Soundstream Rubicon 702 Output transistor Problem?

[tyu527]

Hello,

I have a Soundstream Rubicon 702 Amplifier, about 5-6 yrs old. I can't find the schematics for it, support doesn't seem to help at soundstream either. The amplifier powers up, but the clip lights remain lit. From the research i've done in the past 3 months, i beleive it's the output transistors.

I've read some previous sites a bit, but can't figure too much out. Is there a way to test anything to verify it is the transisitors without tearing the whole board apart. I'm just starting with this type of stuff, trying to salvage this amp, it was really nice. I can't even find somone to fix it for me; hard to beleive (maybe after 3 months, I still haven't looked hard enough!

Anyway, if anyone has an ideas, i'd certainly appreciate it! I was using it to run an AlumaPro BP-10 speaker; I'm thinking I may have had something configured wrong at some point; or maybe it was just this amps time; either way, I'd like to fix it; somehow, thanks.

James

 

[Perry Babin]

With your meter set to ohms, check the resistance between the three pins of the output transistors (right next to the large emitter resistors). If you read anything near zero ohms on any transistor (or group of transistors) you have at least one shorted transistor. You need to check all of the individually. Sometimes one of the emitter resistors opens and takes the defective output out of the circuit.

If there are shorted output transistors, there's a pretty good chance that there are defective components on the driver board.

If you are going to try to repair this yourself, you can probably do it but it will be time-consuming.

Let us know what you find.

 

[tyu527]

Which ones are the output transistors?

I think the biggest problem I have is I can't find the correct transistor. There are so many components, I know what some are, but not all.

Here is a link to a picture of the actual circuit board, if anyone can help point me to which items to test, I'd be grateful...

Front (top) of Soundstream Rubicon 702 - www.unrealpromos.com/docs/top.JPG

Back (bottom) of Soundstream Rubicon 702 - www.unrealpromos.com/docs/bottom.JPG

 

[Perry Babin]

The output transistors are the 28 3-legged devices (14/channel)on the left side of the amp. There are 4 groups of 7.

 

[shagone]

Rubicon 604 with simmilar problem

I have a Rubicon 604 with simmilar problem here "The amplifier powers up, but the clip lights remain lit".

i have replaced several bad darlingtons in one channel that were shorted along with their respective ballast resistors but the problem remains.

i have +/- rail voltage as well as +/- 15v regulated voltage present at the test points.

anyone have a schematic for the Rubicon 604?

could it be the driver board?

 

[1moreamp]

Your outputs are TIP142T and TIP147T these are sometimes hard to come by. I just saw some on flea-bay last week, and good old reliable JandRelectronics should be able to come to your rescue on these devices.

I hope your amps don't look like the Rub805 I currently have on my bench with the wrong outputs from the REF series in them. Some people think anything will work inside these amps
so the previous "tech" put Tip 102's and 107's in to replace the TIP142T's and 147T's and it just does not work.

Oh don't be surprised if the FEB driver board for the bad channel has not been damaged by the failure along with the mpsa14 bias transistor.

Other then these few issues these amps are a snap to bring back to life...

 

[shagone]

i got some 142's and 147's from newark electronics and already replace them. how close do the .33ohm 3watt resistors need to be? i had some .22 on hand but i can get the .33. what should i look for on the feb driver board? i have the schematic for the amp and the driver board now from Soundstream.

Thanks.

 

[1moreamp]

i got some 142's and 147's from newark electronics and already replace them. how close do the .33ohm 3watt resistors need to be? i had some .22 on hand but i can get the .33. what should i look for on the feb driver board? i have the schematic for the amp and the driver board now from Soundstream.

Thanks.

The current sharing resistors on the outputs are what they are and
You might get away with the value change in a pinch but In my case I would put it back to factory spec as soon as possible.

As for the FEB board I always find the dual transistor to be damaged and a source of High DC offset at the outputs JandR has them listed on E-bay, and he also has the complete FEB board for the RUB series but you need to e-mail him about those as I have never seen them listed in the past.
The whole board is pretty affordable and I keep them on hand as a speed up on my repair time. Its just a input diff pair and drivers.

 

[Perry Babin]

If you change the value of the emitter resistors, you'll change the set point for high current/power switching as well as the over current protection (assuming this is like the other Rubicon amps - I don't have the schematic).

On the driver boards, the following resistors open:

49.9 ohm
1k3 ohm
1k33 ohm

Since other components on the board will skew the readings, compare the readings from a good channel to the blown channel.

The driver transistors often fail but don't always short or open. Many times they'll become leaky (electrically) and have to be removed from the board to check them. If you are going to pull the drivers, let us know before you attempt it. There are things that you can do to help prevent damaging the driver board (which are very easy to damage).

 

[shagone]

so it would be advisable to just replace the driver boards with new ones from JandR? i'll change the emmiter resistors asap. so what causes the clip lights in all channels to stay lit if only one channel was bad?

 

[1moreamp]

so it would be advisable to just replace the driver boards with new ones from JandR? i'll change the emmiter resistors asap. so what causes the clip lights in all channels to stay lit if only one channel was bad?

If you have the schematic then look at the emitter resistors that you need to change they are current sense lines going to a MPSA-92 transistor on the output of each channel. This is your DC offset/ over current protection circuitry. The 0.33 resistors are critical to the proper operation of this circuit.

So change those ASAP is my advice.

As for the clip LEDs please see the driver board i.e. the FEB it sends the signal to that clip LED and they are all interconnected so I am thinking if you remove the bad FEB board and the driver transistor located nearby the rest of the LEDs should be extinguished Try this to check my thinking.

Since only one channel is blown I am figuring logically that the rest are OK. Given this situation then the fault from the bad channel is causing the other symptoms. Removal of the defective devices should release the rest of the circuits from being light up. LMK what you find...

The FEBs are fairly cheap to buy save the time and dump it for a new one, Jaime ships fast out of Nor-Cal where we live. Just tech out the little transistors used by the protection circuit also, they might have been fried along the way to your bench

Perry is correct about the resistors opening up and sometimes they are even nice enough to show you by changing color.

Hope this helps...