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Post by tibimakai on Nov 23, 2018 20:13:42 GMT -5
Anybody has any input?
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Post by tibimakai on Nov 23, 2018 20:53:21 GMT -5
I have noticed, that Q4691(KRA102S), is also powered by the same 7V_Main voltage as Q4901 & Q4902.
If I measure this transistor, my meter does not show anything. There are some 10k Ohm bias resistors in it, and maybe because of that? That would be normal?
I'm wondering, why those two 22 Ohm resistors (R4905 and R4906) get that hot(bubbled up the PCB!!)? At the C4903 and C4904, I measure something like 345k Ohm, between the common and + & -.
Todd, I would like to figure out this smoking issue first, before I proceed with the MPU.
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Post by tjmotter on Nov 24, 2018 17:54:22 GMT -5
That is not good. Q4142 is an opamp which means it is powered by the +12V and -12V lines. That could cause some serious damage.
You should always change out components that look like they have been burnt, even if they seem to test ok. I recently repaired an NR636 that had a weird fault. It would shut down immediately after startup but it wouldn't post an error. All main transistors were ok and the Tx0004 pair were all good. In fact, every transistor in the pre-amp tested good but I found that a 100K ohm resistor was showing 50K ohms (all other channels showed 100K). When I removed the resistor, it tested good and what I eventually found was that C5011 (47uF/50V capacitor) was flaky. It is used simply as a DC filter on the input and when power was applied to the system, it would short causing damage to Q5031, Q5520 and Q5530. They would all test ok out of circuit but all were bad. I missed Q5520/Q5530 at first and while the amp worked, it would emit crackling sounds out of the speaker. Once I changed all 3 transistors and the capacitors, all was good.
You should check pins 92 and 91 of that Main Volume chip (Q4001) to see if either is shorted. If they are, I would first remove Q4901-Q4904 and test them again. If they are still shorted, that Main Volume chip is bad. I have seen this before on a different NR636 that was hit by lightning. That chip can usually handle a lot of abuse but it is pretty exposed to a strong power surge.
As bad as it looks, chard resistors they still show their proper value(22 Ohm both of them), which is interesting. Transistors Q4901-Q4902 show .5-.6V each way, which is not OK, but out of the circuit, they look OK. SMD transistors Q4903-Q4904 show OK, after I have removed the other two transistors. What I have noticed, is the Q4142 has a bulge in the middle. Q4001 pin #91 and #92 do not show short, ~250 KOhm. It seems like this IC is not shorted, right?   |
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Post by tjmotter on Nov 24, 2018 17:56:08 GMT -5
I have noticed, that Q4691(KRA102S), is also powered by the same 7V_Main voltage as Q4901 & Q4902. If I measure this transistor, my meter does not show anything. There are some 10k Ohm bias resistors in it, and maybe because of that? That would be normal? I'm wondering, why those two 22 Ohm resistors (R4905 and R4906) get that hot(bubbled up the PCB!!)? At the C4903 and C4904, I measure something like 345k Ohm, between the common and + & -. Todd, I would like to figure out this smoking issue first, before I proceed with the MPU. Those are hard to test but they are cheap so if I had any concerns, I would just change it out. |
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Post by tibimakai on Nov 25, 2018 0:03:39 GMT -5
I will have to test the two filtering capacitors, C4903 and C 4904, they show something like 450uF and 560uF(in circuit). The resistance, at those points(pin #91 and 92 of Q4001), once showed 256 kOhm, yesterday was showing 345 kOhm.
I will place an order on Digikey for those 22 Ohm resistors and NJM4580 IC. Q4691(KRA102S) is not available, but it is definitely not shorted.
If Q4142 is shot, why the +/-7V supply is burning out?
I was thinking to replace the burned/blow parts, and apply +/-12V to the circuit, to see what is happening. Without installing the board.
Do you think, that is a good idea?
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Post by tjmotter on Nov 25, 2018 8:14:53 GMT -5
The KRA102S cross references (in the NR616 manual) to an RN2402 which is still available at Mouser (Digikey has discontinued it).
Not sure I would want to apply external voltage to it but I would definitely check the two voltage regulators (Q9202/Q9203), the diodes around them (D9203/D9204) and the two caps (C9204/C9205) to determine if they are damaged. The +/-7V signal is generated from the +12/-12V regulators so something hit this part of the circuit pretty hard. If you find an issue in the 12 volt regulator section it will explain why the 7 volt rails aren't working properly. You should also consider replacing those two zener diodes (D4901/D4902). They may test correctly as a diode but there is no easy way to determine if the zener breakdown voltage function is still working to spec.
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Post by tjmotter on Nov 25, 2018 12:49:16 GMT -5
Just to be clear, the resistance between pin 91 and pin 92 isn't important. What is important is the resistance of Pin 91 to ground and the resistance of Pin 92 to ground The resistance, at those points(pin #91 and 92 of Q4001), once showed 256 kOhm, yesterday was showing 345 kOhm. |
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Post by tibimakai on Nov 25, 2018 15:09:42 GMT -5
I will have to check those 12v regulators, you are right. I remember that, when everything was still together, some heat was coming from down there, where the 12V regulators are installed. Their heatsink was quite warm.
I have tested the resistance to ground, not between them.
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Post by tibimakai on Nov 26, 2018 0:58:06 GMT -5
I can't find those two diodes, near the Q9202/Q9203 combo. The two regulators do not show any short, though I don't know, how exactly they should show. Some of the legs start up beeping, from minus values and they go over into plus values. That is normal? Tomorrow, I will remove the two capacitors that you have mentioned and also the 7V capacitors as well. I will add to the list he two zeners as well.
I have sent an Email to Digikey, to point me to an alternative to that KRA102S/RN2402(thanks for that) transistor. Hopefully, they will have something.
After I will replace all these parts, I will solder a few wires, to the +/-12V and +/-7V outputs, to be able to measure them, when everything is put back together.
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Post by tibimakai on Nov 27, 2018 22:00:42 GMT -5
I have found D9203/D9204 and they check out OK. Also the two capacitors C9204/C9205 are OK as well. C9204-C9205 are OK as well.
C4903-C4904 (output of 7V) are OK as well. I'm placing the order, at Digikey.
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Post by tibimakai on Dec 9, 2018 17:39:17 GMT -5
I have replaced the two 22Ohm resistors R4905/R4906, D4901/D4902 zeners and Q4142.
I have soldered three wires, to that +7V/GND/-7V output and I'm getting only +0.43V/-0.43V.
I should have soldered wires, to the 12V inputs as well. Now, I will have to take it apart again.
I just hope, that something(Q4001) is not pulling down these voltages.
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Post by tibimakai on Dec 9, 2018 17:42:23 GMT -5
Resistance, between the +7V to common ground is 476Kohm and at -7V to common ground, is 4.8Kohm. That is normal?
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Post by tibimakai on Dec 9, 2018 17:50:18 GMT -5
Managed to reach down there, where the two 12V regulators are( Q9203 and Q9202) and they definitely supply the voltages. Though, the +12V supply, only shows 11.7V.
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Post by tibimakai on Dec 9, 2018 18:17:31 GMT -5
But, it makes the right sounds, without display of course. Even when, I have reset it(CBL/On) it seemed like, it did it.
The +7/-7V is pulled down, at least that is what I seems like. If the Q4001 is bad, I will have to look for another Onkyo, to get that part out of it.
The cheapest would be, a broken TX-NR545.
What else I have noticed, that the Q8000 HDMI IC(HDMI OUT), is getting quite warm. That is normal? The 5V, at pin #18 is there.
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Post by tibimakai on Dec 10, 2018 23:59:37 GMT -5
Ok, I'm an idiot and missed two transistors, Q4903 and Q4904. Forgot to soldered them back in.
After I have soldered them in, the two resistors R4905/R4906, smoked out again.
I have also measured pin #91 and 92 using pin #90 as ground. The resistance, at both pins shows 1.4Mohm.
That means, that Q4001 is not shorted?
After replacing the two resistors, I have assembled everything and using two meters at +7V/GND/-7V (ran wires to the top), the voltages are not going right to +/-7V, it starts building up, from around +2.4V/-2.4V, but I have unplugged it quickly at this stage.
I have to confess, that I have found a solder blob between, two joints and I assumed, that blob must of caused the smoke, but it seems like, it wasn't the case.
Should I cut the traces, that lead to pin #91/92, of the Q4001, to exclude that IC?
When I measure the pair of transistors, at this 12V to 7V power supply, they all show weirdly, like they conduct each way. They show 0.5V, 1.2V. But out of the circuit, they measure as they are good.
Q4142 does not appear to be damaged. There is no short, between pins #4 and #8.
I need help here. Could anybody help? I would appreciate it a lot.
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