Help on power supply problem

t2060079 · 26th July 2008, 01:21 PM

I find the power supply capacitors highlighted in attached file are abnornmally hot. Can anyone advise the problem please?

Mooly · 26th July 2008, 01:41 PM

May be just the caps themselves failing, having developed a high E.S.R. They look highly stressed ripple current wise, try replacing with suitable new ones. The plug/socket to the diode bridge isn't open circuit is it. These limit the max voltage across the caps.
Probably just the caps themselves

t2060079 · 26th July 2008, 07:57 PM

Thanks your advice. Actually I replaced new capacitors with same specification but there is no improvement. I don't know what happen.

Ragnwald · 26th July 2008, 08:16 PM

The polarity of the two caps look wrong on the schematic.
Try nonpolarity caps there.

megajocke · 26th July 2008, 10:13 PM

Quote:

Originally posted by Ragnwald
The polarity of the two caps look wrong on the schematic.
Try nonpolarity caps there.

No it's correct do do it like that. 4700uF NP caps are not a very common item to find.

lineup · 26th July 2008, 10:39 PM

Quote:

Originally posted by t2060079
capacitors highlighted in attached file are abnornmally hot.
Can anyone advise the problem please?

One thing I can think of is:
check the max Voltage rating of those caps.

The other thing is CHECK the polarity.
see to that they are not put the wrong way!
Because if, this is certainly a big problem ...
Correct is:
- cap + .... resistor .... + cap -
if we are to believe in your schematic

Third, as capacitors normally do not get very hot:
Have a look if actually it is caps that produce heat.
Maybe it is some resistor? Close to those caps.

Steerpike · 26th July 2008, 11:10 PM

Do C101 and C102 not get hot?
BR3 is probably damaged.

unclejed613 · 27th July 2008, 02:05 AM

a shorted diode in the bridge rectifier would have been my first choice until i looked closer at the schematic. the bridge rectifiers are actually connected as voltage limiters here. very strange, but the caps are probably hot because a diode in the bridge is open. these are very low voltage caps, and the bridge rectifiers limit the voltage across the caps to about 2v (+/- a sizeable fudge factor of about .8V)

t2060079 · 27th July 2008, 06:54 AM

Thanks for your all advices. I measured the voltage across R106 and it was about 0.8V. Is the BR3 health?

On the other hand, the C101 and C102 are not hot. They are okay.

Mooly · 27th July 2008, 10:04 AM

Dare we even ask what it is

I'll be honest, I can't just at first glance figure it out at all. Has it worked all right in the past and suddenly this problem developed ?

27th July 2008, 02:05 AM	#8
unclejed613 diyAudio Member Join Date: Dec 2006	a shorted diode in the bridge rectifier would have been my first choice until i looked closer at the schematic. the bridge rectifiers are actually connected as voltage limiters here. very strange, but the caps are probably hot because a diode in the bridge is open. these are very low voltage caps, and the bridge rectifiers limit the voltage across the caps to about 2v (+/- a sizeable fudge factor of about .8V) __________________ Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net spammer trap: http://www1284177414881.v-dc.net/

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26th July 2008, 01:41 PM	#2
Mooly diyAudio Member Join Date: Sep 2007	May be just the caps themselves failing, having developed a high E.S.R. They look highly stressed ripple current wise, try replacing with suitable new ones. The plug/socket to the diode bridge isn't open circuit is it. These limit the max voltage across the caps. Probably just the caps themselves

26th July 2008, 07:57 PM	#3
t2060079 diyAudio Member Join Date: Nov 2005	Thanks your advice. Actually I replaced new capacitors with same specification but there is no improvement. I don't know what happen.

26th July 2008, 08:16 PM	#4
Ragnwald diyAudio Member Join Date: Feb 2008 Location: Gotland	The polarity of the two caps look wrong on the schematic. Try nonpolarity caps there.

26th July 2008, 11:10 PM	#7
Steerpike diyAudio Member Join Date: Jan 2006 Location: Johannesburg, South Africa	Do C101 and C102 not get hot? BR3 is probably damaged.

27th July 2008, 06:54 AM	#9
t2060079 diyAudio Member Join Date: Nov 2005	Thanks for your all advices. I measured the voltage across R106 and it was about 0.8V. Is the BR3 health? On the other hand, the C101 and C102 are not hot. They are okay.

27th July 2008, 10:04 AM	#10
Mooly diyAudio Member Join Date: Sep 2007	Dare we even ask what it is I'll be honest, I can't just at first glance figure it out at all. Has it worked all right in the past and suddenly this problem developed ?

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