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SX-P50 Demo OK no keyboard notes

Hi, I'm a repair engineer and have a SX-P50 keyboard in that doesn't seem to respond to the keyboard. Demo mode works fine, all power supply voltages are OK, I see some keyboard scanning activity with a logic probe. I can't change the Midi channel numb…

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SX-P50 Demo OK no keyboard notes

Glenn_FR

Glenn_FR


Total Posts: 3
Joined: December 9, 2017

Hi,
I'm a repair engineer and have a SX-P50 keyboard in that doesn't seem to respond to the keyboard. Demo mode works fine, all power supply voltages are OK, I see some keyboard scanning activity with a logic probe. I can't change the Midi channel number (MODE SET + bottom keyboard notes).
I've tried the procedures described in the user manual (MODE SET + DIGITAL EFFECT) ; (Power-on with top F#) to no avail.
Any clues or suggestions? Anyone out there have the workshop manual?
Thanks in advance
Glenn

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Posted on December 9, 2017 at 11:16 AM
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5 Replies

jd5live

jd5live
United Kingdom

Total Posts: 244
Joined: June 8, 2014

Re: SX-P50 Demo OK no keyboard notes

H Glenn, I note you have gone through the factory reset without success, unfortunately, we have an ever-increasing number of manuals both service and user but we do not have the service data you are looking for. I will, however, pass the post on to a friend of ours who is a UK. based engineer to see if he can add anything to assist you.
Regards John (admin)

Posted on December 9, 2017 at 12:03 PM

Glenn_FR

Glenn_FR


Total Posts: 3
Joined: December 9, 2017

Re: SX-P50 Demo OK no keyboard notes

OK, thanks, John.

Posted on December 9, 2017 at 12:30 PM

davetutt

davetutt
United Kingdom

Total Posts: 117
Joined: January 12, 2015

Re: SX-P50 Demo OK no keyboard notes

I haven't seen one of these for a while but from what I remember there is a known fault in one of the large LSI chips which hangs the input bus from the keys. This is very rare though. The fact that the demo's work indicates that the DAC's are running and that the majority of the internal workings of the voice circuitry is fine so it boots okay. There is no validatory return messages to tell the main processor that it hasn't made the machine work properly so likewise there is no display to tell you that things are not right.
I would be tempted to have a look at the keyboard encoders as I know these can be a problem. They are in any number of other Technics keyboards so its a known problem. Sorry that I can't remember quite how this keyboard is put together but if it is like most other Technics keyboards there will be a dedicated chip that scans the keys. The bus that feeds this chip is bi directional i.e. it needs a 8 bit code download to it for it to function beyond start up and it gets this from the master processor from the main eprom. So I would be tempted to check the soldering between the keys pcbs and the main voice board. These must be 100% for the internal comms to work properly. So if it has a 64 pin gate array on the keyboard pcbs this is where the problem stems from. So if it has this sort of IC you probably need to check the edge connector at pins 4-11 for data to the chip at start up. The gate array pin numbers are 20,21,22,23,24,26,27,28. It should have data on every line at this time. Once the download completes the display comes on so it is in the first few milliseconds.

Hope this helps.
Let me know!

Dave

Posted on December 14, 2017 at 6:21 PM

Glenn_FR

Glenn_FR


Total Posts: 3
Joined: December 9, 2017

Re: SX-P50 Demo OK no keyboard notes

Hi Dave, thanks for your inputs (and sorry for the delay in getting back).
The SX-P50 doesn't have any gate array logic on the KB pcbs, and doesn't have any display as such. The keyboard is a simple multiplexed setup with 74HC138s to do the bank decoding. With a logic analyser connected, all lines seem to be scanned but with no technical manual I can't go much further.
For the moment I'll have to put this unit back together with no success. Thanks anyway.
Glenn

Posted on December 23, 2017 at 4:06 PM

davetutt

davetutt
United Kingdom

Total Posts: 117
Joined: January 12, 2015

Re: SX-P50 Demo OK no keyboard notes

Hi Glen

Just goes to show my memory isn't what it used to be!

So that means that the address and all the interesting bits are on the main logic board. I must have been thinking of another similar keyboard!

I'll keep a look out for the manual too.

The 138's must be addressed to scan 2 switches per key, the first closes when the key first moves and the second when it stops at the bottom of its travel. The time between the switches is the key velocity and this sets the volume of each note so if it doesn't see the first switch action it will not start the timer for each key and thus you won't get any sound.

As I say Technics didn't recreate the wheel whenever they made a new keyboard so my guess would still be that the gate array may have been integrated into one of the other vlsi chips or that the key return signal is not coming back to the main board.

I'll add some more if and when I get the service manual.

Merry Christmas!

Dave

Posted on December 23, 2017 at 5:27 PM