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Old 2nd Aug 2021, 9:47 pm   #1
daveobuchanan
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Default Thurlby PL320 R8 current sense resistor.

Hi,
I have 2 0f these dual output supplies, acquired from different places,,with faults. One has a broken voltage control pot. The left hand supply works on both, where as, on both right hand boards the R8 0.5R resister has been chopped out. Is that normal?
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Old 2nd Aug 2021, 10:45 pm   #2
daveobuchanan
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Default Re: Thurlby PL320 R8 current sense resistor.

Right, I have put in a 0.5r resistor, and now I get current, but the voltage is bouncing around. am confused.

few minutes.

PR1 intermittent...replaced with a 470r and all is peaceful....
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Old 2nd Aug 2021, 10:57 pm   #3
Julesomega
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Default Re: Thurlby PL320 R8 current sense resistor.

Quick work Dave! I don't have any info on this model
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Old 3rd Aug 2021, 1:15 am   #4
mhennessy
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Default Re: Thurlby PL320 R8 current sense resistor.

If it's a QMD - with the 4 switches in the middle - then the current sense resistor is moved off the board for the master (RH) supply. An aluminium-clad type is bolted to the bottom of chassis. This is because it needs to cope with 4A rather than 2A when working in parallel mode. Perhaps a wire has broken between it and the board?
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Old 3rd Aug 2021, 8:10 am   #5
daveobuchanan
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Default Re: Thurlby PL320 R8 current sense resistor.

Yes that must be it. I looked at the circuits and no mention. To investigate what has happened. I know one of them had an "accident" with a car battery .

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Originally Posted by mhennessy View Post
If it's a QMD - with the 4 switches in the middle - then the current sense resistor is moved off the board for the master (RH) supply. An aluminium-clad type is bolted to the bottom of chassis. This is because it needs to cope with 4A rather than 2A when working in parallel mode. Perhaps a wire has broken between it and the board?
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Old 3rd Aug 2021, 10:45 am   #6
mhennessy
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Default Re: Thurlby PL320 R8 current sense resistor.

One of mine came to me with a missing track on the switch PCB. It had been vaporised by a gross overload - no idea what caused it, but suspected it was something like a car battery...

I can't remember how that affected the operation - it was 20 years ago - but since then, I've always made a point of inspecting that PCB. It's easy to overlook as there's not much on it, but it does carry a fair bit of current in certain modes.
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Old 3rd Aug 2021, 9:36 pm   #7
daveobuchanan
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Default Re: Thurlby PL320 R8 current sense resistor.

The first unit is working now, just waiting for some parts. I had a look at the other one, and the right hand channel has a current limit fault. PR3 1K tweaker has failed open circuit like PR1 on the other unit. Feeling quietly pleased with my self.
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Old 6th Aug 2021, 12:15 pm   #8
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Default Re: Thurlby PL320 R8 current sense resistor.

Well done Dave, very satisfying!
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