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DX7 missing a circuit board??
Old 12th September 2012
  #1
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🎧 5 years
DX7 missing a circuit board??

Hello,

I recently bought a Yamaha DX7 (mk1) from ebay, and it seems not working. It powers up, but then (almost never) nothing else happens...i had it alive 4-5 times out of +50 power on/offs. When it powers up normally, as soon as I push the FUNCTION key it goes dead...So i had a look inside the beast (it's not the first Synth I opened), and for me it seems that there is a card missing?!?!

Can anyone help whether this card is necessary or optional??

Thank you,
Richard

left is mine...on the right is a picture i found on google
Attached Thumbnails
DX7 missing a circuit board??-my-dx7.jpg   DX7 missing a circuit board??-real-dx7.jpg  
Old 12th September 2012
  #2
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MarkF48's Avatar
 
🎧 5 years
At a guess from the service manual I downloaded, the missing board would appear to be related to the after touch function. The circuit board in question seems to have two adjustment pots, one IC, a set of yellow and brown wires. The attached schematic shows similar components.

I got the service manual and a parts list from.... ElektroTanya | Service manuals and repair tips for electronics experts

yamaha dx7 as the search string and towards the bottom of the new window it will say "Processing" and then "Download"
Attached Thumbnails
DX7 missing a circuit board??-dx7-aftertouch-pcb.jpg  
Old 13th September 2012
  #3
m.o
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Yes, that's the aftertouch board.
I fiddled around with it and recalibrated when I got mine.

The aftertouch strip acts as a Potentiometer, and I guess this board simply gives out a control voltage based on that (the IC is just a dual op-amp).
Old 13th September 2012
  #4
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Thank you for your anserw. Do you think the DX7 does not power up correctly because of this board missing?

Many thanks
Old 13th September 2012 | Show parent
  #5
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🎧 5 years
Quote:
Originally Posted by davadabeat ➑️
Thank you for your anserw. Do you think the DX7 does not power up correctly because of this board missing?

Many thanks
Difficult to say if it would affect power up. Off hand I would say it wouldn't affect power up as the board just provides a voltage to another control circuit and if with no after touch applied the voltage may be zero as it would be with a missing board.

Curious as to how the ebay ad was written up and was this sold as a working/fully functioning keyboard?
Old 13th September 2012 | Show parent
  #6
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🎧 5 years
Quote:
Originally Posted by MarkF48 ➑️
Difficult to say if it would affect power up. Off hand I would say it wouldn't affect power up as the board just provides a voltage to another control circuit and if with no after touch applied the voltage may be zero as it would be with a missing board.

Curious as to how the ebay ad was written up and was this sold as a working/fully functioning keyboard?
the ebay ad was describing the synth as working, except that no sounds were uploaded, because of a recent batterie replacement before putting the Synth on ebay. The seller kept the DX7 unused for years for his stepson who plays the piano (and prefers still the original piano and no synth sounds...and so the DX7 went on ebay). The seller is very friendly, and if the problem can't get solved, we can arrange something...

Anyway, I do also have a 100% functional DX7s (mk2) in my studio, so probably I can pull out that after touch board for a test, or do you see any concerns about...?

Thanky you
Richard
Old 13th September 2012
  #7
m.o
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🎧 5 years
If the board from your mk2 looks the same (and you have the wiring diagram in this thread too), then I would try that.
Possibly if you're adventurous you could try just running the relevant pin to ground in the connector (the one going to the mainboard), but I'm no EE so don't take my word for it.

As others have said, it doesn't really make sense that anything you do on the front panel would have much directly to do with the aftertouch board, unless there is something about those connections "hanging in the air"/free floating would crash the whole thing.

Have you checked battery (that it IS the right polarity and the right voltage), connectors from the front panel etc?
Old 13th September 2012
  #8
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When it did/does power up is there anything on the display and in the red LED's?

Are you attempting to initiate a Test Mode with the "Function" key followed by 16 and 32 green button?
Yahoo! Groups

I also found "Internal Diagnostics" procedure which uses "Edit" plus 16 and 32
How to run the Yamaha DX7s internal diagnostics | AlexAnnesty.com
Old 13th September 2012
  #9
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🎧 5 years
Quote:
If the board from your mk2 looks the same (and you have the wiring diagram in this thread too), then I would try that.
Did not work with the board of the DX7s...after putting the board back in the DX7s I got distracted playing that one for more then an hour ;-)

Quote:
When it did/does power up is there anything on the display and in the red LED's?

Are you attempting to initiate a Test Mode with the "Function" key followed by 16 and 32 green button?
Yahoo! Groups

I also found "Internal Diagnostics" procedure which uses "Edit" plus 16 and 32
How to run the Yamaha DX7s internal diagnostics | AlexAnnesty.com
Thank you for the link with the "internal Diagnostic"...i will try this tomorrow (it's already 11.30pm here in Luxembourg ;-)

Mostly the DX7 get stuck on the "start display" > *YAMAHA DX7* and "OO" on the leds, so nothing works anymore.

Sometimes it goes further saying that no internal memory was found, but every button works (as the sounds are not loaded, it only shows some signs when selecting a sound). All other Menu buttons seem to work, except the FUNCTION key, which immediately puts the DX7 back to the "start display" ...

Thank you, Richard
Old 14th September 2012
  #10
m.o
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🎧 5 years
Hmm, so one possible scenario is: It has problems whenever trying to access the RAM - This again points towards checking the battery (in the hope that the ram chips aren't broken) and the circuits around it, maybe even try removing the battery - the synth should work without battery but probably have empty or garbled patch data.

But then again the function key... Possibly the synth uses part of the RAM for global functions/settings?

Do you have any sound cartridges to try with? As I understand the cartrigde does not use tha ram, and you wouldn't have to press function key...
Old 22nd September 2012
  #11
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🎧 5 years
Sorry that I didn't answer the last posts. I was on holiday until now...

I do not have any sound cartridges to try without the function the key. I removed also the battery, but as soon as I press the "function" key the dx7 freezes (same with the Internal diagnostics test MarkF48 mentioned...)

Does anybody knows where I can let repair the DX7 in Europe (I'm from Luxembourg/Europe, so France, Belgium or Germany would be great)

Thank you
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