Yamaha Disklavier power supply help - schematic attached

[VintageValves]

That's kind of what I figured. If I'm getting power up to IC1, and the primary side of T2, but not after - would you suspect IC1 as being the defective part? They're available for around $50....

IC1 is pretty much the whole primary side. It is one I have not worked with, but looking at it and hte schematic, it is a hybrid like one of the old STK series audio power amps. It would have the control circuits as well as the transformer drive transistors all in one part.

Your meter will be OK for DC readings, but unlike a linear supply that works at 60Hz or 120Hz, switching supplies work at very high frequencies, like many kilohertz, and on AC it is likely your meter wouldn't respond to it anyway. This is scope terrirtory.

[Enzo]

The mains are rectified into +/-170v, centered around the earth. So if the thing isn't running, I still am not surprised if you see 170 or there abouts to earth on the terminals there.

I do suspect that IC, at least from here, but it is your money I am speculating with.

On many systems there are protections. A shorted rectifier on the secondary - and do check them all - can shut down a switcher. I don't see a feedback path from secondary to primary - normally done with an optocoupler to maintain separation. But the big IC could be sensing draw through the windings of T2.

One test to make is to watch closely to see if there is a momentary voltage spike right at powr up from any secondary output. Like the thing starts up, sees an overload, and instantly shuts down. Maybe a brief flicker of power light.

Also possible something out there is loading the system down. remove fuse F2, do the +8 and +20 return? Pull F3, does +20 return? Disconnect the two connectors on the right edge of the PS drawing, do the voltages now appear on those bare connectors? Just looking to see if ther is any way the IC is not at fault.

[VintageValves]

Thanks Enzo. This is exactly the guidance I need to do some more troubleshooting! I'll try these steps and report back later.

I do want to note that the connectors on the right side of the schematic are disconnected, because I don't have the full system here on my bench. All I have is the PSU, the connectors jump out to the rest of the piano...

[VintageValves]

I'm back. Had to take a break from this over the weekend.

Pulling the fuses one at a time did not get me any power out of the 8v, 20v or HV outputs. I tried power cycling the supply each time. I only have the power supply here, so the terminals are bare except the jumper I put across SW+ and SW-

No blips to the outputs upon power on - there is no power light on this box. There is definitely no action from the RY2 soft start relay either.

I did not see AC on my scope with the probe laid across the transformer. I have it set on 5mV and get no action there. Super interesting to know that my my multimeter won't be helpful on the switching side of things. I'll get a some action on the big power choke on the input.

I did diode check on the Triacs after the T2. I was able to remove and test D6, D7, and D8. All are good. D10 I had to check in-circuit as it and the components around it were fairly glued in. It tested as Expected with forward voltage one way, and ascending voltage as a cap charged the other direction.

Anything else to check before replacing IC1?

The mains are rectified into +/-170v, centered around the earth. So if the thing isn't running, I still am not surprised if you see 170 or there abouts to earth on the terminals there.

I do suspect that IC, at least from here, but it is your money I am speculating with.

On many systems there are protections. A shorted rectifier on the secondary - and do check them all - can shut down a switcher. I don't see a feedback path from secondary to primary - normally done with an optocoupler to maintain separation. But the big IC could be sensing draw through the windings of T2.

One test to make is to watch closely to see if there is a momentary voltage spike right at powr up from any secondary output. Like the thing starts up, sees an overload, and instantly shuts down. Maybe a brief flicker of power light.

Also possible something out there is loading the system down. remove fuse F2, do the +8 and +20 return? Pull F3, does +20 return? Disconnect the two connectors on the right edge of the PS drawing, do the voltages now appear on those bare connectors? Just looking to see if ther is any way the IC is not at fault.

[DownSizing]

I'm back. Had to take a break from this over the weekend.

Pulling the fuses one at a time did not get me any power out of the 8v, 20v or HV outputs. I tried power cycling the supply each time. I only have the power supply here, so the terminals are bare except the jumper I put across SW+ and SW-

No blips to the outputs upon power on - there is no power light on this box. There is definitely no action from the RY2 soft start relay either.

I did not see AC on my scope with the probe laid across the transformer. I have it set on 5mV and get no action there. Super interesting to know that my my multimeter won't be helpful on the switching side of things. I'll get a some action on the big power choke on the input.

I did diode check on the Triacs after the T2. I was able to remove and test D6, D7, and D8. All are good. D10 I had to check in-circuit as it and the components around it were fairly glued in. It tested as Expected with forward voltage one way, and ascending voltage as a cap charged the other direction.

Anything else to check before replacing IC1?

Hi VintageValves,

I have been watching this thread with interest. I have a Yamaha Disklavier MX100II that also appears to have a power supply issue.
Just wondering if you replaced IC1 and if that fixed your issue. Thanks.

[VintageValves]

Hi VintageValves,

I have been watching this thread with interest. I have a Yamaha Disklavier MX100II that also appears to have a power supply issue.
Just wondering if you replaced IC1 and if that fixed your issue. Thanks.

Hi there! I have yet to replace IC1 on this PSU. There was some delay with receiving the device (from ebay seller BocaSemi). They did not have it in stock and had to source it. It arrived just before I departed for Christmas vacation with my family. I got sidetracked on some other easier projects (Including a full rebuild on a Mesa/Boogie D-180).

I have the part, just haven't found the time to do the swap. I hope to get to it this week.

[DownSizing]

Hi there! I have yet to replace IC1 on this PSU. There was some delay with receiving the device (from ebay seller BocaSemi). They did not have it in stock and had to source it. It arrived just before I departed for Christmas vacation with my family. I got sidetracked on some other easier projects (Including a full rebuild on a Mesa/Boogie D-180).

I have the part, just haven't found the time to do the swap. I hope to get to it this week.

Thanks for the reply. Good luck with the installation and please post back - hopefully it will solve the problem.

Interesting comment by Enzo: "That relay closing applies power to the primary circuit, then there is right after it a soft start relay, which the triac shunts after power comes up."
I am suspecting that my unit may have been damaged during a storm. When the unit was working, there was an click (the primary circuit probably) followed by a click, but not as pronounced (soft start relay?). Now all I hear is the initial click and the unit does not power on. I am planning to order the part. I want to sell the piano and it would be really nice to have the Disklavier working. Definitely worth the $60 gamble.

[VintageValves]

Progress....

OK! So I got motivated and swapped IC1. Upon startup something rather excitingly threw a spark tiny spark. Not sure what from. I powered down, caught my breath, checked fuses and tried again. The supply is definitely doing more now than before the IC1 swap. There is a lot of whining (like you'd hear in an old CRT TV). Maybe a disconcerting abnormal amount. Perhaps it doesn't like getting run without a load? As mentioned previously 1.) I only have the bare supply in my possession - no piano or brain box 2.) I have very little SMPS experience.

My wife summoned me inside, so I didn't have a chance to do any further voltage checks.

I should also note that the part that BocaSemi sent is not a perfect match for the one I replaced. The main part number XK413A0 matches, but there are two other numbers that are different. The leads on the new part are shorter which prevented it from being mounted with it's mounting clip. Maybe there is something different internally too (hopefully not). I haven't been able to find any datasheets for this part. See attached photo.

Thanks for the reply. Good luck with the installation and please post back - hopefully it will solve the problem.

Interesting comment by Enzo: "That relay closing applies power to the primary circuit, then there is right after it a soft start relay, which the triac shunts after power comes up."
I am suspecting that my unit may have been damaged during a storm. When the unit was working, there was an click (the primary circuit probably) followed by a click, but not as pronounced (soft start relay?). Now all I hear is the initial click and the unit does not power on. I am planning to order the part. I want to sell the piano and it would be really nice to have the Disklavier working. Definitely worth the $60 gamble.

[Enzo]

Date codes or lot codes.

[VintageValves]

I plugged it up again today. Lots of whining... By the time I could get my meter on it, I saw the Kill-A-Watt go from 2A to 3A (KAW update is real slow) and then I heard a quiet tick, and now I think I'm back to square one... I'm out of time for the next week to work on it, but may revisit.

I found a SMPS repair place on the internet who says they have repaired this supply before. I suppose I may have to send it in... I'm close to wits end on this and have lots of things around that I know I can actually fix. I'll have to include a sob story about how my friendly local tech couldn't figure it out. Too embarrassing to admit failure.

[DownSizing]

I plugged it up again today. Lots of whining... By the time I could get my meter on it, I saw the Kill-A-Watt go from 2A to 3A (KAW update is real slow) and then I heard a quiet tick, and now I think I'm back to square one... I'm out of time for the next week to work on it, but may revisit.

I found a SMPS repair place on the internet who says they have repaired this supply before. I suppose I may have to send it in... I'm close to wits end on this and have lots of things around that I know I can actually fix. I'll have to include a sob story about how my friendly local tech couldn't figure it out. Too embarrassing to admit failure. [ATTACH=CONFIG]46579[/ATTACH]

I spoke with Yamaha service in CA and asked about sourcing the IC from them. They don't source parts at the component level and the P/S itself has been obsoleted. However, they pointed me to their authorized service center that repairs this supply. I called the service center (Tap Electronics) and was told they do the repair for a $200 flat fee. They also stated they are 100% certain the issue is the p/s.

[VintageValves]

Update

Quick Update. I sent the PSU to TAP. Turnaround time was less than a week. Of course they won't tell you how they fixed it. "REPAIRED ELECTRICAL
CIRCUIT BOARD REPAIR SOLDERED CIRCUIT BOARD" is all the invoice says.

$200 flat rate repair (plus the chip I bought and probably blew up) is a small price to pay to stay in my mother-in-law's good graces.

I suppose I have a good bit of learning to do if I actually want to be able to fix SMPS's.

Moderator - feel free to close this thread.

[Enzo]

Fixing SMPSs is like fixing cars. There is not one thing that goes wrong, ther is a zillion things. If the car comes in and needs a new spark plug, you can probably fix that. If your car comes in and needs the valves to be reground, you may need to learn something first and get the special tools. Replacing an alternator is simple, but rebuilding a tranny is not.

An SMPS failure can be simple, like a bad soft start resistor. A shorted rectifier on the secondary side seems simple to me. A SMPS blown up with a bunch of dead parts on the primary side might be above a novice. But then compare the power amp of any 1980s Peavey with say a 400BH board, to the power amp in a Fender FM212R. I think the Fender is hugely complex for what it is, while the Peavey is very direct. A less experienced guy can fix that Peavey, but will need help on that Fender.

Like anything else, you start at the start and learn.

[Fast1300t]

Hello, I have been using this thread as reference for repairing the same type of power supply. I have come across 2 different ones that both exhibit similar issues. What I have discovered is that IC1 XK413A0 is the part that always fails on these boards. I have come across a power supply that was still working but exhibiting the CRT type whining VintageValves had come across. After doing some diagnosis, I found several capacitors to be out of spec and or blown. After replacement of capacitors, the whining sound completely went away and the power supply functions perfectly now. Here is a list of the capacitors that failed in both the supplies:

C12 - Low uF
C15 - Low uF
C22 - Ok uF, High ESR
C33 - Low uF, High ESR
C34 - High ESR
C35 - Low uF, High ESR
C36 - High ESR

Unfortunately, I still have 1 power supply that will not power up due to the bad IC1 XK413A0 and the replacement chip is unavailable with an unknown ETA. I know this thread is several years old, but on the off chance VintageValves still keeps an eye on it, I would like to buy the XK413A0 from you if you still held onto it. Thanks!

Jeff

[VintageValves]

Hey Jeff,
What a blast from the past this thread is. I've learned a lot about SMPS and repair since then. Probably would have been successful repairing this myself if I knew then what I know now.

Anyhow, I sent the XK413A0 I'd bought off to TAP repair who ended up getting the PSU working. Still works to this day to my knowledge.

I bought the one I got from Boca Semiconductor which is now part of Summit Electronics. They're real good for obsolete parts and if their search is to be believed it they have 20,000 available

https://www.summitelectronics.com/se...&searchbtn.y=0

Hope this helps!