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.
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
820 ma ripple
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
330uf 25 vdc
945 ma ripple
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:
6100 ma ripple
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.
All posts by Jim Jones