Bond glue issues and pictures

[restorer-john]

We've been discussing conductive adhesive issues in another thread.

Here's some pictures of what happens. All these items were either dead or dying and brown glue was the cause. Do not underestimate the mess this stuff can do. Your gear, regardless of brand can be a time-bomb.

The poor capacitor is essentially hermetically sealed to the phenolic PCB by the bond glue. It cannot vent even a tiny bit. The glue ages and corrodes the legs, the cap leaks electrolyte because of the corrosion going up the legs and into the cap itself. Cap loses an entire leg or it eats down the pcb hole and reacts with the PbSn and Cu and makes a big mess. Sometimes caps can shoot off like a bullet from this reaction. These days, more caps have a one-time vent on the top, but all smaller electros still have the vent on the rubber base.

Capacitor's legs eaten away from under the glue, completely invisible from either side. This is a small PSU in a vintage amp.

Get rid of those ancient caps and clean up the mess!

New Nichicon UFGs!

This is caused by the glue at the base, reacting with the tinned copper legs, not allowing venting at the cap base and the reaction travels up the inside of the sleeve to the top.

Same cap at base

That wretched glue loves to eat transistors too

Rebuilt. Even used an original perfectly matching Elna cap bracket from my NOS stock. Previous PSU filter cap on right was larger diameter. Holes were predrilled in the factory for the two sizes in 1974.

 

[restorer-john]

Here's a 90s Onkyo receiver a friend asked me to look at as it was completely dead. A nicely finished product from the "Liverpool" range. He'd had it since new and various problems had occurred until it ceased altogether. He had two other matching components (CD needed attention too) and a cute little pair of Celestion UK built bookshelf speakers.

Our friend the brown glue again:

The phono RIAA board was just noisy and non-functional

Front panel selectors were non-functional as was the video switching

The entire uP and tuner was non-functional due to the main crystal having conductive adhesive preventing oscillation.

Phono board fixed

The most interesting fault was after it was all back up and running it was distorting in the preamp. Turned out to be one of the rail voltage regulator reference zeners. (always check your PSU rails, John) Brown glue had caused a reaction which went up one leg and into the glass envelope, affecting the zener voltage and causing the two rails to be a few volts different. A new zener fixed that once and for all. I put the zener under the microscope to see.

The rebuild was a labour of love and I received plenty of wine as in-kind payment (he was our neighbour for a number of years). Now he is back into music again after many years not listening. Shipped over his mum's DCM Timeframes from the US and is looking to upgrade his gear. I may have created a monster.

 

[restorer-john]

Here's that zener. You can see the brown glue reaction has gone up the leg and into the glass:

Resistors

Links

more links

Eww

 

[trl]

Impressive pics with corrosion signs on the components and their legs/pins too, many thanks for sharing.

 

[Doodski]

You do nice clean non-intrusive work. I'd let you work on my gear Definitely not a, "Badur the Butcher." (Inside joke. I replaced a technician many years ago and his name was Badur and so we nicknamed him as Badur the Butcher.")

 

[Wombat]

Any enlightenment on the so-called transistor 'black leg syndrome'?

 

[Doodski]

Funny you mention that. I've seen it lots on older germanium transistors. Possibly the leg was silver coated and oxidized.

 

[gvl]

Planned obsolescence?

 

[Hiten]

Any safe solution/solvent to dissolve glue without affecting PCB and other components ?
Thanks for the effort.

 

[Hiten]

Planned obsolescence?

In those days probably they planned for 30/40 years, these days they plan for 3/4 years.

 

[Doodski]

Planned obsolescence?

I don't think so. It's most likely just engineers doing their job and preventing the capacitors from being microphonic by reducing vibrations from loud music and when the chassis sustains impacts that cause electrons to be let loose in the circuitry. I know I worked with ~15 young engineers fresh out of university and they wanted everything glued and bonded to the printed circuit board.

 

[restorer-john]

Any enlightenment on the so-called transistor 'black leg syndrome'?

'Black leg' can go right inside the package up to the doped junction and make them noisy or fail, especially on the early Hitachi 'tombstone' packages.

It seems too hard for silver oxide, which seems to clean off easily on switch contacts. But it could be a similar substance.

Here's some oxidized switches before and after:

Some grease, various metals and gassing off plastics makes for bad switches

Cleaned in ultrasonic cleaner with some Silvo dabbed on the parts. Non-abrasive and retains the silver plating on the copper contacts with no damage.

 

[restorer-john]

Any safe solution/solvent to dissolve glue without affecting PCB and other components ?

Depending on the age and brittleness of the glue it can vary.

When the glue is young, light brown and still a little bit soft, you can heat it with about 100 degrees on a rework tool and soften it enough to peel like skin.

When its going dark, conductive and corrosive, the only thing I've found that takes it off is acetone. Nasty stuff, but it works. Most components and silk screening can handle it. But you will need to be careful. Use a wooden chopstick sharpened to a flat chisel end and you won't damage the PCB. just re-cut the scraper regularly with a knife. Fine forceps, tweezers, dentist's picks and plenty of patience is required.

When it's really dark, it has gone past conductive and can be chipped off quite easily.

Trouble is, all types of ageing can exist in the one piece of gear depending on what is exposed to the air/atmosphere and what isn't.

 

[JJB70]

Terrific stuff, to me this sort of info is just as valuable as product testing and probably more useful given the older gear I cherish.

 

[sergeauckland]

When I was involved in manufacturing broadcasting equipment in the late '70s, nothing was glued down, capacitors etc just soldered into the PCB. Ditto looking at British-made HiFi equipment of a similar vintage, like Leak or Quad. Now, all equipment seems to have capacitors and other components glued down, which makes them a pain to replace, regardless of whether the glue has gone bad or not.

My question is, therefore, why are components glued down, and who started this and when? What was wrong with not glueing them, as we did in the 1970s even with equipment that had to be extremely reliable?

S.

 

[restorer-john]

My question is, therefore, why are components glued down, and who started this and when? What was wrong with not glueing them, as we did in the 1970s even with equipment that had to be extremely reliable?

I believe it was Japanese exporting to the world. They had to ensure the products would arrive intact and without torn-off capacitors and damaged solder joints after being subject to the 'careful' freight systems they had no control over.

After all, in the UK, gear only had to go (by road) a few hundred miles maximum. Or maybe a nice boat trip to Australia.

Also, capacitors got smaller, able to be PCB mounted and snap-in (for automated insertion) meant the good old brackets and chassis's were outdated.

 

[Wombat]

Or 'audiophool' passive component vibration affecting sound nonsense.

 

[restorer-john]

Or, 'audiophile', passive component vibration nonsense.

Sony made a huge thing of vibration damping inside their analogue and digital gear. Especially in their ES products, where every major large component was carefully attached, isolated or damped with various elastomers, insulators and other compounds.

I remember the first time hearing an amplifier heat-sink "sing" with a test tone and thinking if current can make a noise in a passive piece of aluminium, why can't that aluminium object when subjected to vibration, affect the current in some way? Surely a two way street?

Perhaps the capacitive coupling of the T03P collectors to the heatsink (earth) using the insulator as a dielectric was the issue, I don't know. All I know is Sony (and Yamaha) damp the heatsink fins with a bituminous encircling band on many of their products along with anti resonant measures such as masses cast in at different points along each heatsink fin.

I'm sure you (like all of us) have run your fingernail along heat-sink fins and listened to the sound...

 

[JJB70]

My old gear has the Sony Gibraltar chassis which weighed a ton. That old Sony ES gear was made to remarkable standards, when I looked around earlier this year considering replacing it nothing I looked at (including some very expensive stuff) came anywhere close to the build quality.

 

[solderdude]

I could always tell when owners of Panasonic video recorders lived close to the sea.
There were silver plated mechanism position switches inside.
These turned black much sooner when the air is a bit salty.

Hate the glue as well.