threshold sa-2 powers up no sound help! - diyAudio
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Old 11th May 2011, 07:18 PM   #1
Surfy is offline Surfy  Belgium
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Default threshold sa-2 powers up no sound help!

Hello, I wanted to replace the electrolytic capacitors in my threshold sa-2 (just the two small ones on the front end board) and after doing so I measured 9 V dc on output at startup. I replaced it with the old ones again and voltage gradually dropped while unit was off from 2 Vdc to 0.2...
However when I power up now, with the old caps back in, the front led lights but I have no sound! DC at output drops to zero when off, and around 0.8 when on... All 3 fuses are ok...
Anyone has an idea what went wrong? I really would need a service manual with a list of the parts, and inflated views of the layout on the board, if necessary I would be happy to pay for it.
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Old 12th May 2011, 11:58 AM   #2
Surfy is offline Surfy  Belgium
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Strangest thing. I replaced the old 0.1 F capacitor on the front end board with a new one again and I got music! Dc when on at speaker terminals is at 0.001 V! but when I switch it off, my multimeter rises immediately to -7.6 V...
I do not dare to try the power off/on with a speaker connected... what could be causing this? Or maybe with a speaker connected instead of a multimeter, the voltage would drop fast and current will be too low to harm the speaker? (like when you connect a 9 V battery to test speaker leads, it is 9 V dc, but not powerful enough to harm a woofer)?
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Old 12th May 2011, 12:52 PM   #3
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try with dummy load

any 4R7 -15 Ohms 3W resistor will survive , if everything is ok
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Old 12th May 2011, 09:56 PM   #4
Surfy is offline Surfy  Belgium
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Thx for the tip! I had a 5Watt, 4 Ohm resistor on hand and it had no problems, after that a small speaker was ok too : )
The amp just gives the normal on and off thump, which amps without relais do...
The multimeter measured the voltage, but it could not drop of course, due to the very high resistance of the multimeter there was practically no current flow... this made me think there was a constant dc voltage at output...NOT! just the thump... Well I've learned something
The other mono amp does not "thump" at power off... could it be the big condensators unload more evenly? Does the threshold sa-2 normally have any condensator or resistor to stop the dc thump at power off?
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