Technics KN2000 Fault, No Sound No Backlight No LCD

[TheVintageGuy]

Hi keyboard enthusiasts, fans, and professionals,

I bought my Technics KN2000 back in 1995 at Brash’s in Pitt St, Sydney, during a clearance sale. At the time, it was one of the best arranger keyboards on the market. I’ve been happily playing it for the last 29 years, and it’s still in great condition.

However, one Saturday afternoon, after powering it on, it suddenly lost all power after about 10 minutes. At first, I suspected my surge protector, but it turned out to be something deeper.

I opened it up for inspection and found all five fuses intact (three on the mains transformer and two on the Power Distribution Board, confirmed with continuity checks). What I did find was a blown 2Ω fusible cement resistor (reading open/OL). I ordered replacements online, which took about 3 weeks to arrive.

Before swapping the resistor, I wanted to make sure nothing else caused the fault. Sure enough, I found a shorted SMD capacitor on the main logic board near the CN8 connector. I replaced it with a 10µF 25V electrolytic cap. Since I couldn’t source the original ’90s low-ripple/low-noise SMD polar cap, I mounted the electrolytic sideways so it could fit under the sound module. Functionally, it matched closely enough to work.

After that repair, progress was partial: all panel lights came on, but still no LCD, no backlight, and no sound.

Next, I checked the Power/Amp board. All the voltage regulators seemed fine, but I discovered a shorted output transistor (C4327). I replaced it with a 2SC5200 (PNP), which had the same characteristics, though slightly larger.


On power up, I now get:

• A slight “pop” from the speakers
• Panel lights working
• A low hum from both speakers
• Still no LCD, no backlight, and no sound

I’ve been working on this on and off for the past 6 months—ordering parts, replacing, testing—but I’m stuck at this point. I’m starting to suspect the logic board (motherboard) or possibly the ROMs, though I’m not 100% sure.


Unfortunately, as this model was discontinued decades ago, replacement modules/parts are nearly impossible to find. A technician I spoke to also said sourcing parts would be next to impossible. He also said there would be a $125 Bench Testing Fee, but i think that is as far as it will probably go since he said there aren't any parts for this keyboard.

Has anyone here experienced similar issues with a Technics KN2000, or can they offer advice on where to go from here? Any tips or guidance would be much appreciated.

​

 

[guscar66]

Ah, I feel your pain. I have and love a 5000 and a 6000-----I had a 2600 but my colleague has it now. Thing is that the 2000 series was exactly that ----and it is highly likely that any 2000 series logic/amp boards will do-----so I suggest that you extend your search. ------Now, the key element here is that an output transistor went s/c----unfortunately that is likely the root cause of the failure-----and as such it will have taken out other components , some further back in the amp chain than you might think-----so start to track back to the next stage . Not trying teach grandma to suck eggs here as you seem to have a good grip of the issue BUT start with the ROM self test ----you will need to search the net for this ----I can't remember (two lowest switches on the 'style'----hold while power -up??) but it its something like that.I thinks its unlikely though, your fault seems to be in the amp section. You don't need any fancy kit at this stage-----a pair of ''lug'oles' sorry high impedance head phones-------one side to earth plane ----the other to a wire 'probe' via capacitor ----1Mfd is fine-----then hold a key and 'poke' back from the output transistors ---until you hear something. See what that brings you and post back. Try searching for the tech manual ----which shows the schematic and the circuit elements as well as an explan. You may well get lucky.

 

[Gourockian]

Next, I checked the Power/Amp board. All the voltage regulators seemed fine, but I discovered a shorted output transistor (C4327). I replaced it with a 2SC5200 (PNP), which had the same characteristics, though slightly larger.

When you checked the voltage regulators, was it just a visual check or did you confirm correct voltage outputs and polarities? On some Technics models, they are prone to failure over time.

 

[TheVintageGuy]

Ah, I feel your pain. I have and love a 5000 and a 6000-----I had a 2600 but my colleague has it now. Thing is that the 2000 series was exactly that ----and it is highly likely that any 2000 series logic/amp boards will do-----so I suggest that you extend your search. ------Now, the key element here is that an output transistor went s/c----unfortunately that is likely the root cause of the failure-----and as such it will have taken out other components , some further back in the amp chain than you might think-----so start to track back to the next stage . Not trying teach grandma to suck eggs here as you seem to have a good grip of the issue BUT start with the ROM self test ----you will need to search the net for this ----I can't remember (two lowest switches on the 'style'----hold while power -up??) but it its something like that.I thinks its unlikely though, your fault seems to be in the amp section. You don't need any fancy kit at this stage-----a pair of ''lug'oles' sorry high impedance head phones-------one side to earth plane ----the other to a wire 'probe' via capacitor ----1Mfd is fine-----then hold a key and 'poke' back from the output transistors ---until you hear something. See what that brings you and post back. Try searching for the tech manual ----which shows the schematic and the circuit elements as well as an explan. You may well get lucky.

Thank you for the heads up. There are ROM and oscilloscope test points outlined in the service manual. For the ROM, there’s a service code that can be accessed by pressing a sequence of buttons and keys; however, it requires the display screen to be active to view the result. That means the only reliable way to confirm whether a ROM is alive or dead is by doing a swap test with a known working ROM from another Technics keyboard, which, as you know, isn’t easy to come by. Had I known about the early failure issues with these keyboards, I would have dumped the ROMs earlier for safekeeping.
As for the audio side, I’ve checked the preamp section and traced audio to ground, poking around for any usable sound points. I haven’t found any additional faults on the centre amp board. At this stage, I’m circling back to the logic board, since something there appears to be causing components to fail on the distribution board. All fuses are intact, which likely rules out shorts on the output transistors or capacitors. Power is reaching the panel board, but unfortunately not the LCD or the backlight.

 

[TheVintageGuy]

When you checked the voltage regulators, was it just a visual check or did you confirm correct voltage outputs and polarities? On some Technics models, they are prone to failure over time.

At first, it was a Visual Check to see if there were any burnt or scorched marks, or blown out fuses. then a basic multimeter, diode and Voltmeter output test, which confirmed one of them was shorted, but later ordered a part and replaced that with a drop-in replacement, which is Toshiba 2SC5200 (PNP), they're all working. I did pull all of them out and test them out of the circuit. I replaced the 7905 and the initial C4327 with the one above. The Two Voltage regulators on the right side of the board have also been replaced with similar 7905 and 7805 regulators.

 

[Gourockian]

At first, it was a Visual Check to see if there were any burnt or scorched marks, or blown out fuses. then a basic multimeter, diode and Voltmeter output test, which confirmed one of them was shorted, but later ordered a part and replaced that with a drop-in replacement, which is Toshiba 2SC5200 (PNP), they're all working. I did pull all of them out and test them out of the circuit. I replaced the 7905 and the initial C4327 with the one above. The Two Voltage regulators on the right side of the board have also been replaced with similar 7905 and 7805 regulators.

It sounds like you have been quite thorough checking them out so they can be eliminated from the search.

One other thing that I have learned from experience with my Yamaha organ is that when you start having problems with SMD capacitors, it is highly likely that others will fail also. I ended up replacing all 74 of them on the audio board to fix the problem I was having, which was similar to what you described. I wasn't able to get identical replacements for some of them so for those, I opted for ones with higher current ratings to improve reliability. I never did figure out ehich one of the 74 was faulty, but it fixed the issue. It was quite time consuming but not too difficult and was well worth while.

 

[TheVintageGuy]

Thankyou for the tip, that’s really helpful. I’ve actually been considering the SMD caps as the next suspect, since the regulators and transistors all checked out and have been replaced with good drop-ins. I haven’t gone through all the caps yet, but your point about replacing the whole batch makes sense, once one goes, others are usually not far behind.

Did you use standard electrolytics for your replacements, or did you go with low-ESR / higher-temp rated ones for reliability? The KN2000 board is a bit cramped in spots, so I’ll need to be careful with height and clearance, but I’m thinking a full recap on the audio/power section might be the next logical step. Their is no SMD caps on that board just Ceramic and Electrolytics; however, on the Logic board (where the SoundChips and ROM's are located) their is a few. I haven't found any shorts apart from the one close to the C8 Connection, which I replaced with a 25V 10uf Standard Electrolytic, which seemed to power up the panel board on the Kn2000, but not the others. If this fault lies deeper down, such as a ROM or Sound Chip problem, I won't be able to get a replacement part or board. Unless someone gives one up for sale.

 

[Gourockian]

Thankyou for the tip, that’s really helpful. I’ve actually been considering the SMD caps as the next suspect, since the regulators and transistors all checked out and have been replaced with good drop-ins. I haven’t gone through all the caps yet, but your point about replacing the whole batch makes sense, once one goes, others are usually not far behind.

Did you use standard electrolytics for your replacements, or did you go with low-ESR / higher-temp rated ones for reliability? The KN2000 board is a bit cramped in spots, so I’ll need to be careful with height and clearance, but I’m thinking a full recap on the audio/power section might be the next logical step. Their is no SMD caps on that board just Ceramic and Electrolytics; however, on the Logic board (where the SoundChips and ROM's are located) their is a few. I haven't found any shorts apart from the one close to the C8 Connection, which I replaced with a 25V 10uf Standard Electrolytic, which seemed to power up the panel board on the Kn2000, but not the others. If this fault lies deeper down, such as a ROM or Sound Chip problem, I won't be able to get a replacement part or board. Unless someone gives one up for sale.

I replaced them with mostly similar SMD's. I have a dedicated capacitor meter which is supposed to be able to check them in circuit but I was having trouble with getting consistent readings, even when checking the same one a few times. That's why I decided to replace them all. I've attached a couple of pictures, giving some idea of the project but the first one was taken before removing all of them.

 

[TheVintageGuy]

I replaced them with mostly similar SMD's. I have a dedicated capacitor meter which is supposed to be able to check them in circuit but I was having trouble with getting consistent readings, even when checking the same one a few times. That's why I decided to replace them all. I've attached a couple of pictures, giving some idea of the project but….

What I’ve learned about these SMD capacitors is that they often end up conflicting with each other. Removing them for testing is a real pain, because once a leg snaps off you can’t really pin it back together. It’s not as simple as just desoldering and soldering them back in. Which In your case, you definitely did the right thing by just replacing them all.
They were originally marketed as heat and leak-resistant, with low voltage ripple, but in reality, that hasn’t held up. The quality of SMD components and manufacturing in the ’90s was pretty poor, though I suppose it was the best available at the time.
After doing further digging about the Technics KN2000 you will be surprised that Technics was pretty much a Derivative of Panasonic and Sanyo electronics, even with Toshiba semiconductors, because it was the best sourced at the time when Technics introduced their line of musical instruments. Technics was simply a brand name they could use to
Sell their instruments, I would have doubt they would have made any sales if they branded their keyboard as Sanyo KN2000 or Panasonic 2000, you would pretty much associate these with white goods and toasters. So Using these Three manufactures to put together a keyboard internally, would in future would obviously have reliability issues. Put it this way, Yamaha was
Simply “Yamaha” and “Roland” was
Simply Roland. This is why the two
We’re the leading brands in the industry known for their decades long reliably and consistent output. Used by Artist and song writers back in the 70’s 80’s and 90’s, and
With a keyboard instrument That has low noise, hum, and ripple are absolutely critical.

Coming back to my KN2K I never thought a full recap would be necessary, but now it’s clear that it is. After 30 , years, I guess it’s about time. Hopefully this will resolve some of the underlying issues, or at least move me one step closer in the right direction.

 

[Gourockian]

What I’ve learned about these SMD capacitors is that they often end up conflicting with each other. Removing them for testing is a real pain, because once a leg snaps off you can’t really pin it back together. It’s not as simple as just desoldering and soldering them back in. Which In your case, you definitely did the right thing by just replacing them all.
They were originally marketed as heat and leak-resistant, with low voltage ripple, but in reality, that hasn’t held up. The quality of SMD components and manufacturing in the ’90s was pretty poor, though I suppose it was the best available at the time.
After doing further digging about the Technics KN2000 you will be surprised that Technics was pretty much a Derivative of Panasonic and Sanyo electronics, even with Toshiba semiconductors, because it was the best sourced at the time when Technics introduced their line of musical instruments. Technics was simply a brand name they could use to
Sell their instruments, I would have doubt they would have made any sales if they branded their keyboard as Sanyo KN2000 or Panasonic 2000, you would pretty much associate these with white goods and toasters. So Using these Three manufactures to put together a keyboard internally, would in future would obviously have reliability issues. Put it this way, Yamaha was
Simply “Yamaha” and “Roland” was
Simply Roland. This is why the two
We’re the leading brands in the industry known for their decades long reliably and consistent output. Used by Artist and song writers back in the 70’s 80’s and 90’s, and
With a keyboard instrument That has low noise, hum, and ripple are absolutely critical.

Coming back to my KN2K I never thought a full recap would be necessary, but now it’s clear that it is. After 30 , years, I guess it’s about time. Hopefully this will resolve some of the underlying issues, or at least move me one step closer in the right direction.

Actually, it's not too difficult to unsolder SMD caps using a hot air desoldering tool. I bought a fairly cheap combined solder/desolder station via Amazon and it worked quite well. However, after realizing I was going to end up replacing them all, I ended up just twisting them off and cleaning up the solder pads. You do need a fine point tip (and good eyesight) to solder the new ones in place.

I've had quite a few Technics keyboards plus an EA5 organ over the years, along with some used Hi-Fi units. I'm reasonably familiar with their history and was very disappointed when they eventually pulled out of the music industry.