Technics KN7000 :: Popping sound on PR902

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oliviahutch Total Posts: 2 Joined: September 23, 2015	Hi there, so glad to find this place and hoping to find a solution! I have a Technics Digital Ensemble piano, model SX-PR902. I've had it for about 11 years and it was given to me before that. Not sure how old it is altogether. About a month ago during a piano lesson I was teaching the piano made a loud POP as though the speakers had blown or something. It startled us both but seemed to function fine after that. I was concerned but it didn't do it again that week and I didn't know what to make of it. A friend thought that maybe because I had an air conditioner plugged into the same socket that power surges in the ac unit might be causing the pop. I moved the ac to another wall, but the popping sound has continued, sometimes 2-3 times in a 4 hour teaching session. I have noticed that sometimes I can tell when it's going to happen because there will be a little buzzing that happens when you strike the keys that seems to build up to the pop. It's startled a number of my more nervous, young and autistic students and I've had to stop teaching until I can figure out what's going on or replace the piano. I have learned from various technicians in my area (San Francisco Bay Area) that this model isn't supported any more and that it can be very hard to replace. I have a technician willing to come to my home in two weeks to look at it for a minimum $200 charge. He said that if the power something source (sorry, not technical at all!) had to be replaced it would be an additional $500. I'm trying to figure out what the best plan is. Do I try to sell the piano and buy something else? Do I wait two weeks and pay upwards of $700 for a repair? Two weeks of lost revenue factors into this too. I would be grateful for any suggestions or thoughts. Also, for over a year now sometimes when I turn the piano on all the keys sound as if I am pushing down the damper pedal. When I wiggle the wire in the connection I can usually get it to fix itself, but I kind of hate getting down on the floor at the beginning of lessons to fix the wire. Any suggestions there? Thanks so much! Olivia Posted on September 26, 2015 at 1:44 PM
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davetutt United Kingdom Total Posts: 166 Joined: January 12, 2015	Re: Popping sound on PR902 Hi Olivia Sorry to hear about your problems. I do repairs to many makes and types of keyboards here in the UK. So lets start with the technical bit that your engineer may be able to fix first. The piano is getting old and it will have many capacitors that need to be replaced. The power input on the mains has a filter capacitor that is permanently connected across the incoming supply. This is prone to failure and without it any electrical noise in the house wiring will end up coming through the system. I would be tempted to replace this as a matter of prime importance. After at least 15 years connected to the mains (doesn't make any difference if it is turned off it is still permanently connected to the mains power) it is probably dead. It is an X2 type specifically for mains filtering. On the main voice board where there is a 5 volt regulator circuit based around some switching technology. There should be a 1000uf 6volt capacitor that is definitely a candidate but others in the same part of the board should also be replaced while the board is out. The supply in question is usually called the +5D supply and it is the bit that makes the piano create the sounds and drive the display and scan the buttons and keys so its always hard at work! Because the fault is not a regular predictable thing I would also suggest an experiment before you get an engineer to call. Try using headphones and see if the results come through the phones too. If they do then the fault is unlikely to be in the power amp stages as the headphones are driven from a separate circuit. The candidates are then still the mains filter capacitor and the capacitors on the voice board. I hope you find an engineer who does component level repairs rather than board swaps as there are very few boards out there and those that are could be just as faulty as the ones you have. If I was closer to you then my investigations would center around the things I have mentioned and I would be charging considerably less than $200 for what are very cheap components! Probably no more than $10 worth! As you have said there is in effect no manufacturer support and very little third party support for most electronic instruments so I wish you luck in finding someone who is willing to help in your location. On the damper pedal issue I would think the cable is damaged and unfortunately there are again no spares. I am however trying to investigate the specification for the cable to see if I can make some up for the number of people who have problems in this area. Any questions by all means ask. Regards Dave Tutt Posted on September 28, 2015 at 9:24 AM

Viewing 1 to 2 (2 Total)

Popping sound on PR902

oliviahutch

Total Posts: 2

Joined: September 23, 2015

Hi there, so glad to find this place and hoping to find a solution! I have a Technics Digital Ensemble piano, model SX-PR902. I've had it for about 11 years and it was given to me before that. Not sure how old it is altogether. About a month ago during a piano lesson I was teaching the piano made a loud POP as though the speakers had blown or something. It startled us both but seemed to function fine after that. I was concerned but it didn't do it again that week and I didn't know what to make of it. A friend thought that maybe because I had an air conditioner plugged into the same socket that power surges in the ac unit might be causing the pop. I moved the ac to another wall, but the popping sound has continued, sometimes 2-3 times in a 4 hour teaching session. I have noticed that sometimes I can tell when it's going to happen because there will be a little buzzing that happens when you strike the keys that seems to build up to the pop. It's startled a number of my more nervous, young and autistic students and I've had to stop teaching until I can figure out what's going on or replace the piano. I have learned from various technicians in my area (San Francisco Bay Area) that this model isn't supported any more and that it can be very hard to replace. I have a technician willing to come to my home in two weeks to look at it for a minimum $200 charge. He said that if the power something source (sorry, not technical at all!) had to be replaced it would be an additional $500. I'm trying to figure out what the best plan is. Do I try to sell the piano and buy something else? Do I wait two weeks and pay upwards of $700 for a repair? Two weeks of lost revenue factors into this too. I would be grateful for any suggestions or thoughts.

Also, for over a year now sometimes when I turn the piano on all the keys sound as if I am pushing down the damper pedal. When I wiggle the wire in the connection I can usually get it to fix itself, but I kind of hate getting down on the floor at the beginning of lessons to fix the wire. Any suggestions there?

Thanks so much!

Olivia

Posted on September 26, 2015 at 1:44 PM

1 Reply

davetutt

United Kingdom

Total Posts: 166

Joined: January 12, 2015

Re: Popping sound on PR902

Hi Olivia

Sorry to hear about your problems. I do repairs to many makes and types of keyboards here in the UK. So lets start with the technical bit that your engineer may be able to fix first.

The piano is getting old and it will have many capacitors that need to be replaced.

The power input on the mains has a filter capacitor that is permanently connected across the incoming supply. This is prone to failure and without it any electrical noise in the house wiring will end up coming through the system. I would be tempted to replace this as a matter of prime importance. After at least 15 years connected to the mains (doesn't make any difference if it is turned off it is still permanently connected to the mains power) it is probably dead. It is an X2 type specifically for mains filtering.

On the main voice board where there is a 5 volt regulator circuit based around some switching technology. There should be a 1000uf 6volt capacitor that is definitely a candidate but others in the same part of the board should also be replaced while the board is out. The supply in question is usually called the +5D supply and it is the bit that makes the piano create the sounds and drive the display and scan the buttons and keys so its always hard at work!

Because the fault is not a regular predictable thing I would also suggest an experiment before you get an engineer to call. Try using headphones and see if the results come through the phones too. If they do then the fault is unlikely to be in the power amp stages as the headphones are driven from a separate circuit. The candidates are then still the mains filter capacitor and the capacitors on the voice board.

I hope you find an engineer who does component level repairs rather than board swaps as there are very few boards out there and those that are could be just as faulty as the ones you have. If I was closer to you then my investigations would center around the things I have mentioned and I would be charging considerably less than $200 for what are very cheap components! Probably no more than $10 worth! As you have said there is in effect no manufacturer support and very little third party support for most electronic instruments so I wish you luck in finding someone who is willing to help in your location.

On the damper pedal issue I would think the cable is damaged and unfortunately there are again no spares. I am however trying to investigate the specification for the cable to see if I can make some up for the number of people who have problems in this area.

Any questions by all means ask.

Regards

Dave Tutt

Posted on September 28, 2015 at 9:24 AM

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Popping sound on PR902

oliviahutch

davetutt

Re: Popping sound on PR902

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