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[Solved] Onkyo TX-SR602E No Power, Standby Light Off, CPU VCC 4.7V, Standby 10V Present

_car123 1188 14
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  • #1 21545002
    _car123
    Level 2  
    Hello I have a Onkyo TX-SR602E (European model) that will not show any signs of life the standby light doesn't light up. I have checked all the fuses and they are fine.



    Here's what I have checked

    When plugged in:
    CPU VCC reads 4.7V at the firmware writing port (P701)
    Display gets 5.5V

    When unplugged:
    CPU voltage drops to 3V

    I think the CPU has a problem or the firmware is corrupted.


    Background:

    The last time I used the receiver was in 2022, and it worked fine.
    It was stored in the basement for 2 years.
    Before it went to the basement a factory reset was done.
    I’ve replaced the super capacitor (C704).
    I have the service manual for the receiver and the PDF for the Renesas M16C/62P (CPU).


    Any help is very appreciated.
    AI: When you plug in the receiver, do you hear any clicks from the main power relay or any other relays, or is it completely silent?
    completely silent
    AI: Have you checked for the presence of other voltages from the power supply, such as the main transformer secondary outputs or standby supply rails, and if so, what are their readings?
    standby voltage is present 10 volts from the Transformer that is for standby power
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  • Helpful post
    #2 21545530
    Jarek Pi.
    Level 27  
    Capacitors like to stop working when not in use. C704 too. If a long switch-on doesn't help, you'll have to check.
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  • #3 21546104
    _car123
    Level 2  
    Thank you for answering.
    The U2 board is getting 5.5V, but when I measure the CPU VCC at the firmware writing port (P701), I only get 4.7V. I suspect some capacitors on the CPU board are failing.

    I've already replaced C704, and I plan to order replacement capacitors for C725, C729, C727, C702, C703, and C701.

    I left the unit plugged in for 45 minutes, and the maximum voltage I saw was 4.94V — still no signs of life.
  • #4 21547491
    Elektromonterek
    Level 25  
    Check you have voltage on the LEDSTBY on the front and the standby button and others - K0-K3 Does anything go when pressing the remote on REMIN? You wrote that 5.5V is there so there should be changes. If so, then the proxy is not working. Maybe the internal soft went down, maybe the resonator at it is not working so to check. Stoking them due to lying around is rather unlikely. The voltage on these models has probably never reached 5.6V, and it should be 5 at the proc, so you are making unnecessary fiddling. Also check Reset, Poff, sysin, sysout.
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  • #5 21548469
    _car123
    Level 2  
    Hello, the receiver does not respond to the remote or to any button presses. Tomorrow, I will check the K0–K3 lines. I don't have an oscilloscope to test the oscillator.

    When you say to check Reset, Poff, sysin, and sysout— should I check whether those lines are high or low?

    Also, can I use an FT232 USB UART board to test the CPU through P702?
  • #6 21550080
    _car123
    Level 2  
    The K lines seem to be working fine. I connected a multimeter between ground and the K line, and when I press a button, the resistance changes — so it looks like it's functioning correctly.

    Added after 2 [hours] 56 [minutes]:

    I changed C725, C729, C727, C702, C703, and C701. Now it gets to 4.94V quicker, but still nothing.
  • Helpful post
    #7 21550448
    Elektromonterek
    Level 25  
    You will find a description of what the leg states should be in the service manual. POFF is a power supply fault detection and this can block the possibility of startup. LEDSTBY you have not checked. There is power at all on the remote sensor. It's right next to the standby LED.
    I'm betting on a lockout though since the buttons have voltage, as it's rather given by the processor. I don't see any pull-ups to the external ones.
  • #8 21551142
    _car123
    Level 2  
    I think the POFF line is OK.

    According to the service manual:

    A table excerpt showing the POFF (Power failure detection input terminal) row for pin P83/~INT1.

    Close-up of a printed circuit board section with labeled voltages on wire connections.

    The remote sensor is getting 4.9V, so it seems to be powered correctly.
  • Helpful post
    #9 21551288
    Elektromonterek
    Level 25  
    Well, but in the service manual you have that it is active low, and you have a measurement of 0.57V so it should hardly be taken as ok. Here I think the procec itself puts out 5V or 3.3v depending on what it is powered by and if it drops to 0, it is active, i.e. blocking from starting. Do you have 13V there at all from the standby power supply? Prock faults are more likely to be caused by overvoltage only, and here a lot of things are fed correctly, so there was probably e.g. a rise in mains voltage and it burned the zeners which are supposed to lower this signal from the power supply. Alternatively, someone may have been messing around and put the wrong standby trafo, which I have also encountered. At d704 the voltage should be around 5.1V, as this is the value of the diode.
    P. S. You put cole and sticks if this fault is so trivial 🤣.
  • #10 21551396
    _car123
    Level 2  
    No one has worked on this receiver except me, which is why I'm confused — before I put it into storage, it was working perfectly. But now, after taking it out, it doesn’t power on at all.

    When you say "13V", do you mean on the connector shown in the picture? I’ll check it tomorrow.
    Diagram of connector P354 with 14 pins and their functions labeled.

    I’ll also check D704 tomorrow.

    One question: during testing, I don’t have the video board, tuner board, or U3 board connected. Could this prevent it from going into standby? I don’t think so,

    Really hoping this turns out to be something simple.
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  • #11 21551695
    _car123
    Level 2  
    When I plug in the receiver (before pressing the power switch), the voltage on P354 on 13S is about 1.2V.
    After pressing the power switch, the voltage remains the same — still 1.2V.

    On D704 I'm measuring 0V.


    Close-up of a PCB section with label D704, a wire, and a 0V note at an electronic component.

    Added after 44 [minutes]:

    11 V get to P6931

    Added after 8 [minutes]:

    I didn't think I would say that ever but I'm happy that I found corrosion on a trace
    between P6931 and P354

    Added after 17 [minutes]:

    I will fix the trace and let you know what happened
  • Helpful post
    #12 21551773
    Elektromonterek
    Level 25  
    The 10vs go to the 13s, which means you have broken paths or connectivity somewhere, as it must be at the diodes, as 5v to the prock is also made from this. The pins connect on one of the boards. Check that you don't have these diodes shorted. A lot of tape, so maybe badly assembled. It doesn't go through the boards mentioned, from what I've looked at, so I don't think they necessarily have to, but often the grounds have to be connected in the ampli.
  • #13 21551800
    _car123
    Level 2  
    >>21551773
    the problem was a corroded trace on the U1 board

    Added after 3 [minutes]:

    that was the issue, then it powered on — thank you so much!
    This receiver means a lot to me, and I really appreciate all your help.



    Unfortunately, I still have to fix another issue on the video board, but I’ll take care of that.
    Two broken pieces of green printed circuit board (PCB) with connectors and electronic components on a wooden surface.

    thank you again.
  • #14 21552009
    Elektromonterek
    Level 25  
    _car123 wrote:
    >>21551773 .
    the problem was a corroded track on board U1

    Added after 3 [minutes]: .

    that was the problem, then it turned on


    Corroded where? Didn't it continue to give that voltage? You're asking for help, then at least give an answer so that it's clear what the cause was, rather than guessing. You should give pics of this corrosion along with the markings so that it is clear, not pics of the video board broken when it was dismantled.
  • #15 21552312
    _car123
    Level 2  
    The problem was a corroded trace on the U1 board.

    The damaged trace was between P6931B and P354A, located near some capacitors that likely leaked.

    A section of an electronic schematic with yellow-marked connections between connectors P354A and P801B.


    A circuit board fragment with capacitors, resistors, and a white connector visible.
    Mainboard of an electronic device with highlighted connectors P354A and P691B, and a corroded trace marked.

    A section of a PCB diagram with capacitor C002 highlighted in yellow.

    The 13S pin wasn’t getting any voltage to the CPU, so the power failure detector was active, preventing the CPU from starting.

    After fixing the trace, the receiver is now working fine.
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Topic summary

✨ A Onkyo TX-SR602E receiver failed to power on with no standby light and no response to remote or buttons. Initial checks confirmed all fuses intact, CPU VCC voltage at 4.7V (below expected 5V), and display voltage at 5.5V. Multiple capacitors on the CPU board were replaced, improving voltage slightly but not restoring function. Diagnostic steps included verifying standby LED voltage, remote sensor power, and control line (K0-K3) functionality, all indicating proper signals. Measurements revealed low voltage on the POFF line and absence of expected 13V supply at the CPU power input (pin 13S). Further inspection uncovered corrosion on a trace between connectors P6931B and P354A on the U1 board, likely caused by capacitor leakage. Repairing the corroded trace restored proper voltage to the CPU and resolved the power-on issue. The receiver powered on successfully afterward, though a separate video board issue remained to be addressed.
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FAQ

TL;DR: For Onkyo TX-SR602E no-standby, check D704 (~5.1 V) and remember "POFF is active low." If POFF is asserted, inspect the 13S path and protection parts. [Elektroda, Elektromonterek, post #21551288]

Why it matters: This FAQ helps Onkyo TX-SR602E owners quickly isolate 13S/POFF faults so the receiver powers up.

Quick Facts

How do I fix an Onkyo TX-SR602E that shows no power and no standby LED?

Start at the 13S standby rail. In the documented case, 13S never reached the CPU because a corroded trace between P6931B and P354A was open. Bridge or repair that trace and clean any capacitor leakage. The CPU then exits POFF and the receiver powers up normally. "The 13S pin wasn’t getting any voltage to the CPU, so the power failure detector was active." [Elektroda, _car123, post #21552312]

What does POFF mean on this receiver, and how do I test it?

POFF is the power-fault detect line into the MCU. It is active-low, so a low level blocks startup. Measure POFF and the related protection points: D704 should sit near 5.1 V. If POFF reads low (e.g., ~0.57 V), find why the protection rail is sagging. Edge case: wrong standby transformer or burnt zeners can force POFF low. "POFF is active low." [Elektroda, Elektromonterek, post #21551288]

Where should I measure the standby 13S rail, and what readings flag a fault?

Probe P354 on the 13S net. In a failure example, P354 read ~1.2 V even though the transformer feed at P6931 was ~11 V, and D704 was 0 V. That disparity pointed to an open trace between P6931 and P354, later confirmed as corrosion. Repairing continuity restored proper standby distribution. [Elektroda, _car123, post #21551695]

Is 4.94 V on CPU VCC at P701 enough for the MCU to boot?

Yes, that’s close to nominal, but the MCU still won’t boot if POFF is asserted or the clock is down. The expert guidance here: focus on protection lines, reset, and the oscillator first rather than recapping blindly. "It should be 5 at the proc." [Elektroda, Elektromonterek, post #21547491]

How do I verify the front-panel keys and IR remote input quickly?

Check LEDSTBY voltage on the front PCB. Then verify the K0–K3 key lines change state when buttons are pressed. Test the IR path by pressing the remote and watching REMIN. If these lines have the expected pull-ups and toggle, the CPU is likely powered but held by protection. Also check Reset, POFF, SYSIN, and SYSOUT. [Elektroda, Elektromonterek, post #21547491]

Can I use an FT232 USB‑UART on P702 to test or reflash the CPU?

Only if P702 exposes the M16C/62P’s UART at TTL levels and the board is placed in serial boot mode. Use a 5 V‑logic USB‑UART and connect TXD/RXD/GND as per the MCU’s serial interface. Enter the device’s boot mode per the manual before attempting flash access. Always confirm the pinout from the service manual first. [Renesas M16C/62P Hardware Manual]

Do I need the video, tuner, or U3 boards connected for standby to work?

No. The 13S/10VS path does not route through those boards on this model. However, ensure that common grounds are properly connected during testing, or measurements may mislead. "It doesn't go through the boards mentioned." [Elektroda, Elektromonterek, post #21551773]

Does leaving the unit plugged in help re-form capacitors?

It can raise rails slightly, but it won’t fix an open 13S path. In this case, leaving the unit on for 45 minutes only lifted CPU VCC to about 4.94 V, with no start-up. That pointed to a distribution or protection issue, not simple cap re-forming. [Elektroda, _car123, post #21546104]

Where do I probe CPU VCC on the TX‑SR602E?

Measure at the firmware writing header P701 on the CPU board. In the reported case, CPU VCC read about 4.7 V there with standby present and the display at ~5.5 V, yet the unit stayed off. That guided attention to POFF and 13S delivery. [Elektroda, _car123, post #21545002]

What should D704 read, and what if it’s at 0 V?

Expect around 5.1 V at D704, matching its zener value. If you see 0 V, the protection rail is not being established. Investigate the 13S source path, series components, and associated zeners. A low here holds POFF active and prevents the CPU from starting. [Elektroda, Elektromonterek, post #21551288]

Quick 3‑step: How do I trace the 13S feed from transformer to CPU?

  1. Measure the standby transformer output at P6931; confirm presence.
  2. Check P354 (13S) for proper voltage; compare with P6931.
  3. If P6931 has voltage but P354 is low, inspect and repair the trace between P6931B and P354A, cleaning any leaked electrolyte. [Elektroda, _car123, post #21552312]

What edge cases can still block startup after 13S is restored?

A failed resonator can stop the CPU clock. Burnt zeners on the protection network can clamp rails and assert POFF. In rare cases, an incorrect standby transformer was installed, overdriving the protection circuit. These conditions keep POFF low and the unit off. Verify the clock and protection components before suspecting firmware. [Elektroda, Elektromonterek, post #21551288]
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