Closed Atari Jaguar Capacitor Replacement Question

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johntayloruk

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Hi All, I’ve replaced the caps in my Jaguar (Using high quality Panasonic caps from Farnell). All seems fine functionally, but it’s now making a really loud “hissing” noise which is extremely annoying.

According to the console5 site, this is a known issue and according to their capacitor info it sounds like it’s related to C150.
[h=3]Capacitor note on C150[/h][FONT=&quot]The schematic specifies that the 2200uF cap at C150 should be low impedance, and early Jaguar revisions follow suit. However, later revisions (Rev R, R/P) have a high-temp general purpose capacitor at C150, presumably to reduce the "Jaguar hiss" some consoles were noted for. The "hiss" is noise generated in the filter coil due to the high operating speeds of U38, and while it appears to be harmless, the noise can be quite loud and irritating.[/FONT]
[FONT=&quot]As of 2016 we've switched from a low impedance cap, to a replacement cap with similar characteristics to the late-model parts. The additional impedance / ESR appears to dampen the effects from the regulator & coil and help tame the hiss.

What I’m a little confused by is how I can identify a 2200uf 10v capacitor that isn’t low impedance /ESR to use.

Does anyone here have any experience with this kind of issue and how to resolve?

Thanks,

John

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To my knowledge, they don’t mark capacitors with the ESR rating or any indication of their mOhm value. However, purer capacitors tends to market as low ESR, so if it were me, I’d be looking for a cheaper, standard cap to do the job. Some sellers advertise that their caps are not low ESR, so those would be a good bet too. Other way would be to get the caps and check them with an LCR meter to measure their resistance and calculate it that way. Or you could take a guess by calculating the 2200 against the frequency they run at (e.g. 100hz) and find their impedence. I assume the low ESR caps are closer to 0.001 ohm rating. Therefore anything higher than that should be good for testing to remove the hiss.

c150 is the filtering capacitor for u38, so swapping it out for the same rating with a cheaper cap isn’t going to harm it, and will be the quickest test for removing the hiss. If worst comes to the worst I suppose you could just put a small resistor in line with that c150 to test what rating of resistance you need to remove the hiss and work from there.
 
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