These electric pianos are about 30 years old. They tend to develop a common fault over time. The information stored in the waveform generator chips fails. Parts are no longer easily available from Yamaha. Some electronics techs on another forum site have the same issue. We think we might have a solution for how to replace those chips with more modern ICS. However we need to gain access to the data stored in a good set of chips.
I'd be very interested in talking to people who might have access to a CLP-550 or CLP-570 (same mainboard). Or even if you have a defective one that you might like to get going again.
I can't help you with a board, but if needed, I can read and program a wide variety of memory and microcontroller chips.
What is the part number of the old, failing chip?
Joe
There are three ROMs that hold the wave generator codes, and the tech at Yamaha I spoke to again today is fairly sure they'd be the culprits. (Or at least one of them, but which one??) The Yamaha part numbers are: XE843A00, XE844B00 and XE845A00. We've worked out that modern EEPROMs will substitute quite OK. But getting the ROM codes is another matter. Any assistance you can offer Joe, or words of wisdom are appreciated!
David
Those Yamaha part numbers don't help at all. How have you determined that an EEPROM will substitute? Do you have a real part number for those Yamaha-marked chips? Do you have a schematic with chip pinouts?
These old ROMs are programmed at the factory and cannot be reprogrammed. This type of chip was commonly used in lots of electronic gear decades ago (including HP and Tektronix test equipment). After all this time, it is quite common for these ROMs to start to loose the data programmed into them.
Some of those old ROMs are no longer made. Worse, some of them have different, non-standard pinouts compared to modern chips. If that is the case, adapters can be used.
What I would need is a set of original chips that are known good (if one ROM is failing, the others aren't far behind). Also, any pinouts, schematics or chip part numbers that you have to help identify the original chips. There is a good chance I could read the data from the good chips, and after finding a modern equivalent, program replacements.
If you want to pursue this, PM me and I'll give you contact information.
Joe
Got an expert on another repair site tells me this:
The roms are Toshiba tc534000
These are pin compatable with 27c040 eproms and 29f040 flash chips.
As you say, a good set of ROM chips means I can re-program new EEPROMs. But how do you get your hands on good ROMs without dismantling someone's pride and joy!
However, I do have a final strategy in hand. I am going to put turned-pin IC sockets into the board. And through a process of elimination and hope I might be able to identify the single ROM that has failed (if it is only one). Then I can buy a single programmed ROM from Yamaha at a reasonable price (~$70). THEN I can download the code from all three ROMs and burn replacements for the older ROMs.
Of course, all this depends on a number of factors, like a single ROM being the main cause of the fault.
I see you are getting lots of help over on Bad Caps forum. Since you are half a world away from me, their suggestion of getting someone closer to burn some chips would make more sense.
My only comment would be to use a DIP clip to read the old roms on a known good board. That way you don't have to unsolder them, risking damage to the good circuit board.
Once you have a good ROM dump, then you can unsolder the bad chips on your board. The easiest way to do that is by destroying them. Clip the leads on each ROM and then unsolder each pin separately. This is much easier than trying to remove a ROM intact.
Here is an example of a 40-pin DIP clip:
http://www.mcumall.com/comersus/store/comersus_viewItem.asp?idProduct=4425Joe
I just checked a few datasheets, and if those old ROMs are indeed TC534000, then yes a 27c040 is pin compatible.
Joe
Hadn't thought of a ROM clip - mainly because I didn't know they existed! Of course, I still have that issue of not having easy access to a CLP-550. But you never know - your idea might trigger something further. Someone at your part of the world might stick their hand up and volunteer to have their ROMs read.
Pulled the ROMs from the board and inserted sockets. Trying one ROM at a time didn't help to identify a single faulty ROM. ROM1 inserted on its own produced screeching sounds. Same case with ROM2, although not as fierce. ROM3 produced no audio output. Put all ROMs back in and couldn't get any strange sounds out. Starting to suspect the ROMs are not at fault. Have been tipped off that there might be a chip select problem. Those pins are fed from a hex inverter. Slightly unusual Toshiba type. A search shows at least one case of someone trying to track down a replacement because it had failed in his Casio keyboard. I have located its more common substitute and will exchange that and see if we have any luck. Otherwise I'm a bit suspicious of a crystal that clocks the sound generator chip. Pretty cheap to replace if I want to try that. You can see I feel pretty determined to solve this!
Hi Davo,
Though I have nothing to help you with, you have my total engineering empathy
Good luck,
Paolo
Hi Davo,
Did you ever get this problem fixed? I have a CLP-550 which sounds more like a distorted electric guitar! I have no sounds working except Piano 2 which gives the aforementioned sound!
Any pointers/advice would be gratefully welcomed!
Best regards,
Ian