[Jmitchell3]

I am a newbie to DIY audio! I purchased these monoblocks that were already built 5+ years ago and theyve operated flawlessly until now. A few days ago in my home theater the left monoblock’s blue status light in the front was slowly pulsing, and the connected speaker produced no sound. The right channel block had a solid blue status light and appeared to be ok.

Fast forward i let each block sit disconnected from power and source and speakers overnight then opened them up and swapped the psu boards (smps600v3) and plugged everything in again and now neither blue light illuminates on either device.

I do have a background in building my own computers so im used to and comfortable with working with circuit boards and etc.

Any ideas what could be wrong or what next steps i should take to continue troubleshooting? Please see attached images.

[Doublej]

I would put the PSU boards back in their original positions and see if the right channel block comes back to life. If it does, it would seem to me that you have a failure in the left PSU board and a second failure in the left amplifier board.

[Norman Tracy]

Hi Jmitchell3,

Troubleshooting goes better when one has the manuals.

Power supply: https://www.hypex.nl/media/76/68/ec/1687255443/SMPS600N400_06xx.pdf

NCore NC400 amp board: https://www.hypex.nl/media/85/b5/1c/1646058855/NC400_04xx.pdf

You say you are new to DIY. Be very careful when amps are open and connected to the AC mains the power supply board has 120 or 220 VAC and +-65 VDC present. These voltages are high enough to be dangerous. If you are experienced and comfortable using a multi-meter to check voltages on the live amp that is the next step. If you are too new to electronics troubleshooting to safely proceed take units to a repair shop along with the above documentation.

We all debug modern electronics by swapping modules as you describe. Unfortunately the sequence of events you describe where the right unit failed after the left's power supply was installed could indicate that left power supply has a failure that is damaging the amp modules. As Doublej suggested returning power supply modules to their original units can check that. Hopefully the right amp comes back on.

Looking at the SMPS600 manual we see it outputs four DC voltages. A positive and negative Vaux voltages approximately 17 VDC powering the input and driver circuits. And HV+ and HV- at 65 VDC powering the output stage. Checking those four voltages is the next step in diagnosing the problem. Reading the voltages note this information on page 5 'Note 1' of the PS manual:

Output voltage is proportional to the mains line voltage and load at output. (Min@180Vac, Typical@230Vac, Max@264Vac measured at 0 load). The typical value is not absolute but various over production with 10%

[Jmitchell3]

Yep. Let them sit overnight unplugged to discharge the caps.

[thirdeye]

I don't know, but this looks pretty bad, I would put these speaker wires to the outside of the terminals to get them apart if possible, you look to have exposed wire between the 2 terminals and possibly one strand is shorting out the other not allowing power due to a fault protection or something shorting your speaker cables out. Either way those are so tight together I would separate them and put them in the terminal from the outside on both.

And there are fuses in the unit as seen in photos, I would check them with a multimeter and see if they still have continuity or you need fuses. Which could have blown if those terminals in photos are actually shorting out.

[poseidonsvoice]

Thirdeye,

Agreed. Due to persistent pressure over the years, it almost looks like the red wire has slowly slipped out and if a short is there, then the fault protection will trip immediately in the NCore design.

Sadly, I will have to say that this is a poor, unreliable connection and the wires should be reterminated with ring terminals for a more reliable connection. Safety and reliability is first, transparency is second. Recall that this is being used in an HT setup.

A quick and safe way to check this with the amplifier off and unplugged from the AC mains is to plug a digital multimeter into the output binding posts and set it to ohms. If there is a short, you’ll hear a beep or read “0” ohms.

Best,
Anand.