i just replaced 4 output transistors and source resisitors on this amp that blew out. the channels work now but on one of the channels im getting 1 volt more gate voltage than the other rails, what could be causing this? and the amp after testing at a low power for ten minutes went into fault mode. i checked the other output transistors for shorting and found none. any help?
ok i did some checking and here are my readings from my fluke. for the speaker output test i probed pos to neg output terminals, for the gate test i grounded straight to the input ground terminal.
channel 1 -.014 v
channel 2 +.041 v
chaneel 3 +.002 v
channel 4 +.038 v
no input connected
gate voltages
channel 1 +.990 v
-.938 v
channel 2 +1.056 v
-.860 v
channel 3 +.944 v
-.970 v
channel 4 +.981 v
-.947 v
also i decided to check for speaker output at low power.
channel 2 is much quieter than the rest of the channels.
channel 1 -.014 v
channel 2 +.041 v
chaneel 3 +.002 v
channel 4 +.038 v
no input connected
gate voltages
channel 1 +.990 v
-.938 v
channel 2 +1.056 v
-.860 v
channel 3 +.944 v
-.970 v
channel 4 +.981 v
-.947 v
also i decided to check for speaker output at low power.
channel 2 is much quieter than the rest of the channels.
Bgun said:
Well channels 2 & 4 have unusually high DC offset. To check the source of this I pull the FEB boards for those channels. If the the dc offset disappears then you will either have to repair or replace the FEB boards at your discretion. I have a source so they are available and fairly economical too.
As far as channel two having reduced output have you checked all the switches for the different modes for the channel? They get dirty, and cause bad contact issues. A spray of silicone lube usually cleans them but replacement is always the final cure. They also are available from my source.
On this type of amplifier I generally replace all the output transistors with a closely matched new set, and while doing that I verify all the emitter resistors are intact and measure proper values. I have seen these 3 watter blow like fuses with no visual indication of failure.
Does this amp have little grey circuit breakers on each outputs ? I remember all these Soundstreams had those and they do go bad. Being a thermal device they can get scorched contacts and make very poor contact. These I just replace, but a quick check is to jumper the thing with a clip and see if the output changes.
Well I have sent you on a mission now, with enough to check out and verify. Please repost anything you might find with all of the above checks
I'll be around to pick this back up when you have verified all of the above items.
Oh if you have any doubts about a FEB board just swap them around on re-install, if the problem follows the board in question, well its the FEB board thats causing your headaches, and repair/replacement is your answer.
As always I hope this is found helpful
ok i pulled out the little vertical board on channel 2. with the amp powered on and no inputs connected, i am now measuring
- .369 v. and this is probed at the pos and neg output terminals.
I also checked for the little fuses your talking about and there is nothing in circuit of such between the drains and output terminal.
also i included the power supply schematic on this amp i got from soundstream.
its a pretty bad copy but somewhat readable.
and thanks for your help so far, it is appreciated.
- .369 v. and this is probed at the pos and neg output terminals.
I also checked for the little fuses your talking about and there is nothing in circuit of such between the drains and output terminal.
also i included the power supply schematic on this amp i got from soundstream.
its a pretty bad copy but somewhat readable.
and thanks for your help so far, it is appreciated.
Bgun said:
OK lets talk about this for a minute. The SS amps I remember are all Darlinton output not fets. So your dealing with collectors and emitters, not Source and drain.
Please check the numbers on the outputs they should be TIP102 and TIP107, and on there other amps some will be TIP142T and TIP147T.
But were still dealing with darlington power transistors, not fets.
Now back to the large resistors attached to the outputs, You said they all read the same and are in the low ohm range of your meter, correct?
And you have pulled the FEB board off the channel in question. So at this point I would recheck all the output transistors for that channel, by ohming them out. Any of them reading 100 ohms or less is source of trouble. (they should all read alike, and you might have to raise the center lead of each to get a independent reading of them all.)
Another thing you can do is to swap one of the other FEB boards into this channel and retest just this channel,. First with a voltmeter, and then with sound ( please keep the amp attached to the sink for any testing )
I believe the problem is the FEB board so if you swap one in from another channel and test the amp you might cut your tech time down a whole lot.
let me know what you think or find.
Uplaod a pic if you can of the bad channel, it will help alot and I can guide you better, THX
your right on the output transistors, they are tip102 and 107. the large resisters on the output are .27 ohms 2 watt, and i replace 4 of them. i replaced 2 tip107s and 2 tip102s, two of which were on channel 1, and the other 2 on channel 2. if you want i can pull the board off of channel 3 which i think you said is ok as far as the dc offset, resolder back on channel 2 and retest.
but i was wondering if you have a better way to get the card out, since i spent 25 minutes getting the first one out. i desoldered with wick, desolderd again, scraped some, wiggled it, you get the idea. any quick tricks to this? and i will order 10 more tip102 and 107s to replace all output transistors on channel 1 and 2, as soon as i know this amp will work properly.
but i was wondering if you have a better way to get the card out, since i spent 25 minutes getting the first one out. i desoldered with wick, desolderd again, scraped some, wiggled it, you get the idea. any quick tricks to this? and i will order 10 more tip102 and 107s to replace all output transistors on channel 1 and 2, as soon as i know this amp will work properly.
Bgun said:
Your on the right track, swap the driver board out and if that channel plays then all you need is a FEB, just PM me and I will give you tha info on these boards and any other SS part you might need
I don't sell this stuff, but I can hook you up with the folks that do. They ship same day, and are the best to deal with always.also if the board and the outputs are not the issue then you must go back further to the preamp and the mode switchs which go intermittent with age
as for the wicking and such try using a bit of liquid solder flux on the wick. it always helps me on these, once the solder has been removed as completely as possible a gentle wiggle back and forth should cause any residual solder to release and the board should wiggle out of the slot. Sometimes these slots are tight, just go about it carefully and you should have no problem.
alright, i desoldered the board from channel one and soldered it back into channel 2, with the amp powered on in the same condition as before i now have a dc offset at the plus and neg speaker terminals of .015 v. and this time i used flux and it did work alot better. i had it out in about 5 minutes instead of 25, thanks for the tip.
OK your problem seems to exist prior to the channel all together and we must back track into the frontend of the amp.
Have you checked the switches ? The way to do this fairly straitforward. You just operate them while listening to the bad channel
any problems will become evident audiable. Also the gain controls should be checked.
Check you mode switchs and we will take it from there. I'm sure your getting frustrated by now, but patience is the key to sucess on these amps sometimes. Your problem has common roots, we just have to go thru each step till we get the issue identified.
Your doing great so far though
The 0.015 DC offset is true to the FEB board and the fact that you got that reading on your output stage is a good sign that your all good in that area, So far.
I will pull my docs out for this series and see if I have missed anything.
Back at you shortly
Have you checked the switches ? The way to do this fairly straitforward. You just operate them while listening to the bad channel
any problems will become evident audiable. Also the gain controls should be checked.
Check you mode switchs and we will take it from there. I'm sure your getting frustrated by now, but patience is the key to sucess on these amps sometimes. Your problem has common roots, we just have to go thru each step till we get the issue identified.
Your doing great so far though
The 0.015 DC offset is true to the FEB board and the fact that you got that reading on your output stage is a good sign that your all good in that area, So far.
I will pull my docs out for this series and see if I have missed anything.
Back at you shortly
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