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Post by radiohead314 on Mar 4, 2016 13:30:49 GMT -5
Well it is not as bad as the title suggests but this SMPS suddenly eats the main fuses F100.
When checking with my multimeter the right side of F100 was shorted to ground.
Now it turns out that Q101 the Sanyo 2SC3998 was shorting to ground.
From the schematics I see that this power mosfet is switched fast drawing current through the transfomator coil. Now I wonder what makes such a mosfet suddenly die? Does this just happen now and than after a lot of years or should I look further for a cause?
I plan on buying 5 of them and replacing and trying. Could also measure some of the passive components nearby.
by the way all fuses on the secondary side are ok.
Another smps works fine
the subboard works fine
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Post by radiohead314 on Mar 4, 2016 13:55:50 GMT -5
From the schematics I see this one makes the HTHD. I can check if that one is afjusted right I guess.
I remember that is the past I had a few times that the barco would not start with a scanfail led burning. I think that must have been that the hthd was off. Some times than without doing anything the led went off and the barco would start.
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Post by radiohead314 on Mar 5, 2016 4:36:42 GMT -5
Is there any risk in buying cheap Chines parts from ebay? I remember something that the Chinese now and than fake chips? Or only change the print on other chips with the same package?
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Post by Casethecorvetteman on Mar 5, 2016 6:04:32 GMT -5
I wouldnt do that if i were you. Get the correct parts.
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Post by radiohead314 on Mar 5, 2016 6:32:40 GMT -5
Yes the price is attractive but I buy the German parts  |
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Post by Casethecorvetteman on Mar 5, 2016 6:39:45 GMT -5
Money is no object when it is in lieu of reliability!
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Post by radiohead314 on Mar 5, 2016 9:54:12 GMT -5
One more question about the fuse F100. Is it a slow or a fast fuse? I see this in the part description F100 : F 5x20 F 3A15 H UL. The F could mean Fast or fuse. 5x20 are the size. Next F fast? 3A15 is the amperage. But H and UL?
Probable fast.
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Post by gregstv on Mar 5, 2016 21:02:29 GMT -5
Did you measure it out of circuit? It should measure like a normal NPN transistor. Q1 could also cause the fuse to blow. If one of these has failed I would change the TDA4601 as well.
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Post by radiohead314 on Mar 5, 2016 22:50:25 GMT -5
Did you measure it out of circuit? It should measure like a normal NPN transistor. Q1 could also cause the fuse to blow. If one of these has failed I would change the TDA4601 as well. It shorts in every direction between all pins. It did indeed blow F100. So you are saying the TDA4601 should protect Q1 and there is a good chance the TDA is malfunctioning. Good point. Oh wait it is Q101 the high voltage of the horizontal. |
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Post by gregstv on Mar 6, 2016 2:26:02 GMT -5
The TDA4601 is the drive and error amp for Q101 switching. In the day when I was fixing CRT TV's the TDA4601 and the switching regulator would fail from power surge, lightning, or arcing. I have always changed them both together. If you don't you may blow another 2SC3998. The TDA4601 is around $5 and the same for a 2SC3998 |
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Post by radiohead314 on Mar 6, 2016 6:35:54 GMT -5
Ok I ordered 3 the brand on the tda says infineon so I bought ones from the same manufacturer.
Thanks!
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Post by barclay66 on Mar 7, 2016 5:50:00 GMT -5
Hi,
Those TDAs regularly die because of too much ripple on their supply (Pin 9). Replace C125/C25 with some high quality (105Deg/Low ESR) caps. Same values...
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Post by radiohead314 on Mar 7, 2016 11:38:22 GMT -5
Thanks Barclay. I get some of those.
I also baught the capacitors for the standby 9V. Strange thing is that with my peakatlas esr meter they measure ok but they beeeeep when the smps is on stand by. So I think they are close to failing?
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Post by dummyload on Mar 7, 2016 11:53:26 GMT -5
Stanby or projector on is only little different in load to the +9v sub board ,beep means not necessarily bad .
Look with scoop how +9v output looks like.
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Post by Casethecorvetteman on Mar 7, 2016 13:08:21 GMT -5
Ive got an SMPS here that doesnt work too, the set starts fine, but after a few seconds the FAN FAIL message comes up on screen, all fans are working, but the set shuts down. Havent tried anything on it yet, so not sure where to start looking.
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