Help Identify Blown Component

[hamholfarm]

Hello,

TLDNR: Please identify the blown component in the pics – provide specifications so a dummy can order a new one.

I apologize for the long post; I’m trying to provide as much information as possible to help identify the blown component.

Please see the pics for the blown component needed, it is labeled on the board as RTC. The second blown component was easy to identify and replace (0.1 uF K 275VAC Tenta Safety Capacitor). The PC board is from a Wine Cooler/Refrigerator, Input voltage: 115 V/60 Hz, 140 Watts, 1.9 Amps. If you can identify what component is needed, please be specific so I am able to order a new one, a link would be very helpful.

The Wine Cooler is obsolete and there are no replacement boards to be had. The distributor could not provide any additional information. Two E-mails to the website printed on the PC board have gone unanswered.

The second set of pics is from a newer model Wine Cooler/Refrigerator. The PC board is from the same manufacturer. Since the one component is the same (Tenta Safety Capacitor), I was thinking if the manufacturer was trying to save costs and additional SKU’s; maybe the blown component is the same as the one used in this board?

Could this be the same as the blown component in the first set of pics?

If I can provide any additional information, please let me know.

Thank you!

 

[ronsimpson]

C21 0.22uF X capacitor need to be replaced also.
I think RTC is a "inrush limiter". I do not know the value. It is inline with the power so most likely a inrush limiter. "RT"
Just because it is bad dose not indicate it is the only thing needing replaced.
If the bridge diodes are shorted or if the first MOSFET is shorted it will stress the inrush limiter and fuse.
If you are brave; short out the part and plug it in. (the fuse may pop)

 

[hamholfarm]

I had thought there may be other bad components, but diagnosing is way beyond my skills.
Might try your idea of shorting out the part.
Thank you for your assistance.

 

[ronsimpson]

Might try your idea of shorting out the part.

On power up: The part is cold and has high resistance. Maybe 10 to 50 ohms. The large ele. capacitors charge up slowly. The part gets hot and the resistance drops down. Maybe 1 to 0.2 ohms. This allows full current to flow.

Some power supplies do not have these.

 

[hamholfarm]

I did as you suggested. I soldered in a jumper where the bad component was. I held my breath and plugged the cooler in. Success! The cooler has been running for 30 minutes so far. Can I continue to let it run as is? I have it plugged into a surge protector, don’t know if that matters.

Thanks again!

 

[ronsimpson]

I would let it run.

 

[Nigel Goodwin]

I did as you suggested. I soldered in a jumper where the bad component was. I held my breath and plugged the cooler in. Success! The cooler has been running for 30 minutes so far. Can I continue to let it run as is? I have it plugged into a surge protector, don’t know if that matters.

Thanks again!

Once it's running it's fine, the thermistor is simply to reduce the switch-on surge when you first plug it in. Also, because it's a thermal device, it only works from stone cold - so if you unplug it, and plug it back in a few minutes later then it has no effect, as it's still hot.

They were often used in CRT TV's, basically there were two options - either a thermistor (as in this case) or a wirewound resistor, usually 4.7 ohms 7W - but as the resisotor isn't a thermal device, it works even when warm. I'm very familiar with both, as a common failure in TV's was the bridge rectifier, and this would almost always take out the fuse, and the surge limiter as well.

 

[hamholfarm]

Good to know - I was worried it would not be safe.

Thanks for the help!

 

[debe]

I checked the resistance on my circuit board & it reads 8 ohm when cold, if that's any help to you.

 

[tvtech]

Here where I am, one of the biggest problems is people shorting out the mains fuse with wire....customers....."so called technitians" and others. In many cases, the NTC or wirewound surge resistor goes open. The bridge has than also gone shorted. Due to wire around the fuse. Depending on the thickness of the wire wrapped around the fuse...copper tracks are next to go...if they short out the open (hole in it NTC) or Wire Wound surge resistor. Daily occurance here. Damage to the affected SMPS is substantial. Takes more time than it should. More parts blown than it would if they didnt use wire instead of a fuse. Im used to the abuse though . Comes with the territory.

tv

 

[hamholfarm]

@tvtech

I don't fully understand your post. I am not that savvy when it comes to electronics.

If you are implying I ran a jumper wire across the two fuse terminals, I did not.

I removed the blown (green) component in the first set of pictures and then soldered a jumper in its place. I also replaced the (yellow) 0.1 uF K 275VAC Tenta Safety Capacitor with an identical part.

 

[Nigel Goodwin]

I think you've probably got too suspicious a mind , a VERY common failure in CRT's was the bridge rectifier, which takes out the surge limiter as well, these also often fail if the SMPSU dies. I suspect the wire round the fuse probably did no damage, simply because the surge limiter is already O/C, so wrapping wire round the fuse has no effect.

I used to make up 'kits' for repairing PSU's in our most common failures, saved a lot of time fault finding - simply change all the usual bits, then go from there - usually all is well, and no extra work involved.

Interestingly, on a number of sets the reservoir capacitor (usually 22 or 47uF 400V) would go O/C - and on most sets this causes catastrophic failure of the PSU - and if you don't change it (along with all the blown bits), it all blows again when you turn it on for the first time. The interesting thing though, is that Tatung sets, despite using the same chip and circuit as many others, survived the capacitor going O/C, and even continued to work, but with a noticeable hum bar.

 

[Nigel Goodwin]

If you are implying I ran a jumper wire across the two fuse terminals, I did not.

He wasn't, he was merely mentioning his experiences with customers in South Africa.

 

[hamholfarm]

my apologies!

As I stated, beyond my comprehension of electronics - with the last few posts, I'm lost!

 

[tvtech]

I think you've probably got too suspicious a mind , a VERY common failure in CRT's was the bridge rectifier, which takes out the surge limiter as well, these also often fail if the SMPSU dies. I suspect the wire round the fuse probably did no damage, simply because the surge limiter is already O/C, so wrapping wire round the fuse has no effect.

I used to make up 'kits' for repairing PSU's in our most common failures, saved a lot of time fault finding - simply change all the usual bits, then go from there - usually all is well, and no extra work involved.

Interestingly, on a number of sets the reservoir capacitor (usually 22 or 47uF 400V) would go O/C - and on most sets this causes catastrophic failure of the PSU - and if you don't change it (along with all the blown bits), it all blows again when you turn it on for the first time. The interesting thing though, is that Tatung sets, despite using the same chip and circuit as many others, survived the capacitor going O/C, and even continued to work, but with a noticeable hum bar.

Times have changed with CRT Nigel...remember I work daily on this stuff still. Ive no strength left for further discussion. I dont make up stuff, I live it daily. See you around

tvtech

 

[throbscottle]

my apologies!

As I stated, beyond my comprehension of electronics - with the last few posts, I'm lost!

Dont' worry about it. They are talking about the days of CRT TV's when people would try to "fix" a blown fuse by shorting it with a piece of wire, so making the situation worse. Something you should never ever do! So TVTech was under the impression you'd done this, is all. All the rest is banter...

 

[tvtech]

Yet another scan coil failure. So far only 4 in 14 days. Times have changed. Its not the same anymore.

tvtech

 

[throbscottle]

At least they are keeping you in a skilled job!
I'm curious, how do you know it is the coil and not the circuit driving it? (don't tell me, you've seen the same fault many times...)

 

[tvtech]

Its getting weirder and weirder Bob. Anyway, set sorted. Found some other coils. Best I could do.
Purity and convergence not 100%. Its either customer takes it like that or they/we throw it away.

Im tired.

tvtech

 

[Nigel Goodwin]

Yet another scan coil failure. So far only 4 in 14 days. Times have changed. Its not the same anymore.

Are they all the same make of CRT?, back in the CRT days I don't think I ever changed more than a couple of scan coils, and if you're suddenly getting a massive increase in failures there's something strange.