[YamahaDX] Dead or alive DX7IIFD

[[e-mail] [YamahaDX]]

Hi all,
Im new to the group and this is my 1st post. I purchased a DX7IIFD and when I received it I was told the battery had been changed but the synth would not complete the boot sequence. All I get is 88 and then it freezes up with a Red letter P.
On the display there was just faded gray squares no text. I verified battery and supply and all caps, even the Quartz crystal. All was good. I then erased the Eprom and wrote the 1.9 bin file to the eprom. Then rebooted.


Now on the right of the Display I get "attery" I gather that is Battery and on the far left side I get " ~ ! " Yes the battery is good. Also all buttons are still frozen.


Any Ideas?


Best regards to all and thanks for the add.
Garry

[danforcz [e-mail] [YamahaDX]]

Maybe I'm completely wrong, but this looks like the OS Eprom is not quite OK, or OS file was not good, or there was some problem during burning the Eprom
 or Eprom is OK, OS file is OK, but it is not read in proper way
 Maybe Eprom is not sitting well in the socket
 or even some pin is bent?

Try to reseat all connectors as well


Could you start the test? Probably not, but try it.

Daniel Forro

Post by ***@hotmail.ca [YamahaDX]
Hi all,
Im new to the group and this is my 1st post. I purchased a DX7IIFD and when I received it I was told the battery had been changed but the synth would not complete the boot sequence. All I get is 88 and then it freezes up with a Red letter P.
On the display there was just faded gray squares no text. I verified battery and supply and all caps, even the Quartz crystal. All was good. I then erased the Eprom and wrote the 1.9 bin file to the eprom. Then rebooted.
Now on the right of the Display I get "attery" I gather that is Battery and on the far left side I get " ~ ! " Yes the battery is good. Also all buttons are still frozen.
Any Ideas?
Best regards to all and thanks for the add.
Garry

[[e-mail] [YamahaDX]]

I downloaded 1.9 version from here and burned it to the same chip. I of course erased it prior to burning. I have ordered some new chips but that will take a few weeks. Does anyone have some of the older version bin files for the DX7IIFD? Love to try some others. With the older Version installed I had nothing on the screen and after upgrading to 1.9 I had a little text. ???? Hmmm

[[e-mail] [YamahaDX]]

I would guess that the fact that it's saying something about the battery, on start up, means it's not happy with the battery.

Have you checked what the manual says about the low battery error / warning message?

When you say you've verified it, do you mean with a volt meter / multimeter? There might be track damage, if the previous one leaked.

This may or may not be relevant to the problem:

https://www.gearslutz.com/board/so-much-gear-so-little-time/687407-yamaha-dx7-iifd-program-help.html https://www.gearslutz.com/board/so-much-gear-so-little-time/687407-yamaha-dx7-iifd-program-help.html

- Andy

[[e-mail] [YamahaDX]]

Yes I measured with a voltmeter. There was no damage no no leaked battery. all looks good.
On the schematic there is a tiny section with the battery and the supply 5 volt feeds. TR1 and TR2 and the diode are all good. I am now wondering about IC 7-18 and 20. If anyone could share some light on the functioning of this part of the circuit . It might be a great help. Even better the DC voltage at Pin 11 of IC20. I have 245mv at that pin. Something wierd? Well, Ill keep on going and I will let you all know more as I go. Hope I can find some help here from another Tech.
Best regards to the Group.
Garry

[[e-mail] [YamahaDX]]

Do you have a schematic to work from, Garry? I have one for the DX7 (mark I,probably), but not for that one. I'd need to look at that, to make any sort of useful comment.

- Andy

[[e-mail] [YamahaDX]]

Okay. I found a schematic, and some manuals - some in the Files section, some on Manualslib.

So far, I haven't found anything about a low battery warning, but I have found a couple of hints that it shouldn't say "?attery !", or similar, on startup - maybe someone could verify what it does say?

Most of what I found was about one fitted with a Grey Matter E! board, so I don't know how much is relevant - e.g. this thread:

https://yamahamusicians.com/forum/viewtopic.php?f=35&t=10376&p=61495&hilit=DX7+IIFD#p61495

245mV at pin 11 of IC20 appears to just be a normal logic low level, from the reset circuit (pin 6 of IC7), pulled up by a 1k resistor to 5V, which suggests IC7 has open collector outputs - I haven't found where to look up the ICs, yet. IC20 appears to just be inverters, e.g. a hex inverter chip.

The part I'd suspect first, after the diode, would be C38 (4.7uF, 16V) which is meant to smooth the battery backup voltage, after the diode - probably meant to stop it glitching as the power goes off. Capacitors can fail in different ways... maybe that one's more or less shorting to ground?

I'd suggest measuring the voltage at that pojnt - across that capacitor or at the cathode of the diode, with and without the power turned on, if possible, then trace it to the input of the microcontroller / CPU that reads it. On the schematic, near the 3V battery and the diode, there's an arrow labelled "Backup"... I haven't seen where that goes, yet.

- Andy

[[e-mail] [YamahaDX]]

Some references to grid points in the schematic, to help separate the wood from the trees (see the edges of the schematic):

O8 : "System Reset" includes the 3V battery, diode, C38 etc.

- "Back up" leaves, as an arrow pointing down the page, roughly on the dividing line between O8 and P8

K5 : "Back up" reappears, and feeds to two of the SRAM chips (Vss pins)

- It must also go somewhere else, like an ADC or a microcontroller that has an ADC input, to allow it to be checked by the main CPU.

R10 : IC list, and other parts,

IC20 is an inverter chip (hex inverter, probably similar to 74LS04)

IC6 is a DM74LS14 Hex Inverter with Schmitt Trigger Inputs - used to make a clean transition from high to low, as the capacitor for the reset circuit charges up, when it's turned on (or the orther way, if it's reset).

- Andy

[[e-mail] [YamahaDX]]

Correction;

"K5 : "Back up" reappears, and feeds to two of the SRAM chips (Vss pins)"

- should say "... feeds to the Vss pins of the three SRAM chips at J6-K6".

- Andy

[[e-mail] [YamahaDX]]

Further correction :)

That should say Vcc, not Vss. I thought that was an odd way to label them, but it was a bit blurred. Vcc makes much more sense.

- Andy

[[e-mail] [YamahaDX]]

This post might be inappropriate. Click to display it.

[[e-mail] [YamahaDX]]

Cool. I'm glad you've got it working :)

- Andy

[[e-mail] [YamahaDX]]

Thanks again. It's now on Fleebay. Im a Tech and my love is just rebuilding synths or repairing.I already have too many. LOL I must say its a Beauty.
Chow