DX7s White noise

This section is for all variants of the Yamaha DX series. DX1/DX100/DX11/DX21/DX27/DX27S/DX5/ DX7/DX7IID/DX7IIFD/DX7S/DX9/TX81Z/TX7

Moderators: Derek, parametric, Saul, Fozzer

brianj
Member
Member
Posts: 13
Joined: Fri Oct 06, 2017 12:44 am
United States of America

DX7s White noise

Unread post by brianj » Fri Oct 06, 2017 12:59 am

I purchased a non-working DX7s from eBay about 5 years ago. When I got it, all it would do is output white noise constantly. After poking around in it for a bit, it completely died. I put it in my storage locker and kind of forgot about it. Fast forward to this week - I pulled it out of storage and noticed there was no +5V and no +-12V coming out of PS. I replaced all the caps and it came back to life! I replaced the battery (previous owner had already put in a battery holder) and it passed diags in so far as Batt is ok, RAM is ok, keyboard is ok, display & buttons ok, VCA can be controlled, MIDI test passed (and it is properly sending MIDI when I hit the keys). But, when you first go into test mode, you should hear a tone and all I hear is white noise! So, I have been trying for hours to load a patch bank via Sysex. I finally determined that most of the files I have are not properly formatted with Sysex data - not sure why. But, I finally found some that looked like they were formatted properly and they started to load! But, then I got a checksum error! So, I loaded the file into a hex editor and manually computed the checksum - it was not the same as what was in the file! So, I changed the byte, loaded the file and it worked! But, now it looks like I have proper voice data (at least the names are there) but I am still only getting white noise. When I press different keys on the keyboard, the noise does not change pitch. I removed the main circuit board and there was a sticky film all over it - my guess is someone dumped a Coke or something into it at one time! So, I tried using isopropyl alcohol to clean it up - still same situation. My question is could it be the D/A convertor chip? Since the VCA seems to be ok, this is kind of up the food chain from the VCA. I see that I can get some on eBay. Any other suggestions to try? Oh and I did get a service manual, which isn't much help, except I now have a complete schematic. Once I get it scanned I will get it uploaded.


Thanks!
Brian

User avatar
parametric
Global Moderator
Global Moderator
Posts: 2411
Joined: Mon Jan 18, 2010 1:00 am
Contact:
Great Britain

Re: DX7s White noise

Unread post by parametric » Fri Oct 06, 2017 1:59 am

Hi Brian - and Welcome to the Forums . . .

It would seem that you are well on the way to sorting this out . . .

Only observation I would make is that if you suspect a "Sugary Drink" to be the Culprit - Then, as they are water-based, washing with warm water FIRST may be more successful . . ?

THEN use the IPA to get rid of the water . . . .

Another thought - will it play notes when triggered by Midi?

Might be worth to check if the Drink problem has interfered with the Key contacts?

My only experience here is with my Alesis Fusion - and the actual contacts are fairly well protected by the rubbers that fit over them . . .

I think there are others in here who can better answer the D/A chip issue

Maybe some of that helps?

parametric


Alesis Fusion 8SSD AND 6SSD - BOTH are 384Mb/120Gb SSD/Akai ADVANCE61/Yamaha MOXF6/1024Mb Flash Ram/Yamaha SY85/8.5mb vol/1024k non-vol/DX21/Roland MT32/Bachmann double overstrung Baby Grand Piano/Win10 Pro/Ubuntu MATE 15.0.4/iBook G4/Mac OS 10.4.6/ProTools 7.4/MBox2/M-Audio 24/96 Sector101 2x SYEMB06 / 4 x EXM-E3 128MB DRAM Module
BRAND NEW DSDD (720k) FLOPPY DISKS FOR SALE - viewtopic.php?f=22&t=9217

Watch out now! take care, BEWARE of the greedy leaders! They'll take you where you should not go - (George Harrison)

IT'S TRUE - "MONEY TALKS" - TO ME, IT MOSTLY SAYS "GOODBYE" ;-)
http://www.chrisnmiller.co.uk/Chris

brianj
Member
Member
Posts: 13
Joined: Fri Oct 06, 2017 12:44 am
United States of America

Re: DX7s White noise

Unread post by brianj » Sat Oct 07, 2017 8:58 pm

parametric,

Thanks for the welcome and pointer about warm water. I will give that a shot! Keys all pass diags, so they are all ok. For that matter, *everything* passes diags! I have not tried to trigger with MIDI in - I will give that a shot as well. For me, the biggest pain is I don't see a way to work on the unit and test it at the same time - you have to remove the board to do anything as it is mounted upside down! My old Roland synths you could remove a few screws and lift up the top and work on the unit with everything connected - much easier to tshoot. I will report back!


Thanks!
Brian

brianj
Member
Member
Posts: 13
Joined: Fri Oct 06, 2017 12:44 am
United States of America

Re: DX7s White noise

Unread post by brianj » Sat Oct 07, 2017 11:47 pm

Ok, so I tried the MIDI in - still no change in pitch of the white noise. Tomorrow I will try to clean it better and if that doesn't work, give the D/A chip a shot.


Thanks!
Brian

User avatar
Saul
Site Admin
Site Admin
Posts: 7752
Joined: Sun Feb 01, 2004 1:00 am
Contact:
Ireland

Re: DX7s White noise

Unread post by Saul » Sun Oct 08, 2017 2:31 pm

Hi Brian. Interesting first post to the forum, especially if you manage to fix it :)

Just throwing my 2 cents in the ring. What about the op amps? These have to take a LOT of heat and over the years they do degrade. As everything else seems to check out I would be looking at the actual output side of things before looking at the D/A chip.


Saul
Site Admin
Sign up to the Newsletter
FREE Home Recording Training Video Course
Follow me on Twitter @YamahaMusicians
Follow Us On Facebook
Seagull S6 Original/Roland FA-07/Pianoteq 6 Pro/Amplitube 3.0/Apple iMac 27"/GarageBand 10.0.3/Logic Pro X/Cubase AI 9/Absynth 5/Ableton Live 9/KRK Rokit RP5 G3 Monitors
Website Design & Managed Hostingwww.rabbittree.uk

brianj
Member
Member
Posts: 13
Joined: Fri Oct 06, 2017 12:44 am
United States of America

Re: DX7s White noise

Unread post by brianj » Sun Oct 08, 2017 3:04 pm

Saul,
Thanks for pointing me towards the op amps. Since the VCA test seemed to pass ok, I figured that at least some of the op amps are ok. Here is the thing that is driving me nuts - the service manual has no theory of operation - nothing to tell you what levels you should see at what test points - nothing! It is almost useless! So, I figured since the VCA test seemed ok and the volume control seems to work, the next thing up is the D/A. The op amps are on a "HIBRID (sic)" YA1 and they don't show what kind they are, so I will have to pull it apart again and get part numbers off the chips.

I also just noticed when I reassembled the SM, I put the wrong page 1 on there - will have to fix that.

Thanks! I will post updates...


Thanks!
Brian

User avatar
Saul
Site Admin
Site Admin
Posts: 7752
Joined: Sun Feb 01, 2004 1:00 am
Contact:
Ireland

Re: DX7s White noise

Unread post by Saul » Sun Oct 08, 2017 5:45 pm

Well your right of course and your doing things the correct way in sequence following the path to output. The Op Amps is me taking a short cut ;)

I'm pretty sure you will get this sorted though. You have already brought the thing back to life and seems there is just this final hurdle to a fully working DX :)


Saul
Site Admin
Sign up to the Newsletter
FREE Home Recording Training Video Course
Follow me on Twitter @YamahaMusicians
Follow Us On Facebook
Seagull S6 Original/Roland FA-07/Pianoteq 6 Pro/Amplitube 3.0/Apple iMac 27"/GarageBand 10.0.3/Logic Pro X/Cubase AI 9/Absynth 5/Ableton Live 9/KRK Rokit RP5 G3 Monitors
Website Design & Managed Hostingwww.rabbittree.uk

brianj
Member
Member
Posts: 13
Joined: Fri Oct 06, 2017 12:44 am
United States of America

Re: DX7s White noise

Unread post by brianj » Sun Oct 08, 2017 9:46 pm

Ok, so I took the board out again. After Googling around, I got some distilled water and tried cleaning the board up some more - there is still a lot of gunk, especially near the output YA1 (see attached picture of YA1). The op amps must be SMD and mounted to the other side of the YA1 board. Not going to be fun if those are the culprits! Seeing as the D/A converter is through-hole and easily replaced, I still think I am going to go for that first. I ordered some anti-static swabs from Digikey, so I will wait for them and try to clean the board more thoroughly.

I did notice that there is a resistor across IC31 from pins 1 to 7. According to the schematic, it is supposed to be there and when I look at the board layout, I don't see it *on the board* so that must have been done from the factory. I guess it was "Oops! we missed that resistor - no problem, we'll just stick it right here!"
Attachments
YamahaYA1.JPG


Thanks!
Brian

brianj
Member
Member
Posts: 13
Joined: Fri Oct 06, 2017 12:44 am
United States of America

Re: DX7s White noise

Unread post by brianj » Fri Oct 13, 2017 2:07 am

So, my more through cleaning has had no effect at all! I did mange somehow to mess up the contacts on 1 key, but it still seems to be working, so hopefully that won't happen again! I got the replacement D/A convertor, so I think I will tackle that this weekend. I confirmed this is strictly an audio issue by hooking up the keyboard to my Korg softsynth on my ipad - program change buttons worked, pitch bend and mod wheel work, all keys work.


Thanks!
Brian

User avatar
Saul
Site Admin
Site Admin
Posts: 7752
Joined: Sun Feb 01, 2004 1:00 am
Contact:
Ireland

Re: DX7s White noise

Unread post by Saul » Fri Oct 13, 2017 2:26 am

Thanks for the update Brian. Really hope that new D/A works for you. Keep us posted on how it goes.


Saul
Site Admin
Sign up to the Newsletter
FREE Home Recording Training Video Course
Follow me on Twitter @YamahaMusicians
Follow Us On Facebook
Seagull S6 Original/Roland FA-07/Pianoteq 6 Pro/Amplitube 3.0/Apple iMac 27"/GarageBand 10.0.3/Logic Pro X/Cubase AI 9/Absynth 5/Ableton Live 9/KRK Rokit RP5 G3 Monitors
Website Design & Managed Hostingwww.rabbittree.uk

brianj
Member
Member
Posts: 13
Joined: Fri Oct 06, 2017 12:44 am
United States of America

Re: DX7s White noise

Unread post by brianj » Sat Oct 14, 2017 8:17 pm

Ok, so I replaced the D/A convertor and......it is still the same! Damn, I was really hoping that was it! Of course, the next 2 chips up the food chain are the OPS2 (YM2604) and the EGM (YM3609) and I suspect that I will not find those anywhere - except a donor DX7S or II[F]D. I really don't think the op amps are bad as I am getting output at the headphone jack and the output jack on the back, plus during the VCA test I am able to adjust the VCA level. So, that would mean to me that the op amps are ok and the "fake" D/A convertor that is used to control the VCA level is ok. The other thing would be the master clock - I saw another thread where someone had to replace the 9.4265mhz crystal. The source that was mentioned in the thread is out of business! I'll have to break out my 'scope and see if I can measure the clock, so at least I know that is working. Otherwise, I have an ok MIDI controller :-)


Thanks!
Brian

User avatar
Saul
Site Admin
Site Admin
Posts: 7752
Joined: Sun Feb 01, 2004 1:00 am
Contact:
Ireland

Re: DX7s White noise

Unread post by Saul » Sat Oct 14, 2017 8:39 pm

You can still get output with knackered op-amps just not the output you want.

Worst case as you say, it's still an ok MIDI controller. Excellent keybed anyway :)


Saul
Site Admin
Sign up to the Newsletter
FREE Home Recording Training Video Course
Follow me on Twitter @YamahaMusicians
Follow Us On Facebook
Seagull S6 Original/Roland FA-07/Pianoteq 6 Pro/Amplitube 3.0/Apple iMac 27"/GarageBand 10.0.3/Logic Pro X/Cubase AI 9/Absynth 5/Ableton Live 9/KRK Rokit RP5 G3 Monitors
Website Design & Managed Hostingwww.rabbittree.uk

brianj
Member
Member
Posts: 13
Joined: Fri Oct 06, 2017 12:44 am
United States of America

Re: DX7s White noise

Unread post by brianj » Sun Oct 15, 2017 2:42 am

Ok, so I went to the Yahoo group and found a thread of messages from 2010 from a guy who goes by megamindx4 who had the exact same issue as I am having - except he never says what fixed the issue! Does anyone know how I can find him? For some reason, it looks like I am a member of the group, but I cannot reply to anything.
https://groups.yahoo.com/neo/groups/Yam ... opics/9822


Thanks!
Brian

brianj
Member
Member
Posts: 13
Joined: Fri Oct 06, 2017 12:44 am
United States of America

Re: DX7s White noise

Unread post by brianj » Sun Oct 15, 2017 2:45 am

I need a drink - this is the guy I purchased my unit from! Duh!


Thanks!
Brian

User avatar
Saul
Site Admin
Site Admin
Posts: 7752
Joined: Sun Feb 01, 2004 1:00 am
Contact:
Ireland

Re: DX7s White noise

Unread post by Saul » Sun Oct 15, 2017 10:04 am

Well it was five years ago Brian :lol:

One thing, have you selected a patch and then initialised it? You should get a pure sine wave.

I know you can see the patch names but apparently if there is no patch data present then you will just get white noise.

Must admit I'm grasping at straws here as I have never owned a DX7 in hardware so have never had to delve into the sort of issues you have. Still, anything is worth a try :)


Saul
Site Admin
Sign up to the Newsletter
FREE Home Recording Training Video Course
Follow me on Twitter @YamahaMusicians
Follow Us On Facebook
Seagull S6 Original/Roland FA-07/Pianoteq 6 Pro/Amplitube 3.0/Apple iMac 27"/GarageBand 10.0.3/Logic Pro X/Cubase AI 9/Absynth 5/Ableton Live 9/KRK Rokit RP5 G3 Monitors
Website Design & Managed Hostingwww.rabbittree.uk

Post Reply

Return to “Yamaha DX & TX Forum”

Who is online

Users browsing this forum: No registered users and 2 guests