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SX-1250 Power Amp VR-2 wont adjust.

Hey Mark.
Those readings that I originally posted are what I am reading even with the VR2 at min and Max when I turn VR2 min and max it makes no difference in the voltage readings.
Q4 negative lead Q6 positive lead Collector (1.895) min and max VR2
Q9 positive lead Q10 Negative lead Base (280mv) min/max VR2
Q9 positive lead Q10 negative lead Emiter ( 0mv ) min/max VR2.
These are the reading for the good side.The quick readings that I did with the OPs hooked up looked much closer to the desired voltages I just didnt take the time to read the 10ths voltage as I was not wanting to fry the OPs.
Am I doing something wrong or does uplugging the OPs cause this circuit to be incomplete?
Steve
 
Stevesmullen said:
Hey Mark.
Those readings that I originally posted are what I am reading even with the VR2 at min and Max when I turn VR2 min and max it makes no difference in the voltage readings.
Q4 negative lead Q6 positive lead Collector (1.895) min and max VR2
Q9 positive lead Q10 Negative lead Base (280mv) min/max VR2
Q9 positive lead Q10 negative lead Emiter ( 0mv ) min/max VR2.
These are the reading for the good side.The quick readings that I did with the OPs hooked up looked much closer to the desired voltages I just didnt take the time to read the 10ths voltage as I was not wanting to fry the OPs. Am I doing something wrong or .......
Click to expand...

Mark made a detailed instruction on how to test on post #12 & 15. Those two posting plus #18, he instructed to REMOVE the outputs and LEAVE THEM OUT in order to do the test he instructed you to do until he says to put them back in.

Stevesmullen said:
......does uplugging the OPs cause this circuit to be incomplete?
Steve
Click to expand...

I believe Echo answered that question on the first sentence on post #10 of this thread.
 
ccheath said:
Mark made a detailed instruction on how to test on post #12 & 15. Those two posting plus #18, he instructed to REMOVE the outputs and LEAVE THEM OUT in order to do the test he instructed you to do until he says to put them back in.

I believe Echo answered that question on the first sentence on post #10 of this thread.
Click to expand...
Correct and I have tested the voltages exactly as stated,but the readings arent the desired voltages that we are looking for.Either Im missing something (which I dont "THINK" that I am) or the circuit isnt responding like Mark thought that it would be by unplugging the OPs.

I also knew what EW had said but I was just communicating with Mark as to what I am finding and my thoughts.EW was answering my question if the mv could be adjusted with the OPs unplugged.
Marks theory was that there would still be proper voltages at the Drivers and predrivers with the OPs unplugged.
And like I mentioned earlier I have read the posts several times and I have checked the voltages several times also and I still keep coming up with the posted odd voltages.
When The OPs are hooked up the Voltages appear to be close to the desired voltages.
Steve
 
Stevesmullen said:
Correct and I have tested the voltages exactly as stated,but the readings arent the desired voltages that we are looking for.Either Im missing something (which I dont "THINK" that I am) or the circuit isnt responding like Mark thought that it would be unplugging the OPs.

I also realize that but I was just communicating with Mark as to what I am finding and my thoughts.EW was answering my question if the mv could be adjusted with the OPs unplugged.
Marks theory was that there would still be proper voltages at the Drivers and predrivers with the OPs unplugged.
And like I mentioned earlier I have read the posts several times and I have checked the voltages several times also and I still keep coming up with the posted odd voltages.
When The OPs are hooked up the Voltages appear to be close to the desired voltages.
Steve
Click to expand...

I think Mark is looking for the "baseline" voltage. You will find that measurements on the good amp module with outputs out, THEN compare that to the bad module measurement with outputs out. He may not be looking for ideal voltage but rather what the voltage shows on the good module (baseline) with outputs disconnected. He will also want to see the voltage on the bad module so he can see the comparison.
 
ccheath said:
I think Mark is looking for the "baseline" voltage. You will find that measurements on the good amp module with outputs out, THEN compare that to the bad module measurement with outputs out. He may not be looking for ideal voltage but rather what the voltage shows on the good module (baseline) with outputs disconnected. He will also want to see the voltage on the bad module so he can see the comparison.
Click to expand...

I have those voltages posted and there is no min/max the voltage readings when tested exactly as posted by Mark are unresponsive to VR2 adjustments,And I believe that we (Mark) is looking for the desired voltages as read in the schematics.
If you can see what Im doing wrong please tell me,I cant help what the readings are.
They are what they are!
Steve
 
HEY - I'm the ONLY guy that can browbeat Steve when we're troubleshooting. :D

Steve, unplugging the outputs deprives the pre-driver and drivers of the raw unregulated supply voltages.
I should have looked closer, but when EW said the feedback loop was intact, I didn't continue checking.
Working on the work around....

STEVE: MY BAD

Stevesmullen said:
Hey Mark.
Those readings that I originally posted are what I am reading even with the VR2 at min and Max when I turn VR2 min and max it makes no difference in the voltage readings.
Q4 negative lead Q6 positive lead Collector (1.895) min and max VR2
Q9 positive lead Q10 Negative lead Base (280mv) min/max VR2
Q9 positive lead Q10 negative lead Emiter ( 0mv ) min/max VR2.
These are the reading for the good side.The quick readings that I did with the OPs hooked up looked much closer to the desired voltages I just didnt take the time to read the 10ths voltage as I was not wanting to fry the OPs.
Am I doing something wrong or does uplugging the OPs cause this circuit to be incomplete?
Steve
Click to expand...

You asked the right question, and I wish I had seen this sooner.... I missed it by a MINUTE!!!
The answer is : uplugging the OPs caused this circuit to be incomplete!
 
Hey ccheath.
The readings that are in post #21 are with the OPs disconnected,(you must have just deleted your post) and the readings have been the same for the good side and the bad side I just didnt allways post both sides seperatly.
Thanks for the help.
And Mark thanks for saving me :D
I thought that the OPs disconnected was the problem.
I hope you saw the thread were I swapped the Power Amp Boards to possibly eliminate the OPs.
Thanks for your help.
Steve
 
I wish I had caught the developments on this thread sooner, but I was out rescuing my car. I am also very very beat... exhausted actually. Ever see the cartoon of the guy with this gluteus maximus hanging down to the ground and dragging behind him. That's how I feel.

I missed it by a minute...


Can you insert the plugs for the transistors angled in such a way that only one end pin each (the ones towards the center, 12 & 15 ) is actually connected. Then the UN-regulated voltages can get in to the board and perk things up.

The output transistor's collectors are already hot, even when the plugs are disconnected from the board, it's just that the bases and emitters are floating, thus no effect.
 
Stevesmullen said:
Hey ccheath.
The readings that are in post #21 are with the OPs disconnected,(you must have just deleted your post) and the readings have been the same for the good side and the bad side I just didnt allways post both sides seperatly.
Thanks for the help.
And Mark thanks for saving me :D
I thought that the OPs disconnected was the problem.
I hope you saw the thread were I swapped the Power Amp Boards to possibly eliminate the OPs.
Thanks for your help.
Steve
Click to expand...

I did delete it. I didn't want to interfere with Mark's help with you. I did notice on your posting that you swapped the power amp boards and from what I recall that the problem followed the amp board. In the post I deleted, I stated that I didn't want to speculate why the problem with your measurements, I was actually thinking the same thing as Mark regarding the deprivation when outputs were removed but I'd rather let Mark state it to confirm my theory so as to not cause confusion. So, without further ado, back to Mark. :D
 
markthefixer said:
Can you insert the plugs for the transistors angled in such a way that only one end pin each (the ones towards the center, 12 & 15 ) is actually connected. Then the regulated voltages can get in to the board and perk things up.

The output transistor's collectors are already hot, even when the plugs are disconnected from the board, it's just that the bases and emitters are floating, thus no effect.
Click to expand...
Hey Mark.
I will give that a try and let you know,I wont be able to get back to the unit until tommorow.
If I can get the plugs angled to connect 12 & 15 I will test and post all the voltages as layed out in the diagram.
Hope you get rested up.
Steve
 
Okay now we are getting somewhere Although im not sure that we have completely fooled the circuit because of the high voltages on Q9 and Q10 and they were heating up quickly so I worked fast (I could still touch the heat sink).
Good side readings.
Q4 negative lead Q6 positive lead Collector (2.9min) (3.59max) VR2
Q9 positive lead Q10 Negative lead Base (5.16min) (5.34max) VR2
Q9 positive lead Q10 negative lead Emiter ( 17.46min ) (17.56max) VR2.
Bad Side Readings
Q4 negative lead Q6 positive lead Collector (2.9min) (3.59max) VR2
Q9 positive lead Q10 Negative lead Base (5min) (5.22max) VR2
Q9 positive lead Q10 negative lead Emiter ( 19min ) (19.13max) VR2.
Looks like the emiter side of Q9 and Q10 is were the trouble begins Maybe??
Thanks
 
I see the post, I am thinking about the results and I will hopefully later tonight be able to reread the thread and post.
 
I didn't want it hanging over my head, but now it will be a while before I am back on tonight.

Ok, this is based on the assumption that the good and bad power amplifier boards are interchangable with the left and right sets of outputs:

1. Connect in the good board with the output transistors live.
2. turn vr2 to zero, power it up
3. take the set of 3 readings you have been doing, these are "low left"
4. one additional reading, the voltage at the "100 mV bias current measurement point.

5. turn up VR2 until the bias current is 20% over spec, which should be 120mV.
6. take another set of 3 readings, these are "high left". power off.


7. Connect in the good board to the OTHER set of output transistors.
8. turn vr2 to zero, power it up.
9. take the set of 3 readings you have been doing, these are "low right"
10. take one additional reading, the voltage at the "100 mV bias current measurement point.

11. turn up VR2 until the bias current is 20% over spec, which should be 120mV.
12. take another set of readings, these are "high right".power it off.

We now know what the good board does as well as the conditions of the output transistors. The bad board is now the only unknown.

14. Connect the bad board to EITHER the left outputs or the right output set if there was something wrong with the left set.
15. turn it's vr2 down to zero
16. power it up and read the voltage at the "100 mV bias current measurement point.
17. take the set of 3 readings you have done, these are "low bad left"
18. adjust vr2 upwards while watching the "100 mV bias current measurement point" LIKE A HAWK!!! If the bias current doesn't budge, turn the pot about half way, or if you can remember, hit the 120mV position from the good board.
19. QUICKLY take the three measurements, and shut it down... turn vr2 back to zero. These measurements are "high bad left.

EVEN IF the left and right outputs DON'T perform about the same in the first tests, we won't repeat for bad board and right outputs...

BTW, when I am repeating sets of measurements, I clip on jumper leads to each of the measurement points, and clip the other end to a piece of cardboard, and group the sets of clips on the cardboard together for the readings I am going to take. Then I just probe at the cardboard.
 
Hey Mark.
I was heading off to work and only had time to get 1 set of readings,I will complete the rest tommorrow.These readings are with the OPs plugged in.
Left Side Low (good side)
Q4 negative lead Q6 positive lead Collector (2.926min)
Q9 positive lead Q10 Negative lead Base (1.78min) VR2
Q9 positive lead Q10 negative lead Emiter (.830min)VR2.
Right side Low (Bad Side Readings)
Q4 negative lead Q6 positive lead Collector (2.94min)VR2
Q9 positive lead Q10 Negative lead Base (1.78min)VR2
Q9 positive lead Q10 negative lead Emiter (1.367min)VR2.
Im not sure if I have mentioned that either Q9 or Q10 is not the original transistor,I can identify location and get the part# to confirm its compatability if necessary.
Thanks Steve
 
Q9, Q10... sorta stands out, doesn't it.

on the bad board with vr2 at minimum, using a ground reference, measure Q9 & Q10's bases and emitters. IT MAY reveal something

Q9 2sd610 to-220 200v 2a 25w hfe80 4mhz ft
Q10 2sb630 to-220 200v 2a 25w hfe80 4mhz Ft
 
markthefixer said:
Q9, Q10... sorta stands out, doesn't it.

on the bad board with vr2 at minimum, using a ground reference, measure Q9 & Q10's bases and emitters. IT MAY reveal something
Click to expand...
Hey Mark.
Bad Side Readings
Q9
Base (1.295)
Emit (.75)
Q10
Base (-.59)
Emit (-.703)
Good side readings
Q9
Base (.924)
Emit (.430)
Q10
Base (-.952)
Emit (-.452)
The Reading that made me wonder the most was the Q10 Base (on the bad side) so to make a long story short I checked the voltage at R25 and found -430mv on the Q8,10 side and +450mv on the R23 side that definentaly seems like R25 is open under a load (it Ohm checks fine).
I checked the voltages on the good board to confirm and it has negative voltages on both sides of R25.
What I still dont understand is why there is -.703 on the emiter of Q10 if its is off??
Do you agree that R25 is bad and what do you think of Q10 (which is the original) Q9 is a (ERS 375).
My next thought would be to replace R25 and Q9 and Q10 for Balance.
R25 is a 1 watt resistor I dont want to get jumpy and replace it with out having some idea why it has possibly gone bad (remember that I replaced Q4 in post#7).
Feel free to pull the reigns:D
Do you still want me to do the readings that you have requested in post #36 or have we moved past that at this point?
I will wait for instructions.
Thanks Steve
 
Q9 an ERS 375??????n According to the datasheet, it is an old to-5 case. It is not the same case style as Q10?? (a to-220)

That heatsink on the end of the board should have two transistors on it, and the visual difference between the boards really should have been brought up as soon as it was first noticed.


go to this thread, and look at the pictures:
http://www.audiokarma.org/forums/showpost.php?p=1708896&postcount=68
http://www.audiokarma.org/forums/showpost.php?p=1760571&postcount=86

parts list post:
http://www.audiokarma.org/forums/showpost.php?p=1709685&postcount=72

problem is, the 1250 in that thread was never completed, so the substitutions were never tested.

Test the resistors R26 & R27. Q9 was probably fried by usage, it's not made to take that much power.

Man, a real winner was having at that board...... <muttering> putting an itty bitty to-5 in a to-220 heatsinked slot < grumble grumble grumble>

WHAT transistors do you have laying around? any (q9) ksc-2073's? from power supplies etc? You can install one temporarily

(q9, 2sd610) 512-KSC2073TU_Q npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.53
(q10, 2sb630) 512-KSA940TU_Q pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54

JUST FOR TESTING, at 1.5 amps it may not drive to full power, but we can troubleshoot with it.
 
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