Princeton VL1918 LCD Monitor Repair

An easy fix for a monitor that will not stay powered up

I recently acquired a non-working Princeton VL1918 monitor. When powered up it would continuously turn off then back on at about 1 second intervals. Opening the unit revealed 4 bulged capacitors on the power supply board, all on the +12 vdc rail.
ps board

All 4 capacitors were made by Capxon, a company which seems to have an abnormally high failure rate on their parts. Full specs on the capacitors are:

470uf 25 vdc
1200 ma ripple
0.075 esr

330uf 25vdc
820 ma ripple
0.114 esr

A good exact replacement would be the Nippon Chemicon/United Chemicon KZM series which have the following slightly better specs:

470uf 25 vdc
1330 ma ripple
0.039 esr

330uf 25 vdc
945 ma ripple
0.056 esr

Why use 25 vdc capacitors on a 12 vdc supply when 16 vdc capacitors would work? The 470uf @ 16 vdc capacitors in the above series can only handle 945 ma ripple and have a higher 0.056 esr. Higher voltage capacitors, in the same series, handle more ripple current and have a lower esr. Using an inexpensive style of capacitor with a higher voltage is cheaper than using a good capacitor series at the normal voltage.

For replacement I went with a better style of capacitor, the Skywell SEL series. The SEL series are aluminum solid electrolytic capacitors that use organic semiconductors as electrolytes. Organic semiconductor capacitors have high conductivity, high-temperature stability, high ripple current capacity & low esr.
The specs for the Skywell SEL series replacements:

330uf 16vdc
6100 ma ripple
0.007 esr

With its greater ripple current and lower esr, the 330uf 16 vdc Skywell SEL easily replaces the Capxon 470uf & 330uf 25 vdc capacitors.
Note: Always check the ripple and esr of your replacement capacitors. The new capacitors should have the same or higher ripple current and equal or lower esr.

ps board

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