Twister F6 amplifier stuck in protection mode.

I got a Twister F6 amplifier that when powered on both the green (power) and the red (protect) LEDs turn on. According to the manual when both lights are on it could be because of the following:
1) The switch on sequence is underway.
2) there is a current overload in the loudspeaker circuit.
3) there is a short circuit in the loudspeaker circuit
4) the amplifier temperature has reached the safety threshold.

I tried all the remedies the manual suggests (which of course are the simple....switch rcas, speakers, turn off then turn on).


This amp had the power supply fets blown, they are already replaced with exact replacements from digikey. The gate resistors tested good with in tolerance.

What could cause this amp to be stuck in protection mode. Any help is appreciated.


Ps: I tested all outputs and all are good.I powered it on with no signal or speakers, then tried it with signal but no speakers...same results.
 
Both LEDs are on.

While i was measuring the dc on the ic's i notice that when i had the meter lead on certain legs/pins either the red or green LED would cut off while the other stayed on. I made a note on those pins below. Com/black meter lead was on ground.

3525
1) .001
2) 5.18
3) .025
4) .44
5) 2.07
6) 3.78
7) 2.02
8) 4.915
9) 6.0
10) .001
11) 5.345 *cause it to turn red only and read 0.000 afterwards.
12) .001
13) 13.47
14) 5.302 *same as notes on #11
15) 13.23
16) 5.18


339
1)8.45 *this caused the red led to cut off at first, then later it would cause the green ked to cut off and read 0.08
2) with both leds on it read 0.271 /with only green on it read 16.8 /with only red on it read 0.266
3) 13.28
4) with both leds on it read 0.75 / with only green 0.35 /with only red 2.296
5) with both leds on it read 0.477 / with only red 0.001
6) 5.523
7) with green only 8.31 / withred only 2.2
8) 5.99 this pin would cause one if the leds to cut off when i touch it with my test lead.
9) 8.25
10) 1.675
11) 8.25
12) 0.001
13) 5.7 *same notes as #8
14) 0.035



Now the amp cuts on with both leds on then 2 second later the red led turns off and green stays on. So i tried injecting signal with no speakers to see if i get any ac voltage on the speaker terminals. Well as soon as i do inject signal the green led turns off while the red led turns/stays on and i have to remove remote to reset.


I would also like too add that there is some type of residue around the ic 339 (not flux). I'll see if i can take a good pic and post it.
 
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No, i know what flux looks like (old and new). This looks sticky, like soda residue.

Well since the amp turn on now (well sometimes) with green on and red off, i manage to insert signal and get around 9v on the speaker terminals but any more would cause the amp to go into protect (with green off and red on).

I also notice that when the amp is on with only green led on, a soon as i blow on the 339 it goes into protect (red led on, green off). Which is weird because it doesn't require much air blow/pressure to cause it to go into protect.

I'm guessing the 339 is defective or making poor contact.
 
Will do, I'll have to order that "quick solder" to remove that smd ic. Also the fets that blew up left black residue and the person who replaced the new ones didn't bother to cleaned it up and got mixed with the solder.....think that's a problem also?

It does have high end components.


Don't know if that's what the solder is called, i think is quick chip.
 
ChipQuik. Tech-tips 5, item #20.

If they are using good quality boards, you can remove the IC without it. Apply additional solder to one row of pins so that all will bridge together. Run the iron back and forth in the solder so that all of it is molten at once. Then lift gently on one end of the IC to cause that row of pins to lift slightly. Hold it there and allow the solder to freeze. Use desoldering braid to remove the solder. Do the same to the other row but since the other row is now completely desoldered, you simply have to slide the chip off of the pads when the solder is molten.

By high value, I meant high resistance. Some of the resistors are 10M ohms. That's part of the reason that your multimeter caused problems when trying to read the voltages.
 
Oh ok. Guess that explains why i can use my Scopes ground on the speaker terminals (this also caused the amp to go into protect mode and pops a 10 amp inline fuse.)

I can use my scope on certain channels but not on some?? Why is that, might those channels be defective?


It looks like a good quality board, i have a solder pump and wick, but i think the wick i got from radio shack was old stock because it doesn't suck up solder.

I'll remove it tonight and see what happens.
 
Ok i replaced the 339a and now amp turns on with both red & green leds but after 2 seconds the red goes off and green stays on. So i fed it signal and checked output for all channels. Quickly notice ch right for input/section A is badly distorted and left ch is low power. The channels for both section B and C where good and loud. This is a 6ch amplifier with separate rcas/inputs for each channel.


Am going to check the outputs and pre drivers, OP amps for that section...anything else i should check or look for while am there? Thanks in advance.
 
Okay I did find a shorted output in the right channel of section A. I went ahead and replace both outputs on both channels (total of 4) and tested it. It now produces a clean sine wave on all channels and all clip at 16v. I used exact same replacements (had to buy from different suppliers as they where discontinued?)


Thanks a million Perry for another sucessful repair.