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Post by markuss on Dec 2, 2022 13:01:47 GMT -5
Hello! I received this receiver for repair and the guy says that there is no rush for fixing the unit, so good for me  . He also understands that I am a hobbyist, so it's possible I will return the unit dead as it was, as I am not a professional repair specialist and this is my first time working on such audio equipment. Problem is he says the unit is totally dead, which it is. Plugging the cord in the wall shows nothing and pressing the power button also does nothing. By examining the unit and some videos online I believe that there should have been a relay click, which I hear none when pressing the power button. So I went further to take out my multimeter and checking basic voltages, like the standby voltage which is +5V. I traced the standby voltage through the unit and I stumbled on that the 5V kept dropping at the connection, where power button board connects to front display assembly. Later I realized that this line where the +5V drops to 0V and back to +5V is actually for the standby LED, which is not populated by the manufacturer, so that helps just a little and shows that the unit is not totally dead. So I assume that this would mean in reality that the standby LED would be flashing, which usually in computer terms means that the unit detected a problem and won't proceed to power on. At that point I realized I am out of ideas where to proceed and I give up to continue troubleshooting myself. By reading this forum I see all of you are very knowledgeable and maybe can offer any tip, where to look. I will really appreciate any help I could get!
Greetings!
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Post by mastertech on Dec 3, 2022 11:39:14 GMT -5
You may want to read pages 81 through 85 of that service manual and do a few tests to verify it is not in protection mode. Plus, if you think that led should be blinking look into that also.
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Post by markuss on Dec 4, 2022 7:14:18 GMT -5
Good news, I believe  I didn't notice before that the manual has, as you said check out pages 81 to 85. On page 83 there is section DC-abnormality detection. There is a line which says "When power off, push FRONT ENTER key + AUTO SURR/DIRECT key continuously 2sec." I pressed these buttons, the unit indeed came on, relay clicked, fan started to spin and the error AMP_ERR appeared on the screen for around 2 seconds and everything turned off again. So the unit is indeed in this protection mode. Atleast I am happy that the unit responds to this key combination sequence. Any idea, where to proceed from now on? On page 81 there is a diagram for the DC detection circuit, so I can test that.
Edit: DC-abnormality section also mentions that if this fault is detected, then Power on key will not respond and Power LED will blink, so the unit actually was telling me about a problem!
Edit 2: I gave the circuit a look and I didn't understand how to test these two STK power amplifier ICs. One is a STK412-530 and other one is STK413-530. It's possible they are bad and it's possible they are good, problem is I don't know from which pin I should test for a fault.
Edit 3: I was reading around online and I found this comment from tomsguide.com forums. This comment is not for my unit, it's for a Pioneer VSX-514K unit, but I believe this comment should apply as I also have these large white resistors.
I did just that, negative terminal on ground of the chassis and positive multimeter terminal on the large white resistor. When I pressed FRONT ENTER key + AUTO SURR/DIRECT key and measured from the resistors, I got +40V DC. Should this be happening?
Greetings!
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Post by mastertech on Dec 4, 2022 18:31:52 GMT -5
You need to give part location id number for us to know where you are testing. Large white resistor is not sufficient.
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Post by markuss on Dec 4, 2022 19:31:30 GMT -5
Resistors I was measuring were R668, R622, R785, R617. They are rated for 5W, 0.22 ohms. That was all I really measured so far.
It's possible those values are as they should be and I could be wrong, but atleast the unit is telling that there is a problem in the amplifier somewhere. There is page 85 of diagnosing the amplifier, which I probably should focus on instead, but I don't understand where to check everything. For example
1) Are there any Fuses and IC protectors open?
I'm only aware of the power supply fuse and that tests good. I don't know where I should these IC protectors on the board.
2) After turn on the power, confirm that the supply voltage of the point that can be measured is appropriate.
I don't know where are these voltages, only measurements I took was the 5V standby and that looks like it works. 3) Whether the voltage of pin2 and pin5 of IC601, IC602 or IC603 is equal to (VL-0.7V). If not (eg, equal to VH),
then change the corresponding power pack IC601, IC602 or IC603.
I believe at these exact pins I tested above 0.7V on every power pack IC. I can take exact measurements tomorrow, if that helps. If it helps I can take measurements for every pin on the power pack IC and update my post tomorrow. 4) Furthermore, check the output DC voltage of each channel of power pack IC601, IC602 and IC603
to limit the failure channel and identify the defect power pack.
I don't know what voltages I'm expecting here, so I didn't measure these pins, but if the troubleshooting suggests to do this step, then I probably should. Again if it helps to understand, I can post every measurement for every pin on those STK ICs. • After identify the failure channel, check that each part is not damaged (resistor, diode... etc. value / open /
short)
This step probably is done once the STK ICs are replaced, if I understand this statement correctly.
So as a reminder, I discovered that the unit has entered DC-abnormality detection mode by pressing the Enter and Auto Surr/Direct buttons together. It showed on the display AMP_ERR.
Greetings!
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Post by mastertech on Dec 5, 2022 11:02:16 GMT -5
There is a high likely hood that 1 or both STK's are bad. They are real common to fail. You can spend a good amount of time testing to verify their condition but I have found it is easier to just remove one and see if the unit starts and runs normal and if not remove the other and check startup again. If normal startup occurs you would then need to test surrounding components before installing new STK's.
The bigger problem may end up being trying to find good new replacements. Most are knockoffs. Best option would be finding new old stock but most suppliers that claim they are, are actually not. But, you have no other choice but to try what you can get.
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Post by markuss on Dec 5, 2022 16:19:41 GMT -5
You are spot on correct. Just finished spending an hour de soldering both of the STKs and once I pressed ENTER key + AUTO SURR/DIRECT key, the unit has come back to life. Now the power button responds also.
Well here is the problem then, one or both STK ICs are dead. Also you are correct about the originals not existing anymore, yesterday I found similar comments on forums saying that those STK ICs are no longer manufactured for a long time and now it's mainly cheap copies. I will recommend the guy a replacement unit, as I found out the same model used for around 40-50 euros which are working. My repair will be more expensive, than for him to buy a working used unit or maybe even better quality one, without the STK's. Anyways thank you so much for the help and I learned something new in process of trying to repair this receiver.
Greetings!
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Post by mastertech on Dec 5, 2022 18:22:56 GMT -5
No problem. |
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. He also understands that I am a hobbyist, so it's possible I will return the unit dead as it was, as I am not a professional repair specialist and this is my first time working on such audio equipment. Problem is he says the unit is totally dead, which it is. Plugging the cord in the wall shows nothing and pressing the power button also does nothing. By examining the unit and some videos online I believe that there should have been a relay click, which I hear none when pressing the power button. So I went further to take out my multimeter and checking basic voltages, like the standby voltage which is +5V. I traced the standby voltage through the unit and I stumbled on that the 5V kept dropping at the connection, where power button board connects to front display assembly. Later I realized that this line where the +5V drops to 0V and back to +5V is actually for the standby LED, which is not populated by the manufacturer, so that helps just a little and shows that the unit is not totally dead. So I assume that this would mean in reality that the standby LED would be flashing, which usually in computer terms means that the unit detected a problem and won't proceed to power on. At that point I realized I am out of ideas where to proceed and I give up to continue troubleshooting myself. By reading this forum I see all of you are very knowledgeable and maybe can offer any tip, where to look. I will really appreciate any help I could get!
