[YamahaDX] Yamaha DX9 Circuit diagram

[[e-mail] [YamahaDX]]

I'm in the process of restoring a very old and crusty DX9. It powers up OK, and gives '88' on the LED display as well as "Yamaha DX9 Synthesizer" on the LCD, but at this point it freezes and won't recognise any user inputs. I've been probing the logic with an oscilloscope and I can see there is some initial activity from the CPU, and then I see some odd signals on the data bus on the peripheral side of a 74LS245 transceiver chip. I'm suspecting there might be several devices trying to hit the bus at the same time and they are interfering with each other.


I want to work out all the peripheral device and address decoding, so I'm after a circuit diagram for the DX9. I've been scouring the internet trying to find a complete DX7/DX9 service manual ... but for whatever reason, every one out there (including the copy on the YamahaDX group) is incomplete and is missing the DX9 specific pages.


Anyone out there have a scanned copy of the DX9 circuit diagram?


I know "it's only a DX9" , but this is more of a scientific challenge rather than unleashing the inner beast of a classic FM synth :-)


Cheers



Paul C

[Gregg Sheehan [e-mail] [YamahaDX]]

Before you get all specific with address lines and such, you may want to start with the power supply. 9 times out of 10..in my experience with the DX series.
"Old and crusty" points to filter caps as a very first check and scoping the +5VDC and the bipolar +/- 12VDC. They should be within 5-10% and the ripple should be minimal or nonexistent.
Cheers,Gregg

From: "***@yahoo.com.au [YamahaDX]" <***@yahoogroups.com>
To: ***@yahoogroups.com
Sent: Thursday, October 19, 2017 11:37 PM
Subject: [YamahaDX] Yamaha DX9 Circuit diagram

  I'm in the process of restoring a very old and crusty DX9. It powers up OK, and gives '88' on the LED display as well as "Yamaha DX9 Synthesizer" on the LCD, but at this point it freezes and won't recognise any user inputs. I've been probing the logic with an oscilloscope and I can see there is some initial activity from the CPU, and then I see some odd signals on the data bus on the peripheral side of a 74LS245 transceiver chip.  I'm suspecting there might be several devices trying to hit the bus at the same time and they are interfering with each other. 
I want to work out all the peripheral device and address decoding, so I'm after a circuit diagram for the DX9. I've been scouring the internet trying to find a complete DX7/DX9 service manual ... but for whatever reason, every one out there (including the copy on the YamahaDX group) is incomplete and is missing the DX9 specific pages.
Anyone out there have a scanned copy of the DX9 circuit diagram? 
I know "it's only a DX9" , but this is more of a scientific challenge rather than unleashing the inner beast of a classic FM synth :-) 
Cheers
Paul C

#yiv6428176084 #yiv6428176084 -- #yiv6428176084ygrp-mkp {border:1px solid #d8d8d8;font-family:Arial;margin:10px 0;padding:0 10px;}#yiv6428176084 #yiv6428176084ygrp-mkp hr {border:1px solid #d8d8d8;}#yiv6428176084 #yiv6428176084ygrp-mkp #yiv6428176084hd {color:#628c2a;font-size:85%;font-weight:700;line-height:122%;margin:10px 0;}#yiv6428176084 #yiv6428176084ygrp-mkp #yiv6428176084ads {margin-bottom:10px;}#yiv6428176084 #yiv6428176084ygrp-mkp .yiv6428176084ad {padding:0 0;}#yiv6428176084 #yiv6428176084ygrp-mkp .yiv6428176084ad p {margin:0;}#yiv6428176084 #yiv6428176084ygrp-mkp .yiv6428176084ad a {color:#0000ff;text-decoration:none;}#yiv6428176084 #yiv6428176084ygrp-sponsor #yiv6428176084ygrp-lc {font-family:Arial;}#yiv6428176084 #yiv6428176084ygrp-sponsor #yiv6428176084ygrp-lc #yiv6428176084hd {margin:10px 0px;font-weight:700;font-size:78%;line-height:122%;}#yiv6428176084 #yiv6428176084ygrp-sponsor #yiv6428176084ygrp-lc .yiv6428176084ad {margin-bottom:10px;padding:0 0;}#yiv6428176084 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[[e-mail] [YamahaDX]]

Hi Gregg,

Thanks for taking the time to reply. The PSU is fine, 5 volts and +/- 15 volts are all in spec. The design has 4 74LS138 3 to 8 decoders which appear to be used as peripheral and memory decoders so I wanted to check what should be getting activated and when this should occur. After the display comes up with "YAMAHA DX9 SYNTHESIZER" , there is some weirdness on the data bus as the bit levels go from 5 volts down to around 2.5v and the bits become very distorted. I've attached a photo of the scope screen that shows the issue. The MPU isn't complicated but following the logic by board traces is still pretty hard so if anyone has a circuit diagram it would be greatly appreciated !

Cheers


Paul C

[Gregg Sheehan [e-mail] [YamahaDX]]

I just remembered a few things from my days of doing warranty electronics service for Yamaha pro.I have seen the memory ICs go crappy, both the RAM and the system ROM. Another odd thing that I have seen more than once would be the DAC buffer going sideways. It's a precision op-amp- can't recall the part number. It's a pain in the ass to pull off the  components and replace with fresh, so you should be somewhat confident about your choice, so some troubleshooting is probably wise.As you are doing.... I'll look and see if I have the service manuals for the DX family. Did you check the ripple on all of the PS rails? It should be zero-ish in all cases.Cheers,Gregg



"***@yahoo.com.au [YamahaDX]" <***@yahoogroups.com>

To: ***@yahoogroups.com
Sent: Saturday, October 21, 2017 9:00 PM
Subject: [YamahaDX] Re: Yamaha DX9 Circuit diagram

  Hi Gregg, 
Thanks for taking the time to reply. The PSU is fine, 5 volts and +/- 15 volts are all in spec. The design has 4 74LS138 3 to 8 decoders which appear to be used as peripheral and memory decoders so I wanted to check what should be getting activated and when this should occur. After the display comes up with "YAMAHA DX9 SYNTHESIZER" , there is some weirdness on the data bus as the bit levels go from 5 volts down to around 2.5v and the bits become very distorted. I've attached a photo of the scope screen that shows the issue. The MPU isn't complicated but following the logic by board traces is still pretty hard so if anyone has a circuit diagram it would be greatly appreciated ! 

Cheers
Paul C #yiv6835893641 #yiv6835893641 -- #yiv6835893641ygrp-mkp {border:1px solid #d8d8d8;font-family:Arial;margin:10px 0;padding:0 10px;}#yiv6835893641 #yiv6835893641ygrp-mkp hr {border:1px solid #d8d8d8;}#yiv6835893641 #yiv6835893641ygrp-mkp #yiv6835893641hd {color:#628c2a;font-size:85%;font-weight:700;line-height:122%;margin:10px 0;}#yiv6835893641 #yiv6835893641ygrp-mkp #yiv6835893641ads {margin-bottom:10px;}#yiv6835893641 #yiv6835893641ygrp-mkp .yiv6835893641ad {padding:0 0;}#yiv6835893641 #yiv6835893641ygrp-mkp .yiv6835893641ad p {margin:0;}#yiv6835893641 #yiv6835893641ygrp-mkp .yiv6835893641ad a {color:#0000ff;text-decoration:none;}#yiv6835893641 #yiv6835893641ygrp-sponsor #yiv6835893641ygrp-lc {font-family:Arial;}#yiv6835893641 #yiv6835893641ygrp-sponsor #yiv6835893641ygrp-lc #yiv6835893641hd {margin:10px 0px;font-weight:700;font-size:78%;line-height:122%;}#yiv6835893641 #yiv6835893641ygrp-sponsor #yiv6835893641ygrp-lc .yiv6835893641ad {margin-bottom:10px;padding:0 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[Barry Carson [e-mail] [YamahaDX]]

I can't help with the repairs, but the DX9 was a pretty awesome synth - I
wouldn't say it was 'only a DX9' - I had one for a very short time when I
first got my DX7. I really liked it - it was too redundant to keep, but if
I could find a nice one cheap now, I'd grab it!

Post by ***@yahoo.com.au [YamahaDX]
I'm in the process of restoring a very old and crusty DX9. It powers up
OK, and gives '88' on the LED display as well as "Yamaha DX9 Synthesizer"
on the LCD, but at this point it freezes and won't recognise any user
inputs. I've been probing the logic with an oscilloscope and I can see
there is some initial activity from the CPU, and then I see some odd
signals on the data bus on the peripheral side of a 74LS245 transceiver
chip. I'm suspecting there might be several devices trying to hit the bus
at the same time and they are interfering with each other.
I want to work out all the peripheral device and address decoding, so I'm
after a circuit diagram for the DX9. I've been scouring the internet trying
to find a complete DX7/DX9 service manual ... but for whatever reason,
every one out there (including the copy on the YamahaDX group) is
incomplete and is missing the DX9 specific pages.
Anyone out there have a scanned copy of the DX9 circuit diagram?
I know "it's only a DX9" , but this is more of a scientific challenge
rather than unleashing the inner beast of a classic FM synth :-)
Cheers
Paul C

[[e-mail] [YamahaDX]]

I've got one I dont' know what to do with...it's posed miserably against a wardrobe door.....it's available for anyone who could take care of it....

but here in France ;-)