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KX88 Won't turn on


drewlane

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I have an old KX88 keyboard which I haven't played since we moved several months ago. I decided to get it out and hook it up but it wouldn't turn on.

 

I opened it up and discovered one of the fuses was blown. I tried replacing the fuse, but it keeps blowing out.

 

It looks like the fuse comes right after the transformer, but I'm not completely sure.

 

Is there anything else I can try without spending a fortune?

 

I like this keyboard a lot and would really like to keep it going if possible.

 

Thanks,

 

Drew

Austin, TX

 

p.s. If this is too technical, can you suggest another place I can post this?

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It sounds like a problem with the power supply. The good news is, of all the things to break on a vintage keyboard, that is probably the easiest to fix. Find a local repair shop and they should be able to take care of you. It sounds like a $75 fix to me.
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Originally posted by drewlane:

I have an old KX88 keyboard which I haven't played since we moved several months ago. I decided to get it out and hook it up but it wouldn't turn on.

 

I opened it up and discovered one of the fuses was blown. I tried replacing the fuse, but it keeps blowing out.

 

It looks like the fuse comes right after the transformer, but I'm not completely sure.

 

Is there anything else I can try without spending a fortune?

 

I like this keyboard a lot and would really like to keep it going if possible.

 

Thanks,

 

Drew

Austin, TX

 

p.s. If this is too technical, can you suggest another place I can post this?

If you can see a transformer can you see a capacitor? Should be a fairly large cylinder. Often silver or blue. If may be shorted. Carefully discharge it, for example, by putting a heavy screwdriver across the terminals and then measure its internal resistance with an ohm-meter. At first the ohm-meter will show that its shorted - you have to leave it connected for a while to get a true reading. Make sure your + on the ohmmeter corresponds to plus on the capacitor.
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There are actually quite a few capacitors on the circuit board that holds the power supply. There are some larger caps on the right side of the board.

 

Here is a picture of the power supply:

http://home.earthlink.net/~drew.lane/images/kx88/powersupply_sm.jpg

Click for a High Res Image of the Power Supply

 

You can see where I have removed the fuse that has been giving me problems.

 

Where should I start? :eek:

 

Thanks,

 

Drew

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I'll state the obvious and make sure you are using the right value fuse. Check what the manual says since the previous ones may not be correct.

 

I would suspect those 3 voltage regulators before the caps, too. Those are mounted on the aliminum heatsink.

 

Otherwise, check that the output connector on the power supply board (labeled CN1 in the picture) is seated well and correctly installed.

 

I also noticed that F2 is missing. Is this the one that is blowing?

 

Those two chassis lugs connected by the black wire (near the fuses) look like they could make contact with something when the lid is closed. Rotate them and make sure they don't.

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I think I'm using the right replacement fuse: 3/4 amp, 250V "fast acting" fuse from Radio Shack. This is what is listed on the circuit board and what was in there before.

 

Yes, fuse F2 is the one that keeps blowing.

 

I'll check the chasis lugs, but the fuse still blows even when the case is open, so I doubt that is the problem.

 

Is it possible that a bad power cord could cause the problem I've been having? I can't seem to find another power cord with the correct connector in my wire box to test this, however. I want to check all the simple stuff first. :)

 

Drew

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Well, those fuses are protecting what is happening after the power cord, so that shouldn't be your problem.

 

A schematic, of course, will easily determine what that one 3/4 A fuse is protecting. I'm still leaning towards one of those regulators (or what it provides power to) on the aluminum heatsink.

 

All of the power capacitors in the photo look fine.

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I found a repair guy that is only a couple of miles from my house. He works out of his house (has a shop in his garage). Says he's been doing it for 15 years. I dropped the keyboard off with him this morning since it was approaching the limit of my experience/ability.

 

I mentioned the voltage regulators, so hopefully he can figure it out. I told him I couldn't afford to invest too much into it, however.

 

He said that sometimes a screw or something like that can come loose and short circuit the board but I sure didn't see anything like that.

 

BTW, I was able to get a copy of the service manual but it doesn't have a schematic of the power supply and half of it is in broken english/Japanese! :rolleyes:

 

Drew

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I got my KX88 back today. It turns out there was a shorted capacitor, but it wasn't on the power supply board, it was on the control panel.

 

I'm not really sure how he diagnosed this, but I'm glad it's working again.

 

Cost about $75

 

Thanks for all the help!

 

Drew

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Interesting. It probably wasn't an electrolytic type capacitor, then (those are the blue coffee-can types). I have seen the molded capacitors short on occassion, but it still was quite rare.

 

Well, that's not too bad of a repair cost. Odds are greatly in your favor that it won't happen again.

 

Thanks for the follow up.

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Actually, I think it was an elctrolytic capacitor.

 

I asked the repair man for it, and he gave it to me.

 

It's quite small, coffee can shape, black, says 10v, 100uF.

 

I did a "continuity" check on it with my multimeter and it beeped, so I guess that means it's shorted?

 

I'm not really sure I remember how to check the ohms with my meter, however. What should it read?

 

Drew

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It will read continuity as it charges. Put the meter on Ohms. A good cap will charge and eventually you should read infinite ohms.

 

I guess they must have put a power capacitor locally on the control panel. Not uncommon. It is an infant mortality for those things though.

 

Either way, I doubt you'll experience the same problem in the future.

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Originally posted by drewlane:

I got my KX88 back today.

WOW! This is great - a 2 day turnaround. Often times repair techs are so busy that they take weeks for even simple issues. And the cost wasn't bad either. Good going man. :thu:
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Originally posted by Prague:

I'll state the obvious and make sure you are using the right value fuse. Check what the manual says since the previous ones may not be correct.

 

I would suspect those 3 voltage regulators before the caps, too. Those are mounted on the aliminum heatsink.

 

Otherwise, check that the output connector on the power supply board (labeled CN1 in the picture) is seated well and correctly installed.

 

I also noticed that F2 is missing. Is this the one that is blowing?

 

Those two chassis lugs connected by the black wire (near the fuses) look like they could make contact with something when the lid is closed. Rotate them and make sure they don't.

Wow - such eyes. Even with the magnifier on I could not read the silk screened printing on the board.

 

Glad its all fixed. We never would have found that on the board here. My next step would have been to disconnect the power supply from the rest of the synth and see if the fault went away. In this case it would have and we would have known the fault was elsewhere, but after that it would have been difficult.

 

Sometimes you can spot a bad cap because it will have goo on the outside. If the fuse was blowing fast though it never would have got hot enough for this to happen.

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