Genelec 8020B repair

[davidperrenoud]

As there seems to be a good number of Genelec fans on this forum, I figured it would be the right place to document my repair attempt of some Genelec 8020B speaker.

I recently got 2 speakers: one of them has a weak woofer/bass output and a lower overall volume. The previous owner informed me that the repair shop for Genelec products in Switzerland had closed and that it would not be cost effective to send the speaker to Germany. I tried to contact Genelec for some tips about repairability but I received a very generic answer. In my opinion old school companies were doing a better job before sustainability was even a trend. Lenco were printing service schematics right into their turntables and Studer/Revox are still selling parts for very old products.

The lack of service instructions and parts should not stop us though and we will take this opportunity to learn a thing or two about monitor design and electronics.

Part 1 - disassembly​

• Remove the following screws from the back of the speaker:
  • Four long Torx screws
  • Two Philips screws

---

• Remove the following screws from the controls:
  • Four Torx screws
  • Three self-tapping Torx screws
• Remove the two metal covering pieces. It may take some fiddling to remove the bottom one.

---

• Remove the Torx screw grounding the chassis. Do not forget it. THIS IS THE SCREW YOU WILL FORGET TO REMOVE AND TO PUT BACK!
• Take the two halves of the speaker apart. It will look take some force as the plastic joint making the enclosure air-tight is adding some friction. Separate preferably the right side first, in order not to put any strain on the cables inside.

---

• Remove the two white foam pieces.

---

• Remove the three Torx screws holding the bass port in place.
• Remove the bass port.

---

• Unplug the following connectors:
  • Unplug the left connector going to the woofer, tweeter, LED and buttons.
  • Unplug the right connector going to the transformer by pressing on its locking tab.

---

• Remove the five Torx screws holding the circuit board.
• Slightly unscrew the Torx screw pressing against the audio amplifier chip. You need a long Torx screwdriver for this. If you do not do this step, it will be hard to pull the circuit board as some metal piece is pressing hard against one component.

---

• We are in! We see:
  • Some power circuitry on the bottom and on the left
  • A stereo amplifier LM1876T in the middle
  • Some NE5532 and TL072 opamps on the right
  • Some unknown transistors (M1W?)

---

In the next part, we will try to understand what all of these components do and find the root cause of the problem.

 

[Tonygeno]

When's that next part coming?

 

[srrxr71]

I have an 8010 with issues. I suspect it may be a fuse. This will be helpful. Of course I can send them to Massachusetts but if it just a fuse I’d rather repair them myself.

 

[YSC]

just wonder, how long did both speakers serviced before dying?

 

[davidperrenoud]

I have an 8010 with issues. I suspect it may be a fuse. This will be helpful. Of course I can send them to Massachusetts but if it just a fuse I’d rather repair them myself.

To check if it's the fuse without disassembling it, you can disconnect all power (!), put the power switch to the ON position and check the resistance between the positive and negative power pins with a multimeter. If you get an infinite resistance (OL), the fuse is probably blown. If you get some resistance that start at 0 ohm and quickly gets to 100-150 ohm, you are loading the capacitor behind the fuse which means that the fuse is not blown and you have another problem. Good luck.

Note that the Genelec 8010A does not have any visible screws. I guess that there is a single screw centered behind the word "WARNING" of the label.

just wonder, how long did both speakers serviced before dying?

My Genelec 8020B have written "May 12" on them, so I guess they were used for 10 years.

 

[YSC]

To check if it's the fuse without disassembling it, you can disconnect all power (!), put the power switch to the ON position and check the resistance between the positive and negative power pins with a multimeter. If you get an infinite resistance (OL), the fuse is probably blown. If you get some resistance that start at 0 ohm and quickly gets to 100-150 ohm, you are loading the capacitor behind the fuse which means that the fuse is not blown and you have another problem. Good luck.

Note that the Genelec 8010A does not have any visible screws. I guess that there is a single screw centered behind the word "WARNING" of the label.

My Genelec 8020B have written "May 12" on them, so I guess they were used for 10 years.

ok, 10 years is a fair life time for electronics IMO, though personally I hope mine would last longer

 

[srrxr71]

just wonder, how long did both speakers serviced before dying?

So I used them for about 2-3 years. I think it was my fault. I turned the volume up really high and they suddenly stopped. That’s why I think it’s a fuse issue.

I thought the protection would protect them.

Hard to say what happened but I feel like some protective measure was activated and a fuse change or some kind of reset should get them working again.

It was sudden and I didn’t smell burning.

 

[srrxr71]

To check if it's the fuse without disassembling it, you can disconnect all power (!), put the power switch to the ON position and check the resistance between the positive and negative power pins with a multimeter. If you get an infinite resistance (OL), the fuse is probably blown. If you get some resistance that start at 0 ohm and quickly gets to 100-150 ohm, you are loading the capacitor behind the fuse which means that the fuse is not blown and you have another problem. Good luck.

Note that the Genelec 8010A does not have any visible screws. I guess that there is a single screw centered behind the word "WARNING" of the label.

My Genelec 8020B have written "May 12" on them, so I guess they were used for 10 years.

Thank you. I’ll try that over the weekend.

 

[RubinDrums]

As there seems to be a good number of Genelec fans on this forum, I figured it would be the right place to document my repair attempt of some Genelec 8020B speaker.

I recently got 2 speakers: one of them has a weak woofer/bass output and a lower overall volume. The previous owner informed me that the repair shop for Genelec products in Switzerland had closed and that it would not be cost effective to send the speaker to Germany. I tried to contact Genelec for some tips about repairability but I received a very generic answer. In my opinion old school companies were doing a better job before sustainability was even a trend. Lenco were printing service schematics right into their turntables and Studer/Revox are still selling parts for very old products.

The lack of service instructions and parts should not stop us though and we will take this opportunity to learn a thing or two about monitor design and electronics.

Part 1 - disassembly​

View attachment 199040

• Remove the following screws from the back of the speaker:
  • Four long Torx screws
  • Two Philips screws

---

View attachment 199041

• Remove the following screws from the controls:
  • Four Torx screws
  • Three self-tapping Torx screws
• Remove the two metal covering pieces. It may take some fiddling to remove the bottom one.

---

View attachment 199049

• Remove the Torx screw grounding the chassis. Do not forget it. THIS IS THE SCREW YOU WILL FORGET TO REMOVE AND TO PUT BACK!
• Take the two halves of the speaker apart. It will look take some force as the plastic joint making the enclosure air-tight is adding some friction. Separate preferably the right side first, in order not to put any strain on the cables inside.

---

View attachment 199050

• Remove the two white foam pieces.

---

View attachment 199051

• Remove the three Torx screws holding the bass port in place.
• Remove the bass port.

---

View attachment 199052

• Unplug the following connectors:
  • Unplug the left connector going to the woofer, tweeter, LED and buttons.
  • Unplug the right connector going to the transformer by pressing on its locking tab.

---

View attachment 199053

• Remove the five Torx screws holding the circuit board.
• Slightly unscrew the Torx screw pressing against the audio amplifier chip. You need a long Torx screwdriver for this. If you do not do this step, it will be hard to pull the circuit board as some metal piece is pressing hard against one component.

---

View attachment 199054

• We are in! We see:
  • Some power circuitry on the bottom and on the left
  • A stereo amplifier LM1876T in the middle
  • Some NE5532 and TL072 opamps on the right
  • Some unknown transistors (M1W?)

---

In the next part, we will try to understand what all of these components do and find the root cause of the problem.

Hi David, My Genelec 8050B making intermittent noise and I was wondering if you are able to tell maybe what causes it to make that noise, I am suspecting it's a cap going bad, has anyone experianced that king of noise? Can you please help? I will attach a recording of the noise...

 

[AnalogSteph]

Sounds quite crackly, which suggests something more like bad solder joints or a failing semiconductor of sorts to me... can you pinpoint the issue to the tweeter or does it come out of the woofer as well? There are some classic trouble spots when it comes to cracked solder joints, like power amplifier IC legs or those of regulators... basically everything subject to thermal cycling and associated mechanical stress.

 

[RubinDrums]

Thank you so much for your supar fast reply. it comes and goes, I'll check today if it comes out of the tweeter only or both speakers or both tweeter and woofer, there is also a very quiet constant low noise coming out of that speaker (I'll try to record it today as well. Would it be easy for me to find it with a multimeter and solder it?

 

[davidperrenoud]

In this long overdue part we will look for the root cause of the weak bass output of the Genelec 8020B. We will fail to find it... but we will learn a lot along the way.

Circuit board overview​

Let's first have a look at the board to see if there are no bulged capacitors or some overheated components.

We see some N5532 and TL072C amplifiers which probably have to do with the feedback and limiting circuit. The 2x20 watts power amplifier is a LM1876T. Some other components have part numbers M1W (transistors?), KBP01, 8L12A and 9L12A.

Replacing the main power amplifier​

We decide to replace the LM1876T with the hope that one of the 2 channels had some defect.

Our replacement LM1876TF has a plastic casing which we sand down at the back to get better contact with the speaker enclosure that serves as heat sink.

Unfortunately the weak bass output persists. This means that the problem happens in some other place such as the feedback/limiting circuit.

Measurements​

We verify that the power circuit is delivering 12 V correctly. My electronics friend hoarded devices over the years from the trash bin so we can measure that the power output is precisely 11.7969 volts.

With a vintage oscilloscope we see that the bass output of the power amplifier has some noise. The signal should look like a pure sinus wave without the spurious noise.

By inserting a floppy disk we can take screenshots of the signal. As researchers usually throw their floppies with their oscilloscopes, we format one floppy containing some measurements from 4th October 1994 that still need "to be looked at". Hopefully no Nobel prize was contained in it.

I cannot find the signal screenshots anymore and we switch to another way of debugging.

Reverse engineering the circuit​

This circuit board is a simple 2-sided board. This makes it easy to follow traces on the top and on the bottom.

My electronics friend decides to follow all the traces and draw a schematics from it. This is a tremendous work! It allows us to understand each part of the system, the DIP switches and even the unmarked calibration potentiometers. As the speaker has no firmware you can understand its features just by looking at the schematics and the components datasheets.

You can find the full schematics in "output.pdf" file attached.

After this extensive reverse engineering we lose patience and decide to replace the whole board. It is safe to assume that a repair technician would do the same.

Replacing the amplifier board​

At the time of writing there are no repair technicians for Genelec in Switzerland. I bought my first replacement board from Sertronics AG for the equivalent of 250 USD. They have now stopped delivering replacement parts to customers. Arocom AG is the B2B distributor for Switzerland but they do not sell to customers. After going through my local audio shop I could get a second replacement board for the equivalent of 145 USD.

See how you can replace the board in the disassembly part of my first post.

Calibrating the speaker​

Each Genelec speaker is calibrated in factory. The 3 calibration potentiometers correspond to:

1. B-CAL
2. T-CAL
3. EHF-CAL

If you do not have a Genelec factory or a precise microphone, take a reference Genelec 8020 speaker and compare it to your uncalibrated speaker.

Turn the potentiometers a few times until both speakers match and you have a "calibrated" speaker!