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Kennwood KA-3020 distorted
Kennwood KA-3020 distorted
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Old 1st December 2017, 05:06 PM   #11
SuperSKD is offline SuperSKD
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Hello again, I still didn't find the fault but I took some measurements. This is what the Signal looks like:
Click the image to open in full size.

I observed that IC2 (right channel, upc1298V) was way hotter than IC1 (left channel). After that I ordered a new one and just replaced it. Now the Gain is higher but the right channel is still distorted. The IC is also still getting quite hot while the left channel stays cool.
Click the image to open in full size.
Click the image to open in full size.


After that I measured all the Pins on both ICs (Speakers connected and on, volume at middle, but no sound connected):

Left Right
1 44,3V 44,3V
2 44,3V 44,3V
3 38,1V 38V
4 0,09V 0,03V
5 0,09V 0,03V
6 -42V -41,5V
7 -2,1V -1,3V
8 -0,03V -0,7
9 -44,2V -43,7V
10 -44,2V -43,9V
11 -0,4V -0,6V
12 0,02V 0,6V
13 0V 0V
14 0V 0V

Pins 7, 8 and 12 differ, the other ones are pretty much the same.
I also noticed something else: Last time I soldered a bridge over the pins of the speaker relay to make sure it's not the relay. This bridge is still there. Now when I switch the Amp off while music is playing I can still hear the music for about 2 seconds on the left channel while the right channel is instantly gone. Could this be a faulty cap?

Last edited by SuperSKD; 1st December 2017 at 05:23 PM.
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Old 4th December 2017, 11:25 AM   #12
SuperSKD is offline SuperSKD
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*bump*
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Old 4th December 2017, 01:33 PM   #13
Mooly is offline Mooly  United Kingdom
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Kennwood KA-3020 distorted
Lets start again from the beginning because tbh I couldn't really understand your first post description of the fault

What does this mean ?

Quote:
The sound is very silent even if I turn it up and it's also distortet unless I don't turn it very silent.
Have both channels got a problem, or is it just one channel ?

Can you measure (with no speakers attached) the voltage between TP 7 and 8 and TP 9 and 10 which will give a clue as to what current is flowing in the output stage.
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Old 2nd January 2018, 10:38 AM   #14
SuperSKD is offline SuperSKD
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Okay, I try to explain again (sorry for my bad english!). When I started the volume level of the amp was too low (compared to the volume level that was adjustet) and one channel had even lower volume than the other. If I remember this right both channels hat this problem although the effect on one channel was stronger than on the other. When I turned the volume above ~40% the sound started to become very distorted.

Now after I replaced the upc1298V (right channel), the volume on the right channel is higher again but Im still having the distortion problem and I can still feel that the IC (the new one) is getting very hot while the left one stays cool.

What do you mean with TP? The Pins of the UPC1298V?
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Old 2nd January 2018, 10:50 AM   #15
turk 182 is offline turk 182  Canada
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TP = test point as per the amplifier schematic.
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Old 2nd January 2018, 10:51 AM   #16
Mooly is offline Mooly  United Kingdom
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Kennwood KA-3020 distorted
The TP numbers would have referred to test points on the diagram relating to output stage bias.
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Old 2nd January 2018, 11:08 AM   #17
SuperSKD is offline SuperSKD
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I'm sorry, I couldn't find the test points in the diagram. Could you tell me to which page of the pdf you referring?
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Old 2nd January 2018, 11:20 AM   #18
Mooly is offline Mooly  United Kingdom
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Kennwood KA-3020 distorted
They are shown on the main circuit diagram of the power amp next to the output transistors. Page 8.

No speakers and no signal for the measurement.
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Old 2nd January 2018, 12:29 PM   #19
SuperSKD is offline SuperSKD
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Okay, the transistors differ to the ones in the KA-3020SE, mine has the A1693. Anyway this is the measurement:
(no signal source connected, volume pot at 50%)

Left channel
C: -45.2V DC
E: 0.007V DC or 0.02 V AC

Right channel
C: -45.2V DC
E: 0.025V DC or 0.07 V AC

Click the image to open in full size.

Click the image to open in full size.

Last edited by SuperSKD; 2nd January 2018 at 12:44 PM.
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Old 2nd January 2018, 01:21 PM   #20
Mooly is offline Mooly  United Kingdom
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Kennwood KA-3020 distorted
Those readings are fine (low DC offset) but what we really want is the voltage between the test points so that we can calculate and derive the bias current. That might just give a clue as to whether there is a problem around that area of the circuit.

The TP's are across the pair of 0.22 ohm emitter resistors of the output transistors and so a reading in the region of 20mv to 45mv would be in order.
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