Yes, I would think so - but I already mounted the combo (2*3 pin) in Q1, and posts from #78 are with the combo sub for Q1 in place 🙂.
How ever I failed to mention that center voltage is not affected when turning VR2 one half turn in both directions - so there must still be something to repair 😉
New readings
Hi
I hope you haven't spent too much time on the next step, because I discovered I had left 2 resistors up in one end (R7,R8)
That said I did read the voltages listed on the schematic:
Note polarity is reversed 😕
Checking center voltage.
Positive lead to pin 10, negative lead to chassis
Initial reading at -0.85 mV
Adjusting VR2 gives very small changes: 1 turn ~ 0.02V
Hi
I hope you haven't spent too much time on the next step, because I discovered I had left 2 resistors up in one end (R7,R8)
That said I did read the voltages listed on the schematic:
HTML:
Read Spec
intersect. C4,C5,R6: -0.6 (+0.6)
intersect. Q1,R3,R33: -0.02 (0.0)
Q4c -7<- (+3)
Q4b-R8 +60.6 (-58.2)
Q3b-R7 +60.56 (-58.2)
Q3c +1.0 (-1.2)
Q5c +0.83 (+1.2)Note polarity is reversed 😕
Checking center voltage.
Positive lead to pin 10, negative lead to chassis
Initial reading at -0.85 mV
Adjusting VR2 gives very small changes: 1 turn ~ 0.02V
Hi
Please disregard #84 - polarity is correct - I had swapped the probes
.
I hope you haven't spent too much time on the next step, because I discovered I had left 2 resistors up in one end (R7,R8)
That said I did read the voltages listed on the schematic:
Checking center voltage.
Please disregard #84 - polarity is correct - I had swapped the probes
. I hope you haven't spent too much time on the next step, because I discovered I had left 2 resistors up in one end (R7,R8)
That said I did read the voltages listed on the schematic:
HTML:
Read Spec
intersect. C4,C5,R6: +0.6 (+0.6)
intersect. Q1,R3,R33: +0.02 (0.0)
Q4c:
Starting at +9V drop to +6.5 (+3)
Q4b-R8 -60.6 (-58.2)
Q3b-R7 -60.56 (-58.2)
Q3c -1.0 (-1.2)
Q5c -0.83 (+1.2)Checking center voltage.
HTML:
Positive lead to pin 10, negative lead to chassis
Initial reading at -0.85 mV
Adjusting VR2 gives very small changes: 1 turn ~ 0.02V
Pin readings:[HTML]
1 -62.3 (-60)
4 +23.4 (+23)
5 -23.2 (-23)
8 +61.9 (+60)
12 +61.9 (+62)
22 -61.9 (-62)
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Hi
Please disregard #84 - polarity is correct - I had swapped the probes.
I hope you haven't spent too much time on the next step, because I discovered I had left 2 resistors up in one end (R7,R8)
That said I did read the voltages listed on the schematic:
Replaced Q4 with new spare - no difference for Q4c.
Checking center voltage.
Please disregard #84 - polarity is correct - I had swapped the probes
. I hope you haven't spent too much time on the next step, because I discovered I had left 2 resistors up in one end (R7,R8)
That said I did read the voltages listed on the schematic:
HTML:
Read Spec
intersect. C4,C5,R6: +0.6 (+0.6)
intersect. Q1,R3,R33: +0.02 (0.0)
Q4c:
Starting at +9V drop to +6.5 (+3)
Q4b-R8 -60.6 (-58.2)
Q3b-R7 -60.56 (-58.2)
Q3c -1.0 (-1.2)
Q5c,Q6b +0.8 (+1.2)Replaced Q4 with new spare - no difference for Q4c.
Checking center voltage.
HTML:
Initial reading at -0.85 mV
Adjusting VR2 gives very small changes: 1 turn ~ 0.02V
Pin readings:[HTML]
1 -62.3 (-60)
4 +23.4 (+23)
5 -23.2 (-23)
8 +61.9 (+60)
12 +61.9 (+62)
22 -61.9 (-62)
Last edited:
Still struggling with power amp
Transistors Q1 (2 of them in the combo sub) Q2, Q6, Q7, Q8 have been pulled, and all read between 0.6 - 0.7 V e-b and c-b.
Q3, Q4 and Q5 have been left un-tested since they just have been replaced with new ones.
Q1 is now the combo of 2 KSA922.
D2 is replaced (was new from rebuild) again just in case, but with no effect.
I took a glance at the power meters, and when the relay clicks in right ch meter jumps to -27 db, and stays there, regard less if no function button is depressed (all out) or if any one is.
Just a symptom that right ch is srewed up, I guess.
Please see all the voltage readings on attached image.
Transistors Q1 (2 of them in the combo sub) Q2, Q6, Q7, Q8 have been pulled, and all read between 0.6 - 0.7 V e-b and c-b.
Q3, Q4 and Q5 have been left un-tested since they just have been replaced with new ones.
Q1 is now the combo of 2 KSA922.
D2 is replaced (was new from rebuild) again just in case, but with no effect.
I took a glance at the power meters, and when the relay clicks in right ch meter jumps to -27 db, and stays there, regard less if no function button is depressed (all out) or if any one is.
Just a symptom that right ch is srewed up, I guess.
Please see all the voltage readings on attached image.
Attachments
Hi Ole,
Voltages actually look not bad. But what is KSA922? I can't find a datasheet for it...
Cheers,
Valery
Voltages actually look not bad. But what is KSA922? I can't find a datasheet for it...
Cheers,
Valery
Right, they look fairly good, except the Q4c (+3V).
The KSA922 is the transistor that is used a pair of, to build a Q1 - the data sheet:
http://www.mouser.com/ds/2/149/KSA992-88789.pdf
But the constant low output must be a symptom on something too😕
Ah, ok - it's 992, not 922 🙂 Now I see.
Is R22 really = 160 Ohm?
And you test with 2x4pin plugs unplugged, right?
Is R22 really = 160 Ohm?
And you test with 2x4pin plugs unplugged, right?
OK, cool.
Can you please check the big output transistors (the ones we keep unplugged so far) with the ohm-meter, the same way you did it before with the other transistors?
We need to make sure none of them is shorted.
Also, please measure the voltage, putting the leads between the pins 15 and 20
Can you please check the big output transistors (the ones we keep unplugged so far) with the ohm-meter, the same way you did it before with the other transistors?
We need to make sure none of them is shorted.
Also, please measure the voltage, putting the leads between the pins 15 and 20
But they were never connected again after they were tested and unplugged, and they aren't part of the present circuit (unplugged) ?
Will do...
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Good. Try to make it a bit less, let say 1.2V, carefully turning VR1. In both channels.
I have to move from home to the office - will be back in couple of hours.
I have to move from home to the office - will be back in couple of hours.
I need to go to work too, but will try if I can make this before I leave 😉
But VR1 is for adjusting idle current?
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OK, can adjust to minimum 1.322 by VR1, but VR1 is maxed out (not multiturn).
Left Ch. pin 15-20 fluctuates between 8.7 - 9.1 V, with decreasing values....
Have to leave for the office now😉
Left Ch. pin 15-20 fluctuates between 8.7 - 9.1 V, with decreasing values....
Have to leave for the office now😉
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OK, let's leave it at the minimum. Is it roughly the same in both channels?
This is preparation for connecting the output transistors.
We set the idle current to the minimum to be on a safe side.
This is preparation for connecting the output transistors.
We set the idle current to the minimum to be on a safe side.
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