DX7 II FD collapses to white noise on boot

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

Great Britain
Burfix
Member
Member
Posts: 29
Joined: Wed May 22, 2019 4:47 pm

DX7 II FD collapses to white noise on boot

Unread post by Burfix » Wed May 22, 2019 5:02 pm

Fast-Forward to the end to avoid a long read: I've put a summary for the main issue there :D .

---------------------------------------------------------------------------------------------------------------------------------

Hello new friends,

I picked up this DX7 II FD last week. Got it home and it all seemed ok at first. Then I noticed on a couple of patches a few of the keys didn't work - the same keys in each octave in fact. So I thought it could be the patches. So I initiated them and checked all 6 oscillators. All seemed ok. Then on Monday, I noticed some strange keying behaviour. Some notes only sounding on key release. This got worse until there was a kind of downward crescendo of all operators ending up in a kind of white noise roar. Nearly blew my amp actually.
I switched it off and on again and things seemed ok. But the next day the same happened and now happens every time I power it up. There is a high pitched squealing that drops to a low white noise rumble. Also the red LCD characters look like random rubbish and the green LCD just has a solid bar.
I checked the battery and its just about 3V. The boards I can see look clean enough with no obvious water damage. One note, after lifting the board to see the battery, I rested it back down and powered it up and she was ok for a few minutes. Thanks for your time. N
Attachments
DX7 IIFD crashed.JPG
DX7 IIFD crashed.JPG (66.17 KiB) Viewed 1081 times
Last edited by Burfix on Fri Aug 30, 2019 9:21 am, edited 2 times in total.
Great Britain
Burfix
Member
Member
Posts: 29
Joined: Wed May 22, 2019 4:47 pm

Re: DX7 II FD collapses to white noise on boot

Unread post by Burfix » Wed May 22, 2019 5:17 pm

Update: I just powered it up again (for the first time today) and the display looked normal. But no buttons were responsive. Powered off and on again and the display is now the same as shown in the previous photo. Any help greatly appreciated. N
User avatar Germany
Miks
Specialist Moderator
Specialist Moderator
Posts: 1912
Joined: Fri Oct 31, 2008 1:00 am

Re: DX7 II FD collapses to white noise on boot

Unread post by Miks » Wed May 22, 2019 5:18 pm

Hi Burfix,

welcome to the forum (Y)

Have you checked the psu's voltages to see if they're within their specs? First thing I highly recommend here is to maintain the DX's psu - please have a read here:
viewtopic.php?f=35&t=11766
Many issues on a DX7 are caused by a faulty battery or psu - believe me :wink:
If you need the service manual for your DX7II/FD please let me know... 8)
My (key related) gear (in alphabetical order):
Ferrofish: B4000+
Kawai: K1 II
Korg: M1 (up'd to EX, w/ 'Cool Blue'), M1REX (w/ 'Cool Blue'), Poly-800
Roland: D-50, D-110, D-550, PG-1000
Yamaha: AW1600, DX7IID (w/ 'Cool Blue'), EX5R, RM50, RX5, SY99 (w/ 'Cool Blue'), TG500,
TX-802, YMM2
Sector101: SYEMB05 (5x), SYEMB06 (3x), EXFLM2 (1kit), MCD Sweet16 (1x), DataBlade32 (1x),
WaveBlade 8MB Card (1x) & 1x Programmer Unit for WaveBlade
Great Britain
Burfix
Member
Member
Posts: 29
Joined: Wed May 22, 2019 4:47 pm

Re: DX7 II FD collapses to white noise on boot

Unread post by Burfix » Wed May 22, 2019 5:53 pm

Thanks Miks for the info. I tested the PSU connector pins and they check out ok against the North Europe PSU diagram. I get 11.9V instead of 12 on the 2 adjacent pins but that could be my cheap multimeter. I think I'm going to pull the main board and re-seat all the connectors as I'm guessing it could be a thermal/stress problem. Fingers X'd anyways. R's N
User avatar Germany
Miks
Specialist Moderator
Specialist Moderator
Posts: 1912
Joined: Fri Oct 31, 2008 1:00 am

Re: DX7 II FD collapses to white noise on boot

Unread post by Miks » Wed May 22, 2019 6:35 pm

Burfix wrote:
Wed May 22, 2019 5:53 pm
I get 11.9V instead of 12 on the 2 adjacent pins but that could be my cheap multimeter.
That looks very good. There is (only) one potentiometer (VR1) on the psu's pcb to adjust all voltages at once (+12V -12V +5V). Since the 5V is for the digital part and the ±12V is for the analog part of the synth it's recommended to adjust the +5V as close as you can get it to 5V - the other voltages 'will fit automaticly' thereafter...
My (key related) gear (in alphabetical order):
Ferrofish: B4000+
Kawai: K1 II
Korg: M1 (up'd to EX, w/ 'Cool Blue'), M1REX (w/ 'Cool Blue'), Poly-800
Roland: D-50, D-110, D-550, PG-1000
Yamaha: AW1600, DX7IID (w/ 'Cool Blue'), EX5R, RM50, RX5, SY99 (w/ 'Cool Blue'), TG500,
TX-802, YMM2
Sector101: SYEMB05 (5x), SYEMB06 (3x), EXFLM2 (1kit), MCD Sweet16 (1x), DataBlade32 (1x),
WaveBlade 8MB Card (1x) & 1x Programmer Unit for WaveBlade
Great Britain
Burfix
Member
Member
Posts: 29
Joined: Wed May 22, 2019 4:47 pm

Re: DX7 II FD collapses to white noise on boot

Unread post by Burfix » Mon May 27, 2019 9:20 am

Hello!

Yesterday I un-plugged and re-plugged everything on the main board. On power up I had about 12 seconds of normal function before the same characteristic dreaded white noise crescendo returned. I did notice that IC32 was capacative-sensitive, in that when I placed my finger near to or on, the sound of the white noise changed dramatically with some 16 bit kind of stepping in some frequencies. By the way, IC34 looks a bit lighter in colour on its top surface, as if some talc had been dropped on it - maybe it's just 30 years of normal temperature running. Please let me know if the IC32 capacitive behaviour is a clue.

Many thanks - have a great day.

NB
User avatar Germany
Miks
Specialist Moderator
Specialist Moderator
Posts: 1912
Joined: Fri Oct 31, 2008 1:00 am

Re: DX7 II FD collapses to white noise on boot

Unread post by Miks » Mon May 27, 2019 9:46 am

Burfix wrote:
Mon May 27, 2019 9:20 am
Please let me know if the IC32 capacitive behaviour is a clue.
Hmmm - hard to judge. Never heard of or experienced such behaviour myself.

Have you measured the voltage (+5V) at Pin 1 & 32 of IC32? If yes, was it OK? Do you have an oscilloscope? If the answer is Yes I recommend to look if there's ripple visible (check ALL voltages!)...

If at hand try to (carefully!) cool IC32 by using some cooling/freezing spray to see if that changes anything...
My (key related) gear (in alphabetical order):
Ferrofish: B4000+
Kawai: K1 II
Korg: M1 (up'd to EX, w/ 'Cool Blue'), M1REX (w/ 'Cool Blue'), Poly-800
Roland: D-50, D-110, D-550, PG-1000
Yamaha: AW1600, DX7IID (w/ 'Cool Blue'), EX5R, RM50, RX5, SY99 (w/ 'Cool Blue'), TG500,
TX-802, YMM2
Sector101: SYEMB05 (5x), SYEMB06 (3x), EXFLM2 (1kit), MCD Sweet16 (1x), DataBlade32 (1x),
WaveBlade 8MB Card (1x) & 1x Programmer Unit for WaveBlade
Great Britain
Burfix
Member
Member
Posts: 29
Joined: Wed May 22, 2019 4:47 pm

Re: DX7 II FD collapses to white noise on boot

Unread post by Burfix » Mon May 27, 2019 2:24 pm

Ok Miks. That's a great help. Many thanks. I switched her on before lunch and there were no problems - for about 15 minutes, all worked fine.
After my sandwich, I turned it on and the white noise came back. On IC 34, pin no's 1 and 32 have zero volts (this is the IC with the white coating). Also when it was running before lunch, I noticed is was quite warm. I sprayed the top with contact cleaner and it showed an evaporation pattern that identified the chips location within the DIP package. This was the same for both with white noise and working properly. The pins no 1 and 32 on IC 32 have 5V. IC15 and IC24 also are warm to the touch but maybe that is not significant. Do you thing I should I artificially apply 5v to pins 1 and 32 of IC 34?

Thanks and best regards

NB
User avatar Germany
Miks
Specialist Moderator
Specialist Moderator
Posts: 1912
Joined: Fri Oct 31, 2008 1:00 am

Re: DX7 II FD collapses to white noise on boot

Unread post by Miks » Mon May 27, 2019 2:55 pm

Burfix wrote:
Mon May 27, 2019 2:24 pm
On IC 34, pin no's 1 and 32 have zero volts (this is the IC with the white coating).
That is correct. On IC34 the Pin 62 carries the +5V. The Pins 1, 17 & 32 must have 0V = ground potential.
The pins no 1 and 32 on IC 32 have 5V.
This is good too.
Do you thing I should I artificially apply 5v to pins 1 and 32 of IC 34?
Absolutely NOT! :o

If you do this you'll have short-circuited the +5 Volt rail of the psu! :naughty:

A few days ago you've got the schematics (via PM) from me - please take a closer look there.

P.S. when your DX is producing this 'white 'noise - does spraying some coolant onto IC 32 change anything anyhow (audio-wise)?
My (key related) gear (in alphabetical order):
Ferrofish: B4000+
Kawai: K1 II
Korg: M1 (up'd to EX, w/ 'Cool Blue'), M1REX (w/ 'Cool Blue'), Poly-800
Roland: D-50, D-110, D-550, PG-1000
Yamaha: AW1600, DX7IID (w/ 'Cool Blue'), EX5R, RM50, RX5, SY99 (w/ 'Cool Blue'), TG500,
TX-802, YMM2
Sector101: SYEMB05 (5x), SYEMB06 (3x), EXFLM2 (1kit), MCD Sweet16 (1x), DataBlade32 (1x),
WaveBlade 8MB Card (1x) & 1x Programmer Unit for WaveBlade
Great Britain
Burfix
Member
Member
Posts: 29
Joined: Wed May 22, 2019 4:47 pm

Re: DX7 II FD collapses to white noise on boot

Unread post by Burfix » Mon May 27, 2019 4:29 pm

Hi Miks. Thanks for the warning. The cleaner only makes a difference if it touches the pins. If I'm careful and only cover the top of the package, nothing changes in the sound. I'm starting to think the problem is in the boot sequence (if there is one) as the display is a mess as soon as the power is on. Or it could be with the display driver I'll take a good hard stare at the schematics and start checking pin voltages.

Thanks

NB
Great Britain
Burfix
Member
Member
Posts: 29
Joined: Wed May 22, 2019 4:47 pm

Re: DX7 II FD collapses to white noise on boot

Unread post by Burfix » Sat Jun 01, 2019 8:23 pm

Hello Synth friends,

So today I:

1. changed the battery and added a remote battery case for the CR2032 which is now stuck against the back panel of the LCD module.
2. Re-soldered the pins of ICs 34 and 32 as here was showing the strange capacitance interference effect and
3. brushed around the back of the main board to clear all the pins and solder of any fluff/dust that could be shorting things. There were a few strands of fluff across adjacent pins on closer inspection.

I saw on one good start-up that the on board patches had all gone and some crazy characters were showing as the patch names. I know this is normal when the Ram is de-energised by disconnecting the battery. The new battery shows 3.26 volts. the old one was on 3V. So whilst Mrs me held the synth up I pressed the Edit, 16 and 32 buttons at the same time and the firmware version showed with no error warnings.

I plugged my only ram cartridge in and powered it up again and all patches from the ram seem to play OK apart from 2 which has several notes that don't play. The same in each octave. I think that problem is just patch specific and will initialise them just to be safe.

I've had 1/2 hour of playing and all seems OK. But I don't know what I have done that made things better.

Backing a bit, it's worth mentioning that a few days before the trouble started, I tried to write some downloaded patches to the on-board ram from my PC using a USB-MIDI cable bought from EBay.

I didn't have any success using this with MidiOx but I'm not sure if that is due to my lack of MIDI know-how. But I am now starting to think that maybe I corrupted something via the midi connection that caused the problems to start. But its strange to think that this would stop the machine from booting properly.

Now I need to check my MIDI patch rite method before connecting again.

I hope it helps. Thanks for the support.

Regards

N
Great Britain
Burfix
Member
Member
Posts: 29
Joined: Wed May 22, 2019 4:47 pm

Re: DX7 II FD collapses to white noise on boot

Unread post by Burfix » Sat Jun 01, 2019 10:18 pm

I just watched TheMusicTechGuyUK on YT talking about how to configure for MIDI (How to...Set the Midi Channels on a DX7 II). He recommends to NEVER set "all channels" as this can result in sticking keys and corrupted patches. Hmmm! Maybe that is what I did.
Great Britain
Burfix
Member
Member
Posts: 29
Joined: Wed May 22, 2019 4:47 pm

Re: DX7 II FD collapses to white noise on boot

Unread post by Burfix » Thu Jun 20, 2019 6:59 am

I’m still waiting for the new ROM to get fitted but in the meantime - what are the chances of finding a replacement YM2604 IC? The current one looks like it has some talc on it which I’m wondering might be heat damage or where someone has been blasting it with cooling spray maybe. I’m going to try the same by the way when it arrives. Thanks.
Great Britain
Burfix
Member
Member
Posts: 29
Joined: Wed May 22, 2019 4:47 pm

Re: DX7 II FD collapses to white noise on boot

Unread post by Burfix » Fri Jun 21, 2019 5:49 pm

Just want to put this here because it’s a good tip. Today I found an old pc and used the ATX power supply to test the DX. The atx pc PSUs have 5, 12 and -12 V outputs and enough power to drive the synth. So now I’m more confident that the DX psu is not the cause of my problems. Another step....
Great Britain
Burfix
Member
Member
Posts: 29
Joined: Wed May 22, 2019 4:47 pm

Re: DX7 II FD collapses to white noise on boot

Unread post by Burfix » Fri Jul 05, 2019 3:41 pm

Hello

Status update:
Initial and current symptoms:

When cold, display looks normal as the system boots to a certain point. No response from keyboard or buttons. Then after a few seconds, white noise crescendo. This time period has gotten shorter indicating some degradation somewhere. Touching the tops of IC 32 or IC 34 makes the tone change in an 8bit way (junk theramin!).
2nd and further power cycles (when something is pre-warmed I guess) : random text on red LCD and solid bar on green LCD straight away. No buttons or KBD response. White noise crescendo happens straight away.

What I've done:
1. Tested with separate PC PSU and got the same behavior. Not 100% sure its a power spike issue, however I thought the modern PC's would be more fussy about spikes. Awaiting delivery of a proper working oscilloscope. I did get a Tektronix 465 from the local dump for £20. It kind of worked but not with enough confidence. I've since sold it on EBay for considerably more! :-).
2. Changed all electrolytic and ceramic disk caps - no change.
3. New battery on board - lost all the patches in the process - no change to symptoms.
4. Been around all IC and socket pins with soldering iron to re-flow - no change.
5. New Rom installed - no change. Actually it does the same thing without the ROM plugged in.
6. Cleaned salt deposits from both sides of board - no change.

I did get some replacement diodes (1SS133) but the band is yellow instead of the incumbent green. I read that the green banded ones use lower power but wondering if its not an issue with the newer ones. Didn't put them in yet. Should I go for it?

Once the oscilloscope arrives, I'll check for power spikes around the DM board. Then I'll try and check the data bus. Somehow!
I'll start by checking the input to IC 37 (DAC to audio feeding the output amp) because the jazzy white noise is a kind of 8-bit sound.
Then I'll move back to the inputs YM2604 and YM3609 (data bus) to try and see if there is junk on the bus. But that will get deep. Also, because the data bus parallels with a lot of IC's it will be hard to do any process of elimination work without fully de-soldering - unless I can hold them in a reset state.

Question 1: To hold the IC's in a reset state, generally do you ground the reset pin or take to 5V?

Question 2: Are IC 15 and IC 16 factory loaded with program or do they get it from the ROM on startup? If the latter applies then I am in with a chance to change them.

Thanks anyone. I hope this helps anyone in a similar fix. Frustrating but kind of fun.

Happy weekend

Nigel
Post Reply

Return to “Yamaha DX & TX Forum”