How To Repair Blown Transistors

If you are interested in repairing amplifiers professionally, THIS may be of interest to y'all. If you lot're simply trying to repair your own amplifier, the information and links on this page should help yous get information technology repaired. You lot can email me if yous need help.

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Transistor Testing Basics
When checking transistors (bipolar or FET) with your meter set to ohms, you should not read anything near 0 ohms when the probes are touched to the terminals of any individual transistor in any configuration. If whatever are shorted (~0 ohms betwixt any 2 legs of whatever individual transistor), they will likely be shorted from leg 2 to leg iii just y'all should check i-2, 1-3 and 2-3.

Check all of the transistors individually. If it appears that several are shorted, you'll need to remove all that appear shorted from the board and check them individually. In the case of the output transistors, if you lot find merely i shorted in a group of parallel-continued transistors, you can reinstall the ones that are non shorted to come across if the amp will ability up. If it does, you lot demand to replace all in that group of parallel transistors. This is more often than not but feasible for audio output transistors. By and large, when 1 ability supply FET shorts, all will neglect and all will accept to be replaced.

Notes:

Above, it was stated that you shouldn't read anything near 0 ohms between the legs of whatsoever private transistor. This is the case for MOST transistors. There are a few exceptions. 1 notable exception is the JFET. A JFET like the J108 will read ~8 ohms between its bleed and source when no voltage is applied to it's gate. These are used extensively as muting transistors in PPI amps. Other similar JFETs are used as muting transistors in various other amps.

If you're trying to repair an amp, please read the Basic Amplifier Repair page Earlier attempting to do any repairs.

	To open up the bipolar transistor test form for through-pigsty transistors, click Hither.
When the window opens, click the black bar at the right of the window for instructions.

	To open the bipolar transistor test form for SMD transistors, click HERE.
When the window opens, click the black bar at the right of the window for instructions.

If you're testing FETs, follow the instructions beneath. This only works with the FETs out of the circuit. This is only a simple test only it'south relatively reliable. This is for enhancement mode MOSFETs (power supply and output transistors in car amps). The diagram shows an N-aqueduct FET. For a P-channel FET, you lot would contrary the probes.

Yous should read an open circuit when y'all have one meter probe on leg i and the other probe on leg 2 or leg iii. If you run into the meter change from OL (or whatever information technology reads when the probes are not in contact with anything) for more than a fraction of a second, the FET is defective.

For FETs with leaky gates (defective but non quite a expressionless brusk), you will be more probable to detect faulty transistors with the meter set up to ohms, than y'all volition with it set to diode-check.

Connect leg i to leg iii with an alligator clip pb and place the probes across legs two and three. With the meter in diode-check mode, you should accept a reading of approximately 0.5-0.ix with the probes ane way and no reading (OL) with the probes reversed. If you don't read OL with the probes in i of the configurations (encounter graphic), the FET is defective.

This shows the reading with the meter in diode-check mode.

The following are some of the FETs that tin be checked with this procedure.

Mainly Used in Power Supplies

IRFZ34

IRFZ44

IRFZ46

IRFZ48

IRF3205

IRFP1405

IRFP064

Mainly Used as Sound Output Transistors

IRF540

IRF640

IRFB42N20

IRFB31N20

IRF3415

IRFP3415

IRFP360LC

FQA28N15

FQP19N20

The post-obit are some of the FETs that can exist checked with this procedure but y'all'll demand to opposite the leads. These are P-Channel FETs.

Mainly Used as Audio Output Transistors

IRF9540

IRF9640

IRF6215

FQA36P15

FQP12P20

Links to other helpful pages:

Testing the head unit'southward shield footing to brand sure information technology'southward non open (a common trouble for Pioneer head units) click Hither.

Troubleshooting a system with an amp that's going into protect style click HERE.

Troubleshooting an amplifier that's not working and may have defective internal components click Here for the Basic Amplifier Repair folio.