Soundstream Class A 5.2 Won't Power Off

[madHD]

I have a Soundstream Rubicon Class A 5.2 amp. I used it regularly about 12 years ago. It sat until about 2 weeks ago. I reinstalled it driving 2 Rubicon 12" subs in parallel for a 2 ohm load which is needed to get any output from the amp. It sounded fantastic for about 5 hours of moderate use.

I heard a quick and light snap sound and lost all output. With car and deck off the amp remained ON. Clip indicator LEDs where on but there was no sign of DC output to speakers or speaker short. I checked the remote supply immediately with a test light incase that had picked up 12 V somewhere. No sign of 12V from the remote. Also checked for shorted wire from power to remote, all good there.

After about 2 minutes I started to smell hot electrical stuff so I pulled the fuse. Upon opening it up I found a resistor near the power / remote in area on the board was cooked. It is R118 and I believe it to be 2W 110ohm that had derated to about 80ohm. I can replace that but I don't think that was the entire problem, just the result of some other failure.

Has anyone ever experienced an amp remaining on and where you able to find the culprit?

Thank you for your time.
madHD

[1moreamp]

R118 is the common connection between the 12 volt ground and the audio ground. It likely toasted up while the amp was operating, and is likely not the smell of burning hot electronics you reported. resistors de-rate by burning UP in value so they meet UL safety standards. Burning down in value would cause more serious current draw issues so in order for them to past safety design criteria they must burn up and or open like a fuse, especially the ceramic ones. So your 80 ohm reading is probably false or incorrect somehow.

If the amp was still hot and smelling with no power lead turn on signal then you have most likely blown the amps power supply fets and they are a dead short against the the 12 volt supply. What was your fuse rated at? As it should have blown open if spec'ed correctly for the amp.

You will likely need to repair the amps power supply and they usually don't fail unless a channel has also blown out prior to its failure. In about 99% of all cases your power supply failed because one or more of your channels failed. So your likely looking at some serious repair work being needed to your amp to bring it back to life...

[1moreamp]

The only other possibility that comes to mind other then a blown channel outputs is the possibility of a dual diode failure in the secondary audio side of the power supply. this is a typical failure of SoundStream amps, so much so I actually stock all the replacement dual diodes.
So you might just luck out and only need a new dual diode in the power supply along with a mosfet repair. The mosfet repair will also likely need gate resistors 33 ohms, and possibly gate drivers 2n2222, and 2SA1562 transistors.

[Perry Babin]

Some of the SS amps have a problem with intermittently shorted transformers. This can cause the primary/secondary ground resistor to burn.

[madHD]

So I now have the schmatics in front of me and will do some testing on the things you mentioned this weekend. My past amp experience is with tube guitar amps so it will take me a bit to get up to speed. Thank you all for your feedback and I will let you know what I find.

Also, R118, according to the schematics, is 110 ohm and with it out of the circuit it measures 90 ohm.

[azvrt]

Hopefully those schematics will be of help.
It's a nice amp I use it with the Airbass accessory for my sub.
At the moment I am using it at 4 ohms mono, I was previously using it at 8 ohms mono. I was impressed with its power even at these higher impedances, though I must admit I mostly use speakers with a sensitivity higher than 90 dB.

[madHD]

I finally had the opotunity to poke around a bit. Power FETs are not shorted. There is good continuity from 12V+ to primary center tap then out to the FET drain. The source terminal is grounded to battery with no short.

The interesting thing is that the transformer appears to be shorted. I have a dead short from 12V+ to all secondary terminals includng audio ground. I can't see a backdoor short possibility to the secondary but I might be missing something. Do I need to pull the tranny to be able to say for certain that it is shorted? What is the likely hood that it is shorted? Where can I find a replacement or rewind?

Also, if the only tie between audio ground and battery ground throught the 110ohm (R118 ) || 0.1uF? I seem to get intermittent continuity from battery gnd and audio ground.

[madHD]

BTW - I had a 60 amp fuse in the amp (factory spec) and a 60 amp at the battery (80 amp allowable according to SS manual).

[Perry Babin]

If you twist the transformer, does the short between the B+ terminal and the non-bridging speaker terminals become intermittent?

[madHD]

Yes, when I twist the transformer a little either way it opens up the short from B+ to non-bridging speaker outputs. Just to make sure, by non-bridging you are refering to the R- and L+ that are tired to audio gnd?

I assume that unless I can physically find the short then fix and ensure insulation I will need a new transformer.

So where do I find a transformer, Specs are (for each half of winding), Primary: 4 turns of 9 x 18G
Secondary: 10 turns of 4 x 18G

I am not affraid to try to rewind it if I have to.

Is there anything else that might be bad with the amp that I can check before deciding to spend that kind of time on it?

Thanks for the help.