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.

what sub model accord, v6 LX ,
manual or full climate control option??? guess full.
fuses not checked PCM scanned for DTC errors EVAC, hopeless/?
so car starts and runs sand drives ok, <<< not told that.
yes the AC brain on most modern cars is BCM brain controls
and the brain does control the AC compressor. if that is dead so be AC, THE COMPRESSOR CLUTCH, is run by PCM RELAY.
NOT TOLD OUTSIDE TEMPERATURE NOR COUNTRY../
HERE IS A LIST.
1: CHECK ALL FUSES FIRST, CAB AND ENGINE BAY ALL FUSE BOXES SKIP NONE.
2: CHECK IP CLUSTER FOR ERRORS ,ALARMS ERRORS OR LAMPS GLOWING OR IMMO LAMP SHOWS IMMO IS UNHAPPY, MODE.
3: ENGINE STARTS AND RUNS AND CAR DRIVES.?????????
4: HEAD LAMPS WORK KEY ON AND OFF. ,
5: OTHER ELECTRIC FAILURES OR JUST THE BLOWER ONLY?
6: SCAN THE pcM FOR ERRORS, AC IS CUT DEAD EVEN FOR ENGINE OVERHEATING OR OVERLOADED !!! OR IN LIMP MODE/
yah can't fix modern cars lacking a scan tool, no way./

bLOWER FACTS
PER THE SM BOOK REAL

THERE IS A BLOWER RELAY AND SOME FUSES. 12VDC SIDE.
FUSE 30 DASH
AND 21 HOOD, BOTH MUST BE GOOD. and fuse 12 V6
THE bLOWER gets GROUND FROM THIS
Audio-HVAC--Display Panel
l AND ITS BLOW POWER TRANSISTOR MODULE
SO WE KNOW THE TRANSISTOR IS off. IS CAUSE 1.
ONLY WHY REMAINS!!!!
YES THE CONTROLLER DOES NOT WANT TO RUN ANY DEAD BLOWER AND RISK ICE DAMAGE TO THE EVAP CORE.

THE Audio-HVAC Display Panel, READS MOTOR SPEED ACTUAL. speed (a kind blower tachometer wire)
IF SAY A INSECTS NEST JAMMED UP THE BLOWER FAN
THE AUDIO -HVAC, MODULE SEE THAT AND CUTS AC DEAD BY DESIGN AND HARD GOOD REASons/
the THE Audio-HVAC , has the ICE up sensor and monitors R134a
high/low switch and if wrong, tells the PCM to shut down its
Clutch solenoid to compressor ending all AC .
I am no sure what blower does.
but I can say this tell of blower works in heat mode or blower + no AC no HEAT mode. yes then the blower is not bad, nor the controller
what is wring is inputs to the controller are dead wrong
and not scanning the PCM after fuses is why you don't know.

l;earn now this works
Audio-HVAC
Display
Module
https://eautorepair.net/Marketing/Default.asp



not checking fuses first then scanning the PCm is why answers simple are not found.

like these and scads more.

Trouble Code: HVAC 12 (3.0L V6 VIN - Std)
A Problem in the Blower Motor Circuit

Trouble Code: HVAC 13 (3.0L V6 VIN - Std)
HVAC Control Unit Internal Error


Trouble Code: HVAC 14 (3.0L V6 VIN - Std)
An Open in the Evaporator Temperature Sensor Circuit (ICE Up preventions)

Trouble Code: HVAC 15 (3.0L V6 VIN - Std)
A Short in the Evaporator Temperature Sensor Circuit(ICE UP)

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.

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...

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....

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.

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.

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.

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.

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.   

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.