Yamaha YC-45D 8' & 4' stops not working on Ab³ (top manual)

[DemeterOphelia]

Hello,

I just acquired a Yamaha YC-45D yesterday. I was informed that the 8' and 4' stops did not work on the Ab (3rd octave on the upper manual), but for $500 I had to buy it. I spent around four hours dusting with my air compressor, cleaning contacts, wiping everything down with a rag, re-dying the black leather exterior, polishing all visible metal/wood, gluing any peeling leather, et cetera, so everything looks great... Unfortunately, the stops still do not work (I didn't really expect cleaning the contacts to help, but I knew it also wouldn't hurt).

Along with the 8' and 4' stops, the 'piano', 'harpsichord', and 'marimba' stops also do not work on the Ab³ key. I can hear what sounds like a 1' muted stop on the marimba setting which leads me to believe that those are just presets of the 8' and 4' stops with some other added effects (bright, vibrato, et cetera).

I pulled all of the circuit board cards out and checked for any obvious signs of blown circuitry. In which I found none. Upon reading the original service manual (found here: http://dl.lojinx.com/analoghell/Yama...viceManual.pdf), I saw that Ab³ was generated by board UE5. That's all I know so far.

Any help on this matter would be greatly appreciated. I'm ready to play this thing!

Regards,
Demeter

[revtonynewnham]

Hi

There's a fault somewhere in the keying system.  I think these organs use some form of electronic keying, rather than the multiple contacts of older designs (?).  Check the active components in the keying circuit for the relevant note (power off resistance checks of diodes & transistors should do the trick - compare with an adjacent circuit.

Every Blessing

Tony

[DemeterOphelia]

A. Applied new solder to joint in case of loose connection or 'cold joint'.
B. All diodes to the right of "B." and facing the same direction (i.e. upward current) gave a measurement of 67 kΩ
C. Oddly, the diode for Ab3 gave a reading of .97 MΩ
D. Applied new solder to all joints in wiring buss for Ab3

Shorting "A." to an adjacent contact gave me the Ab3 tone in all registers, including the stops that weren't working before. So, I'm assuming that this is an issue in the keying circuit and not the stops.


My questions:

Why would the diode to the key that is not working give a higher reading than the other working keys' diode?
Shouldn't the reading be lower if the diode is bad?
Does this mean that a resistor is bad and letting more power through?

Again, thank you for any help!

Regards,
Demeter

[revtonynewnham]

Hi

Diodes can go open circuit!  I would try replacing the faulty diode & see what happens then.

Tony

[KB7DQH]

Apart from operating the diode at close to its failure point causing a shift in its forward-bias condition (extremely rare) the other (50%) failure mode is "open" ;) ;D  I hope your wiring diagram also includes a parts list as that will significantly aid your selection of a suitable replacement, assuming the original type is not still available.......

[DemeterOphelia]

I'm not as good as I would like to be in reading schematics. Would it be too much to ask for you to look at the link in my first post and see if you could give me a little information? I think it's a Toshiba 1S1555, but I want to be for sure. I'd really appreciate it!

Regards,
Demeter

[revtonynewnham]

Hi

I get an error when I try & open the link.

I would guess that pretty much any small signal silicon diode would work - I doubt that the characteristics are at all critical.  I'm out of touch with what's readily available these days.

Every Blessing

Tony

[DemeterOphelia]

Hello,

   I replaced the diode with a new one and I'm still getting the same reading on my diode checker. I checked the voltage and it, too, is giving me a ~1V difference than the rest of the diodes. I'm assuming that it was as I thought and it wasn't the diode, but something before the diode, not getting the right amount of power to the key. I would think a capacitor, but I'm no expert (hence why I'm asking on here). Any other ideas would be helpful. Thanks!

Regards,
Demeter

[JBR]

I would think a capacitor, but I'm no expert (hence why I'm asking on here).

Sorry to butt in here, but I think you may have hit the nail on the head.  I'm no expert either but, from what I've read, of all 'solid state' components capacitors are probably the most likely to 'go'.  You can often tell if one has blown simply by looking at it.

Don't just take my word for it, though.  I should google something like 'failed capacitors' and read up on how to test them and diagnose a failed one.

Good luck.

[DemeterOphelia]

No one is butting in. I need all the help that I can get! I have looked at every capacitor that I can see and none look blown (bulging, seeping or busted) to the naked eye. I'll have to keep looking, because the repair shop around my area said that, due to the age, they won't work on it. Strange since they fix organs from the 1800's. I guess they don't want to fool around with the endless electrical components though. I'm still open to suggestions and appreciative to the ideas that I've received so far.

Regards,
Demeter