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Ken Hill 11th July 2007 06:02 PM

Soundstream 404s
I have a Soundstream 404s amplifier with a problem. It powers up with the high current LED illuminated and I get no sound out of any of the 4 ouputs.

I have repaired amps in the past with great sucess, but I have never worked on a SS before. From my research I found the "s" models have an auto-select circuit for high current or high power opperation that can be troublesome. The amp is supposed to power up in high power mode so I assume the problem is in this auto-switching circuit.

My trouble shooting has revieled all the outputs and power supply components to be good. I did find one bad rectifier diode pair (FEP16DT) so I replaced all four devices.

After searching this forum I think schematics from SS are out of the question. Can anyone offer any advice on this problem?


Perry Babin 11th July 2007 06:34 PM

The schematic for that amp is available.

Does the power supply oscillate and then shut down?

Ken Hill 12th July 2007 03:56 AM

Where can I get a schematic? Soundstream has not replied to my e-mailed request.

The power supply does not oscillate. It just sits there idling pulling 1.95A while I looked around with a scope to find were the incoming sigal gets lost.

Perry Babin 12th July 2007 04:11 AM

If they don't respond, email me directly so I can attach it to the return email.

If the PS isn't oscillating, the problem is before the transformer. The FETs are the most likely suspect. The PS driver IC could also be defective.

Is anything getting hot?

If the power supply isn't oscillating, the signal won't make it past the first op-amp. The power supply must be up and running to have power for the op-amps.

The Rug Doctor 12th July 2007 07:46 AM

The remote circuit is open, It happened on my Picasso - If the board is like the the P', you need to replace pairs of triodes. I'll find the numbers - MPS8599, MPS8899, MPSA18 and J175 and also you should change the capacitor 22uf 25v.

Speak to Jamie at he will be able to help you out.

I got the parts from him, and then had then fitted here in the UK.

Ken Hill 18th July 2007 04:58 PM

Just an update for anyone looking at this thread. I did get a schematic from Soundstream, about 4 days after my request. With it I found the LM317 was toast. This regulator delivers +16VDC for the preamp section. The preamp was only getting -16VDC; keeping the incoming signal from leaving the preamp section.

After replacement of both the LM317 and LM337 (for good measure) the amp powered up and played beautifuly from 3 of the 4 channels. I found the switch to send the incoming signal from channels 1&2 to channels 3&4 is flakey cutting out the signal to channel 4. I ran out of time last night to pull this switch out so I will get to it tonight. I hope a new switch will be easy to find.

Perry Babin 18th July 2007 05:25 PM

J&R Electronics (ebay) may have it.

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