Scott,

From the reported symptoms I suspect power supply problems, either dried out electrolytic capacitors or possibly a three-terminal regulator is going out or from years of heat has simply desoldered its ground pin.

Inspect the underside of the board under all or any three-terminal regs and resolder if it looks flaky, check the voltages of each and if the DC voltage isn't spot on the voltage for that partigular reg, replace it.

A quick way to determine if electrolytics have dried out is to heat that area of the board and the caps with a hair dryer (NOT a heat gun, hair dryer on high is enough) and then fire the thing up and see if you have better operation. If you do, shotgun those eleclectrolytics with appropriate value and voltage for each one.


--Mac

Thanks - this won't happen for at least a month, but I will bookmark this thread for future reference.

This sounds like a similar problem I had with my old Kurzweil K1000. I bought it new in 1987. I started losing sound from random keys and the display was going wonky. I bought a new keyboard and gave that one to a friend who used it as a sound module and controled it from another old keyboard. Finally one day he opened it up and played with a big ribbon cable inside and some of the keys came back. He finally cludged a regular old PC IDE cable and fitted it and it worked.

I just discovered something similar with my 2001 Mercedes CLK430 that I just bought. It has a partial digital readout in the instrument cluster. The pixels are known to go out with that dash as the cars get older. Merecedes wants $900 for a new cluster. Over on the MBZ forum there's a guy who posted nice pics of how to fix it and it involves a similar small ribbon cable with two clips on each end that power the display but those clips are not quite strong enough to make a good solid connection. He took a very small screw and drilled a equally small hole in the board right next to the connector where there's no soldered parts. The screw head gives just enough pressure against the middle of the connector along with the two clips at the ends to insure a good connection and problem solved, the pixels light right up. I mention this because the dealer I bought the car from had to fix my dash as part of the deal and they use a guy who charges $350 and this fix takes maybe an hour and costs what, 5c for the screw? Circuit boards are remarkably simple to fix in some cases. Btw, the instrument binnicle pops right out with two wire hooks that anybody can make.

Mac, you're an opportunist you should check this out. If I wasn't so busy doing taxes I might start a little side business. You have any idea how many Mercedes there are around here?

Bob

I have indeed had a few keyboards pass over my testbench where a ribbon cable failure of some kind was the culprit. Most times a cleaning of contacts or a simple blanket replacement of said cable is the cure. In the case of the mentioned Ensoniq, desoldering the cable pins and hard soldering the ribbon cable from board to board is the preferred method that lasts. In the case of this particular Ensoniq, it was stated that the ribbon cable had already been hard-soldered at a previous time. If that is still holding up, and no other ribbon cables have failed, the power supply would be the next logical area of investigation for this kind of fault. The good news is that the problem is most likely to be caused by one or the other, going by the number of them I've worked on, which isn't a statistically significant amount, really. The older keyboards are actually built like tanks in comparison to some of the newer ones in this regard, the technology of that era tends to lend itself more favorably to less expensive repairs like the ones mentioned as versus the need for proprietary parts replacement, that't the good news.


--Mac