Kawai DX900 mains hum + other faults.

[steenamaroo]

UPDATED - PLEASE SEE REPLY #5.

Hi all,
I recently acquired a Kawai DX900 in lovely cosmetic condition.

It had PSU issues which I have now fixed, however...

Certain keys are MIA with certain drawbars in the upper and lower organ sections.
I can rule out the key contacts themselves as orchestral/percussion patches work fine.

For example. A and A# notes across upper and lower keyboard don't work on 16,8,4, or 2. (GA-22 divider board)
whereas they do work on 5 1/2, 2 2/3, 1 1/3, etc. (GA-23 board)
There are other notes which are vice versa.

There's a GA22 board for every pair of notes so 6 boards in total.
Swap boards - fault travels.

I'm thinking this comes down to the 8671 chip on the GA22 + GA23 divider boards?
I'm starting to realise it's a massive long shot, but does anyone have a source of these or know anyone who might have old stock in a shed somewhere?

Service manual is at this private direct link www.steenaudio.com/shared/dx900.pdf.

 

[ArnauTS]

Not worked at one but i do on others pianos/organs,first i will try to make sure first that all the contacts are clean because kawai's have usually a contact problem in the keys.

Look at http://www.organforum.com/forums/showthread.php?36501-Kawai-DX900-Buzz-hum there are tons of threads with info that could help you.
And last i can say, if you specify wich part of the circuit fails or have some problems maybe we can help looking at the schematic, sometimes two new eyes help

Hope you repair all the problems soon!

 

[steenamaroo]

Hi there,

Thanks for the response.

Unfortunately the problem is nothing to do with the keys as they work for the orchestral patches.

The power supply issues are now sorted and I've removed unnecessary info from the thread - sorry about that.
I've also added a link to the service manual, although the detail isn't great.


The missing note faults have been narrowed down to the GA-22 and GA23 divider/gate cards.
There's not a lot on those cards and the transistors on them check out fine so I'm looking at this 8671 chip.

Problem is, they don't seem to be available anywhere - The data sheets aren't even available online.
Big call out to anyone with info on these, please.


PS: That thread you linked is mine.
Specific to this model and that chip there really aren't tons of threads, unfortunately.

 

[ArnauTS]

Unfortunately i think it will be quite hard to find the exact sanyo lm 8671 so maybe you would need to design a small pcb with another cmos dividers to make it work.
I'll supose that they aren't socketed but it might be worth to swap lm 8671 with another card for example the ga-24 or ga-25 so you are sure that it's the problem.

Quite a trouble and long work but hope you can solve it.

 

[steenamaroo]

Thank you.
Yes, that was my next plan, if I can do it.
I've ordered some 42 pin sockets and solder wick.
If I can remove the chips without damage I'll probably socket them all for troubleshooting purposes and take it from there.

Designing an alternative solution has been suggested by a few people and it's probably the best solution but, unfortunately, it's beyond my knowledge right now.

Maybe I should be testing the diodes and caps on these boards in the mean time?
I don't know - Are they likely to fail across several boards?

 

[steenamaroo]

Great news!
I was able to source (the last?) 5 8671 chips and, having socketed all the chips in my organ for troubleshooting, determined that I only needed 4.
I've swapped bad for good and now everything works as it should.


I'm loving this organ already but it has a little bit too much noise right now for studio recording purposes.
I wonder can anyone help with this?

Two noises.
There's a sort of whine/interference sound in the background which is accentuated/attenuated with master volume and expression.
Engaging functions, operating switches, etc may slightly alter the sound - It would remind you of the kind of interference you might hear with cheap computer speakers and onboard audio.

The other is a very mild (but audible on recordings) mains hum, despite having recapped the PSU and amp.
I also bench tested PSU voltages for safety today and they're all as they should be.


I'd swear there was no buzz/hum on the day of the 8671 chip swap, but it was there the next day.
It doesn't change with volume/expression and isn't present on the headphone output.


If I was only able to eradicate the mains hum that'd be fine. The interference noise isn't awful by any stretch.

 

[FredW]

HI steenamaroo,

I know this topic is old, but please read ...
I have the same problem with my DX-900, and I'm also searching for 8671 chips. Cannot find anything about it on google, contacted Kawai, old parts sellers, nothing ! Would you have the kindness to give me the address where you found those chips ? Or do you have some ideas where to get them ? Or...Maybe you would have 1 or 2 to sell... For me, it's the whole percussion section which is dead. When I bought the DX-900, only few notes were working, and after few hours of playing, this section  stopped working definitively.
I don't have any informations, pinout, nothing so I don't know how many chips I need to repair this section...