How I repaired my defective Yamaha HS80M studio monitor

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2013-08-16
Senast ändrat
2014-05-29
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Problem:
I have a pair of Yamaha HS80M, and one of them have this problem. After about 5 minutes after power-on, no matter if playing music or not, the woofer makes a really big uncontrolled movement resulting in an awful bump/noise. I think the tweeter does the same, but it is not as violent as the woofer. After that, if you play any music, the monitor is dead. Then you can power cycle and the problem repeats after roughly 5 minutes.

I made a small video clip to demonstrate:
http://www.youtube.com/watch?v=rG_rs7laZTA

Diagnose:
If you have the same symptoms I have, it is very easy to find out if you have the same actual problem. In my case the problem was a damaged voltage regulator. To verify this, all you need is a screwdriver to remove the woofer, tweeter and the rear panel. And also you need a multimeter, any cheap one will work, to make a couple of measurements on the PCBs.

Solution:
To switch the faulty voltage regulator, which can be a little tricky to desolder, for a new one you might want to have a little soldering skills and some proper equipment. Maybe you can do it yourself if you feel up for it, maybe you have a friend who can do it or maybe you can let a professional do the actual switch for you. It might not be so expensive to let a professional do it if you already know the problem and you have done all the required disassembly beforehand.

Below I will try to guide you through it with some pictures.

See pictures below

Service manual at ElektroTanya:
http://elektrotanya.com/yamaha_hs80m_hs50m.pdf/download.html

Edit 2014-05-29
I've been told there might be a chance to fix this without the hassle of buying new regulators and desoldering. You can try to resolder the three voltage regulator joints to get a better electrical connection, as this might have been damaged. If this works it really saves a lot of work. Thanks gonkius for the suggestion. Any one trying this, please let my know as it will help others as well.

Also, there are several stories of successful repairs at my youtube area. I'm really glad to hear it!!! Good work!

The defective HS80M. Let's get started.

First we need to loosen the 6 screws on the woofer cover.

The screws and the cover is removed.

Now we need to loosen the 4 screws on the tweeter.

With the 4 screws on the tweeter removed we can lift up the tweeter from the cabinet.

Disconnecct the two cables from the tweeter.

Now the tweeter is removed.

Let's remove the 6 screws on the woofer.

When the screws are removed the woofer can be lifted out of the cabinet.

Disconnect the two cables from the woofer.

When the woofer is removed we can disconnect the cable to the front Power On LED.

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.

The disassembly so far.

A closer look of the inside parts.

AC inlet PCB
Trafo
Input PCB
Amplifier PCB with heatsink
Bass reflex port.

We will focus on the amplifier PCB, where the voltage regulators are located.

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.

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.

The amplifier PCB and heat sink can now be removed from the rear panel.

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.

A closer look at the bottom side of the input PCB. Connector CB101 is visible.

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.

The voltage regulators visible.

Another view.

We need to remove both the regulator and heatsink from the PCB in order to change the regulator.

Back side of the PCB.

Pins of U2 and it's heatsink pins are visible.

New voltage regulator ordered from Farnell.

In this case LM7915CT.

I ordered two in case of future incidents, and I also ordered two of U1 regulator as well.

The new voltage regulator.

Components are now removed from the PCB

U2 removed.

The faulty regulator mounted on its heatsink.

The new regulator mounted on the heat sink

The new regulator is soldered onto the PCB and a quick measurement verifies that there is -15 VDC at the output pin. Great!

Now we can assemble everything and enjoy the sound out of this!

HS80M front and back.

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.

Zoom-in on the connector CB101.

Pin 3: +15 VDC
Pin 4: GND
pin 5: -15 VDC

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.

Schematic.

Regulator marked with RED.
Connector CN602 marked with BLUE.

Zoom-in on the pins.

These need to be desoldered.

Gallery picture.