Yes, having D5 working is important - otherwise there will be no thermal feedback and the big transistors go to thermal runaway until they kill themselves.
stable between 76 and 78 mV.
Will the next step be to power off and connect the left ch output transistors, and repeat the procedure, or should I try to adjust idle current on the right ch., or wait a little longer.
Will the next step be to power off and connect the left ch output transistors, and repeat the procedure, or should I try to adjust idle current on the right ch., or wait a little longer.
This one is fine, so leave it as is.
Now you can connect the big transistors on the other one and carefully repeat the procedure.
OK, looking good 🙂
14:57
starting at 1,7mV with max ressistance.
easily adjusting to 75mV.
14:59
increased to 87mV, trimming to 80mV
15:03
increased to 84mV, trimming to 80mV
14:57
starting at 1,7mV with max ressistance.
easily adjusting to 75mV.
14:59
increased to 87mV, trimming to 80mV
15:03
increased to 84mV, trimming to 80mV
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This one seems to run fine as well 
Adjust it to the same 76-78 as the other one after some minutes when it gets warmer - and you're done.
Just in case, before connecting the speakers, check DC offset at the output terminals.
You can carefully adjust it with VR2 as close to zero as possible. It will slightly fluctuate anyway, but if it's within, say, +/-30mV - you're ok.
Then you can connect the speakers and - here we go 😉
Adjust it to the same 76-78 as the other one after some minutes when it gets warmer - and you're done.
Just in case, before connecting the speakers, check DC offset at the output terminals.
You can carefully adjust it with VR2 as close to zero as possible. It will slightly fluctuate anyway, but if it's within, say, +/-30mV - you're ok.
Then you can connect the speakers and - here we go 😉
Ahh, GREAT 🙂
But ... according to the manual, shouldn't I do the idle current adjustment by measuring between pins 13 and 23, adjusting to 30mV?
But ... according to the manual, shouldn't I do the idle current adjustment by measuring between pins 13 and 23, adjusting to 30mV?
Ah, OK. We are actually doing the same thing now, I just did not know they recommend 30mV. Then you can reduce to 30. My assumption about 70-80 is based on previous experience - many amps run close to that.
If idle current is too low, you will have crossover distortion.
But if Pioneer recommends 30mV (which in your case is equal to 30mA idle current) - than it's perfectly fine. It will just run cooler.
OK, good, I'll try and follow the manual on this topic, then.
But... if not later then now, I want to let you how grateful I am! I don't think I could have without your help - I was running in circles.
I'll probably post a few more statuses here, just for the complete history.
All the best
Ole
But... if not later then now, I want to let you how grateful I am! I don't think I could have without your help - I was running in circles.
I'll probably post a few more statuses here, just for the complete history.
All the best
Ole
OK, seems the amp part is working, but.... there is only output in the left channel 
, and I'm not sure where a good place to start looking would be...
It could be one of the switches, but again which one...?
It doesn't matter which input channel I activate, same for FM,AM,AUX and Tape 1, 2.
Perhaps you will spend some more time with me on this
, and I'm not sure where a good place to start looking would be...It could be one of the switches, but again which one...?
It doesn't matter which input channel I activate, same for FM,AM,AUX and Tape 1, 2.
Perhaps you will spend some more time with me on this
OK, seems the amp part is working, but.... there is only output in the left channel
It could be one of the switches, but again which one...?
It doesn't matter which input channel I activate, same for FM,AM,AUX and Tape 1, 2.
Perhaps you will spend some more time with me on this
No problem, you are welcome 🙂
Usually the power section is the most difficult one.
Finding the place where the signal gets lost is usually easier. And less dangerous in terms of possible damage 🙂
🙂
I can confirm that 😉
Perhaps a little info of what I have done prior to all of the power amp trouble:
I have replaced all electrolytic caps everywhere.
I have taken some (don't recall which ones now, but at the tape/mono/loudness board) of the flip switches apart for a thourough cleaning, and the volume pot have been replaced with a good (not tested - don't know how to) one from ebay, but it was in better condition than my old one.
PS: The center voltage now read 2 - 5mV on all 4 speaker output terminals 🙂
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Center voltage is perfect!
Power section is like new now )
Probably it's one of the switches. You need to find the way to test the signal...
Oscilloscope would help, but it is actually possible even without it.
For example, some small headphone with resistor (470R or 1 K), connected serially with it. Not perfect (still low impedance), but it will work. This way you can hear if there is line signal in the places where it is expected to be, and see if it is there in one channel, but not there in the other.
I would start with checking the signal at the volume pot - first at the "top" pin (opposite to the grounded one), and then at the central one (set the volume to rather high position, but don't forget to disconnect the speakers for the time being).
Depending on the result, we will at least know where to dig deeper - before the pot or after it.
Power section is like new now )
Probably it's one of the switches. You need to find the way to test the signal...
Oscilloscope would help, but it is actually possible even without it.
For example, some small headphone with resistor (470R or 1 K), connected serially with it. Not perfect (still low impedance), but it will work. This way you can hear if there is line signal in the places where it is expected to be, and see if it is there in one channel, but not there in the other.
I would start with checking the signal at the volume pot - first at the "top" pin (opposite to the grounded one), and then at the central one (set the volume to rather high position, but don't forget to disconnect the speakers for the time being).
Depending on the result, we will at least know where to dig deeper - before the pot or after it.
Yea, this is real pleasure to know! BTW, the q1 is composed of two KSA992, glued and tied together by a plastic-strip, but since they seem to work well, there is no need getting a regular 5-pin replacement off ebay, I suppose?
And moreover, I got myself a gluegun - should I use it on the combo for more thermal stability? It is listed to operate at 200C, which means that the gluestick melts at a lower (unknown) temperature, but it must be higher than the maximum q1 temp ....Just a thought.
Uhh, can't make an image of how that would be put together. I do have a pair of headphones, though, so I guess I can make one, if you could describe or draw for me...
I'm looking at p. 52 i the manual for the Flat Amplifier Assembly - could you point out in more detail, what I should do?
Right 😉
Ahhh... cool. What kind of scope is it? If you give me the model, it will be easier to assist as I will know what controls we've got where 😉
🙂
It's a Tektronix TDS 2022B. I got a (very) brief intro as how to operate it, and a suggestion as to where to set the probes, as per your suggestion.
I'll let you know when I'm set at home.
It's a Tektronix TDS 2022B. I got a (very) brief intro as how to operate it, and a suggestion as to where to set the probes, as per your suggestion.
I'll let you know when I'm set at home.
Good one.
Will you be able to connect the sound output of your computer to some AUX input of your Pioneer receiver?
Will you be able to connect the sound output of your computer to some AUX input of your Pioneer receiver?
Sure - I have Y-cable: mini-jack<=> L/R phono.
I also have a CD-player connected, and the FM receiver does give a signal as well, but maybe the PC should be used for a special signal?
I also have a CD-player connected, and the FM receiver does give a signal as well, but maybe the PC should be used for a special signal?
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