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I recently acquired an IBM 5154 EGA monitor that works pretty well. The only minor problem is that the screen is slightly off-center. I decided to take it apart to adjust it, but discovered that many of the capacitors look as though they are leaking, including on the main board.

Is this a leak or is it glue? I know it wasn't uncommon to glue capacitors like these down back then, but I have very little experience with electronics of this vintage.

capacitor

It's a little challenging to see in the picture, but whatever this is seems to be dribbling down the side from near the top. Most of the capacitors (at least the larger ones) look similar.

The PSU definitely has a very busted tantalum capacitor, so I'll be recapping most of the PSU, but was hoping to not have to do the rest of the monitor as it's pretty difficult to take apart.

Edit: here's another pick from the PSU, after some capacitors were removed...glue?

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    I never saw leakage around electrolyte (it usually evaporate to air)... the usual symptom is the capacitor is slightly loose (you can swing it a bit without bending the pins) and or the topside is curved outwards (like pressurized balloon). so my bet is its the glue ... or some Quality check marker... – Spektre Jun 30 '18 at 20:06
  • Nowadays they use white polyurethane something like tan subfloor adhesive. to prevent movable parts from vibrating and fatigue on leads. – Tony Stewart Sunnyskyguy EE75 Jul 1 '18 at 1:57
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    To me, that stuff on the Cs looks very much like the goo that has been spread over the transformer windings - I would assume, it is the same and was used to relieve mechanical stress on the solder joints. – tofro Jul 1 '18 at 9:31
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    That is the typical look of glue that is used to stop large capacitors from vibrating and breaking their leads off. Electrolyte usually leaks out through the capacitor's top vents (which your capacitors don't have) or its leads, and dries to a light colored powder. Your board looks clean in the lead areas which indicates this stuff is not leaked electrolyte. – Bruce Abbott Jul 3 '18 at 11:54
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There are basically two distinct "tell-tales" for electrolytic capacitor leakage:

  1. Bulging pressure release plates at the top of the capacitor, with possible signs of leakage emanating from there.
  2. Fishy odor.

Absent both of those indicators, I'm inclined to think the staining of the PCB is from another source. Also, the electrolyte from the caps is highly corrosive to the PCB. If you don't see anything that looks like corrosion, then you are lucky, and also should not blame the stain on electrolytic leakage.

Another point worth noting is that caps that have leaked their electrolyte don't retain their rated capacitance. Naturally, that leads to symptoms of device failure. If you have a device that is working perfectly, and don't see any evidence of leaky caps, then removing and replacing caps is just a preventative measure - Many previously working retrocomputers have been rendered non-functional by preemptive re-capping using the wrong tools and technique.

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