PeteS in CA
Badcaps Legend
Last Activity: Yesterday, 11:43 AM
Joined: 08-10-2005
Location: San Jose, CA
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Someone else will have to interpret the code, but that may be a TVS diode or rectifier. -
I can't make out the brand of the two large caps, which probably should be replaced, since one is bulged. The small ones are Illinois Capacitor, which is a fairly good brand. Replace or leave alone depends on lots of factors. Age is one. At 30YO or greater, I'd consider it. The ambient temp when in use is a factor (e.g. 85C caps in a 70C internal ambient are probably not going to last as long as if the internal ambient is 50C). The application matters. Use as a switching P/S output cap is more stressful than use as a decoupling capacitor in an analog or digital circuit. Not being powered on for...Leave a comment:
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Replacing electrolytics with high value MLCCs is probably not a great idea. They have very different impedance vs. frequency characteristics, and high value MLCCs usually (almost always?) have tempcos such as Z5U or Y5V, in which the capacitance at operating temperatures could be 20%-40% or the nominal value.Leave a comment:
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The Fluke 87 DMM I use is powered by a 9V battery, but the voltage for testing resistance is limited to 2V or so. As for testing capacitance, what a DMM can test is best learned from the DMM's specifications. I haven't used my Fluke 87 to test capacitance. AFAIK, an ordinary DMM doesn't test ESR or impedance.Leave a comment:
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So, picking out a few bits and pieces:
It looks like the TDK transformer has an 8823 date code, i.e. 23rd week of 1988.
The switch device may be a clone of the MJ12006, an 8A, 450V NPN transistor, designed for switching power supply use.
I don't see an output inductor, so I think the topology is discontinuous flyback.
Putting these latter two together I'd guess the power rating would have been 100-150 watts. Given that its some 35 years old, it is possible that the electrolytic capacitors have dried out and/or the aluminum oxide dielectric has thinned, making...Leave a comment:
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Be sure to match the temperature coefficient if you know it. If you don't, use X7R or CGO.Leave a comment:
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Maybe the frequency was too high and a TWT should have been used....Leave a comment:
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Electrolytic capacitors, typically, are +/-20%, so on the low end the cap can be as low 544uF.Leave a comment:
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Back when I was in Component Engineering at Curtis Instruments (the motor controller division in Livermore) the sloppy-kneed zener problem was noticed, and dug into. It turned out that many brands' zeners actually came from a single company (in China, IIRC). I do not recall whether a better source was found or designs were tweeked to compensate for the sloppiness (~15 years and two employers ago). Maybe this background single-sourcing has changed in the past 15 years or so, but the diffusion process for rectifiers and zeners is older technology compared to the lithography process for ICs and power...Last edited by PeteS in CA; 01-05-2024, 09:13 AM.Leave a comment:
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Diodes Inc. has been around for quite a while. They're good.Leave a comment:
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68uF, 16V tantalum or polymer. "519" is the date or lot code.Leave a comment:
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They look compatible, if the package is the same:
[url]https://alltransistors.com/transistor.php?transistor=39155[/url]
[url]https://html.alldatasheet.com/html-pdf/895307/ISC/2SD867/53/1/2SD867.html[/url]https://They look compatible, if the...867.html[/url]They look compatible, if the package is the same:
[url]https://alltransistors.com/transistor.php?transistor=39155[/url]
Leave a comment:
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NCC's LXZ series is a low impedance series designed for use as filter capacitors in switching power supplies and DC-DC conversion circuits. Depending on how the capacitors you replaced with "standard audio series" parts are used in the circuit, your replacement parts might not have a long life.
FWIW, NCC's LXZ series, Nichicon's [COLOR=#c0392b][B]P[/B][/COLOR]W series, and Panasonic's FC series are pretty much equivalents.NCC's LXZ series is a low impedance series designed for use as filter capacitors in switching power supplies and DC-DC conversion circuits. Depending onLeave a comment:
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Pictures of the MOSFET and of the P/S would help with answering your question.Leave a comment:
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The problem with a heat gun or hair dryer and with freeze spray is that it affects a large area. With freeze spray I soak the tip of a cotton swab with it and then touch the suspect component with the cotton swab tip. Doing something similar with a heat gun is a bit more difficult, and if your probe is metallic, you need to avoid shorting to something.Leave a comment:
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Depending on how much you want to repair/upgrade, replacing those 330uF input caps with 470uF or 560uF parts and the MJE13007 clones with MJE13009 clones might bump up the power capability and/or improve the output noise. The output inductor, output rectifiers, and heatsinks will still make the practical limit 235W or 250W. Half bridge topology and use of bipolar transistors will keep the efficiency in the ~70% range. Is the fan decent or a POS?Leave a comment:
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Based on the 330uF input caps and the heatsinks, the P/S might be good for 200W. It does look to be half-bridge topology, and based on the yellow inductor core (probably Micrometals 26 material), the switch frequency is probably be between 20 KHz and 50 KHz, and the switch devices may be bipolar transistors.Leave a comment:
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Typical values: ,33uF for the X cap ; 2200uF for Y caps. Check whether CY1 and CY2 are agency approved Y caps, not just parts rated 1000 VDC. If they are not agency approved parts rated for AC voltage, replace them. For the X cap, just match the lead spacing and available space. The Y cap locations are probably sized for ceramic Y caps.Leave a comment:
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C(Vcc), the 120uF cap may be bad. If the ESR is out of spec high, it cannot provide the energy needed to start up the UC2842.Leave a comment:
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