Soundstream ref 405 repair sub ch

[dhamia]

Hi guys, Happy New Year.

I have a SS ref 405 with sub channel down.

the satellite channels work great, and there is no protection light.


OK the story so far - when the amp came to me I powered it and the red power led was very dim,also my bench power supply went into protect mode indicating there was a problem.

I didn't want to damage the amp, so I stripped it down and did a quick test on the transistors.

There was a TIP 107 and TIP 102 down in the darlington power array (sub section) I think.

I had a SS ref 414 board lying around so I used the transistors from there and replaced the defective items. Q616 and Q610

I cleaned up the board and re assemble and it powered up as it should.
Bright red power led and my bench supply didn't trip into protection.

I tested for sound and the satellite channels sound great.

The sub channel causes the terminal to spark and pushes the speaker clean out the cone

And Ideas?

I have the 414 board available if needed

Thanks in advance.

 

[1moreamp]

Your sub channel is still dumping DC voltage to the speaker so it's more then a then the few bad outputs you found and replaced. This explains why the cone is displaced and the spark when you attach speakers. Pull the FEB board for the sub channel and retest all the outputs. it is likely that some of them are leaky, and or the FEB board is defective and needs to be repaired.

 

[dhamia]

Can I use a donor feb board from my ref 414 board?

 

[1moreamp]

Can I use a donor feb board from my ref 414 board?

If they look exactly alike then you can sub that FEB board. SS used two different designs of FEB board back when these were made and they do not sub for each other to my knowledge. the big difference is the input section of the FEB board, so look dead center of the board and if they do not match then you will have to repair the existing board, or possibly buy one from Jaime. If your having troubles with parts for repair try looking on ebay for jandrelectronix Jaime may still have exact parts for these. If not then PM me perhaps I can help more.

 

[NickParr666]

Here's a link to his eBay shop:

jandrelectronix | eBay

He has both an FEB1 & 2 boards for sale.

 

[dhamia]

O.K so I removed the FEB board and found the transistor marked on the pic with a red arrow to be out, so I swapped it with a good one from my donor

I also swapped out the two resistors marked with red arrows as they were out - all good now

Q616 and Q611 were both out so I have replaced them too

Everything stays within tolerance now, Q616 and Q611 measure the same as the rest in the bank.

I measured the output voltage on the sub channel and it reads 51v DC (plenty of sparks)

Note - I noticed U103 U102 and D107 look like they have been replaced or soldered at some point - Question is could they be causing the problem?

I know I'm close to getting this one singing again -

Your advice and experience are greatly appreciated in advance, thanks

 

[1moreamp]

Ok first off you should not have any DC output above 5 to 30 milli-volts DC on the speaker terminals. So something is still amiss if you have 51 VDC on the terminals.
SS often changed out all of the outputs to repair one of these amps. I think you should remove the FEB board and see what voltage you get on the speaker terminals.
If the FEB board is the source of the high output your DC on the speaker terminals should drop back to something very low. If not then you have leaky outputs and should consider replacing them all as a set with new devices. And after that you will still need to check each transistors Voltage drop across each emitter resistor. Also it very important that all of the emitter resistors measure exactly as spec'ed so they will not cause the measurement to be off. Since you replaced a few of them you must make sure they are all of the same value and none of the others have been scorched from the failure.
Once you have the output stage correct if you reinstall the FEB and you get high output again then something else is still burnt on that FEB board, and it must be tech'ed out and repaired properly. Also do not leave the FEB board powered up too long into those new outputs. Just do a quick output voltage test and then power it all back down to protect those new outputs from whatever might be bad on the FEB board.
I have the SS test spec documents in hand and I am just going by them for all of the above directions. So no guessing here as this is how SS did it... let us know what you find...

 

[dhamia]

Thank you 1moreamp,

one of the new resistors began overheating and my PS tripped into protection.

So, I removed the FEB and the resistor and the Q611

The amp powers up as normal again and plays on the 4 working channels as before.

I checked the sub channel voltage again and it's stil 50-51v DC

I will go with your advice and change all the output transistors, I think it might be leaky outputs, at the same time I will also replace all the emitter resistors.

Finally - there is a blue resistor just below the high current high voltage switch -below the bottom right corner next to the transformer - it gets very hot.

Is this normal?

 

[1moreamp]

Yes those noise filter resistors get very hot. Unless they are not on value, or have bad solder joints, don't worry about them, they all run hot.

 

[dhamia]

tip107 and tip 102's arrived today for the sub channel

can somebody confirm the resistor value of R631
I'm going to replace the whole bank of resistors, FEB board and TIP's

Shall I use the same resistor value or is there another value I can use to upgrade?

 

[1moreamp]

R630 thru R641 are all 0.27 ohm 1 watt ceramic type resistor

 

[dhamia]

Anyone know where I can get hold of these 0.27 ohm 1 w ceramic resistors?

 

[Perry Babin]

Virtually all resistors are ceramic resistors in that they have a core made of ceramic material. You should be able to get them from any electronics distributor.