DX7s White noise

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brianj
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Re: DX7s White noise

Unread post by brianj » Sun Oct 15, 2017 11:44 am

Thanks for giving me things to try, Saul! I was thinking about the whole op amp thing and something occurred to me - since there is sound all the time, then something must be stuck on. I have done the diag test on the keyboard and I know that all of the keys are good, so it can't be that. Therefore, it is back to that hybrid YA1 and trying to see where it is messed up. Today's task will be to make a test rig with a battery powered amp and probe around the pins on YA1 from the back side and see what I can find.

Also, does anyone know if I need to initialize the voice, tuning and performance data for the unit to work properly? So far, I have just been doing the voices when uploading sysex data. Does anyone have a good set of sysex dumps from a DX7s? It seems that most of the files I have found are bad - either checksum is bad or file is missing sysex data (it just has the raw data from the unit).


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Brian

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Re: DX7s White noise

Unread post by brianj » Sun Oct 15, 2017 6:39 pm

So today I found a set of DX7s data that worked from the Yahoo group - that loaded without issue. No change to the sound. When I hooked up my battery powered amp to the output of the DAC, the sound stops, but nothing comes out of the amp! Hit some keys - nothing. I then start to mess with my oscilloscope - I should mention I am not an EE and I just recently got the 'scope, so I'm am still learning how to use it. I did check the clock outputs - as far as I can tell, they are good. Without some good reference notes, really hard to tell what should be what. I really don't want to remove YA1 unless I have to - looks like it will be a pain to remove and a pain to put back in!


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Re: DX7s White noise

Unread post by brianj » Sun Oct 15, 2017 6:45 pm

Oh, and one more thing Saul, you mentioned about init a patch - that results in the same thing. And, I should correct my earlier statement about everything passing diags - the first thing that should happen when you go into test mode is you should get a sine wave - I do not get this!


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Re: DX7s White noise

Unread post by Saul » Sun Oct 15, 2017 7:21 pm

Thanks foe the updates Brian. I'm at a bit of a loss now as to where you would go with this. I'm sure some of our members who are electronics engineers might be able to suggest something but I know they have day jobs that keep them quite busy so might be a little while before they see your post and can share any info they may have.


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Re: DX7s White noise

Unread post by brianj » Mon Oct 30, 2017 12:28 am

Ok, sorry for disappearing for a bit - had a family emergency & also was waiting for a proper desoldering gun from eBay - got a $108 special and it worked perfectly! The Radio Shack bulb desoldering iron just wasn't cutting it. I got the YA1 off the board in one piece without damaging the main board! Now, to try to identify chips:
YamahaYA1-Bottom.JPG


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Re: DX7s White noise

Unread post by brianj » Mon Oct 30, 2017 1:22 am

So, all of the op amps on the bottom side look like JRC4558 (see attached data sheet). It says it is compatible with the MC1458, so I got those. I also ordered the 4066 & 40174 parts while I was at it - since I have it apart, might as well replace everything I can. Parts from Digikey should be here in 2 days, then I will have fun trying to replace SMD components!
Attachments
JRC4558.pdf
(298.5 KiB) Downloaded 5 times


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Re: DX7s White noise

Unread post by Saul » Mon Oct 30, 2017 1:43 am

brianj wrote:
Mon Oct 30, 2017 1:22 am
Parts from Digikey should be here in 2 days, then I will have fun trying to replace SMD components!
Hope your eyesight is better than mine! A VERY large magnifier is required for me doing anything like this these days :(


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Re: DX7s White noise

Unread post by brianj » Fri Nov 03, 2017 1:36 pm

I have received parts and I am waiting for some Chip Quik to help with SMD chip removal, so hopefully I won't kill it! But, in the mean time, I just purchased the main board for a DX7s from eBay - looks like the old drink-in-the-cartridge-slot problem, but hopefully the board works! I am planning on messing with it tomorrow, so hopefully I will know by tomorrow night. Here is the eBay board:
DX7s-eBay-BoardOnly.jpg


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Re: DX7s White noise

Unread post by Saul » Fri Nov 03, 2017 1:46 pm

Eagerly awaiting the outcome of all this work. Got everything crossed for you Brian :)


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Re: DX7s White noise

Unread post by brianj » Sun Nov 05, 2017 1:15 am

Well, after replacing all of the !@#$% SMD op amps and the 40H174 on the YA1 board - basically the same, except now the headphone jack doesn't work! I was planning on replacing the 74HC4066 as well, but somehow I ordered the wrong size chip! And, to make matters worse, all of the op amps were *glued* to the board! So, I had to destroy them all to get them off! The next thing up the food chain is the YM2604 (OPS2) which I am pretty sure there is no chance in hell that I will find those! I think I will wait for my board to arrive from eBay and see if that is the answer to my problems. That should arrive in a week or so. I need a beer....


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Re: DX7s White noise

Unread post by brianj » Mon Nov 13, 2017 10:24 pm

Board arrived, in pretty good shape. Put it in, and......It works! Sort of. Battery is dead. I cannot get anything to load via MIDI. Boards passes tests (RAM, A/D, tone, VCA, MIDI). I guess I'll have to yank it out and replace the battery with a holder - looks like someone tried to replace the battery once with a solder-in type, but the tabs were in the wrong place or something, so they tried to make it work. Since the RAM passes, I can't quite figure out why the MIDI upload of the voice info isn't working. I do see a message that it received the data - sometimes, I also see a MIDI Checksum error, so I have tried to slow down the upload, but still nothing, I am getting close!


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Re: DX7s White noise

Unread post by brianj » Mon Nov 13, 2017 11:47 pm

So, I messed with it some more and I set my sysex dump program to go as slow as possible - and it works! I was able to load all of the patches and the performance memory! Now, I just have to change the battery holder so it will retain everything and I should be good to go! At some point in the future, maybe I will try to compare outputs from chips on the bad board to the good one, but for now, I'm going to play!


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Re: DX7s White noise

Unread post by Miks » Tue Nov 14, 2017 12:35 am

Good job, well done! (Y) Glad to see you finally got your synth 'back to work' ((i))


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Re: DX7s White noise

Unread post by Saul » Tue Nov 14, 2017 12:22 pm

That's a job very well done Brian! Shows what a bit of determination and patience can do :) Also of course this is a VERY useful thread for anyone experiencing a similar issue. Thanks for posting all the details :)


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Re: DX7s White noise

Unread post by brianj » Sun Nov 19, 2017 12:12 am

Well, surprise, surprise! I went to replace the battery - and the traces were *gone*! Whoever did that really screwed the pooch on that one! I looked at schematic, used a different point on the board to hook up the battery, and now it is 100%!


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