Bad output transformer? ( newb question )

[buildafriend]

Okay so I purchased 2 hairball 1176 rev F kit and I put them together. One I got working with the help of a good friend and the other has been sitting on the shelf since I cant seem to figure out why it's acting funky. I think it might be the output transformer.

1) Is it rare to get a bad output transformer?

2) If the signal seems to be going bad pre and post the transformer, is it safe to assume that my problem lies in transformer?

3) Are there any ways that I can test the transformer without putting my other 1176 at risk from desoldering and resoldering?

4) The output is about 1/3rd the volume of the functioning unit. It is also distorted.

5) Could this be a phase issue? ( that guess is a total shot in the dark )

6) Is it possible that I damaged the output xfrmr?

7) Do you think hairball would replace the xfrmr if I believed I received it in not working condition?

Here are some pictures of the signal pre and post the xfrmr to show exactly what is happening.

Oscilloscope scale is set to .1V per division at 5 milli seconds per division. Probe is set to 1x.
Test tone is approx 1v and 1K sine wave.

Pre xfrmr:

Post xfrmr:

 

[pucho812]

Okay so I purchased 2 hairball 1176 rev F kit and I put them together. One I got working with the help of a good friend and the other has been sitting on the shelf since I cant seem to figure out why it's acting funky. I think it might be the output transformer.

1) Is it rare to get a bad output transformer?

2) If the signal seems to be going bad pre and post the transformer, is it safe to assume that my problem lies in transformer?

3) Are there any ways that I can test the transformer without putting my other 1176 at risk from desoldering and resoldering?

4) The output is about 1/3rd the volume of the functioning unit. It is also distorted.

5) Could this be a phase issue? ( that guess is a total shot in the dark )

6) Is it possible that I damaged the output xfrmr?

7) Do you think hairball would replace the xfrmr if I believed I received it in not working condition?

Here are some pictures of the signal pre and post the xfrmr to show exactly what is happening.

Oscilloscope scale is set to .1V per division at 5 milli seconds per division. Probe is set to 1x.
Test tone is approx 1v and 1K sine wave.

Pre xfrmr:

Post xfrmr:

if the signal is bad pre transformer, then it's not the transformer. Or did I read that wrong and you wanted to say the signal is good before the transformer and bad after the transformer.  You can try the unit bypass and see if the signal going in is as clean as the signal going out. You can also test the transformer by itself if you know the ratios of what it's supposed to be.

I would first make sure the PSU is out putting the voltages. Next calibrate the unit.  If the unit is still behaving funny I would feed it a 1K sine wave and start signal tracing. Grab a schematic and use the probe on your scope, thats what it is for. 

Output transformers can go bad just like any other part but they are less likely to go bad then other parts like a capacitor or transistor. Almost forgot since you have 1 working unit, you have a compressor to compare it to

 

[bruce0]

All I have are questions and ideas.

why is the signal so much larger post than pre?  Is the scope set up the same for both readings?  Is the transformer set 1:1 ?

Given the strange shape of the wave, i am having a hard dime imagining that the transformer is doing that.  I don't know what all one can do to a transformer but mostly that is burn out a winding, or magnetize the core but that seems unlikely on an output transformer.

It seems like there may be something capacitive or inductive happening to the signal, or another signal overlayed on the signal.  Or perhaps the core is saturated because you are feeding it a ton of DC? Perhaps you have a grounding problem on the "pre-transformer side?", or some sort of load connected, bad output cap (C15 on the schematic I dug up).

I would start by measuring the continuity to ground (I am assuming from my schematic that the transformer primary is grounded on one side) and then possibly for a signal coming off the ground connection on the primary side of the output transformer (there should be none and not some sort of signal coming off a bad power supply etc)

Take a DC reading off the primary, make sure you are not saturating the core with DC.

Out of ideas.

Assuming you have the scope set to different ranges on the two pictures (and that is why the signal is so small on the primary) , then I am assuming that you have a grounding problem on the transformer, or DC on the primary.

Other thought is that the terminating resistor is of the wrong value (like 10 ohms instead of 1000, but I can't see that would get you a larger looking signal on the secondary)

 

[buildafriend]

okay awesome ill try poking around and seeing if any of your suggestions lead me anywhere. I said in the first post what the scope was set to, it did not change from pre to post xfrmer.

 

[buildafriend]

It appears that I have 15.1V DC from before the output coupling cap and 0V DC after it.

 

[bruce0]

0 VDC after that output cap is as it should be - that's what it is there for.

I have no idea of whether 15v on the output is high, but it sure seems high (I have not built an 1176 yet) since I am guessing rails are probably +-16 or something. Maybe post a schematic, or maybe someone with more experience with this design will chime in.

You could compare the pre-output cap voltage to the working unit.  I would expect a volt or less not 15 volts, depending upon the op-amp, servo or what have you and circuit.

As far as the transformer...

If the scope is set to 5ms per div, then a 1K signal should show 5 waves per division right?
The wave on the pre transformer side is showing about a .05V  peak to peak 50 or 60HZ waveform.
The trafo output is a roughly .1 v peak to peak waveform of the same frequency, with some distortion overlayed (perhaps the 1K signal?).  It is hard to tell whether that distortion exists on the input signal (crank the scope in some to .05 v per division, maybe it is on the input too).

I don't have a schematic for the hairball kit, but is the transformer wired for 1:2 step up?  Which would explain the increase in the wave form, and imply that the transformer is doing what it should be doing.


I am out of ideas, but I think your problem may be in the circuit, not the transformer.  Figure out whether 15V on the output is reasonable, and assuming it is not, figure out why you have that.

 

[buildafriend]

Things I noted are that brown orange red and yellow ( all connections from the primary of the output xfrmr ) all seem to be hitting ground when tested. gray blue purple and green do not hit ground. This seems like it should make sense since all primaries are attached to a coil that hits ground.

I just got fed up and swapped the transformer from the working unit to the non working unit. I still seem to have the same exact problem. What makes this so confusing to me is that the signal appears to be perfect before going into the xfrmr. I feel like I have hit a brick wall and I am dying to get this thing going.

 

[bruce0]

Well I may be misunderstanding your "perfect signal"

But you are describing a 1K Hz signal

The scope is showing a 50Hz or 60Hz signal (like power hum)

Zoom the resolution on the input side, I bet you will see the same distortion you are seeing on the output side.

Do you have good power on the rails ?  +15 V on the +, -15 V on the -?

 

[edanderson]

the output transformer for the rev F is a step up, so it is normal to see a bigger signal on the secondary.

it is rare but possible to have a defective transformer.  if the problem follows the transformer when you put it into a working unit, then the transformer may be defective.  i'm sure mike will take care of you if you've received a defective transformer.

from your description, it sounds like the problem is with the unit, not the transformer (since the known good transformer from the working unit doesn't fix the broken unit).  i would compare the signal in the working unit to the one in the broken unit, and work your way backwards from the output cap.

ed

 

[buildafriend]

I think it was something really stupid... The star ground was loose. They both work and sound amazing. Now it's stereo link time

 

[CJ]

remove the star ground hardware, rent a big iron, and put down a blob of molten hot solder for ground,
there is no such thing as absolute ground, but this will make you better than the best,