EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: slowpoke on October 14, 2014, 10:58:10 pm
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I'm reworking power supply (primary) circuit and changing out caps, as i dont have the means to test them properly - no ESR or even capacitance meter.
Three of those caps, what appear to be line noise suppressor caps, dont carry any capacitance info...
Thru hole, casing is yellow plastic, box shaped 18x12x6mm, lead spacing 16mm, resin/epoxy filled.
Here's what is printed on two of them:
MPX/TSC MKP GMF
0.1 K 275V~ X2
40/100/21 011
(Note .1 K, its not a typo, it is K on the cap, not m/u/p or other usual capacitance symbol)
Third is slightly smaller in dimensions and reads:
MKT .001 M
GPF 250V~ Y2
40/85/21 008
MEY/TSC
Can someone point me to replacements on farnell (uk)?
I'm new to electronics, trying to find my feet here, so any advice is appreciated. Nothing is obvious to me at this stage.
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The first should be 0.1uF and the second 0.001 (1 nF). The X2 and Y2 are very important as they tell you their safety ratings, so they must be replaced with at least X2 and Y2 rated capacitors at the rated voltage.
Those are film capacitors, and film capacitors have an extremely low failure rate. And even if they did, the supply would still likely work fine. If you're just shotgunning your repair, you don't bother replacing those. The focus would be on the electrolytics which have a very finite lifespan.
That said, the shotgun approach to repair is not the best. Have you run through all the semiconductors looking for dead shorts?
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Yep, shotgunning. However not blindly :D
The commercial treadmill that i'm fixing has been sat in a non-heated garage for quite a while, corrosion on solder is evident, one of the caps made me very suspicious, it was kind of bulging on the side, but it was just surface corrosion, cap is not short or deformed/bulged on top.
I also have one small cap (47uF, 25v cant make out ac or dc)that is mounted near TOP224Y diode PWM switch, is lightly charred on one side. Highly suspect. No deformation. Probably from 224Y's heat...
Tested all resistors, all good and correct values (to stripes). Checked some diodes, no blown found yet. I'm still working through components. Loads of real small caps, cant test.
Board gets 120v~ from main PSU, but there's no life. There are several led's that should indicate +14v and +5v and 8 led array that is also not showing any signs of life.
Also tested both transformers, both good.
Dont have much experience solving/fixing, have some shotgun exp from before though :D
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For every 10 degree temperature rise, an electrolytic capacitor's lifespan is halved. So any near a good heat source like that 47uF one is a good candidate for failure. Also electrolytics can leak their electrolyte which will corrode the components around them. As for the 47uF polarity, it is almost definitely DC unless it is unusually large. There will be a stripe indicating the negative side if it's DC. Also often the markings on the board will give a hint so the assembler will put them in the right way around.
It's likely that the small caps are ceramic or film which are all very unlikely to fail. There is another type of small capacitor called "tantalum" which can fail shorted. Google for what they look like. Confusingly, the marked side of them is the positive side.
If you can post a picture.
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Film capacitors fail by overvoltage. Obviously this wouldn't have happened in storage, but perhaps it was stored for a reason?
Tim
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Its been stored because the price for this faulty board replacement is near 500 quid.
However there is nowhere near the amount of parts on this board. If anything the scariest board is in working condition, thankfully. THAT would be even more expensive to replace.
Why i'm doing this ? For one its a learning project for me and wor two i bought this commercial treadmill for peanuts and fixing it will leave me with an item that costs many times of what i paid for it... Also, i'm a sheap-ass... :D
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The K & M are EIA value tolerance codes.
http://www.niccomp.com/help/voltage-codes.asp (http://www.niccomp.com/help/voltage-codes.asp)
As others have said the X & Y class caps are quite reliable, normally a visual inspection will see failures.