Resistor exploded in my monitor

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sandord
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Re: Resistor exploded in my monitor

Post by sandord » Sun Dec 23, 2018 9:20 pm

So, all the windings of the transformer measure okay, allways between 1-4 Ohms, which sounds ok to me.

Both capacitors I meantioned, measure properly using my multimeter. I realise that doesn't mean they haven't been compromised at all but I guess I'll just take the chance.

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Re: Resistor exploded in my monitor

Post by exxos » Sun Dec 23, 2018 9:54 pm

sandord wrote:
Sun Dec 23, 2018 9:02 pm
Yup, at least I hope it didn't happen because of some other problem (could this have been caused by a short in the LOPT for example?)
Normally the monitor would (or should) go into a protection mode when the LOPT and/or driver fails.. But that will be another section, normally something like a BU508 drives the LOPT close by on its own heatsink.

It's pretty common for switching transistors on the primary side of transformers to fail. They are switching like 400VDC very fast, very spiky high voltage & frequency switching, So they are under alot of abuse and get pretty hot operating which doesn't help.

As for the smaller caps, I would suggest you change the electrolytic ones as its possible they going bad could have contributed to the failure.

Looks like you got 2x 50V 22uF in series there, I would be tempted just to put in a single 10uF (or 22uF) 100V cap instead.
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Re: Resistor exploded in my monitor

Post by sandord » Sun Dec 23, 2018 10:01 pm

exxos wrote:
Sun Dec 23, 2018 9:54 pm
Normally the monitor would (or should) go into a protection mode when the LOPT and/or driver fails.. But that will be another section, normally something like a BU508 drives the LOPT close by on its own heatsink.

It's pretty common for switching transistors on the primary side of transformers to fail. They are switching like 400VDC very fast, very spiky high voltage & frequency switching, So they are under alot of abuse and get pretty hot operating which doesn't help.
I better order two regulator replacements then (for both monitors), they aren't that expensive anyway.
exxos wrote:
Sun Dec 23, 2018 9:54 pm
As for the smaller caps, I would suggest you change the electrolytic ones as its possible they going bad could have contributed to the failure.

Looks like you got 2x 50V 22uF in series there, I would be tempted just to put in a single 10uF (or 22uF) 100V cap instead.
The caps were brand new, I replaced all caps in the monitor a few months ago.
exxos wrote:
Sun Dec 23, 2018 11:55 am
EDIT2:

Looking at the small heatsink, if you could bolt something on making it "larger" then it will increase the life of the IC if it can run "cooler".
By the way, is the heatsink really that small?

IMG_20181223_224525.jpg
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Re: Resistor exploded in my monitor

Post by sandord » Sun Dec 23, 2018 10:10 pm

I was thinking, maybe I could solder a fuse in the path between the rectifier and the blown resistors. That would prevent a handful of blown parts in a future regulator-breakdown event. But how would I calculate the right fuse value? I guess I really should start that electronics base course now.

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Re: Resistor exploded in my monitor

Post by exxos » Sun Dec 23, 2018 10:10 pm

sandord wrote:
Sun Dec 23, 2018 10:01 pm
The caps were brand new, I replaced all caps in the monitor a few months ago.
If they are new, then would assume they still be good.

sandord wrote:
Sun Dec 23, 2018 10:01 pm
By the way, is the heatsink really that small?

It depends. I mean that could easily hit 80c over a long run time for example. IC's will generally run happy for years like that. I was really just suggesting something to increase its lifespan as you recapped it already, so obviously you are looking to keep the monitor running good for years to come. The hotter things run, the shorter their lifespan.
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Re: Resistor exploded in my monitor

Post by exxos » Sun Dec 23, 2018 10:15 pm

sandord wrote:
Sun Dec 23, 2018 10:10 pm
I was thinking, maybe I could solder a fuse in the path between the rectifier and the blown resistors. That would prevent a handful of blown parts in a future regulator-breakdown event. But how would I calculate the right fuse value? I guess I really should start that electronics base course now.
You can get fusible resistors . They don't blow on current exactly, they blown on temperature increase. So if you could find a 1ohm fusible 2watt resistor or something, that should work. Its basically what the SR98 PSU's do but with 10R.
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Re: Resistor exploded in my monitor

Post by sandord » Sun Dec 23, 2018 10:35 pm

exxos wrote:
Sun Dec 23, 2018 10:15 pm
sandord wrote:
Sun Dec 23, 2018 10:10 pm
I was thinking, maybe I could solder a fuse in the path between the rectifier and the blown resistors. That would prevent a handful of blown parts in a future regulator-breakdown event. But how would I calculate the right fuse value? I guess I really should start that electronics base course now.
You can get fusible resistors . They don't blow on current exactly, they blown on temperature increase. So if you could find a 1ohm fusible 2watt resistor or something, that should work. Its basically what the SR98 PSU's do but with 10R.
Interesting. I'll investage that as I've found regular 2W+ resistors to be quite expensive at Mouser. Better spend that money on something fancy then :lol:

By the way, I just powered up the monitor and...... it works just fine again. Phew! :yay2:

Thanks so much for all the help, I REALLY appreciate that, learning so much and enjoying it!

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Re: Resistor exploded in my monitor

Post by exxos » Sun Dec 23, 2018 10:39 pm

sandord wrote:
Sun Dec 23, 2018 10:35 pm
Interesting. I'll investage that as I've found regular 2W+ resistors to be quite expensive at Mouser. Better spend that money on something fancy then
:lol:
Had a quick look, only saw this one..

https://www.mouser.co.uk/ProductDetail/ ... SJFw%3d%3d

EDIT:
Oddly only looks like the 1R can take 300V.. So you might have to link 2 in series to be sure...

sandord wrote:
Sun Dec 23, 2018 10:35 pm
By the way, I just powered up the monitor and...... it works just fine again. Phew! :yay2:

Thanks so much for all the help, I REALLY appreciate that, learning so much and enjoying it!
:dualthumbup:
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Re: Resistor exploded in my monitor

Post by sandord » Mon Dec 24, 2018 11:37 am

I turned it on today and something seems to be quite wrong... (please turn up the sound!)



I think I'll check for arching tonight, when it's dark. But my senses say this doesn't sound like arching.

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Re: Resistor exploded in my monitor

Post by exxos » Mon Dec 24, 2018 11:45 am

sandord wrote:
Mon Dec 24, 2018 11:37 am
I turned it on today and something seems to be quite wrong...
I think I'll check for arching tonight, when it's dark. But my senses say this doesn't sound like arching.
Kinda looks likes what happens when got "noisy presets" which control H&V sizes etc.
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