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NHT SA-3 Ben- Please explain how to do the checking you mentioned. I have (if I can find them) schematics for the SA-3. Let me know how to do the testing you mentioned. I have a multimeter to check V/A/ohns. Do I need something to check resistance (ESR?) as well? Thanks. Jeff

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  • Jscopus Jan 04, 2009

    The schematic is helpful. I have the 5 page schematic somewhere and am trying to track it down. Those are the correct transistors. You have to take the transistors out to test them? I was hoping I could just test them on the board as it will be a pain to pull everything out. Is it possible to do a board test, and if okay check other things before I start pulling things apart? As Mentioned I already replaced the two paired 10K and 6800uf electrolytics that had leaked all over. I cleaned up the board as well.

    Thank you for your well thought out input.



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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.
NHT SA-3 - 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.

Posted on Jan 04, 2009

  • Louie  Role
    Louie Role Jan 04, 2009

    Testing them while still on the board would not be conclusive. You would also be testing the other components connected to the 3 pins.

    Why not try this first. Power it up, Set the VOM to 100VDC or thereabouts, test the voltage across each of the capacitors that you have replaced with respect to ground. One would be +, the other would be -. Do the same to the 2 fuses. Again, one would be +, the other would be - with respect to the ground. Do the same to the collector/center leg of the transistors, similarly one would be +, the other would be - with respect to the ground.

    pls post back results.


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