Author Topic: Universal NiMh charger repair (Philips TEA1400)  (Read 483 times)

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Offline reflowman

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Universal NiMh charger repair (Philips TEA1400)
« on: October 18, 2019, 03:07:07 pm »
I've tentatively repaired a mid 90's Philips shaver with (essentially) this universal charger circuit (from a Philips app note):
[attachimg=1 align=left width=400]
The input resistor (marked "33E") had burnt out and one of two series 3/4 AA NiMh cells (LOAD) was dead.
It's charging happily (but slowly) again now from a bench supply at 20Vdc 40mA.
I'm a bit wary of plugging in 240Vac though.
That 33E input resistor's colour coding had burnt off. I'd guess it's black, yellow, grey. The black could be toasted brown. The yellow is pretty definitely yellow and the "grey" band has virtually disappeared and could be anything. At any rate it's not a 33R resistor - more like 14R (toasted brown, yellow, very toasted black). It's the size of a 1/4W thru hole but cement coated - I'm guessing 1/2 or 1W.

I don't think the value is critical to circuit operation (one schematic for the TEA1400 omits it entirely) but is more to limit instantaneous current through C 2.2uF and a very slowblo fuse for failing batteries. I've replaced it for now with 3x100R // 1/4W.

Rough calcs for R = 33R:
@20Vdc with new cells the charge current is 40mA quiescent; guess ~100ma max. so max 4W total.  max dissip. 33R =~ 330mW. Instantaneous current at switch on = 20/33 = 600mA.

@240Vac 17mA (assumes same 4W total),  dissip. 33R ~ 10mW
Max. instantaneous current at switch on = 240*1.414/33 = 10A yikes! No wonder it was a cement type. A lot of thermal shock there.

I can't find a repair manual for the actual shaver, nor a comprehensive spec sheet for the TEA1400 to check what value/dissipation is needed.

What value and dissipation would you think reasonable as a permanent fix?
« Last Edit: October 18, 2019, 03:39:52 pm by reflowman »

Offline martfoxy

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Re: Universal NiMh charger repair (Philips TEA1400)
« Reply #1 on: February 22, 2021, 12:32:46 pm »
Have you still got this shaver?

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