| There is two types of transformers in the market- | | | | secondary load)and will blow the power section which |
| linear transformerand switch mode power | | | | consist of power fet, pwm icand etc. Swith mode |
| transformer. The transformers design isdifferent. | | | | power supply are designed to run with load |
| Sometimes it is just referred as ac transformer. | | | | whilelineartransformer can be test without load. |
| Linear transformermostly used in radio, project kits, | | | | The best way to test a switch mode power |
| VCD and etc while switch modetransformer can be | | | | transformer is first removeitfrom the board. Check |
| found in Monitor, Tv, Fax and so on. | | | | only the primary winding as secondary windingfailures |
| A transformer consists of two or more coils wound | | | | are exceedingly rare. How do we know which one is |
| on the same core. | | | | theprimary winding? Trace from the big filter cap the |
| For power transformers, the core material is usually | | | | positive pin tosee where the circuit goes. It will go to |
| iron. For aradio-frequency transformer, the core | | | | one of the pin of thetransformer. Then look for the |
| material is usually ferrite orair. The basic property of | | | | power fet middle pin which is the |
| a transformer is to change AC voltage. A | | | | Drain and it will lead to anotherpin of the transformer. |
| transformer cannot change direct current voltage. A | | | | This two pins is the primary winding of |
| step downtransformer has a lower AC output | | | | thetransformer. Checking the resistance of the |
| voltage at its secondary windingthan the AC input | | | | primary winding only canreveal whether it is open but |
| voltage to its primary winding. Conversely, a stepup | | | | it cannot check if it has developed ashorted winding. |
| transformer has a higher secondary than primary | | | | Only by using a ringer test you will know if itshorted |
| voltage. | | | | or not. A shorted turn in the primary winding can |
| The transformer laminations or coating of shellac, | | | | cause thepower section to blow. |
| enamel or varnishis to insulate adjacent turns from | | | | The cheapest ringer tester that i came across is Dick |
| shorts between winding. | | | | Smith LOPT METER or flyback tester. Just connect |
| I will not go too details about how transformer work | | | | the probes to the primary winding andthe result are |
| and transformer calculation as you can read more | | | | instantly seen from the Led bar graph. 4-8 |
| details from most electrical andelectronic | | | | barrepresenta good winding, 1-2 bar represent partial |
| transformers books. | | | | short and if the led goesoff means there is a heavy |
| How to test transformers: | | | | short in the winding. Besides checkingthe transformer |
| Transformer failures are relatively rare in most | | | | it can be use to check B+ COIL, horizontal yoke coil |
| electronicequipment, compared with other | | | | and flyback primary winding and ballast (choke). |
| components. If too much current goesthrough a coil | | | | The expensive ringer tester is from sencore |
| or winding, the winding heats up and can either | | | | equipment. Sencore LC102and LC103C besides |
| openup completely, or the insulation between turns | | | | checking capacitor it also have the capability tocheck |
| of wire can breakdown, causing the coil to be partly | | | | all kind of winding. Whether it is a low voltage |
| or completely shorted. | | | | transformer,high voltage transformer, current |
| Just like a coil, you can check continuity of any | | | | transformer, pulse transformer,electric transformer, |
| primary orsecondary transformer winding. The actual | | | | custom transformer this equipment will be able to |
| value of DC resistance youread is rather meaningless, | | | | check and test it. |
| but at least you will know whether awinding is open. | | | | If you do not wish to invest on this tester you may |
| Checking linear transformer is quite straightforward. | | | | use a light bulbto check it. Remove one of the |
| Apply the ac voltage to the primary winding and | | | | primary winding pin and connect a 60watt light bulb. |
| expectoutput voltage at the secondary side. No or | | | | One end to the circuit while the other to |
| low output voltage meansthe transformerwinding has | | | | thetransformer pin. If the bulb light and didn't goes |
| open or shorted winding. Look for any evidence | | | | off suspect ashorted winding and if the light goes |
| ofoverheating, such as darkened or blackened areas | | | | off, the winding is ok. |
| or a burnt smell. | | | | Transformer repair is not easy and it require a good |
| About how to test a power transformer-it is a little | | | | skill to do it. Most of the transformer repairer |
| bit complicated. | | | | preferred to rewind bigger windingsuch as fan, car |
| You cannot apply ac voltage to the equipment and | | | | alternator and starter. Swith mode power |
| expect the desireoutput at the secondary side | | | | transformeris a little bit difficult to rewind because of |
| without connect to load otherwise overvoltage will | | | | the small size and lowprice. |
| happen (because you have removed all the | | | | |