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Spot the deliberate mistake

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Centauri View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Centauri Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2013 at 10:48am
Spade terminals not fully inserted into the board?
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mini-mad View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mini-mad Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2013 at 10:57am
Originally posted by kedwardsleisure kedwardsleisure wrote:

Spot the deliberate mistake(s).

a venerable Cloud VTX1500



should L1 be a feck off large wire wound resistor?

...AND the relay under specc'd?

If it sounds like a gorilla is trying to escape, turn it down.
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studio45 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2013 at 12:59pm
thats not a resistor, its an inductor. relay in backwards?
Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA
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Peter Jan View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Peter Jan Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2013 at 1:12pm
Shouldn't that be a 10-16A SINGLE contact relay ?

The board says LTX instead of VTX ? Don't know if that's a mistake or not...

Edited by Peter Jan - 03 June 2013 at 1:17pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2013 at 1:52pm
The inductor has been put in the wrong way around?  LOL

"The board says LTX instead of VTX"

That?


Earplugs Are For Wimps!
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service dept Steve View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote service dept Steve Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2013 at 2:18pm
What's the prize?
Is it obvious and staring us in the face? or is it something subtle?
It doesn't look like the relay is wrong, Yes it is only 8A but it is double pole so 16A which is correct, 24vdc coil, also correct, resistors and diode looks right, is the relay supposed to be a push away rather than a pull towards, thereby only letting the amp run in fault mode?
We are not "They", We are "The others"http://www.servicedept.co.uk -
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Peter Jan View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Peter Jan Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2013 at 3:44pm
Originally posted by service dept Steve service dept Steve wrote:


It doesn't look like the relay is wrong, Yes it is only 8A but it is double pole so 16A which is correct

Wouldn't make much difference in making contact, close but still not the full 16A capacity though, no problem if the amp is in normal working order. It's not okay for breaking in a faulty situation (full rail DC for instance).  Relay contacts are never 100% in "sync". The one lagging contact will almost take the full capacity the PSU can deliver into the connected speaker(s), arc itself into a solid contact and take the speaker(s) out with it. The lower the connected impedance, the easier the contacts will arc. DC rail fuses are usually roughly calculated to blow in case of a short or near short, but they hardly ever blow in a case like that. If they do, it's usually because the speakercoils have already burned into total destruction/near short-circuit.
I know it's somewhat common practice to use double contact relays, on first sight it makes sense and nobody will ever notice a thing... till the amp fails.
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slaz View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2013 at 3:48pm
Magnetic field - relay and inductor could influence each other ?


REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
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kedwardsleisure View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2013 at 8:40pm
There are 3 seperate faults and they're all to do with the relay.

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Kevin

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service dept Steve View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote service dept Steve Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2013 at 8:53pm
48 volt relay, pass on the others though
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Peter Jan View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Peter Jan Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2013 at 8:54pm
1) as said earlier, must be single contact.
2) is it the wrong relay maybe, as in : NC instead of NO contacts for instance ?
3) should it be another coil.. 12V, 48V or something, not 24V ?
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kedwardsleisure View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2013 at 9:06pm


24V relay fitted - should be 48V

DPDT 8A fitted - should be SPDT 16A. On Cloud amps this age, the relay is configured to short the DC bus to ground if the amp goes DC. The DC is backed up by T15A fuses in this model. I have seen otherwise healthy amps like this used on bass duty actually melt the relay covers with the heat from imperfect contacts.

Quench Magnet missing. There should be a strong magnet glued to the relay to quench any DC arc before it gets established. I assume Cloud fitted these based on experience.




Kevin

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