How important is the value on this 9uF NP cap?

[robertbaruch]

I have an Amdek monochrome monitor from the 80s. You can see the schematic here, 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 from their 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.

[TheMG]

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.

[themadhippy]

what are my alternatives

. 8.2uF or 10uF are all you get.

10uf in parallel with an 8.2 uf gets you 18.2uf , 2 of them in series gets 9.1uf

[CaptDon]

The capacitors for horizontal deflection had a design optimized
to handle high circulating current going through the yoke coils.
That current could be in the area of 4 amps. Some tweeter speaker
N.P. crossover caps should work, but to be on the safe side I would
probably parallel a pair of 4.7uf or 5uf to handle the current if there
is room. B.T.W. two polarized electrolytics hooked in series + to +
or - to - DOES NOT work like a non-polarized capacitor. Many will
argue that point, but in a circuit where the caps are conducting
current (especially in the 'amps' range) the smoke and smell will
tell you this old trick DOESN'T WORK. Don't let anyone try to tell
you it does!!

[coromonadalix]

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 ??

[CaptDon]

I calculated the Xc of your replacement capacitors at 15,734 hz
which was the standard frequency of a color television receiver.
9uf=1.124ohms and the 10uf is 1.01 ohms. So at two amps of
yolk circulating current you could possibly gain about .24 volts
of extra voltage across the yolk meaning you may have to adjust
the width coil for slightly more inductance as the picture may be
ever 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 of
5uf non-polarized speaker crossover capacitors in parallel to handle
the high circulating current if you have room. Those yolk coupling
capacitors were a source of problems. They develop some ESR
and then heat up from the high current and pop their tops!!

[wraper]

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