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YAY! So, as suspected, Hypex did NOT test with any load? Disappointing...After having read @phoenixdogfan Purifi amplifier plight and sympathizing with the expense of shipping modules back and forth to Europe, I PM'd him and offered to help. I got the amp about 2 weeks ago and have been working with Hypex on it.
Initially I thought that it was a standby signal issue as the power supply would not hold maintain any voltage long enough to do much. After disconnecting the cables to the amp module, found the power supply would stay on. I checked the cabling and it was fine. However, as soon as any load was applied to the AUX power pins, it would shutdown. At this point as the power supply behavior was questionable, I contacted Hypex. Their previous repair was to the AUX power protection circuits and they shared some details with me. As mentioned, the SMPS was still in-warranty and so I was not tempted to do much, but they encouraged me to do some troubleshooting. Here is what I found that I thought might be useful to share...
R92 and R99 were open. These are 1 ohm SM resistors that are part of the SMPS AUX power protection circuit and are mounted on the bottom side of the board. As a quick test, shorted them out and the power supply started to behave normally. I hooked it back up to the amp and did a quick test on my QA401 and things were looking brighter.
I ordered some replacement resistors from Mouser and they arrived earlier this week. I got around to soldering them in and started re-assembling the amp to see if anything caused them to blow. The bad news is I did not find anything; the good news is that it continues to work! I have tested on my QA401 and did a quick listening test and all is well. Am packing it up today and preparing to ship it back to its owner.
Here is a pic of the amp with the LED shining just as @phoenixdogfan was hoping he would get to see someday…
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