Tip & How-To about Audio Players & Recorders

Checking shorted transistors

TIP: when checking transistors, if the transistor appears shorted in circuit, you need to test it outside the circuit. This is because they are sometimes across a coil and will therefore appear shorted while in the circuit, even though they aren't shorted at all.

To remove them from the circuit I find it's easiest to simply clip 2 of the 3 leads, test, and solder the lead back together if it's ok. If it's bad, I clip the third lead, and then desolder each leg individually...much less effort and time that way!

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My AV-502A main amplifier fuse was blown,I checked the power transistors and found 2 shorted,C5198.I replaced it with new one, but the fuses still blown up, including the new transistors.


There are several reasons. If you find one shorted transistor in a push-pull stage you should always replace both. One might be faulty but not shorted, but when in operation it does the other one in. You might have also missed another shorted part such as a diode or voltage regulator. Hunt around looking at the circuit of the confirmed shorted parts and test or replace anything off that circuit.
Finally check your speakers and wiring to them. Shorted output transistors have generally two ways of going like that. Wires touching each other or bad speakers, or having it too loud!

Feb 02, 2016 | Audio Players & Recorders

1 Answer

Channel A on my PMP 1280s is blown


This website appears to have diagram for it. You will have to register to log in. http://elektrotanya.com/?q=hu/content/how-change-site-language-english
May of been some other component burnt out. Only way is by test meter and testing. Quite possible transistor burnt out.
You should be able to test it in circuit for Short circuits.
If output transistors faulty make sure you check driver transistors as well. Hope some of that helps.

Nov 19, 2013 | Audio Players & Recorders

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toshiba 37av635DB,no display.fuse check:ok,lead: ok there was lightning and thunder.could possibly cut off one of the transistor. what could really happen?


very possible. look for punched through transistors, open 0 ohm resistors (they use them as fuses), open surface mount fuses (the flat green ones), other surface mount fuses (small rectangular white box looking things) and bulging/leaking electrolytic capacitors.
Remember that if you find what appears to be a shorted transistor, to remove it from the circuit and re-test it. Sometimes a transistor will be across a coil, and therefore read shorted.
look at any 120lead postage stamp sized ICs to see if they cracked their tops.

Chances are you'll find a fuse and a transistor and maybe a couple caps that need replacing.

TIP: when checking transistors, To remove them from the circuit I find it's easiest to simply clip 2 of the 3 leads, test, and solder the lead back together if it's ok. If it's bad, I clip the third lead, and then desolder each leg individually...much less effort and time that way!

Mar 02, 2011 | Televison & Video

1 Answer

my tv is making a squeaking noise its a model 736668.


If you have that loud noise and no picture it may need the horizontal output transistor, this noise comes from the h drive circuit and usually is caused by a shorted h.o. transistor. Some times is not enough to replace the transistor, and a hv transformer may have to be replaced also. The model does not appear to be correct, but if you are a bit able with how to use a multimeter you can test the transistor which is the easier component to test. Technical expertise will be needed for the inspction of a hvt unit or something elese. hope this helped you and please leave feedback if your question was answered. thanks!

Aug 28, 2009 | RCA Televison & Video

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401s Rockford Fosgate Amp. Not turning on. No power light. Pos+ and GR- are solid. Thought it may be remote, so tried running a wire from the POS+ to REM to test it, no luck


Amp Failure:
There are many different ways that an amp can fail but the two most common failures are shorted output transistors and blown power supply transistors (< those are not blown). There are several types of protection circuits in amplifiers. The most common are over-current and thermal. The over-current protection is supposed to protect the output transistors. Sometimes it doesn't work well enough to prevent the failure of the output transistors but it will work well enough to shut the supply down before the power supply FETs are destroyed. If the amp remains in protect mode, goes into protect mode or blows the fuse as soon as the remote voltage is applied, shorted output transistors are almost certainly the cause. If the fuse protecting the amp is too large, if the protection circuit doesn't respond quickly enough or if the power supply is poorly designed, the power supply transistors may fail. If you see a lot of black soot on the power supply transistors (near the power transformer), the power supply transistors have failed. Soot on the board doesn't necessarily mean the transistors have failed. Sometimes, technicians don't clean up the mess from a previous failure. Transistor Failure/Checking Transistors:
In general, when a transistor fails, it will either short (common for output AND power supply transistors) or open (common for power supply transistors). Transistors act like valves. They control the current flowing through a circuit. A shorted transistor acts like a valve that's stuck open (passing too much current). In the case of an output transistor, the shorted transistors tries to deliver the full rail voltage to the speaker output terminal. If you've ever seen a damaged amp that pushed or pulled the speaker cone to its limits when the amp powered up (common on some Rockford amplifiers), that was almost certainly due to a shorted output transistor. When checking transistors, you most commonly look for shorted connections inside the transistor. You do this by using a multimeter to look for low resistance connections between the transistor's terminals. Note:
I used the terms short and open on the previous paragraph. A short (short circuit) is a path through which current flows that should not be there. An open (open circuit) is a break in the circuit.

These repairs are best left to a repair tech familiar with car audio amplifiers. Check with your local shop to get a reccomendation. If the light isnt even coming on, chances are your input or power supply has been taken out.

Jan 01, 2009 | Rockford Fosgate Punch 401S Car Audio...

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