Medion digial TV tuner doesn't power on – Bulged capacitor in power supply

[ntoskrnl]

I have a Medion digital TV tuner that has strange and varying issues powering up from standby. I opened it up and found out that a small 470uF electrolytic capacitor on the power supply board is clearly bulged.

All the dozen or so secondary side capacitors on the power supply are G-Luxon, which is listed in the "Bad Cap Manufacturers" list. The primary capacitor is a Samxon, but I've heard that primary capacitors usually don't fail.

If I were to replace all the secondary caps, is there something I need to consider, other than voltage, capacitance and physical size, when choosing replacement caps? Which caps would you suggest?

I can take photos and give more details if necessary.

[Peter9DO]

Re: Medion digial TV tuner doesn't power on – Bulged capacitor in power supply

Nope all you want to look at is the physical size, capacitance and voltage. When I replace caps I only use Panasonic which I purchase from Mouser.com. Once you replace them it should fire right up, the problem you described with the power sounds like it's a cap issue. Then verified when you saw the popped cap. Good luck!

[ntoskrnl]

Re: Medion digial TV tuner doesn't power on – Bulged capacitor in power supply

Thanks! So I don't need to consider any ESR ratings or such?

[Pentium4]

Re: Medion digial TV tuner doesn't power on – Bulged capacitor in power supply

We'd love to see some pictures

[ntoskrnl]

Re: Medion digial TV tuner doesn't power on – Bulged capacitor in power supply

Here are a couple of pics of the power supply board in question. The bulged capacitor is C13; other caps seem fine but might be dead anyway.

[ntoskrnl]

Re: Medion digial TV tuner doesn't power on – Bulged capacitor in power supply

I'm going to order some Panasonic FC, FM and FR caps tomorrow. Does this sound reasonable?

The replacement caps are physically a bit larger, but the board seems to have room for them. The current caps don't completely fill the painted circles and the legs are bent.

[Th3_uN1Qu3]

Re: Medion digial TV tuner doesn't power on – Bulged capacitor in power supply

You should match the ESR too, I'm pretty sure Panasonic FC or FM will match, so go ahead and order them.

[tom66]

Re: Medion digial TV tuner doesn't power on – Bulged capacitor in power supply

You should match the ESR too, I'm pretty sure Panasonic FC or FM will match, so go ahead and order them.

It looks like it's just a flyback; I thought ESR wasn't crucial as long as it was lower or the same? I'm an SMPS noob, but am considering taking a course on it in uni if the option comes up.

[Th3_uN1Qu3]

Re: Medion digial TV tuner doesn't power on – Bulged capacitor in power supply

I see a 8-pin chip on the primary, that's likely a 3842 or some derivative. ESR of the capacitor does play a role in the compensation of this type of circuit. It does not matter on self-oscillating supplies, in anything with a controller it will make a difference.

[momaka]

Re: Medion digial TV tuner doesn't power on – Bulged capacitor in power supply

It does not matter on self-oscillating supplies.

In my experience, it does.
I've seen the 2-transistor 5VSB circuit of 3 ATX PSUs now not regulate properly due to bad output capacitors.

I'm counting at least 5 diodes on the output of this power supply, so there may be up to 5 outputs. In any case, replace all of the capacitors on all of the output voltage rails.

[Th3_uN1Qu3]

Re: Medion digial TV tuner doesn't power on – Bulged capacitor in power supply

In my experience, it does.
I've seen the 2-transistor 5VSB circuit of 3 ATX PSUs now not regulate properly due to bad output capacitors.

Bad capacitor = no capacitor, so it's obvious it will act up. Let me rephrase that: In self-oscillating supplies, the lower the ESR, the lower the ripple. Regardless of what caps it had in the first place. When a controller is involved, things aren't that simple and you have to match the specs of the originals as close as you can.

[momaka]

Re: Medion digial TV tuner doesn't power on – Bulged capacitor in power supply

Ah, I see what you meant now.