Soundstream RubiconA4 repair

[Petererc]

Hey there,

Picked up a Soundstream RubiconA4 to mess around with and see if it can be repaired. I have had no luck finding a service manual. Powered up the amp and the power light fluctuates from bright to dim red. The amplifier produces no sound. Opened up the amp and noticed one of the screws that clamp the board to the heatsink was loose, the screw will not tighten, seems the heatsink is stripped or was tapped improperly from the start. That can be addressed if the amp is functional and when the board is removed from the sink.
Test point TP9 reads 0VDC, TP7 +12.3VDC, TP8 +11.7VDC, TP 10 +Rail fluctuates between +8-12VDC while TP11 fluctuates between -8 - -12VDC.
Hopefully this is an fix

Thanks for your time

 

[barber02]

Did you check Q18 and Q20 for shorts. If that screw was stripped out, then the mosfets in the bottom of the board probably weren’t held tightly against the heatsink. They potential could have overheated and gone into thermal run away and shorted.

While your at it go ahead and check all of your other mosfets, Q2 through Q15 in the output section. Looks like you have biasing transistors in between your mosfets in the output section.

 

[Petererc]

Checking continuity Q18 and Q20 both ring out one leg to ground, so they are shorted? The other Q’s seem to been fine. Thank you for help

 

[Perry Babin]

You check transistors across the legs of the transistor, not to ground.

Ring out isn't used as a term in amp repair. Explain what you mean.

 

[Petererc]

When set the meter to continuity, touch one probe to ground and the other to a leg of transistor and the meter beeps, thats what i mean by, it ring out

Thanks

 

[Petererc]

With meter set to ohms , meter shows a fluctuating numerical value across any two legs of transistors Q18 and Q20

 

[Perry Babin]

Short beep or steady tone?

The same as when you hold your probes together?

Leg 3 of the output FETs are directly connected to ground. Again, you don't check transistors to ground.

 

[Petererc]

Steady tone, yes as when probes are held together

 

[Perry Babin]

The FETs appear OK.

I'd suggest that you read the following page, in its entirety.
bcae1.com - Car Amplifier Repair Tutorial - The Basics

 

[Petererc]

thanks Perry,. Is the repair tutorial still available?

I read the suggested pages, and will read them again

 

[Perry Babin]

Yes but it's not for someone wanting to repair one or two amps. It's wide ranging and takes a lot of reading. Use email if interested. The forum frowns on sales of anything except on specific pages.

 

[Petererc]

thanks Perry,
I read through the bcae1 website and did some checking.
I believe Q16 Darlington TIP107 is bad. I checked ohms across the three legs of all the transistors. All of the readings fluctuated consistently except for Q16. Across two legs the reading was .1 ohms.
I should replace both the TIP102(Q10) and TIP107, correct? or should I replace all of the "Q" transistors.
Or is it time to remove the TIP107 from the board and follow more testing procedures?
I tried to follow the IC SG3524N datasheet but that was way over my head.
Is there anything else I can test to verify the transistor is bad or something else on the board causing it. I did check to see if any resistors or diodes were shorted and didn;t find anything.

thanks

 

[Perry Babin]

I'd replace the two output transistors in that channel. Check the emitter resistors in that channel to confirm that they are still within tolerance. There may be other damage but you may have to get the new outputs in the amp to know for sure.

 

[Petererc]

The emitter resistor R26 has a different value from the other which read 0.2, 0.3 ohms. The R26 starts out at 5.xx ohms and steadily increases which would lead me to believe it is bad. I included a pic as the resistor appeared with my bad eyes to have a different color band and it does. Could that resistor have a different value than the others causing the problem, or just a color variation in the batches? What would be the correct value to google to find replacement.
Thank you

 

[Perry Babin]

The value is 0.15 ohms. Probably 2 watts (measure and buy the same size). The color is different because it's burned.

 

[Petererc]

Fantastic, thank you.

 

[Petererc]

Do you think this one will work? Not much finding the same size. I measured them, and rough tape measure measurements converting inches to mm I came up with.

4.76mm x 14.28mm and the ones linked are 5.21mm X 14.22

they are rated at 150 mOhms which I believe is 0.15 ohms? at 3W

just want to be sure to order right ones, thanks again

LVR03R0150FE70 Vishay Dale | Resistors | DigiKey

 

[Perry Babin]

That one is 15m ohms.

See if this search will work:
Through Hole Resistors | Resistors | DigiKey

 

[Petererc]

Thanks for the link, search function was kicking my butt
Hows this may be a little longer, may be measurement

ROX3SJR15 TE Connectivity Passive Product | Resistors | DigiKey

 

[Perry Babin]

That looks OK.