2014
01.25

Capacitor replacement

Dad’s large screen TV has been having issues for quite a while, taking an increasingly long time to finally power up, culminating in a failure to power on at all.  He discovered that this is a fairly common issue with that model (Samsung LN-T4061F), and that the root cause is failing capacitors in the voltage regulator section.  This reminded me that I still had to fix a friend’s Slingbox with the exact same issue, so it was off to the Makerspace to do some desoldering and order replacements.

The highlighted area shows the problematic caps on the board.  I have to say, this is one of the nicest PCBs that I’ve ever seen – all of the components are clearly labeled, test points are called out, saw cuts in the board provide additional voltage isolation, etc.  In an age where including circuit diagrams with a piece of electronics equipment is but a distant memory, could this board have actually been created with diagnosis and repair as design goals rather than the all-too-common approach of repair by replacement?

Left to right, top to bottom, the capacitors are:

CM880: Sam Young KMG 1000uF 25V 105°C (replaced with Digi-Key 493-4504-1-ND)

CM876: Sam Young KMG 1000uF 25V 105°C (replaced with Digi-Key 493-4504-1-ND)

CM852: Samsumg VMA 2200uF 10V 105°C (replaced with Digi-Key 493-4495-1-ND)

CM853: Samsumg VMA 2200uF 10V 105°C (replaced with Digi-Key 493-4495-1-ND)

CM881: Sam Young LXV 47uF 50V 105°C (replaced with Digi-Key 493-4512-1-ND)

CM854: Sam Young LXV 47uF 50V 105°C (replaced with Digi-Key 493-4512-1-ND)

CM851: Sam Young LXV 47uF 50V 105°C (replaced with Digi-Key 493-4512-1-ND)

CB850: Samsung VDE 1000uF 10V 105°C (replaced with Digi-Key 493-4494-1-ND)

The two components (LM852 and LM851) that look shrouded in heat shrink tubing are inductors and don’t need replacement (inductors are just coils and unlike electrolytic capacitors, don’t have electrolyte to evaporate away over time).  Obviously, the brown corrosion at the tops of CM852 and CM853 point to leakage on these caps, but it’s prudent to replace them all.

On the Slingbox I found:

CB18: 220uF 25v 105°C (replaced with Digi-Key 493-13386-ND)

CB45: 470uF 16v 105°C (replaced with Digi-Key 493-4499-1-ND)

CB43: 470uF 16v 105°C (replaced with Digi-Key 493-4499-1-ND)

If you look up the specific Digi-Key part numbers I listed, they’re all 125°C rated caps at the next highest voltage rating I could find.  I’ve heard that the rule of thumb is to just bump the voltage rating when replacing failed capacitors, but I figure upping the thermal rating in addition can’t hurt at all.  A bulb-type desoldering iron made quick work of removing them from the boards.

After waiting a few days for my Digi-Key order to arrive, I was ready to install the replacements.  I started with the Slingbox board, which had ample room for the larger replacement caps.  However, the solder pads were hesitant to actually take on any new solder.  By comparison, the Samsung board took solder on the pads with aplomb.

In comparison to the Slingbox board, the new caps on the Samsung board had to be shoehorned into place.  This was expected, though, as an increase in voltage rating or in thermal rating generally incurs an increase in package size as well.  I’ll happily take a board that may be less aesthetically populated in exchange for having it able to withstand a nuclear winter, zombie apocalypse, or Justin Beiber album.  While the initial failure of the Samsung board is a bit disheartening, I’ll still give Samsung praise for a superb, easily repairable PCB.  So to the unknown engineer(s) who toiled away on the design of IP-231135A to make it better than ‘good enough’, dad says ‘thanks’.

4 comments so far

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  1. You stated that inductors do not need replacement, but my lm851 has a scorch mark on the top which the lm852 does not. Please email me with contact information so we can discuss this. None of my capacitors are bloated and I could use some help

    • Inductors generally do not need replacement – there’s not much that can go bad with a simple coil of wire! However, that doesn’t mean they’re invulnerable – I’ve seen a very small number of inductors go bad (specifically solenoid coils), but in my experience it’s always been something in the connection between the device leads and the very fine wire that forms the coil itself. Also, just because none of your capacitors are bloated, leaking, etc, doesn’t necessarily mean that they’re in perfect working order (hence why I replaced the entire gaggle of caps (assuming that the collective noun for capacitors is a ‘gaggle’.))

      It’s pretty hard to argue with scorch marks, however – carbon tracks indicate that electricity is getting to somewhere it should not. If I were trying to diagnose it, I’d desolder the inductor from the board and then test it to be sure the coil is unbroken and working at the specified inductance rating.

      You can always reach me at X @ X.org where X = ‘haveblue’, but I’d love to have you respond here so that other, smarter people can respond (just because I have a soldering iron doesn’t make me an electrical engineer!)

  2. Thank you for the DigiKey equivalents. About to replace some caps in my TV, and you saved me some headache.