ProKeys 88 with intermittent sound ... help with repair ...

[dallas kruse]

I have a prokeys 88 that has an issue.

It gives little to no sound output and intermittently will crackle and then the sound will blast out (because I have my volume all the way up)...then crackle and the sound will go out or down to almost nothing at all.
There is also no headphone sound at all

I'd like to try and fix this issue myself and not pay to get repaired ... anyone else have this issue or know what to try to fix it?

I opened up the back panel and reseated the connecting ribbons but that didn't help. I tried jiggling some connections while the DEMO was playing to see if it was maybe a faulty connection but there's no correlation. I won't even touch the keyboard and it'll go into the intermittent crackling. I get full volume maybe 1% of the time it's on.

anyone help?

 

[happyrat1]

Sounds to me like a dirty or defective potentiometer volume control.

Two options.

First buy a can of potentiometer cleaner and spray it into the works of the pot and twist it/slide it thru the full range a dozen or so times and see if that fixes it.

If not, check the numbers on the pot and replace it with a brand new one. It should have a matching form factor, matching resistance and a matching number of legs (probably a dual stereo pot).

Here's a video on how to clean a dirty pot.

Those videos cover rotary pots but sliders work fundamentally the same.

Good luck

Gary

 

[dallas kruse]

thanks for the post and links.

the volume slider doesn't crackle at all. In fact, when just sitting there playing the demo, the keyboard outputs (volume) will crackle and get REAL loud then back to VERY soft ... almost inaudible. If I crank the gain on my mixer, it adds so much noise it's just unusable and risks blowing the channel if the keyboard output decides to burst into triple forte.

I haven't had anything that leads me to believe the volume slider is the issue but I'll certainly try it.

It sounds to me like a loose connection or intermittent part on the circuit board ...

 

[happyrat1]

Contact cleaner is STILL the first thing I'd try before looking for defective components.

Even if it's constant, it probably still is a dirty pot with a fluctuating resistance.

 

[dallas kruse]

no dice.

Any other ideas?

The crackling/popping sounds like it might be getting intermittent power surges or something.

I did look at the L/R output solder points and they look brown. Not BLACK (burnt) but brown ... not the same color as the other solder points ... maybe thats a clue? pic attached
But, I still dont get any sound out of the headphone jack either which leads me to believe it's a bigger problem than I expected.

 

[happyrat1]

The brown is just a resinous solder flux used to clean the contacts while soldering. it's harmless.

As for any other suggestions, it largely depends on your skill levels. Other suggestions may do your board more harm than good unless you know what you're doing.

It could be a simple cold solder joint, but I dunno if you're capable of finding and rewarming one without damaging your circuit boards or components.

Otherwise, my only other advice would be to take it to a pro to fix it.

Gary

 

[dallas kruse]

I'm wondering if it's a faulty power issue? Possibly a transformer or something that needs to be replaced?
I'm game to try and suggestions as I'm not sure I'm willing to spend 300 to get it fixed and sell it for 200.

 

[happyrat1]

Where do you get $300 for a professional repair? An intermittent dirty audio problem is a one hour job for a competent tech.

Any half decent electronics tech should be able to repair it for about $100.

 

[happyrat1]

BTW, when you cleaned the volume pot, did you clean all the other pots and sliders as well?

 

[happyrat1]

And transformers don't go "noisy" or bad. They either work or they don't.

Worst case scenario it's a blown output transistor. A $10 part and about $80 labor to diagnose and replace.

Do you at least own a DVOM you can test the circuits with?

 

[dallas kruse]

I've never had any keyboard in repair for less than 150 bucks. It's always at least 80 to just open the keyboard up and then they charge an arm and a leg.
I do have a DVOM but I don't have the service manual for the keyboard.

 

[dallas kruse]

Yes, I cleaned everything I could get to. I haven't taken the keyboard completely apart so obviously some pieces I couldn't reach.

 

[happyrat1]

Find a local computer repair shop and talk to their tech. Be friendly and ask him what he thinks it is and how much he'd charge for a repair.

You don't have to take it to a music shop for this sort of repair. There's no special techniques or parts involved. Any consumer electronics tech could fix this in under an hour.

 

[dallas kruse]

thats a good idea. the previous keyboard repair shops (2 of them) won't even touch my keys if they're not a licensed repair shop for the specific brand (Yamaha, M-Audio, etc).

 

[happyrat1]

Yup. Find a mom and pop computer shop run by a tech and he'll happily negotiate a price you both can live with.

Worst case scenario, failing that, you could always put it up for sale on Craigslist or eBay as is and take $100 for it and be done with it.

It really depends if you plan on keeping it or not.

Gary