A Quick question on recapping - Page 1
Forum section: electronics / repair

author: tohtorizorro
author_rank: Contributor
timestamp: March 07, 2025, 03:43:48 pm
content: Hi,I'm recappin a Samsung Syncmaster 735s CRT monitor. The main board has two below 1uF electrolytic caps and I wonder if it would be smart to replace them with ceramic or plastic ones.See the caps in the attached main board schematic:C505 220nF 50V 85°CC414 470nF 50V 85°CWas thinking the same thing about these three on the smaller "video" PCB which is attached to the end of the tube:CB2 1uF 50V 105°CCG2 1uF 50V 105°CCR2 1uF 50V 105°CI've kind of thought that Al electrolytic caps should be avoided when possible (ie. if they're not the only type that will fit in) due to their limited life span but is there a specific reason some or all of the mentioned capacitors should be electrolytics?Thanks!

author: indeterminate
author_rank: Regular Contributor
timestamp: March 07, 2025, 11:53:52 pm
content: Just do a like for like swap of the Al electrolytic capacitors. and use a decent brand not sourced from flebay of aliIt is not always predictable what effect changing a component type will have.

author: Kurets
author_rank: Regular Contributor
timestamp: March 08, 2025, 01:31:32 pm
content: The three capacitors are part of low pass filtering for red green blue probably driven by a transconductance amplifier. One feature of low capacitance electrolytics is that they usually have high ESR, this allows them to work as an RC network which can sometimes be useful.Here the high ESR could contribute to the amplifier seeing a resistive load around cutoff. I would not be surprised if this circuit is dependent on the ESR for stability.Unless you have issues with the picture I think those probably don't need changing.

author: club
author_rank: Newbie
timestamp: March 08, 2025, 03:37:55 pm
content: The use of electrolytic capacitors is mainly driven by the need for high capacity values, which with other types would entail huge dimensions.They are an important topic of both study and experience in electronics. However, they differ (sometimes significantly) from other types of capacitors in many other functional characteristics; therefore it is not advisable to replace them carelessly, especially if there is no need.In some cases, electrolytic capacitors are even used NOT as simple capacitors, but as complex circuits that include their ESR (equivalent series resistance) or even their leakage current!To prolong the lifespan of the electrolytic capacitor as much as possible, it is advisable to use one with the voltage reported on the casing significantly higher than that of its normal operation.P.S = When the electrolytics remain inactive for long periods, their internal structure changes (slightly or more, depending on the time interval, the temperature and the quality of the component): when they then receive voltage again at the terminals, they initially behave like a resistor: for a while (sometimes a few seconds, sometimes hours) they absorb current, until they stabilize. The phenomenon is due to the "reformation" of the dielectric, which has become damaged over time.It is often possible to completely recover an electrolytic apparently in excellent condition, but electrically with a significant loss current: just connect it to a stabilized laboratory power supply, with Vconst=half of the printed value, and Iconst=1uA/1uF (example for 2200uF-50V: Vconst=25V, Iconst=2.2mA).Good luck!

author: hanakp
author_rank: Regular Contributor
timestamp: March 08, 2025, 10:59:16 pm
content: A few years ago, I recapped a Philips CRT. I replaced all <=1 uF electrolytics with ceramic X7R, with no apparent side effects. I even replaced them in signal paths, like CR04, CB04 and CG04 near the tube in your video board schematic. If memory serves, I used 1u/250 V, because 160 V is not normally available.