Fixing a Yamaha SPX-90 II

[Systolic]

I was given a SPX90II. It powers on, the menus work, it sees the input signal, but no sound is output on either channel.

Is there something easy I can fix on here, or should I put it up for sale on ebay broken as is...

[mjrippe]

The SPX-90s are notorious for power supply problems. They use a switching supply that was a bad idea to begin with and only gets worse with age. It is quite possible that the digital and logic voltages are good but the audio voltages are not. Depends if you want to pay to fix it or sell it as-is.

[Jidis]

Well I've got Systolic's box now.

I've got a bunch of parts coming Monday and grabbed all the electrolytics for the power board just for the heck of it, along with a new battery, but if anybody knows any other common problem areas in the 90II I might be able to check, I'd be interested. I'll also be looking around for a service manual (no luck thus far). It has several miniature slide switches and trim pots on the mainboard and it would be nice to at least have the peace of mind in knowing they were still on the correct settings.

Voltages weren't way off from what I could see with no load and the power board removed. The 5V line was 5.23. The +/- 18V audio rails weren't exactly equal (18.89/-19.15) but they hit a pair of 15V regulators over on the other board. Didn't check the voltages over there as the PS was already pulled out, but will in a few days.

One scary part is that one of the electrolytics is electrically wide open and the casing has a "bubbly" look to it, like it melted at some point or something. Sort of looks like it's been run over by a car. That's one of the reasons I want to make sure all the stuff that's in there is indeed stock values and the ratings are high enough. If that's all correct I guess I'll want to figure out what overloaded it.

I'll attach a picture. The melted cap is the 470uF on the left.

Thanks

PS- There was brown crusty glue crap all over the legs of several power supply components as well, so that's cleaned up now. Some other thread was saying that whatever they used can corrode or go conductive or something.

[tmarra]

Is that the picture of the bad supply or a good one because I don't see anything wrong in that picture. And those voltages don't really seem that far off to me. It won't hurt to recap it providing you install the correct caps, install them the correct way and don't bridge any solder joints. Most of the time the only problem with these is just a broken solder joint in the PSU. While recapping it you should encounter that joint if that is the problem.
Good luck.

-Tony

[Ike Zimbel]

I've also seen cracked solder joints on the output jacks. That could explain the "input - no output thing".

[tmarra]

Ike's right. Common fault on those 1/4" jacks. Forgot about that.
-Tony

[mjrippe]

Here's the service manual. Also check out this thread regarding PSU problems:
Problem with my SPX90

[Jidis]

Much thanks mjrippe for the manual and everyone for the comments!!

Tony- Yeah, that is indeed the actual supply with original caps. You can't see that cooked one from the picture, so I'll attach a solo shot just because it died such an intriguing death. The large cap in the center is also bulging on top, but I'm not sure what it started off like, as it's one of those weird high voltage low profile jobs and has a plastic coating even on the top. Capacitance is in range and it actually reads lower ESR than what I think my meter says it should be, but it's not real specific at those odd values.

The electros I was looking at all appear to be correct now per the schematic.

Solder joints on the bottom of the PSU board look surprisingly good. All the board space in the central area of that giant heatsinked transistor is slightly "browned", but maybe that's normal for this supply and the unit's age?

"Good input and no output" isn't quite accurate at this point. I couldn't get much of anything but some random flickering on some of the meter segments. The underside of that main board doesn't look too horrible either and a few areas I might have suspected near the rear check for continuity OK.

I've got a couple days to poke around before the recap parts get here. I'll probably reheat a bunch of joints and check as many diodes and resistors as I can on that power board.

Do you guys think it's safe to assume that if I'm getting something in the 'area' of +/-18 and 5V off those two connectors that this "no audio" issue is going to be somewhere over on that other board? I'll look around over there anyway.

Thanks!

[Ike Zimbel]

I wouldn't go too nuts until you replace that cap. It can't possibly be working in that condition. It's caps like that which give all the other caps a bad name...
best,
Ike

[Jidis]

Originally Posted by Ike Zimbel

I wouldn't go too nuts until you replace that cap. It can't possibly be working in that condition.

Good call Ike!

Caps showed up today and it's back up.

Sounds like I'm missing the right output channel though (except in bypass). I'll work on that over the next couple days. Damn mainboard is chock full of bipolars that I assumed were regulars when I ordered caps. If I don't have the right ones around here I may be doing another Mouser order.

Does anybody know right off if any of the other power supply parts in these things don't age well? Seems like some of the threads I read implied that it was more than just the electrolytics that crapped out in the SPX supplies. I'd stick some other stuff on the order too if it's still available.

-Thanks!

George

[Radardoug]

Some of the yamaha revs have bypass relays on the outputs, I'm not sure about the 90. Also the slide switches for +4/-10 are generally suspect.

[Jidis]

Yeah, this has 'em too. So it's an actual hard bypass. I think there's also a relay doing a brief power on mute or something.

I didn't realize these things were just an SPX90 with a ROM update and some added delay time or whatever.

George

[Tim Farrant]

If it is the power supply, I have removed the standard PSU and put in a linear supply on these. Fairly expensive, but gets it going again - forever!

[Jidis]

Originally Posted by Tim Farrant

I have removed the standard PSU and put in a linear supply on these.

I think that's what mjrippe did in that linked thread above too. It's weird how that same PSU board made it through to the newer revs of the SPX if it was so flaky (unless maybe they hadn't all started to self destruct yet). I've got cheaper stuff here that doesn't use switching supplies.

Tim- Just out of curiosity, aside from the +/- 18V and 5V lines, I think there were two others headed to the mainboard (PC/PE or something). You know what they do?

Thanks!