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TV keeps burning the fuse

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vladstamate

Experienced Member
Joined
Dec 2, 2012
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Location
Orlando, FL, USA
So I have this old Sony TV that I use to connect some of my old computers to (TI 99/4A, Atari 800, NES, etc). You can see it in the left side of the picture here https://sites.google.com/site/digiloguemuseum/home. The problem is once every 3 power-on's the 10A fuse inside blows up (melts) so I have to replace it. Any idea why is that and is there anything I can do. I know this is not much information to go by, but I am just looking for likely causes. Other equipment connected to the same power strip seems to be ok.

Regards,
Vlad.
 
You are probably right. But if it was a short, would it not blow up the fuse every time I turn it on? Right now it does not happen anytime.

How do I go about tracing the short? It has few circuit boards as it accepts a variety of inputs. I guess I can look on the power circuit board. What would I be looking for?

Regards,
Vlad.
 
Early Sony sets were notorious for power supply problems. I'd start there and see if you can find a Photofacts for the set. Alternatively, there are several sites offering circuit diagrams for long-obsolete sets.
 
The reason I put in a 10A fuse is because that is what it was in after I bought it from eBay. And it blew up the very first time I turned it on. But, after replacing it, I could use it for a while, turning it on and off without problems. But now I am gone through 4 fuses, it is time I figure out what is going on.

Would not a 2-3amp fuse melt sooner?
 
I am looking at the power board (which btw has 6.3A written on it) has some black spots. Should I be worried about those?

I'll go ahead and trace and see if I can find anything shorted to ground.

Regards,
Vlad.

photo 2 (2).jpgphoto 1 (2).jpg
 
If we're looking at the same thing, those are just soldering flux left over from assembly. What I see is that this thing wants a 6.3A fuse--how big is the screen? What's the model/chassis number?
 
I would do a thorough inspection for cracked solder joints... it's a fairly common issue on those old Sonys, and a common symptom includes fuses blowing at random. Prime suspects would be the flyback transformer, horizontal output transistor, and RGB driver transistors, but it'd be wise to check out everything in the power supply and HV sections.

I'm going to assume since you've already opened it up and poked around, that you know how to not die when working on CRTs, but the standard disclaimer still applies as a reminder if nothing else: be careful, and make absolutely certain that everything is discharged before working on this stuff.
 
I was lucky enough to find the Sams manual for it which includes all the schematics. I do not know how to read them very well though as I am software engineer not a HW one :(. However I am trying to learn.

http://antiqueradio.org/art/temp/2393_2n.pdf

And yeah, I do not touch it after it has been on, I let it few hours to discharge and even then I do touch anything that has warning signs over it and I use insulated tools.

Regards,
Vlad.
 
vladstamate said:
And yeah, I do not touch it after it has been on, I let it few hours to discharge and even then I do touch anything that has warning signs over it and I use insulated tools.
Click to expand...
A few hours isn't necessarily enough. Sometimes a few days isn't enough. You need to run a ground wire to the annode in order to be safe and certain.
 
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