Hot answers tagged

46

This practice is generally known as 'Percussive Maintenance'. Any touching contacts, for instance in connectors, valves and their bases, and between the wiper of a potentiometer and the track, have a tendency to build an insulating film between the contacts. This happens most readily at higher temperatures, in high humidity, and when there is airborne ...


35

Yes, higher voltage rating is fine. It just means more safety margin against mains transients (which is good). The only difference between the -4 and the -6 is the voltage rating (see datasheet).


31

Non-reversible temperature-sensitive labels are available which will change colour irreversibly if they experience a defined temperature. These for example are 14 mm diameter which should be small enough to attach near one of your transistors, or even on the transistor itself. Another option could be to slip a small piece of heat-shrinkable tubing over ...


29

It's a shield. It absorbs EM radiation by draining it to the electrical ground of the phone. They are used in order to meet emission specifications created by the FCC or similar authorities, or to prevent EM radiation from interfering with other parts of the device.


24

Generally as the comments and answers already state it's ok to use a diode of higher voltage rating when the amp rating is sufficient. It would even be ok to have a slightly higher amp rating normally. In your case however i see no fuse in the wiring diagram and it looks like the diode could have blown due to a defective heating element. A short circuit ...


24

It is some kind of soft-open-cell foam, wrapped in conductive tape, to ensure a good grounding and shielding contact between pieces. The foam may or may not have large amounts of carbon particles in it to make the foam itself conductive.


19

It's worth noting that older TV's were constructed with point-to-point electronics soldered by hand, lacking a firm place for the components to be anchored to, such as this image showing the underside of the chassis of a 1948 Motorola VT-71 7" television. (image taken from the wikipedia page for Point-to-point construction) From the image alone it is clear ...


18

The part is a bog-standard Texas Instruments TPS62007DGS 3.3V buck regulator. They're about three bucks each in singles. Why not buy a couple, swap it out and see what happens?


17

This is what I found, these tiny little copper bridges were all over the board. Problem solved, thank you for the help.


17

IEEE Std 315 suggests that you use "TP" for testpoints. The single letter "E" can be used for many things, including "circuit terminal", "electrical contact", or "terminal {individual)". However, there's no reason to think that every manufacturer follows that standard in every detail. If you really want to ...


17

It's a pad for a flying probe test (which happens at assembly and you can see indentations from a probe or meter, if this is a production board then it's probably a flying probe test point). Flying probes are used mostly by PCB assembly services to test PCBs to make sure that the components have been installed correctly, and can be used to check things like ...


15

The actual text is: 10A MAX FUSED Maybe this should be read as "10A max" and "fused" — two different statements, not one sentence. What I am trying to say is that you should not read the two lines on the multimeter as "fused at 10A", but as "rated (=guaranteed) to measure up to 10A" + "fused to prevent brute abuse". Note that even a 10A fuse is ...


15

From the marking beside it (ZD) and its appearance, it would be a zener diode. Zener diodes can be used as (simple) voltage regulators. They can also be used to protect signal lines from over voltage. Given so many of them in a row, I'd expect this to be the usage in your case. Zener diodes are often color coded. I had a chart that showed values for ...


14

By the limited information you give and the (not too great) photo, it seems it is a mechanical encoder, not an optical one. You don't give any information about the equipment it is mounted on, but 15 years of continuous operation may be quite a lot for a mechanical encoder. Probably the contacts have worn out and there is no reliable way to fix them using ...


13

The typical universal input range switching power supply uses a circuit topology much like shown here: The larger valued high voltage capacitor (highlighted in yellow) has the job of smoothing the rectified DC voltage from the AC power line. There are two main failure modes for this capacitor. One is high voltage spikes at the input of the supply that ...


13

The main reason for everything you ask can be summed up in one simple statement: ESD Protection Diodes. Pretty much every digital input on any chip has them. It's the voltage drop across those diodes that is being tested. Diodes tend to fail short circuit when exposed to overvoltage (as in the case of using a metal lever to replace the battery in an apple ...


12

They are Zener Diodes in a Metal Electrode Leadless Face (MELF) package (*). The blue paint indicates the cathode. It is difficult to identify the characteristics of the diode if it is broken. However as there are four of them, they may well be the same, so you could probably remove and measure one of the other ones to try and find the Zener voltage rating....


11

I was wondering what is the name and purpose of the white box component ? It seems to be just a wire with some white body around. Is it a resistor or a fuse ? It's a resistor, perhaps wirewound. Look at the PCB where that component is soldered. Its component designator will probably be a number prefixed by "R". In combination with that capacitor C25, this ...


11

Check if the unwanted waveform is 50/60/100/120Hz. If this is the case, suspect a huge ripple on the power supply of a specific stage, perhaps due to a dry electrolytic capacitor. If it is in the 20-50 kHz range, suspect a dry/dead cap at the output of a SMPS.


10

It all depends on what you mean with safe. To cut it short: if what you are doing is some sort of professional work, the answer is not at all. As @Jodes said in a comment, the right thing to do is to use some specialty chemical made for the job. If, however, you are doing some hobbyist work and you are going to take some risks then your approach may work, ...


10

Those two main filter caps definitely look bad, as though the electrolyte has boiled away. I'd try replacing them next.


10

Yeah, you lifted the pad- it's missing entirely now (well, actually I see it on one end of the cap). It can be fixed by soldering the capacitor down to the remaining pad and jumpering the free end of the cap to the led of the SOIC chip package where it is supposed to go. You can use a very fine bare wire. If you don't have any, strip some stranded wire and ...


10

Match and mark Wire positions , clean old solder joints with vacuum solder sucker tool or gauze wire to absorb solder and clean out plated thru hole. Mark wire with ink for pin 1 so ensure same as original connections. Separate and cut wire to staggered length with 2cm incrments. Strip insulation to 1 cm so exposed wires do not touch adjacent joints. Twist ...


10

You could use a blob of wax on the components that you suspect are getting hot to see if it deforms due to the high temperature. Waxes come in many different melting points. For example, beeswax melts at about 62 °C. If something is getting really hot, you could use hot melt glue, which melts at about 110 °C. As user71659 pointed out in the ...


10

Congratulations, you've rediscovered the surprising electrical properties of a loose connection, which have historically played a major role in radio engineering. In the 1900s, this phenomenon was used to make the first RF detectors, known as a coherer, and numerous variants have been made. The most basic coherer has a loose metal connection, and when an RF ...


9

Bad connections, corroded vacuum tube sockets making poor contact, cold solder joints and so on could sometimes be temporarily mitigated by the judicious application of 'percussive maintenance' techniques.


9

Figure 1. An LCD connector. Units are cm. Look closely for the stripes in the middle layer. Source: Elastomeric Connector. The elastomer strip is known as a "zebra strip". It has a sandwich construction with insulating bread and filling consisting of alternating strips of insulation and conductive plastic - probably a carbon filling. Usually the strips are ...


9

Those caps look like they’re failing. Notice that the ends are bulged out - the score marks on the caps provide a relief point for them to ‘vent’. And it looks like they’re doing exactly that. That ‘rust’ is electrolyte being expelled from the cap. What to do then? Stop using this monitor - the caps may eventually short out and catch fire. Now, as far as ...


8

Figure 1. Relay datasheet extract. Checking the relay datasheet we find that the coil current should be about 33 mA. At the instant of switch-off the coil inductance will maintain that 33 mA through the flyback diodes. Figure 2. Extract from the Vishay 1N4148 datasheet. Checking the Vishay (chosen at random) datasheet we see that 33 mA is well within ...


8

Test point? That's the designation we use for such things. Edit 1 Note, we also use "E" for the uses Elliot mentioned in his comment. I'm gonna venture a guess that someone along the way decided that "electrical contact" included test points.


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