How important is the value on this 9uF NP cap? - Page 1
Forum section: electronics / repair

author: robertbaruch
author_rank: Regular Contributor
timestamp: May 12, 2020, 01:45:08 am
content: I have an Amdek monochrome monitor from the 80s. You can see the schematichere, and the section that I'm looking at is redrawn in DaveCAD here.The manual lists C423 as a 9uF 35V nonpolarized electrolytic. Now, I can't find a 9uF capacitor anywhere, but I've found a 10uF NP.How mad would the monitor get if I change out the 9uF capacitor for a 10uF capacitor? Would it be usual for the horizontal width adjustment to be able to handle that? If the 10uF capacitor doesn't work, what are my alternatives?The original capacitor is from Teapo, marked "9uF 35V NP SR 85°C 09/86". From what I can tell fromtheir catalog, SR is the series for horizontal deflection circuit capacitors, +/-10% tolerance, and they certainly don't have 9uF anymore. 8.2uF or 10uF are all you get.

author: TheMG
author_rank: Frequent Contributor
timestamp: May 12, 2020, 01:59:52 am
content: Chances are the tolerances on the original 9uF cap were probably fairly wide, modern capacitors for the most part are much closer to rated, even though the tolerance is +/- 10%, but in the past it was common for capacitors to have a large +% tolerance and they tended to mostly be higher than the rated capacitance when new, so that could be the reason for the designer selecting a 9uF capacitor. Very likely the adjustment would be able to compensate for the 1uF of extra capacitance.If not, could always parallel an 8.2uF and a 1uF, for 9.2uF.

author: themadhippy
author_rank: Super Contributor
timestamp: May 12, 2020, 02:01:51 am
content: QuoteQuote10uf in parallel with an 8.2 uf gets you 18.2uf , 2 of them in series gets 9.1uf

author: CaptDon
author_rank: Super Contributor
timestamp: May 12, 2020, 08:19:29 pm
content: The capacitors for horizontal deflection had a design optimizedto handle high circulating current going through the yoke coils.That current could be in the area of 4 amps. Some tweeter speakerN.P. crossover caps should work, but to be on the safe side I wouldprobably parallel a pair of 4.7uf or 5uf to handle the current if thereis room. B.T.W. two polarized electrolytics hooked in series + to +or - to - DOES NOT work like a non-polarized capacitor. Many willargue that point, but in a circuit where the caps are conductingcurrent (especially in the 'amps' range) the smoke and smell willtell you this old trick DOESN'T WORK. Don't let anyone try to tellyou it does!!

author: coromonadalix
author_rank: Super Contributor
timestamp: May 12, 2020, 08:31:03 pm
content: I think it could work if the circuit is not too tight in tolerance, ive done it only one time in a tv, and it worked very well, had to fiddle a deviation adjustment just 1/4 of a turn ??If everything work fine i would do it, just to be sure the ac is disconnected, and wait 15-30 mins to be sure the capacitors are discharged ??

author: CaptDon
author_rank: Super Contributor
timestamp: May 13, 2020, 01:19:56 pm
content: I calculated the Xc of your replacement capacitors at 15,734 hzwhich was the standard frequency of a color television receiver.9uf=1.124ohms and the 10uf is 1.01 ohms. So at two amps ofyolk circulating current you could possibly gain about .24 voltsof extra voltage across the yolk meaning you may have to adjustthe width coil for slightly more inductance as the picture may beever so slightly wider. You probably won't even notice the difference.I would probably still go with either a pair of 4.7uf or a pair of5uf non-polarized speaker crossover capacitors in parallel to handlethe high circulating current if you have room. Those yolk couplingcapacitors were a source of problems. They develop some ESRand then heat up from the high current and pop their tops!!

author: wraper
author_rank: Unknown
timestamp: May 13, 2020, 01:31:15 pm
content: I would use two 4.7uF (or 4.7uF +3.9uF ) 50V film capacitors in parallel for better reliability.https://eu.mouser.com/ProductDetail/WIMA/MKS2B044701K00MSSD?qs=sGAEpiMZZMv1cc3ydrPrF7l45uRd9dVhqkEsoguMRc4%3D