Crest VS900 burning hot resistor R92 - diyAudio
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Old 9th July 2015, 08:42 AM   #1
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Default Crest VS900 burning hot resistor R92

I recently opened my Crest VS900 and noticed that the big, vertical mounted 330ohms/10W resistor marked as R92 gets extremely hot, so hot that you can already smell it after a minute the amplifier was switched on, let alone touching it.
You can also see burn marks on the fan connector that's directly next to it.

What could be causing it? The fan (115VAC Sunon) was already lubricated and cleaned some time ago.
My VS is an original euro version and we have around 225-228V in the socket.

Click the image to open in full size.

Click the image to open in full size.
(The mentioned resistor is just under the TR1 triac)

Last edited by czolgista778; 9th July 2015 at 08:46 AM.
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Old 9th July 2015, 08:48 AM   #2
sajti is offline sajti  Hungary
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Hi,

is the fan original, or different? Is it running well, with low speed?

Sajti
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Old 9th July 2015, 08:53 AM   #3
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Hi Sajti,

The fan looks 100% stock to me, it's a SUNON SP100A - 115V 0.26A.
To be honest the fan noise is not at jet engine level but it's easily audible.
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Old 9th July 2015, 09:01 AM   #4
sajti is offline sajti  Hungary
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Quote:
Originally Posted by czolgista778 View Post
Hi Sajti,

The fan looks 100% stock to me, it's a SUNON SP100A - 115V 0.26A.
To be honest the fan noise is not at jet engine level but it's easily audible.
As I calculate the 330W resistor will dissipate about 7.3W, if it running from 115V AC, and series connected with the fan.
Maybe You can change the resistor to 470ohm/10W. It will reduce the fan speed somewhat, the dissipation of the resistor will be about same (7.4W).
If I would do the design of this amplifier, I would use 20W resistor....

Sajti
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Old 9th July 2015, 09:05 AM   #5
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I measured that the fan runs at 68,3V now. The VS900 seems to have a 3 step fan control, it's always on and at 55*C it speeds up and at 75% it should go full throttle.

Crest did a trick to somehow cool it - they let the fan suck the air inside the amplifier, alongside the radiator and it comes out on the sides of the amp.

Click the image to open in full size.

Last edited by czolgista778; 9th July 2015 at 09:07 AM.
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Old 9th July 2015, 09:09 AM   #6
sajti is offline sajti  Hungary
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Quote:
Originally Posted by czolgista778 View Post
I measured that the fan runs at 68,3V now. The VS900 seems to have a 3 set fan control, it's always on and at 55*C it speeds up and at 75% it should go full throttle.

Crest did a trick to somehow cool it - they let the fan suck the air inside the amplifier, alongside the radiator and it comes out on the sides of the amp.
If You want to keep everything same, than change the resistor to 330ohms 20-25W. Multicomp has 330ohms 25W resistor, available from Farnell. And it's not expensive.

Sajti
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Old 9th July 2015, 09:45 AM   #7
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I'm concerned whether it will fit or not. The 10W is already packed quite tight. Is the 25W also a cement resistor or wirewound?
Wirewound will most prbably not fit, unless I cut the mounting flaps and let it hang on the wires...

I think that I could just disconnect the fan, I'm using the Crest at home and since it's an Class H amp it should stay cool.
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Old 9th July 2015, 09:46 AM   #8
sajti is offline sajti  Hungary
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Quote:
Originally Posted by czolgista778 View Post
I'm concerned whether it will fit or not. The 10W is already packed quite tight.
I guess, that it will. It's just longer comparing to the 10W version.

Sajti
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Old 9th July 2015, 10:05 AM   #9
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Thanks, I think that I should give it a go then. I have the amp running with the fan disconnectend and the top cover removed but after 15 mins it's getting warm.
I think that due to it's design, active cooling is mandatory.

Last edited by czolgista778; 9th July 2015 at 10:13 AM.
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Old 9th July 2015, 10:16 AM   #10
sajti is offline sajti  Hungary
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Quote:
Originally Posted by czolgista778 View Post
I think that due to it's design, active cooling is mandatory.
Yes. If You don't use the fan, it will turn off itself, in few minutes with closed box.

Sajti
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