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Now, when both speakers and the front LED are disconnected we can start to remove the rear panel.
First remove the 10 screws on the rear panel.
The rear panel can now be lifted straight away from the cabinet.
A closer look of the inside parts.
AC inlet PCB
Amplifier PCB with heatsink
Bass reflex port.
We will focus on the amplifier PCB, where the voltage regulators are located.
PCB layout. The faulty voltage regulator, U2 in my case, is marked with RED.
It's very convenient to measure the voltage levels on the bottom side of the PCB at connector CN602, marked with BLUE, or on the Inout PCB at connector CB101.
A closer look at the voltage regulators placement on the amplifier board. The actual regulators are not visible in this picture, since thay are attached on the two aluminum heat sinks to the right side in the picture.
To be able to measure anything we need to connect the AC cable.
WARNING The 110/230 VAC is exposed and be very carefull not to touch anywhere on the AC inlet board or on the trafo.
Also be careful not to short the speaker cables. To be safe you can temporarily connect the speakers at this time if you want.
There is only -4,5 VDC on the output of the U2 regulator. Typical value should be -15 VDC. This one is indeed need of a replacement.
The other regulator (U1) is working properly. There is +15 VDC on the output.
Now we know what is wrong, and we can disconnect the AC power cord.
In order to replace the the U2 regulator some more disassembly is required. We need to remove the amplifier PCB and heatsink from the rear panel.
Remove the 5 screws on the rear panel.
We need to remove both the regulator and heatsink from the PCB in order to change the regulator.
New voltage regulator ordered from Farnell.
In this case a -60 VDC to -30 VDC. LM7915CT.
I ordered two in case of future incidents, and I also ordered two of U1 regulator as well.
The new regulator is soldered onto the PCB and a quick measurement verifies that there is -15 VDC at the output pin. Great!
Comparison of HS80M and HS50M
I have had the HS50M in my belongings for many years and I just recently acquired the HS80M's. I knew they were a little bit bigger, but they are crazy big, at least for desk use. I think they deserve a stand and some air and distance to fully appreciate them. The sound is what i expected of them.
That's all for this time. I hope you enjoyed the gallery, and maybe someone with the same kind of problem can have some use of this.
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