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Thread: Crown CTS600 Repair...maybe

  1. #1
    Supporting Member tbonuss's Avatar
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    Crown CTS600 Repair...maybe

    So, for better or worse, I've decided to take a simple shot at fixing this thing. I started with the CTS600, because it doesn't have an "i" in its name I'll save the CDi 1000 for later, maybe...

    Crown, CTS600, no sign of life. Massively complicated piece of gear, but the good news is, the service manual is very good (evidently it is too large a file to post here--if anyone knows how to resolve that, I'll upload it).

    So far, I've found that this electrolytic cap is failed.

    I just took a picture of my screen with a camera, so if its not clear, I can certainly do something different.
    I have absolutely no idea if that would completely kill the amp the way it is. Maybe it could, I dunno...

    Click image for larger version. 

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    Thanks in advance for any of your thoughts / humor.

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Still has a SMPS tho..

    Thy this Crown_CTS600_Sch.pdf

    That cap if the reservoir for the 24V auxiliary power rail. If that cap is bad the rail will be low voltage. That could stop the SMPS from running and so will bring the whole thing to a grinding halt.

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    Supporting Member tbonuss's Avatar
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    Quote Originally Posted by nickb View Post
    Still has a SMPS tho..

    Thy this Crown_CTS600_Sch.pdf

    That cap if the reservoir for the 24V auxiliary power rail. If that cap is bad the rail will be low voltage. That could stop the SMPS from running and so will bring the whole thing to a grinding halt.
    Thanks Nick--I'm hopeful this is all...we'll see...the 470uf cap is listed as 35V, biggest one I could find laying around was 25V, so I went ahead and ordered a handful of them. I'll stick it in when it gets here and let you know what happens.

    Thanks again!

    Steve

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    Don't forget the joker g1's Avatar
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    If you have a link to the full service manual, post the link.

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    Supporting Member tbonuss's Avatar
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    Quote Originally Posted by g1 View Post
    If you have a link to the full service manual, post the link.
    https://medias.audiofanzine.com/file...ual-479799.pdf

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    Supporting Member tbonuss's Avatar
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    Quote Originally Posted by nickb View Post
    Still has a SMPS tho..

    Thy this Crown_CTS600_Sch.pdf

    That cap if the reservoir for the 24V auxiliary power rail. If that cap is bad the rail will be low voltage. That could stop the SMPS from running and so will bring the whole thing to a grinding halt.
    Hey Nick (or anyone else) if you happen to have the CDi 1000 schematic I may pry it open too while waiting for parts.

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    Supporting Member tbonuss's Avatar
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    Replaced C917--now its got 14.4VDC across it (gnd to TP 143).
    I don't fully understand what this thing is doing, so its kinda fun to try to figure it out. Wish they had the TP expected voltages posted--seems odd that they don't with all of the test points and the quality of the service manual. So I feel like I'm just missing it. Oh well, let's see...you turn the crank, the boot kicks the bucket which spills the marble down the stairs, and the thing is still dead as a doornail.

    Thanks,

    Steve

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    Supporting Member tbonuss's Avatar
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    Pretty "lucky" so far, I scoped TP134 and TP147 (below) so I pulled T901 and verified one of the primaries open. Will order, install, and see what's next.Click image for larger version. 

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Not only is the voltage low at 14.4V but it also looks like the ripple is at 60Hz. Since it's full bridge rectifier it should be 120Hz. I'm assuming your scope was set to 5ms/div. Please, if you post scope shots we need to know (1) H & V scales (2) AC/DC coupling (3) Where 0V is on the vert scale. Seems unlikely that one of the primaries (connected in parallel for 120V) could cause such a large voltage drop.

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  10. #10
    Supporting Member tbonuss's Avatar
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    Quote Originally Posted by nickb View Post
    Not only is the voltage low at 14.4V but it also looks like the ripple is at 60Hz. Since it's full bridge rectifier it should be 120Hz. I'm assuming your scope was set to 5ms/div. Please, if you post scope shots we need to know (1) H & V scales (2) AC/DC coupling (3) Where 0V is on the vert scale. Seems unlikely that one of the primaries (connected in parallel for 120V) could cause such a large voltage drop.

    Thanks Nick. Right. Sorry I didn't post the v/h scales. I would do that now, but I'm 1000 miles away from my o-scope

    I really just looked at it qualitatively and could see that the curvy part was the coupled sine wave and the straight parts were the caps discharge--and then there's a cusp where the sine starts again. Since they were symmetrically missing the same part, I knew that part of the wave was missing from the source (there isn't anything on the secondary side that would do this symmetrically. So, it had to be either one of the primaries open or one of the protective thingies shorted. If you look hard at the way the primaries are wired it makes sense. And I thought that since half the input power is missing, 14.4VDC measured instead of the 24VDC made sense (?). Anyhow, thats just how it seemed to me, and one of the primary windings is in fact open.

    So the transformer costs 12 bucks, not sure why they have the protective (thermal I think) devices. Seems like just one more thing to go wrong, with the relatively inexpensive transformer...I dunno.

    Thanks!

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    Last edited by tbonuss; 04-23-2019 at 04:24 AM.
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  11. #11
    "Thermionic Apocalypse" -JT nickb's Avatar
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    It looks to me like the primaries are wired in series for 240V and parallel for 120V. There's no way they could cause the 60Hz ripple on the DC. Most likely one of the 1N4148 diodes is open.

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    Supporting Member tbonuss's Avatar
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    Okay Nick. Thanks--I'll check them when I get home--hopefully this weekend.

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  13. #13
    Member patlaw's Avatar
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    That's another one of those amps with TOO MANY PARTS!

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