Author Topic: Philips Lumea SC1992 Teardown / Repair help needed  (Read 2150 times)

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Offline FelicitusTopic starter

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Philips Lumea SC1992 Teardown / Repair help needed
« on: May 21, 2018, 01:24:16 pm »
Curiosity killed my device. I was keen on confirming my theory of operation of my Philips Lumea SC1992, but in the process of tearing it down (ugly one way clip mechanism) I killed R202, unable to find it again.

It seems they're using the L6562A to charge the capacitor, the resistor in question was connected between the CS pin and the 100 Ohms current shunt resistor. Unfortunately I didn't figure out how to calculate R202, maybe someone can give me a pointer? The datasheet for the L6562A unfortunately doesn't give many formulas, and the reference schematics also don't fit the use case.

Maybe someone has a (defective) device and can measure R202 for me?



 

Offline fourtytwo42

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Re: Philips Lumea SC1992 Teardown / Repair help needed
« Reply #1 on: May 21, 2018, 05:57:08 pm »
Having a stab, it's very unlikely the current shunt is 100R as this would give an output power of only a few hundered mW if that. There is probably a capacitor from CS to ground so the resistor is there to form an RC filter to get rid of the mosfet turn-on spike and prevent false triggering of the current sense input. If R is to large the delay will be to long, but as you almost certainly dont know C (SMT brown blob with no markings) some experimentation would be nececery, its better to err on the low side and work up so I would go for 100R and no more than 1K if that helps :)
 

Offline FelicitusTopic starter

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Re: Philips Lumea SC1992 Teardown / Repair help needed
« Reply #2 on: May 21, 2018, 07:53:52 pm »
Having a stab, it's very unlikely the current shunt is 100R as this would give an output power of only a few hundered mW if that. There is probably a capacitor from CS to ground so the resistor is there to form an RC filter to get rid of the mosfet turn-on spike and prevent false triggering of the current sense input. If R is to large the delay will be to long, but as you almost certainly dont know C (SMT brown blob with no markings) some experimentation would be nececery, its better to err on the low side and work up so I would go for 100R and no more than 1K if that helps :)

Whoops yes, you're right, I've most likely read it upside down. It's more likely to be 0.001 Ohms, odd thing is that the dot is on the right side. I think I'll desolder the cap and see which value it reads, but yes, something between 100R and 1K is certainly a good idea. Realized later that the resistor is in series and not in parallel, forming a filter instead of a voltage divider.

Thank you :)
 


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