Digital piano won't power ON

[Alektron]

So here is the Happy Ending...


I replaced Diode 23 with an original Technics part MA738. I put back the 1000uF capacitor and the Q8 transistor on the Main Board.

For the 2 x ( 2 Ω 2Watt ceramic resistors ) I used a single 4.7Ω 5 Watt cement ceramic type resistor.
I moved this baby up from the board in case it dissipates a lot of heat using 18 gage copper wires. Please see the attached photos.

And the "Moment of Truth" has finally arrived!

Piano turned on successfully, ladies and gentlemen, with all the bells and whistles this instrument has to offer along with a beautiful LCD color display.

Conclusion:
This digital piano's fault was one diode that failed, and brought down two other resistors that were in series the 2 Ω 2 Watt ceramic cement resistors, one of them completely open. Here is your final cartoon... for this story...


That's all Folks !

I would like to thank everybody who helped me with this project.

And a major "Thank You" goes out to -----> Sir 73's de Edd , merci monsieur...







It's aaaaaaaaliiiiiiiiiiiiiivve !!

 

[Bluejets]

Good to see you stuck with it.
Good job.

Now don't go annoying the neighbours......

 

[Tha fios agaibh]

Great job! Not only for replacing the failed part, but for being patient and checking all components around it.
As for the reason D23 failed, I'm not sure. Perhaps just heat?
As a precaution, you may want to verify you are now getting a steady + and - 15volts.

With your new found electronic success, you may now be cursed with the chore of having to fix all your friends stuff.

 

[Alec_t]

Nice one!

 

[Alektron]

Thank you.

For now I'm going to leave it ON for couple of hours every day, just to see that everything holds out, then if things stay good, I'll assemble its feet, polish up the furniture, clean the panel, the keys and find a nice spot for it.


Some Extra information about this digital piano:

The Technics SX-PR 902C was the top of the line among digital pianos of the time, back in the late 90's. The price for this instrument in 1999 was $ 10,000 US dollars.

Features:

- 88 keys

- Polyphony 64 (the total number of keys that you can play simultaneously and will make a sound)

- 317 Sounds + 12 Drum Kits (sounds like Piano, organ, guitar, sax etc)

- 128 Rhythms x 4 Variations (Variation means your rhythm goes from a basic pattern to a more advanced and you have four of these per rhythm)

- Automatic accompaniment - ( Besides the fact that you have a drum going on, you also get 4 extra instruments to play along with the drum. These are: Bass and 3 other different instruments that will play automatically based on what chord is provided)

- 16 Track Sequencer - ( In my opinion this was one of the best features Technics has ever included with their digital pianos. You could play Midi songs created by others or create your own backing tracks, a very useful feature. Sometimes I wonder what Bach and Beethoven would've done with such an instrument ?)




Specifications from the User Manual:

 

[73's de Edd]

Sir Alektron . . . .et al . . .

Before getting that puppy all buttoned up, how about taking the DC voltage readings, both before and past the pair of two ohm * power resistors to see what voltage it normally is.
Since you now have a 4.7 ohm* replacement, take the voltage reading across it also, so the we can calculate the actual power level, needed to be dissipated in it.
That one 2 ohm resistor must have decided to open up at the very last 11th hour, 59th minute and 59th second of testing, or we wouldn't have had that very low voltage that was there.
Also go to AC mode metering and test the AC voltage across the 1000ufd main filter of that +5VDC Dee supply to get its ripple value. That will be a useful number to know to evaluate the/any time related decline of filtering in that supply.
By their still utilizing a high value of filtering capacitor, and this being in their infancy of experience in using a switch mode power supply I feel that it is operating up (down) in the 20--'s of Khz frequency. Plus they even used 85 deg rating caps. Nowadays design freq switching is up in the Mhz and only needing a series of monolithic layered block capacitors for bulk filtering.

Now don't go annoying the neighbours......

Annoying . . .Annoying ? . . . I'll just bet that there are some neighbors up and down the block that are still checking on him, after he initially let out those multiple { start 72 font size} YAHOOOOOO's { end 72 font size} back at the moment of truth.

ASIDE . . . .Hear one and all . . . . .
On my computer power supplies, an initial task is to take the secondary filters and use two capacitors instead of the single ones. This done by stacking the second one vertically above the initial one with an insulative bakelite disc placed atop the primary cap and insulative polyolefin sleeving insulating for routing the side wires down to the bottom one . . .with microdots of E2000 adhesive assisting in wire dress and hold down.

A final test is logging in all of the filters AC ripple readings to reference against for future analysis.
UBER reliability experienced . . . . . the oldest case is a computer that is having 8 years of use and only a 2 and 5% ripple increase on the 3.3 and 5 supplies . Lo o o o o o ng way to go on that !

Thassssssit . . . .
73's de Edd
.....

 

[roy blake]

What a Fantastic forum Item on SX-PR902c
cannot wait to get mine working which has Similar Problems
Just keep Fingers crossed cos I'm 83 years of age and I am just learning about Electronics and their Foibles
I only Wished I'd searched the Web with the Right Questions Months ago !
I find that this subject is most Fascinating and certainly good for testing Patience
This is my FIRST visit to this Site and certainly will not be my Last
Now all please wish me well for I am Venturing into the Unknown World of CV19 having my Second Jab of Pfizer tonight
Hope everything Works after that !
Thanks a Lot to all who helped with the Project to get a Retired Surveyors Technics SX -PR902 up and Running once more
More than Panasonic has ever done for all Technics Keyboard owners !

 

[Harald Kapp]

@roy blake : this thread is old from 2018. Please creat your own thread if you want to start a discussion. Thanks for understanding.
I'll close this thread.