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Old 10th Jul 2017, 11:18 am   #1
Linnovice
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Default Resistor help

Morning all, I have had a resistor blow on a Revox A77 4 track Drive Control Board. One of the old Rifa caps blew and took the resistor with it. In the manual it is labelled as R 121 Resistor Carbon Film 4.7. It has a colour bands of Yellow, Violet, Gold and Silver.

I've searched ebay and various suppliers but am having trouble locating a supply. Is there an alternative I could use or can anyone suggest a supplier please?

Any polite suggestions would be very welcome.

Regards, Mike
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Old 10th Jul 2017, 11:24 am   #2
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Default Re: Resistor help

It's a 4.7R resistor. You don't mention the power rating.

Plenty of sources. For example:-

http://www.maplin.co.uk/search?text=...or+4.7&x=0&y=0

http://uk.rs-online.com/web/c/passiv...ons=4292049429
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Old 10th Jul 2017, 11:42 am   #3
Linnovice
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Default Re: Resistor help

Hi, thanks for the response. There is no power rating listed in the manual. It just quotes the resistance as 4.7. Not very helpful but I suppose when the manual was written they assumed only professional technicians would use it. Not enthusiastic but ignorant amateurs ��
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Old 10th Jul 2017, 11:57 am   #4
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Default Re: Resistor help

It looks to be in series with a 0.47uF, I can't figure out what voltage is across the circuit but if we take 240 AC max and Xc of the 0.47uF = 6.7k that's 35mA, that won't be a lot of dissipation by a 4.7 ohm resistor, I think 1/2 watt would be ample.

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Old 10th Jul 2017, 12:40 pm   #5
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Default Re: Resistor help

Thanks Lawrence, so, should I ignore the colour banding on the resistor and just go for any 4.7 ohm 1/2W resistor? There are another two with the same banding on the board. If I can't match them (which is proving to be the case) should I change all three so they are the same?
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Old 10th Jul 2017, 12:44 pm   #6
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Default Re: Resistor help

4.7 ohm 1/2 watt should do, no need to change the others unless they're faulty.

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Old 10th Jul 2017, 12:45 pm   #7
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Default Re: Resistor help

Any replacement resistor should be colour coded unless it's wire wound, in which case the value will be written on it.

A 0.6W resistor will be fine and there's no need to change any others of the same 4.7R (4 point seven ohms) value.
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Old 10th Jul 2017, 12:46 pm   #8
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Default Re: Resistor help

Crossed. I said 0.6W as they're available from Maplin.
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Old 10th Jul 2017, 7:30 pm   #9
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Default Re: Resistor help

The colour banding is correct for 4.7 ohm.
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Old 10th Jul 2017, 9:30 pm   #10
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Default Re: Resistor help

With 10% tolerance, not that tolerance would matter much here.
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Old 10th Jul 2017, 9:40 pm   #11
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Default Re: Resistor help

Thank you all for your suggestions and advice. I have ordered the following from RS.

TE Connectivity LR1 Series Axial Metal Film Fixed Resistor 4.7Ω ±1% 0.6W ±100ppm/°C

Hopefully that should do it.

Regards to all.
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