Soundstream Reference 705s problems

[azvrt]

Hi,

I purchased a malfunctioning 705s for a friend of mine.
The seller told me only two of the five channels were functional.
We removed the board, refreshed some solderings and sprayed some contact cleaner on the switches and worked them back and forth many times.

We did an ohms test with the DMM on the rectifier diodes which are problematic on Reference amps but they did not appear to be shorted on this amp.

The solderings were pretty good, but I must say I often find them to be better on these s /sx amps than on the original Reference amps (mainly driver board solderings), though the s / sx have other issues.

We put the amp back together to see what happens and when I hooked it up (without any speakers) it idled nicely at about 1.5 ampere.
Then I fired it up with speakers connected and I noticed the analogue amperage indicator of out power supply went over 3 ampere for a fraction of a second, during which their was a loud POP out of the speakers before it idled nicely.

All 5 channels produce sound, though very low, much lower than I have ever heard even out of the less powerful models such as 200s and 405s.
The mono-output was even weaker than the rest of the channels and it was noisy.

When I tried to turn up the gain of the mono output I heard some crackling, then one of the speakers connected to one of the 4 primary channels inflated or deflated (probably DC voltage on speaker outputs ?), not sure whether it inflated or deflated as I hastily turned back down the gain before the speaker overheated.

When I turn-off the amplifier there is also a POP on the speakers and one can see the speakers stay in a inflated or deflated position for a short while.

Anyone have any ideas ?

[mike49504]

Sounds like you have bad outputs,,

With your meter set to diode check Do you get anything near 0 on any of the outputs?? Tip102 and Tip 107

Leg1-2
Leg1-3
Leg2-3

[azvrt]

This is all quite me new to me, so I will have to ask you some stupid questions:

Would you like me to do this check when the amplifier is powered on or off ?

I have read many times people talking about Tip102 and Tip107 but don't know what they are ? Are these the simply the transistors in the output section ?

Here is a pic of a Reference Picasso indicating the parts I guess you are referring to:

[IMG][/IMG]

Thanks

ps if the image doesn't work:

http://imageshack.us/photo/my-images/171/picasso5b.jpg/

[marko]

with the amp powered off, yes they are the devices that look like fets but they aren't.. check the big emitter resistors next to them too..

[azvrt]

So I need to check the three-legged thingies in the output section while the amp is powered off ? Will do ! How should they measure, and how should they not measure ?

How do I need to check the big emitter resistors ? How much should they read ?

[marko]

check your schems for the resistor values, just measure straight across them, the outputs should not read anything near a short across any legs, well into the K's and M ohms

[azvrt]

All right, will check tuesday evening and report.

Aha, I found a picture of a 705s board. Could you have a look please ?
ImageShack® - Online Photo and Video Hosting

I marked some parts in red and in yellow, did I indicate the right parts ?

Also, we keep wondering what the parts indicated in green are ?
They can be found on models from the s / sx era, though not on the Ref Picasso (same era). What do they do ?

[marko]

Yellow are the emitter resistors, the red are the outputs and the greens are relays, not entirely sure what their purpose is though, maybe they mute off as soon as remote is turned off to stop on/off pop, this is just a guess though..

[Perry Babin]

The schematic diagram shows the locations for the TIP102s and 107s.

The devices indicated by the green lines are circuit breakers that open when the current passing through them exceeds their rating.

Do you get DC on all channels when you remove remote voltage?

With the black probe on the primary ground, do you see voltage of the same polarity (positive or negative) on all bridging speaker terminals that have DC when you remove remote voltage?

[azvrt]

I went over to the house where we try and work on the amps yesterday evening and checked the output devices and big resistors. I suppose the resistors are of such low value that my DMM showed 0.00 in the smallest range ?

I did not have readings close to zero ohms on any of the output devices.
But my knowledge and skills are too little, I'll have to wait until tuesday-evening to have a look the my more skilled and experienced person I am doing this with.

Perry, tuesday-evening we will do the tests you are mentioning.
By the way, the DC-voltage on the speakers was just a guess (from how I saw them react), have not done any measurements on the channels yet. Will do !

With help, I am confident we can get this amp fully functional. It is a step forward from the easy-to-solve issues we had on the amps we repaired up till now, but we cannot ignore the amps with more difficult to find problems any longer, time to get better at this. Thanks, and will let you know what we find tuesday !