Help With Audio Upgrade Board

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This topic contains 7 replies, has 3 voices, and was last updated by  samson7point1 9 months, 2 weeks ago.

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    I have a 1.5 OSSC and purchased an audio upgrade board for it some time ago. I installed the board following the linked instructions and when I reassembled everything and applied the firmware update there was still no audio coming out of my DVI-HDMI cable.

    When I disassembled the OSSC again to check my work, I realized I had missed step 1 – cutting the three traces.

    So I removed the board, cut the traces, reinstalled the upgrade board and tried again, but with the same result. The OSSC showed it had the -aud firmware installed. I reinstalled it anyway, and also reset all of my saved settings. I still get audio from the analog port, but nothing from the DVI-HDMI port. I tried plugging the HDMI end directly into three different televisions and my audio receiver – and each time I got a picture but no audio.

    Today I finally got around to cracking it open again to see what’s going on. I figured the most likely scenario was that I hadn’t managed to fully cut the traces so I desoldered the upgrade chip and scraped between them until they were definitely cut – I used a multi-meter to verify there was no continuity between the two sides any longer. In the process of cutting, there was still a dab of solder on the I2S pad and caught it with the blade and tore the pad off of the PCB so I ended up having to wire that connection directly to the appropriate pin on the IT6613, but I’ve double and triple-checked continuity and everything is connected solidly and according to the instructions. I’m still not getting any sound from the DVI-HDMI port.

    Is there anything I can do to validate the upgrade board isn’t bad or damaged somehow? Do I need to use a special type/brand of DVI-HDMI cable? Any help or suggestions would be welcome.



    No special cable is needed. Make sure TX mode is set to HDMI not DVI.



    I checked that and it was apparently set to that by default. Just for good measure I switched it between DVI and HDMI a couple of times but it didn’t make any difference.



    Is there any kind of debug firmware or menu that I can use to verify that the audio board is working? Is there some point on the board I can test with a multi-meter to confirm whether or not it’s dead? What’s the next step here?



    A multimeter won’t get you very far. You can only use it to measure if the upgrade board gets all the correct input voltages (3.3V & 5V) from the AP7361C voltage regulator and supplies them to its ICs… and you can use it to check for continuity problems because of broken traces.
    Some multimeters may have the ability to measure the capacitance of capacitors – but it won’t work 100% error free, while the capacitor is a soldered-in part of a circuit.

    I may be wrong, but i would say: you need an oscilloscope to see if your audio upgrade board outputs a signal…



    With my limited understanding of how this board works, I realize this might be an ignorant question, but doesn’t the fact that I still get analog audio after cutting that trace mean that at least that part of the signal is going through the board?



    No. Those three traces you are cutting are all originally connected to ground (since they are for the I²S digital audio data and clock input of the HDMI transmitter IC, which isn’t used without the upgrade board -> so the input pins are grounded… to avoid digital noise, i guess). While cutting the traces and installing the upgrade board (by soldering it to the digital audio input pins of the HDMI transmitter AND to the analog audio input pins of the SCART connector ← i hope you did the last part too), you are connecting the HDMI transmitter to the analog-to-digital converter IC of the upgrade board, which takes the analog audio from the SCART input, converts it to digital data and feeds the data into the HDMI transmitter IC.

    However the analog audio pins of the SCART input are directly(!) connected to the 3.5mm audio output jack of your OSSC 1.5 too. And those directly connected traces aren’t cut or modified while installing the audio upgrade, since it’s simply not necessary.

    Or to put everything in a simple diagram:


    Long story short:
    Having the analog audio output working after installing the audio upgrade board sadly proves nothing. But it may be helpful, if you post a picture of your installed upgrade board. It could be you simply forgot to connect something or connected something wrong…



    Morpheus_79, thank you so much, that was just the information I needed to spot the gap in my understanding – everything is working perfectly now!

    I tested continuity to the SCART conductors _before_ I removed the board and never re-tested them because I thought getting analog audio confirmed that they were connected. The process of removing the board weakened two of the wires (I really am going to stop using 30 AWG wrapping wire for stuff like this). When I went in to take pictures of the board and re-test continuity I found that the solder joints were fine but the wires had weakened on the ends, broken loose and were just loosely resting against the SCART conductors.

    So the first mistake I made was not fully cutting those traces (because I eyeballed it instead of checking continuity) and the second was not re-testing continuity of all of the other connections AFTER reassembly.

    What’s ironic is that I should have known better about the analog audio thing. I don’t know jack about electrical engineering so portions of it still seem like black magic to me, but in hindsight this was obvious. I had to refer to the 1.5 PCB diagram to figure out which pin on the IT6613 was the I2S so I could bypass the lifted pad, and I saw that all three of those traces were put to ground, but I didn’t realize what I was looking at until you said something.

    Again, thanks for your advise, it was exactly what I needed!

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