Summary of the current findings:
IC5-MC34063(Buck converter IC) Pin 2 has 2.7 volts and not 5volts
R1 and R2 on daughter board has +/-15 volts as should be.
U5-LM1117 Pin 3 has +1.5v instead of 5v, and Pin 2 has +0.2v instead of +3.3v.
The audio signal when measured on the incoming pin to the dsp daughter board was sometimes ragged and sometimes smooth and linear depending on positioning of the board, and sometimes pressing it in the area of IC6 I think, but now there is a square wave on Pin1 and Pin7 of IC6 (NJM2068) while there is a clean 50hz sine wave entering the amp and making it all the way to Pin5 of IC6. The square wave's amplitude goes up and down with the turning of the gain knob just like the sine wave did before when measured on IC6 pin6 and the daughter board input pin, but on Pin7 of IC6, it is a fixed square wave with no variation.
Hoping it is something simple to check and repair, but these are the currently found inconsistent voltages and issues...
IC5-MC34063(Buck converter IC) Pin 2 has 2.7 volts and not 5volts
R1 and R2 on daughter board has +/-15 volts as should be.
U5-LM1117 Pin 3 has +1.5v instead of 5v, and Pin 2 has +0.2v instead of +3.3v.
The audio signal when measured on the incoming pin to the dsp daughter board was sometimes ragged and sometimes smooth and linear depending on positioning of the board, and sometimes pressing it in the area of IC6 I think, but now there is a square wave on Pin1 and Pin7 of IC6 (NJM2068) while there is a clean 50hz sine wave entering the amp and making it all the way to Pin5 of IC6. The square wave's amplitude goes up and down with the turning of the gain knob just like the sine wave did before when measured on IC6 pin6 and the daughter board input pin, but on Pin7 of IC6, it is a fixed square wave with no variation.
Hoping it is something simple to check and repair, but these are the currently found inconsistent voltages and issues...
IC5
1. 13.1
2. 2.7
3. 1.4
4. 0
5. 0.5
6. 13.1
7. 13.0
8. 13.0
These are the voltages on IC5. I definitely do not have any MC34063 here other than in the KXA800.1 that also needs repair. Is there any other IC that can substitute, even if only for testing purposes? I would have to order the MC34063 which would take some time to get here...
1. 13.1
2. 2.7
3. 1.4
4. 0
5. 0.5
6. 13.1
7. 13.0
8. 13.0
These are the voltages on IC5. I definitely do not have any MC34063 here other than in the KXA800.1 that also needs repair. Is there any other IC that can substitute, even if only for testing purposes? I would have to order the MC34063 which would take some time to get here...
So I took some readings of both MC34063 ICs in both amps I have here and they read identical on both resistance and diode settings but I swapped them anyway, same result, 2.7v on pin2. I then lifted the 2nd leg of IC5 off the board and it reads 11.7v when off the pad. Is there something else in that circuit that could be dragging down the voltage?
I have been using the GND terminal for these measurements.
The KXA800.1 has a different DSP board as it has the remote plug in also. That one will not power up The mains limiter lights up full bright upon power up just like this one but it doesn't stop pulling current and the red power LEDs come on immediately, instead of turning on a second after the initial heavy current draw.
The KXA800.1 has a different DSP board as it has the remote plug in also. That one will not power up The mains limiter lights up full bright upon power up just like this one but it doesn't stop pulling current and the red power LEDs come on immediately, instead of turning on a second after the initial heavy current draw.
Found that Leg 1 and Leg 2 of the LM1117 were reading 0.8 ohms between them. I removed the regulator and discovered the low ohm reading still exists in the pads. The regulator is not shorted between legs 1 and 2 but it reads 760 ohms, 4.1mohms between legs 1 and 3, and 4.1 ohms between legs 2 and 3. If leg 1 is ground, that means that the pad if leg2 is grounded somewhere
So, I reinstalled the regulator with only legs 1 and 3 connected and leg 2 and the tab not attached to the board. Leg 2 has +3.3v output and Leg 3 has +5.6v.
So, I reinstalled the regulator with only legs 1 and 3 connected and leg 2 and the tab not attached to the board. Leg 2 has +3.3v output and Leg 3 has +5.6v.
So, after spending some time with the KXA800.1, I was able to get it to power up and output audio, so I may be able to use that semi-functional amp for comparison/reference.
What exactly does the +3.3v regulated output do and where all does it go. There may be a defective component or a solder bridge that is grounding out the +3.3v output of leg2 of the LM1117.
What exactly does the +3.3v regulated output do and where all does it go. There may be a defective component or a solder bridge that is grounding out the +3.3v output of leg2 of the LM1117.
There are multiple circuits that use the 3.3VA. I suspect that U2-ADA1701 is most likely the culprit. If that is the case replacing would be problematic. It would require firmware which isn't available assuming that you could remove and replace the physical chip. It's possible that a pull from another board might work.
Pins 36,39,48 can be lifted to see if U2 is shorted. C32,C30,C29 are tied to each pin and may have failed.
Q5 and U23 use the 3.3VA. I doubt if this is the culprit, but can be looked at.
Unfortunately, problems with DSP and Microcontrollers are not very serviceable. I don't see this very often, but when I do I will swap out the board or replace the amp. I know this is not an option for you.
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