amp does not turn off

Hello:

I searched and found a thread on this but it does not apply to my situation.

Soundstream Reference 300 amplifier. I am currently bench testing it, because it has sat for a few years. Both channels sound fine. However, upon powering off the deck, the amplifier stays powered up. I remove power to the amp inputs by throwing a breaker, and when I do this, and re-set the breaker, amp stays off until told to go on by the remote turn on lead from the deck. I have already checked the remote lead, and it shuts off with the deck, as it should. There is nothing to keep the amplifier on except the internal switch in the amplifier, as far as I can tell.

Have had other amplifiers hooked up to this deck and they power on and off just fine.

I am thinking there must be a relay on the board. Is this correct? I would like to locate it and replace it. What am I looking for to do this? What does this look like? Any help is appreciated.

Mike

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Chronic, late stage optimist.

With the amp on and the radio turned off, is there ANY voltage present on the remote terminal of the amp? Now disconnect the remote wire and check the voltage on the terminal and on the wire. Which one has voltage?

Chances are there is not a relay. More than likely there is a leaking transistor. Remove the amp from the heatsink and follow the trace from the remote terminal. It will go through a few components on it's way to the Pulse Width Modulator IC. Somewhere in that path there could be a faulty transistor.

I will check that and see if there is a voltage reading at the amp turn on terminal.   I know already there is no voltage from the wire. I believe that I have already checked voltage at the terminal with the wire still attached but the deck off, and there was none, but to be sure I will try what you said to do.

So, if there is a faulty transistor, what am I measuring to see if it is bad?   If I follow the circuit to transistors, am I using a multi-meter to run tests of the transistor on the board?

I did take the back cover off to take a look at the path, and I figured a relay would look like a small box soldered onto the board (that is based on a relay I have seen on an old Marantz home receiver I have), but I found no such object, just very small items, way too small to constitute any type of electrical/mechanical relay.

Does a Pulse Width Modulator IC have a certain appearance in terms of components on the board?

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Chronic, late stage optimist.

The PWM chip will be a 16 or 18 pin chip with numbers such as TL494 or TL594. Or SG3524, SG3525

OK, so are you suggesting this chip is the possible culprit? Can I test it to see if it is working properly?

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Chronic, late stage optimist.

I am not thinking the chip is the problem. You asked about it so I gave you some information to locate it. Near the end where the power terminals are located, give me the number of all the IC's greater than 8 pins.

OK, will check tomorrow and post the information. Thank you for your help.

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Chronic, late stage optimist.

OK. Rechecked the unit.   No voltage reading at the turn on terminal at the amplifier. And after a few minutes, the "high power" light faded off. So it appears whatever lights that lamp, which is the default lamp unless it switches to high current, has something feeding it some juice for a few minutes after the amplifier actually turns off.

I also checked the current draw at the incoming positive power wire and there was none after the deck turned off.

Thanks for your help. I also emailed someone who worked for Soundstream in California, and he said he had never heard of that amplifier having a shut off issue.

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Chronic, late stage optimist.

fuster wrote:

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OK. Rechecked the unit.   No voltage reading at the turn on terminal at the amplifier. And after a few minutes, the "high power" light faded off. So it appears whatever lights that lamp, which is the default lamp unless it switches to high current, has something feeding it some juice for a few minutes after the amplifier actually turns off.

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This is normal behavior.

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