Miks wrote:keep in mind that mostly the internal waveforms (samples) are stored to eproms too. But these are very often OTP (one time programmable) which means they have no window to be esased by using UV light so they look like an ordinary IC.
OTP PROM's... I'm learning more new stuff each day...
My SY99 has (among others) several OTP which have 42 (!) pins. Before ordering an eprom programmer you have to make sure that it can handle ALL of the required pins!!! That's why one of my programmers can handle up to 48 (!) pins...
If you're interested what type it is: look here...
http://www.yamahaforums.co.uk/forum/vie ... =45#p26639
It's the link with the BX48 in it...
Thanks for the heads-up about the pins, Miks. That thread contains very interesting reading material.
Those IC are M534001C, a 524,288-Word x 8-Bit MASKROM which means they had been pre-programmed by the manufacturer with the data given by Yamaha. I'm not familiar with the W7 but I think there's a good chance that they contain the OS (firmware).
Yeah, I had a feeling that those 2 might be the ones I was looking for. Thanks for confirming my thoughts, Miks !!!

It makes sense to me to have the firmware in removable IC's, like the BIOS firmware chip(s) in PC's.
They can easily be read-out by an eprommer... and then stored away (as a file) for future handlings...
And therefore the eprom programmer you mentioned in your first post should satisfy your needs.
That is great news !!!
BTW: what type is that IC on the left side of your opened synth, the one with the sticker on it...?
I think that's the beast that makes it all work, the CPU itself. It's a 64-pin
H8/325 4K2 (HD6473258P12). A model based on the Hitachi H8/300 CPU architecture, from what I can find on the net. I found a document online that has quite a lot of technical data on it : (
http://www1.futureelectronics.com/doc/R ... 58P10V.pdf).
Here's a close-up picture of it :

- H8/325 4K2 HD6473258P12 (XQ456A0)
I have no idea why that sticker is on there, though, or what "XQ456A0" means (Yamaha seems to have a lot of "XQ" stickers for parts, maybe it's a Yamaha part reference number ?). I don't think it covers an erase window. This seems to be the chip that controls the whole synth (32KB ROM, 1KB RAM, lots of I/O ports, clock timers, ...).
It runs at 5V if I read the technical document correctly. So does this mean that the rest of the W7 also runs at 5V (including the 2 removable PROM's) ?
mikesblunt wrote:I see the pics of his W7v2 and from these it is apparent that it contains OTP's (one time programmable) devices, whereas the W7 contains EPROM's.
Aha... So Yamaha chose to upgrade the W7v2, and that these 2 IC's are in fact the ones I was looking for. Thanks for confirming my thoughts, Mike !!!
Judging from the pictures I attached, do you believe that Yamaha made any other changes to the W7v2 (compared to the W7v1) ?
OTP's are effectively fuse link devices and have no data decay mechanism whereas EPROM's have a vaguely defined data retention life of around 10-30 years.
That is actually good news for me and other fellow W7v2 users. That means that they won't go bad. That's 1 machine less in my setup I have to worry about in terms of firmware corrupting.
EPROMS do die. My Philips LCR meter (electronic test equipment) suffered this some time ago but so far neither of the W7's in my family have fallen over.
Rest easy all of you who have these OTP's, they do not suffer from data rot.
Once again, Mike, thanks a lot for your assistance and your technical expertise. This is very much appreciated, and very interesting stuff to know !!!
Question-time again : what EPROM/EEPROM models/types would be compatible with the
M534001C ? (for backup and - worst case scenario - replacement purposes)
Just an idea for the webmaster/admins :
Maybe it's interesting to post pictures and information of all different Yamaha gear models/versions, as a reference for fellow Yamaha gear users ? Things like EEPROM/EPROM/PROM locations/models/types/operating voltage, compatible replacement EEPROM models/types, battery type, ... and everything else that might come in handy if some fellow Yamaha gear owner wants/needs to DIY, modify, upgrade or repair his/her machine(s). I think it would make an awesome addition to the site.
