosure and being neglected by me (I live near a shore) the PCB and the rest of the kit have got very corroded.

I'd like to restore it and continue to work right where he left it. Part of that work includes cleaning the kit, finding it a decent enclosure, and modifying the kit and potentially resoldering a lot of things to make the kit fit in the enclosure.

I'm not too fuzzy about changing some of the components when necessary. I am sure the caps will need to be soldered on the underside if I want an enclosure that shows the tubes outside it but hides the PCB inside it.

I do have some ideas for the enclosure, but right now I need some advise regarding the corroded PCB.

I'll post some pictures and any feedback is appreciated

Thanks guys.
Cheers,
Ivan

P.S. the two audio transformers will get replaced after putting the project in an enclosure. The power transformer will probably stay, but it would be nice if I can paint or polish it somehow.

[ivan747]

And by the way, is there a way to protect this from further damage? Apart from putting the PCB inside a box.




Edit:

This is the worst bit:


If that can be repaired, I think the entire board can be repaired as well.

I believe the copper has corroded under the solder mask for some reason

Edit:

I'm glad to say that the underside is brand new:

[Armadillo]

The circuit traces are so wide, even if it's corroded, it can be repaired by wire bridging.

Take the tubes and transformers out for manual wiping with cloth and water/IPA.

The circuit board, Spray/hose the board with water and scrub with brushes and dish cleaner, no worry, you can dry the board later. Make sure all the surfaces rust, dirt and dust get scrubbed away. if you are fussy, the potentiometer and knob can be replaced. I will replace the turning knob, not that it's corroded, but to something majestic, big and elegant. Like a triangle knob resembling gryphon knob, but generally BIG :-)

Then dry the board with cloth, then spray with WD40, after wipe the board again and leave it for a day of drying.

As for the transformer and tubes, spray with WD40 on the surface and contacts and wipe off with cloth.

Some may not like WD40 because of smell, you can find one that contact clean the surface as well as prevent oxidation and protection. But I personally use WD40 since I just want to protect the surface for sure and avoid any future pain.

Then after repair any broken traces.

It didn't look that bad really, I have seen much worse than yours and still nicely repaired.   

[ivan747]

Sounds great! I got the tubes out already, I cleaned those with a cloth. The transformers are next in line for the cleanup.

I also wanna check all the traces for continuity. Last time I checked, the amp was working fine, but that must have been like a year or two ago.

I'm a little bit surprised about the dish soap though, is that really safe? O_o

I will replace the pot with something of better quality. The knob will get replaced too.

I want to use one of these Hammond cases. The PCB will be on the inside of the case, but the tubes and the transformer will be on top of the case. Those are the hottest components in the circuit, so the enclosure can have no vents. I don't think the rest of the circuit dissipates more than 10 or 20W, and the top and bottom panels are metal, so they dissipate some of the heat.

[eKretz]

That doesn't look bad at all to me.  The corrosion won't actually hurt anything as long as it's not INside stuff like the pots. The rest can probably be cleaned mechanically.  Very unlikely that the traces are corroded under the solder mask. 

Scrubbing with dish soap won't hurt anything as long as you dry everything well before you apply any power - I've done this many many times. I just finished cleaning up a newly purchased secondhand oscilloscope by washing all the boards with hot water, dish soap and gentle cleaning with a soft scrub brush (they were filthy with years of accumulated dust and grunge). Afterward I baked the boards at 150°F for an hour and put them right back in the scope and fired it up. It's working great with no issues at all. I would try to keep  directed water out of any enclosed components like pots and switches if possible though - just don't directly spray water into those or submerge them,  a little spray hitting them won't hurt anything.

Edit: Ian reminded me that I forgot the rinse bit. I use reverse osmosis water for rinsing,  DI works well also. 

[Ian.M]

It can be worth desoldering and removing parts that cant safely be immersed in water so you can clean it more thouroughly and easily.  I wouldn't want to immerse the pot or the transformers - everything else on that board should be OK.

Since it uses high voltages, to minimise any surface mineral contamination, it would be a good idea to give it a final rinse with distilled or deionised water after washing and rinsing the board.  Shake off as much ordinary water as you can before the distilled water rinse.

Isopropyl alcohol forms an azeotrope with water, which gives a boiling point of 80 °C.  The composition is 91 vol% isopropyl alcohol, so if you give a final rinse with dry IPA and use at least 20 times more than the residual water on the board, you can dry it far quicker while keeping the temperature safely under 95 °C.  Caution: the lower explosive limit for IPA vapour is only 2% so you need to dry off most of the IPA outside before using any heat source that could cause a spark.

You'll need to lacquer any tracks that have lost their solder mask to seal them, as its very difficult to remove all traces of chloride contamination,  (copper I chloride is nearly insoluble in water, but when exposed to oxygen and humidity, causes ongoing corrosion).

[rdl]

I have one of those amps. The company that makes the kit appears to be still in business. Maybe they would be willing to sell a replacement board. Everything else looks like it just needs to be cleaned up (maybe some sanding and a paint job for the transformers).

http://www.s5electronics.com/

[ivan747]

It can be worth desoldering and removing parts that cant safely be immersed in water so you can clean it more thouroughly and easily.  I wouldn't want to immerse the pot or the transformers - everything else on that board should be OK.

Since it uses high voltages, to minimise any surface mineral contamination, it would be a good idea to give it a final rinse with distilled or deionised water after washing and rinsing the board.  Shake off as much ordinary water as you can before the distilled water rinse.

Isopropyl alcohol forms an azeotrope with water, which gives a boiling point of 80 °C.  The composition is 91 vol% isopropyl alcohol, so if you give a final rinse with dry IPA and use at least 20 times more than the residual water on the board, you can dry it far quicker while keeping the temperature safely under 95 °C.  Caution: the lower explosive limit for IPA vapour is only 2% so you need to dry off most of the IPA outside before using any heat source that could cause a spark.

You'll need to lacquer any tracks that have lost their solder mask to seal them, as its very difficult to remove all traces of chloride contamination,  (copper I chloride is nearly insoluble in water, but when exposed to oxygen and humidity, causes ongoing corrosion).

Thank you. What sort of lacquer would you recommend?

[ivan747]

I have one of those amps. The company that makes the kit appears to be still in business. Maybe they would be willing to sell a replacement board. Everything else looks like it just needs to be cleaned up (maybe some sanding and a paint job for the transformers).

http://www.s5electronics.com/

Sure, I could use a replacement board, but I plan on replacing a lot of the caps anyway. At least some part of the kit should stay original don't you think?

I'm still deciding on what to change and what to keep. So far, rusted resistors and crappy caps are the ones I want to replace.

The audio transformers are probably gonna get replaced, but the power transformer definitely stays.


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[Electro Detective]

WD-40 sprayed and brushed in and left on for a few days, and reapplied if necessary should sort out the rust problem.
You can always hose it off later with a cheap can of non residue contact cleaner especially in areas that need soldering.

Wrap pots in glad wrap and masking tape to keep your cleaning activity out of there! 

Don't change parts unless sure they no longer perform.
If the caps are a good brand, leave them there

Less is more approach, Good Luck   

[ivan747]

Everyone keeps mentioning the pots...

The pot is already rusted to the point of being useless so no point in saving that! I already added a Bourns audio pot in my shopping cart in Mouser, along with a nice enclosure.

But I guess Electro Detective is right. I shouldn't change components just for the sake of it.

I'll try WD-40 on some random corroded board to see if I like it. Same for dish washing soap.

The tube amp is a one shot deal.


Bit of an unrelated question:

I have an audio pot mounted on the top side of the PCB. Audio pots are logarithmic. If I mount the pot


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[Ian.M]

*DON'T* use WD40!
https://www.eevblog.com/forum/chat/just-so-you-know/
Once you put it on the board its FUBARed - the residue will attract dust, causing leakage and degrading contacts,  and its *EXTREMELY* difficult to remove, and will prevent many coatings that actually work to stop further corrosion sticking properly.

[eKretz]

Same.  I'd never use WD40 on a PCB.

[Armadillo]

*DON'T* use WD40!
https://www.eevblog.com/forum/chat/just-so-you-know/
Once you put it on the board its FUBARed - the residue will attract dust, causing leakage and degrading contacts,  and its *EXTREMELY* difficult to remove, and will prevent many coatings that actually work to stop further corrosion sticking properly.

WD stands for "water displacing" and its main use is as a solvent or rust dissolver. Firstly you need to breaks-down the rust or dissolve it and inhabit it from further rust. That was the primarily objective of using it on the rusted circuit board in the first place. The objective was rescue.
But you normally don't need to use WD40 in Electronics kind of works, because they don't normally rust, right?
The broken down substance of rust or residue needs to be wipe away. I have been there and used it to attest by it. You want to break down the rust and inhabit it in the quickest of ways, use WD40, otherwise find other kind of much more effective lubricant or solvent and don't use WD40 entirely.
On the rest of the other negative claims on WD40, I would say... hey you need to know why you are doing and how to use your tools effectively?
If you aren't comfortable with it, don't use it.   You'll need to hands on to learn from it, anyway Cheers

[Ian.M]

WD40 + a nylon panscourer or similar mild abrasive pad is somewhat useful for removing light rust from smooth steel surfaces.  WD40 does not chemically convert or dissolve rust so it wont do any good without abrasion.  Even wiping down with a paper towel is abrasion as loose rust particles will form a grinding paste with the oil from the WD40. However it isn't really practical to scrub an assembled PCB with a panscourer and if rust has broken through the plating of the few steel component leads that may be present, you'll have worse problems that WD40 certainly wont solve.

The O.P. has a PCB with corrosion due to suspected chloride contamination from salt microparticles in the air.  WD40 wont help remove the chlorides and if used first, its water displacing properties will make their removal even more difficult.

I have experience with trying to salvage a PC motherboard that an idiot sprayed with WD40 - at the time I didn't have access to an ultrasound tank or a vapour phase degreaser so was limited to repeated solvent washing - and after cleaning, it worked for a few days, before intermittent contact problems on the slots and SIMM sockets would start again, only alleviated by yet another solvent wash.   After I had repeated this cycles four of five times with no end in sight, it became obvious that replacement was the only option, as the cost of the solvent was already well over the value of the board!   There were still faint oily traces migrating onto card contacts on the final go-around, presumably from WD40 trapped in crevices in the socket bodies - its far too persistent and difficult to remove to *EVER* consider its general use on PCBs.

See https://www.eevblog.com/forum/repair/corrosion-removal-motherboard-with-leaky-nicd-battery/ for a recent fairly heroic corrosion removal and PCB repair thread.  However that was electrolyte contamination and copper carbonates are a *lot * easier to deal with than copper chlorides.

[Electro Detective]

*DON'T* use WD40!
https://www.eevblog.com/forum/chat/just-so-you-know/
Once you put it on the board its FUBARed - the residue will attract dust, causing leakage and degrading contacts,  and its *EXTREMELY* difficult to remove, and will prevent many coatings that actually work to stop further corrosion sticking properly.

WD stands for "water displacing" and its main use is as a solvent or rust dissolver. Firstly you need to breaks-down the rust or dissolve it and inhabit it from further rust. That was the primarily objective of using it on the rusted circuit board in the first place. The objective was rescue.
But you normally don't need to use WD40 in Electronics kind of works, because they don't normally rust, right?
The broken down substance of rust or residue needs to be wipe away. I have been there and used it to attest by it. You want to break down the rust and inhabit it in the quickest of ways, use WD40, otherwise find other kind of much more effective lubricant or solvent and don't use WD40 entirely.
On the rest of the other negative claims on WD40, I would say... hey you need to know why you are doing and how to use your tools effectively?
If you aren't comfortable with it, don't use it.   You'll need to hands on to learn from it, anyway Cheers

They don't get it, too locked in their safe methods      and don't bother to read product labels or experiment. 

I even mentioned earlier you can hose it off ANYTIME with non residue contact spray, but apparently no one is home 

Hopefully OP ivan747 will give it a try, lose the rust and recover the board. 

I've fixed worse than this, maybe 3 to 4 non stop hours on a good day to have it working (with no beer)


The tube sockets need to be checked too, for corrosion and correct pin tensions

Forgot to mention that earlier

 

[Armadillo]

Regarding the board leak, maybe you should substantiate with technical evidence or demonstration but failed attempts at repairing a board will be deemed as inconclusive evident due to a lot of factors, so please bear it in mind.
Many have not encounter with such problems. Misuse, probably.
Yeah! but I agree some idiots will just blame on anything, you know what I mean.

I sprayed WD40 on a life motherboard without any problems!.
Read the datasheet.

[Electro Detective]

                                                     

                                                          Beware   those    anti-WD40ites !!!

[Ian.M]

Read the datasheet.

That's a completely different product from the WD-40 company.  "50-state VOC compliant" and "biodegradable" implies that it cannot contain a significant concentration of organic solvents or mineral oils, so comparing it to the 'classic' WD-40 spray oil in a can (officially 'WD-40 Multi-Use Product') is disingenuous at best.

'Classic' WD-40 will of course dissolve greases, waxes, and some types of gums and varnishes from oxidisation of oils etc. that may be binding loose rust to a surface so may appear to 'dissolve' rust, but I'd be very surprised if it is capable of converting more than a trace of rust into organo-Iron compounds or complexes soluble in its Stoddard solvent base.   

Its quite difficult to set up a quantitative test for 'Classic' WD-40's rust dissolving powers without access to a gas chromatograph to detect traces of dissolved organo-Iron compounds in the solvent, due to the variable hydration and oxidisation levels in the iron oxide/hydroxide system commonly known as rust - which make it very difficult to wash and dry a sample of rust without changing its mass or composition.

An empirical qualitative test is much easier: take a strip of rusty steel, degrease iit and wash thoroughly without abrasion to remove loose rust and allow to air dry at room temperature, then immerse it in a jar of 'Classic' WD-40, seal it and take a photo.  Wait, taking a new photo every day without moving the jar for the first week then every week for the first two months then monthly for the rest of the year.   If it actually dissolves rust, when you compare the photos it should be pretty obvious if its effective. 

[Armadillo]

soak test

[eKretz]

One CAN do all sorts of things.  That doesn't mean that one SHOULD,  or that those things are necessarily the BEST way.

[rdl]

The WD-40 Company makes many different products and apparently none of them are named simply WD-40. *

The WD-40 most people think of, and probably mean when they speak of it is the "WD-40 Multi-Use Product" and is not at all the same as "WD-40 Specialist Rust Remover Soak".

Personally I'd never put anything with WD-40 as part of the name on a circuit board unless there was one specifically described as being for that purpose. I've always been inclined to just run dirty boards through the dishwasher anyway.


* interestingly the company refer to themselves as a "tribe"

[Electro Detective]

FWIW  I've been using the poor man's   "WD-40 Multi-Use Product" spray can stuff  on corroded electronics for YEARS with no problems,
applied with a brush, cotton bud or the spray method, whatever gets it to where required without drama

If the corrosion is bad news or stubborn, leave it on for a few days, wipe off, and re-apply

Once it's done the 'tribe voodoo magic'     I hose the stuff off with the cheapest decent non residue contact spray,
and scrub where necessary 

You can then flux about and do any solder touch ups, plug components back in etc

It's not rocket science, and good enough for Australian conditions, YMMV   

 

[ivan747]

Can contact cleaner help me with this one? Specially the leads of resistors and such?

By the way, I just tested the amp and it works. Very noisy, presumably from the carbon pot, but it works.

[ivan747]

What's this coating on the transformer for? Preventing vibration?