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Nht subtwo blowing f1 fuse on ac input module. found shorted Q16 2SA1302 and Q15 2SC3281 transistors what was the reason for these parts failing and what else should i be checking.

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  • e_norin Mar 07, 2009

    For the NHT SUBTWO with the Q14,15,16 and17 transistors removed measured the three pads on both Q15 and Q16 and the voltages are as follows E= 0.5, C= 126, B= 126. I had replaced all the 2SA1302,2SC3281 transistors and all six IRF 640's before i got your post, powered the unit up without input signal and got a green light. but when i hooked up input it then poped the F1 fuse on the ac input module again.if the problem is in the driver circut could u walk me thru this.thank you

  • Anonymous Apr 15, 2009

    the drivers transistor 2SC4793 or 2SA1837 are likely defective too, My has same problem. found Q13, 14, 15 shorted out. Also 1 large electrolytic capacitor 2200mf/200 open, I think the capacitor opened, cause the output transistors failure.

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BE AWARE OF FAKE TOSHIBA 2SC3281 & 2SA1302 SOLD ON EBAY. THEY WILL KEEP ON SHORT OUT THE CIRCUIT. ANOTHER SOLUTION IS, REPLACE THEM WITH MOTOROLA MJL3281A & MJL1302A.ALSO CHECK THE POWER SUPPLY FILTER ELECTROLYTIC CAPACITORS 2200MF/200V, WHEN CHECK THESE LARGE CAPACITOR, MAKE SURE TO DRAINED OUT BY SHORTED 2 TERMINAL WITH 1K RESISTOR BEFORE TESTED.

Posted on May 19, 2009

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Try turning on the unit without the two transistors installed. Measure the DC voltages on the 3 pads to ground. These should read .6V,40V and 0, both +and -. If you read anything else, the driver circuit has a problem.

Dan

Posted on Mar 02, 2009

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Additional detail about my AUREX STEREO AMP MODEL SB 130. I have change the rexridiwe / power diode but to no avail. This same result. The fuse rated 3.15 blown up 2 times. I wonder will is the cul


A module or an amp is doing a short cicuit. It's time to check if all transistors are valid. Be careful, bipolar and FET transistors behave differently. It can help to compare one by one each transistor from the RIGHT and LEFT amps. Good luck.

Mar 07, 2014 | Audio Players & Recorders

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Fuse keeps blowing (LCD,Projection,Standard,Flat panel TV.)


A blown fuse is very common on Electronics Appliances like TV's, DVD's, Receiver's etc. Sometimes fuse blew because of power surge, replacing alone with exact volt/ampere cure the problem. It is necessary to understand that blowing of fuse second time around you replaced it means that you have a shorts in the circuit.

jdvillanueva_4.jpg

Troubleshooting the shorted parts on the power supply section needs an experienced in electronics because you will isolate the shorted parts one-by-one. Since we are working on the power supply section (110v/220v AC) this is fatal and can cause you an electric shocked with a simple mistakes only.

Usually shorts are quite near to the AC power line where you can locate this components :

1. Power Cord - Even a very low of chances for short but still to be checked because this is a part of AC line input. This is due to frequent bending and pulling, internal wire will shorts.

2. VDR (Voltage Dependent Resistor) this serves as a guard for voltage fluctuation or excessive voltage to avoid further damaged to other parts. If there was an over voltage(reach the peak allowable voltage designed by the manufacturer) from the AC line, this parts will vary its resistanceand drive the line to excessive current which causes the fuse from blowing.
http://en.wikipedia.org/wiki/Varistor

3. Posistor (for standard TV) - connected here the degaussing coil.Check it also for shorts.

jdvillanueva_5.jpg

4. Rectifier Diode - Some unit this is come in bridge type package.
jdvillanueva_8.jpgjdvillanueva_10.jpgjdvillanueva_11.jpg
This is very common parts that are prone for shorts. For more info click this link
http://www.fixya.com/support/r8519792-shorted_rectifier_diode_fuse_keeps

5. Main filter electrolytic capacitor.

jdvillanueva_13.jpg

6. Voltage Regulator IC/Transistor.
7. H-out Transistor (for standard TV)
8. Flyback Transformer- (for standard TV)

Isolation technique is done to locate the shorted parts. Pull-out the suspected parts one-by-one in the board and test it using the ohmmeter.

Hope that it may help you find the solution on your problem.

Have a nice day!
Thanks for using fixya


JDVillanueva

on Jan 30, 2011 | Televison & Video

3 Answers

Amp has power ,is getting signal , meter moves when I hit the strings of the bass. but no sound coming out of either cab. ran a line out and it works that way ,


Hi,

Looks like the power module went out, could be either LM3886T Power IC or Mosfet Module But certainly is in the output stage where your problem is, hope this helps to troubleshoot the issue at least...

Nov 03, 2013 | Behringer Bx4500h Ultrabass 450w Bass...

1 Answer

No power just went out.....


Hello,

  • A blown fuse is a very common type of fault due to poor design very often triggered by power surges due to outages or lightning storms. However, the most likely parts to short are easily tested, usually in-circuit, with an ohmmeter and then easily removed to confirm.Note that it *may be* useful to replace a fuse the *first* time it blows (though it would be better to do some basic checks for shorted components first as there is a small chance that having a fuse blow the second time could result in additional damage which would further complicate the troubleshooting process). However, if the new one blows, there is a real problem and the only use in feeding the TV fuses will be to keep the fuse manufacturer in business!
    Sometimes, a fuse will just die of old age or be zapped by a power surge that caused no damage to the rest of the TV. However, it must be an EXACT replacement (including slo-blow if that is what was there originally). Else, there could be safety issues (e.g., fire hazard or equipment damage from too large a current rating) or you could be chasing a non-existent problem (e.g., if the new fuse is not slo-blow and is blown by the degauss circuit inrush current but nothing is actually wrong).
    If the fuse really blows absolutely instantly with no indication that the circuits are functioning (no high pitched horizontal deflection whine (if your dog hides under the couch whenever the TV is turned on, deflection is probably working).) then this points to a short somewhere quite near the AC power input. The most common places would be:
    • Degauss Posistor - very likely.
    • Horizontal output transistor.
    • Power supply regulator if there is one.
    • Power supply chopper (switchmode) transistor if there is one.
    • Diode(s) in main bridge
    • Main filter capacitor(s).
    You should be able to eliminate these one by one.
    Unplug the degauss coil as this will show up as a low resistance.
    First, measure across the input to the main power rectifiers - it should not be that low. A reading of only a few ohms may mean a shorted rectifier or two or a shorted Posistor.
  • Test the rectifiers individually or remove and retest the resistance.
  • Some sets use a Posistor for degauss control. This is a little cubical (about 1/2" x 3/4" x 1") component with 3 legs. It includes a line operated heater disk (which often shorts out) and a PTC thermister to control current to the degauss coil. Remove the posistor and try power. If the monitor now works, obtain a replacement but in the meantime you just won't have the automatic degauss.If these test good, use an ohmmeter with the set unplugged to measure the horizontal output transistor. Even better to remove it and measure it.
    • C-E should be high in at least one direction.
    • B-E may be high or around 50 ohms but should not be near 0.
    If any readings are under 5 ohms, the transistor is bad. The parts sources listed at the end of this document will have suitable replacements.
    If the HOT tests bad, try powering the set first with your light bulb and if it just flashes once when the capacitor is charging, then put a fuse in and try it. The fuse should not blow with the transistor removed.
    Of course, not much else will work either.
    If it tests good, power the set without the transistor and see what happens. If the fuse does not blow, then with the good transistor (assuming it is not failing under load), it would mean that there is some problem with the driving circuits possibly or with the feedback from the voltages derived from the horizontal not regulating properly.
    Look inside the TV and see if you can locate any other large power transistors in metal (TO3) cans or plastic (TOP3) cases. There may be a separate transistor that does the low voltage regulation or a separate regulator IC. Some TVs have a switchmode power supply that runs off a different transistor than the HOT. There is a chance that one of these may be bad. If it is a simple transistor, the same ohmmeter check should be performed.
    If none of this proves fruitful, it may be time to try to locate a schematic.
    A blown fuse is a very common type of fault due to poor design very often triggered by power surges due to outages or lightning storms. However, the most likely parts to short are easily tested, usually in-circuit, with an ohmmeter and then easily removed to confirm.
  • hope this helpout.....


    Jul 08, 2010 | GE 25GT240 25" TV

    1 Answer

    It is not coming on


    Hello,

    A blown fuse is a very common type of fault due to poor design very often triggered by power surges due to outages or lightning storms. However, the most likely parts to short are easily tested, usually in-circuit, with an ohmmeter and then easily removed to confirm.

    Note that it *may be* useful to replace a fuse the *first* time it blows (though it would be better to do some basic checks for shorted components first as there is a small chance that having a fuse blow the second time could result in additional damage which would further complicate the troubleshooting process). However, if the new one blows, there is a real problem and the only use in feeding the TV fuses will be to keep the fuse manufacturer in business!

    Sometimes, a fuse will just die of old age or be zapped by a power surge that caused no damage to the rest of the TV. However, it must be an EXACT replacement (including slo-blow if that is what was there originally). Else, there could be safety issues (e.g., fire hazard or equipment damage from too large a current rating) or you could be chasing a non-existent problem (e.g., if the new fuse is not slo-blow and is blown by the degauss circuit inrush current but nothing is actually wrong).

    If the fuse really blows absolutely instantly with no indication that the circuits are functioning (no high pitched horizontal deflection whine (if your dog hides under the couch whenever the TV is turned on, deflection is probably working).) then this points to a short somewhere quite near the AC power input. The most common places would be:

    Degauss Posistor - very likely.
    Horizontal output transistor.
    Power supply regulator if there is one.
    Power supply chopper (switchmode) transistor if there is one.
    Diode(s) in main bridge
    Main filter capacitor(s).

    You should be able to eliminate these one by one.

    Unplug the degauss coil as this will show up as a low resistance.

    First, measure across the input to the main power rectifiers - it should not be that low. A reading of only a few ohms may mean a shorted rectifier or two or a shorted Posistor.

    Test the rectifiers individually or remove and retest the resistance.

    Some sets use a Posistor for degauss control. This is a little cubical (about 1/2" x 3/4" x 1") component with 3 legs. It includes a line operated heater disk (which often shorts out) and a PTC thermister to control current to the degauss coil. Remove the posistor and try power. If the monitor now works, obtain a replacement but in the meantime you just won't have the automatic degauss.

    If these test good, use an ohmmeter with the set unplugged to measure the horizontal output transistor. Even better to remove it and measure it.

    C-E should be high in at least one direction.
    B-E may be high or around 50 ohms but should not be near 0.

    If any readings are under 5 ohms, the transistor is bad. The parts sources listed at the end of this document will have suitable replacements.

    If the HOT tests bad, try powering the set first with your light bulb and if it just flashes once when the capacitor is charging, then put a fuse in and try it. The fuse should not blow with the transistor removed.

    Of course, not much else will work either.

    If it tests good, power the set without the transistor and see what happens. If the fuse does not blow, then with the good transistor (assuming it is not failing under load), it would mean that there is some problem with the driving circuits possibly or with the feedback from the voltages derived from the horizontal not regulating properly.

    Look inside the TV and see if you can locate any other large power transistors in metal (TO3) cans or plastic (TOP3) cases. There may be a separate transistor that does the low voltage regulation or a separate regulator IC. Some TVs have a switchmode power supply that runs off a different transistor than the HOT. There is a chance that one of these may be bad. If it is a simple transistor, the same ohmmeter check should be performed.

    If none of this proves fruitful, it may be time to try to locate a schematic.

    A blown fuse is a very common type of fault due to poor design very often triggered by power surges due to outages or lightning storms. However, the most likely parts to short are easily tested, usually in-circuit, with an ohmmeter and then easily removed to confirm.
    Hope this help....

    Jun 27, 2010 | Televison & Video

    2 Answers

    Where is the fuse in a 3701 LCD Polaroid TV/Monitor


    In the Polaroid FLH-3701, the fuse is located on the power supply board, next to the AC power connector. It is a small black cylinder. It is labelled F1. Value is 5 amp, 250 volts.
    A fuse does not blow for no reason. Most commonly a fuse will fail because of a short someplace on the board. I have this same TV. The fuse blew. The reason was transistor Q6 had shorted. There are two identical paired transistors on the output side. Q6 and Q7. They are both Infineon 11N60C3 MOSFET transistors. Check those for a short. There may be a burnt smell.
    More commonly, this TV will fail because of bad capacitors on the power supply board.

    f0aca626-8c0e-4fbe-adec-105f02f6518b.jpg

    May 08, 2010 | Polaroid FLM-3701 Television

    1 Answer

    Blawn AC fuse


    Almost every modern set will just go into power supply shutdown if the horizontal output transistor is bad or other problems place a heavy load on the secondary side of the supply. Usually that results in a ticking or whistling from the set, but it won't blow the main fuse. A blown fuse typically means shorted parts in the primary side of the power supply.

    The switching supplies used in today's sets can be a real pain. Check for a shorted input bridge rectifier or shorted switching transistors. There are also optical isolators used to provide control feedback and they can go bad, causing the supply to run away and blow up parts. A service manual or at least schematic diagram is very helpful. You might be able to find one online. I've checked my files and I don't have anything for the chassis used in this set.


    Apr 01, 2009 | Panasonic Televison & Video

    1 Answer

    NHT SA-3


    Appreciate the direct "Ask Me". With reference to your post here;

    Voltage checks are done with the power on whereas resistance/continuity check are performed with the power off and preferably the component out of circuit. The VOM would do.

    You posted that the fuses have not blown and therefore you are assuming that the output transistors are not defective. Pls confirm this by performing a check on the base to collector to emitter of the output transistors. This page would illustrate how to check a transistor using a VOM. The output transistor once removed from the circuit (pls mark which goes to where), laying flat with the pins/feet pointing towards you would be base, collector and emitter. Although the real outputs if 2SA1302/2SC3281 would be larger.
    c05c37f.jpg
    Most NHT sub amps are standard design amplifiers. To my knowledge, NHT amps (but not all) uses a unique design to supply power to the output transistors. The fuses does not tie directly to the output transistors from the +/- of the power supply. Instead the fuse goes to several power MOSFETS (IRF640) that regulate/control/monitor the current/voltage supplied to the output transistors. If any of the IRF640 is blown, the output would have no voltage even if the fuses are good.

    To be more specific and to confirm the above, would appreciate if you could post/share the schematic diagram.

    May I also inform you that there are posts made by other members of the community (our co-experts, I am aware that you have provided solutions yourself in some other posts) that would be of additional help. ginko has posted the method/manner by which you could test the transistors and other components, while bunnydawg addressed the fuse not blowing. welcomejee has posted with an amp schematics of an NHT Subtwoi.There were however and I would expect more posts that are too general/generic to be of any real use to you. I would leave it to your discretion to filter through the flood of information.

    As a site policy, once you rejected a solution or give it a "Thanks for Trying", that particular post/expert would no longer be viewable. For your benefit, may I suggest that you copy and paste the "workable solutions" to a document that you would have a record of previous or no longer viewable postings.


    Jan 04, 2009 | Audio Players & Recorders

    1 Answer

    Keep blow fuse on power supply board, viewsonic vx910


    Replacing the fuse twice is OK but going beyond that doesn't make sense.
    I don't know where the fuse is located in the circuit, AC input or some output point.
    If it is the main AC fuse, the main power supply is probably faulty and one needs some experience to locate the shorted component.
    If it is on the output side you have a shorted part and the above admonition applies; you need some training to know what you are looking for.
    If the supply is on a separate board as is common, look for a part (assembly) number and do a search to see if there are companies offering repairs on that supply; if not, you may get stuck buying a new one and there is no guarantee that the supply didn't fail for a reason. You could have a 'downstream' problem that killed the supply.   

    Oct 10, 2008 | ViewSonic VX910 19" LCD Monitor

    2 Answers

    Vcr repair


    If you have a voltmeter and some tech savvy, you could check the output voltages (voltages which run the VCR circuitry, motors, etc.). You should find a +5 volt, +12 to 14 volt, possibly a -35 volt (for the display if it has one). If these are missing, then the unit will be utterly dead. Check the fuse: If blown, check associated circuitry on the primary (line voltage) side. The fuse almost always poofs for a reason, and until the bad components are found, it will blow again, perhaps causing more component damage. The switching transistor may be shorted, plus nearby resistors/diodes/capacitors poofed/shorted/defective. In many VCRs I've worked on, a capacitor on the primary side will fail, and cause a dead condition, sometimes causing the noted transistor to short. A thorough check is highly suggested. It isn't fun to install new parts, only to have them poofed by a yet remaining problem somewhere. Common failures on the secondary side (where the voltages noted above are rectified, filtered), are the electrolytic capacitors. Common values here are 1000MFD/16 volt, 1500MFD/10Volt, 2200MFD/10volt or close. Many of the older VCRs pre-90's developed this problem.

    Sep 18, 2007 | Televison & Video

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