AU-717 Deadly Glue

EchoWars · Mar 17, 2006

As if you needed proof, here's one that is actually better than most. Caps are removed for a better view.

Note the nifty 'fuzz' from the corrosion of the leads on the zener diode and the resistors. Thank you Sansui... :finger:

I'll post an 'after' pic sometime later.

dr*audio · Mar 17, 2006

I'm beginning to wonder if that friggin' glue isn't reacting to something in the air, moisture, salt, whatever. Because most of the time I don't see that corrosion. Only 2 out of 10 units, I'd say. And if it hasn't corroded anything in 20 years, I'm thinking it won't start now. Maybe the corrosion is caused by some chemical that oozed out as the glue cured, like acetic acid from RTV.

seadzz · Mar 17, 2006

Let me guess.....F2663. Been there saw that. Very commom for AU717. If left unchecked you can expect all sort of nasty symptoms.

sdz

Kegger · Mar 17, 2006

Just curious what do you guy's use to clean that?

Or maybe better yet what would be the best thing to do?

qboneus · Mar 17, 2006

I've used an exacto blade but am curious as to what the real guru's use too.
Tal

Morden2004 · Mar 17, 2006

New FAQ on the glue shortly!

Kegger said:
Just curious what do you guy's use to clean that?

Or maybe better yet what would be the best thing to do?

Please stand-by. Do not adjust your set. I am working an a new FAQ that will address the issue of the infamous Sansui glue.

I will announce this FAQ when it's ready for prime-time. :thmbsp:

Paul

dr*audio · Mar 17, 2006

I scape it off with a dental pick.

markdi · Mar 17, 2006

same thing happened to my bsr eq

and a stereo timer I have

Leestereo · Mar 17, 2006

I've used acetone to soften the glue and then it can be scraped off much more easily. On the boards I've tried it on, the acetone did not do any damage to the component silk screening YMMV.

scottrt · Mar 17, 2006

I know that EW has stated many times he uses a small wire brush attachment in his Dremel tool to deftly abrade away the glue. That will be my technique. I dont think i could complete half my project without the aid of a Dremel in some capacity. A must have.

Scott T.

bill d pro · Mar 17, 2006

I God We Trust, All Others Bring Data...

Hey EW...

I have seen similar on circuit boards in missiles used to defend the American (and Japanese) way of life. (You'd be amazed how cranky both the soldier and the US Gov't get when the toy don't go "BOOM"!)

Solder needs some form of electrolytic action to clean surfaces and move the crap to the surface of the solder pool. Rosin fluxes (that I'm assuming Sansui used) have a weak acid that remains on poorly cleaned soldered areas. I suppose the glue could break down and interact... solder is anodic/sacrificial to just about any thing else in the universe.

Wanna do some high zoot analysis and become confused on a much higher plane? I have contacts with access to amazing analytical devices. We could come up with several definitive examples of the crud and get high mag photos and matching local chemical analysis and see if we can make a detailed story.

Who knows, not to take away your fun, but maybe we could even figure out a way to prevent some of it...

BuildPro

LBPete · Mar 17, 2006

I use 3M adhesive CLEANER and a green scotch bright pad. This stuff softens the glue so you can scrub it off with the scotch bright pad. You do have to be a little careful not to remove the silk screening when scrubbing with the scotch bright pad.

- Pete

dr*audio · Mar 17, 2006

Leestereo said:
I've used acetone to soften the glue and then it can be scraped off much more easily. On the boards I've tried it on, the acetone did not do any damage to the component silk screening YMMV.

Acetone is a carcinogen. Use with caution and adequate ventillation.

merrylander · Mar 18, 2006

Looks like the voltage regulator board in the AU-717 I did. Amazing how their glue corrodes component leads. I also found that when resistors were covered by this glue their values changed, whether from heat or chemical reaction I have no idea. I had to change eight resistors and both zeners.

I clean that crud off with a modified Xacto knife. I ground down one of their flat chisel blade until it was 1/8" wide (I had actually modified this blade so that I could cut the slots in a new Sl1600 Mk2 TT platter mat). Usually by the time this stuff has been cooked it is quite brittle and comes off easily. The funny part is that while the glue in the Yammies looks similar it does not corrode and only hardens where it has been exposed to much heat.

Rob

DanTana · Mar 18, 2006

I don't know if Sansui is the only one that uses that specific glue, but everytime I see that stuff I scrape it off. I've also heard, maybe wrongly, that it can even become conductive after some time and short things out.

jleon92f · Mar 18, 2006

Hello,

I have been reading this thread , is that from inside the caps or how they glue the caps to the board? I just bought an AU-717 , So I should open it up and look for this 1st?

John.

glen65 · Mar 18, 2006

jleon92f said:
I have been reading this thread , is that from inside the caps or how they glue the caps to the board?

They apply glue to the board or the bottom of the cap just before inserting it.

I just bought an AU-717 , So I should open it up and look for this 1st?

You can but you wouldnt necessarily need to pass one up if this was starting to take place. It can be cleaned before it causes an actual problem.

crooner · Mar 18, 2006

I guess they used the glue to minimize the possibility of solder joint failure due to vibration and shock, specially during transportation. Back in those days the Japanese were obsessive about quality and a unit had to work perfectly right out the box. They didn't want to take any chances and ruin their reputation

Personally, I think it was overkill and now we are facing the consequences of dealing with the nasty residues. :no:

dr*audio · Mar 18, 2006

Actually it is to prevent the leads on the caps breaking from vibration. Sounds incredible but I have seen firsthand results of not securing the cap. If you have a relatively large cap, say 1/2" diameter by 1" length, the cap has enough mass and length that it acts as a lever on the leads, wiggling back and forth as it vibrates during shipping, eventually breaking the leads. I have seen caps like this that were not staked down and the leads broke. It's not overkill, but with the decreased size of modern caps it may not be necessary anymore on anything smaller than 2200uF.

crooner · Mar 18, 2006

I've also seen wax covered PCBs specially in old transistor radios. The wax was used to seal certain critical RF components against humidity, thus preventing drift and loss of alignment.

AU-717 Deadly Glue

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