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Re: Roland Keyboard Works for 50 seconds... then dies

Posted: Mon Apr 18, 2011 3:26 pm
by snod_donkey
To be honest its easy to change if you know what youre doing and have the tools...... would not recommend this repair if youve not done it before. You will damage the pcb

Re: Roland Keyboard Works for 50 seconds... then dies

Posted: Mon Apr 18, 2011 5:05 pm
by th0mas
The tool I use for removing IC's is this:

Image

With a bit of solder on your iron's tip, you apply heat to the IC pin by pin and use this vacuum pump to suck the solder out of the hole.

Re: Roland Keyboard Works for 50 seconds... then dies

Posted: Mon Apr 18, 2011 5:53 pm
by snod_donkey
th0mas wrote:The tool I use for removing IC's is this:

Image

With a bit of solder on your iron's tip, you apply heat to the IC pin by pin and use this vacuum pump to suck the solder out of the hole.

This is the sort of thing i use too

The board you are repairing is a double sided plated through hole type and not easy to do with this tool without a good deal of practice

Re: Roland Keyboard Works for 50 seconds... then dies

Posted: Mon Apr 18, 2011 7:41 pm
by cornutt
What you might could try is: If you can find a set of cutters with very thin, pointed blades, cut the legs off as close to the IC body as you can. Then you can desolder and remove each leg, one by one. Clean out the holes and you're ready to insert the replacement IC.

Re: Roland Keyboard Works for 50 seconds... then dies

Posted: Mon Apr 18, 2011 9:10 pm
by sam
Yes....I agree with the last post.

In most cases I have to cut the chips out, It also saves the board from over heating and saves the tracking.

I always clean up the area and use a tooth brush with isoprop alcohol.

Re: Roland Keyboard Works for 50 seconds... then dies

Posted: Tue Apr 19, 2011 6:30 am
by melbournesurprise
Well, things keep getting stranger.

I was poking around trying to make sure it was the IC before I went about ordering another one.

Underneath the green PCB containing the troublesome IC sits a metal foil-like sticker which acts as a ground. Usually the PCB is seperated from this ground by plastic legs.

However, I noticed that pressing down on the IC so that parts of the soldered joints underneath touched this grounding material would often have the effect of making the keys work again!

Lifting the PCB up, I connected one end of a probe to this ground, and used the other end to poke around under the PCB. I've identified various points that, when connected briefly to ground, almost seem to act like a 'reset' switch, and make the keys work again. I emphasize briefly, because the keys will NOT work while I make this connection, in fact, any sound within the speakers is immediately cut off. But if I quickly touch and release one of these points with the probe, the keyboard goes back to normal. These "points" are usually one specific end of certain resistors.

In fact, after I started all of this, now the keyboard refuses to fail! I have to manually "fail" it by poking around in other places on the PCB with my ground probe (shorting the circuit, I presume), and then I can "reset" it by touching those specific points, and hey presto, the keys work again.

I can leave the keyboard on for a couple of hours and more with zero failures ever since I started doing this. The IC is still hot, but again, the keyboard is now not failing.

I am baffled. I'm pretty tempted to install a switch/button connecting one of these points to ground, which I would then mount on the keyboard panel as an "emergency/panic" button to reset the the keys if the problem rears its head again!

Thoughts?

Re: Roland Keyboard Works for 50 seconds... then dies

Posted: Tue Apr 19, 2011 4:18 pm
by rhino
Most (even tech-heads) don't grasp how much is going on inside even the simplest microprocessor. Shocking the CPU into a reset by grounding something can seem to be a "fix". Looks more and more like some obscure gate in the Hitachi has gone thermal.

Re: Roland Keyboard Works for 50 seconds... then dies

Posted: Wed Apr 20, 2011 12:14 pm
by melbournesurprise
Okay, so over the last two days, I've been able to leave the keyboard on for extended periods with no faults whatsoever. I haven't touched or have needed to touch any of the grounding points I mentioned.

Rhino: your point is well taken, if anything I've stumbled unwittingly on a "fix" (which may not be a fix at all, but pure luck!) In the interests of practicality, what I think I will do is connect a "reset" switch as I explained above and then put the keyboard back together, inserting an insulating layer in between the troubled PCB and the metal foil on the keyboard's base (I had a suggestion made that unwanted contact with this ground might have been the cause of the trouble).

If the problem recurs, I will know exactly where to go -- take out the IC; stick in a socket and put a new IC in. (Please) correct me if I am wrong, but I see the worst-case outcome of my solution will be damage to the suspect IC, in which case the solution is what I am putting off anyway: replacing it! The IC is not putting out any abnormally high voltages into the rest of the circuit by my measurements. It it still hot to the touch, but not quite as hot as before.

This has been an interesting few days! Thanks to everyone again for all the help.

Re: Roland Keyboard Works for 50 seconds... then dies

Posted: Sun Apr 24, 2011 8:51 am
by waveterm
I would suggest that you measure the powersupplys DC outputs ( +/-15V and +5V ) for any AC voltage. It is a very common fault when capacitors get old.

Set your voltagemeter to AC and measure between ground and each DC output. If you have any AC voltage on the +5V ( which powers the Hitachi chip ) you´ve got a problem to fix. Check for dry joints on powersupplyboard and replace Capacitors. If this doesn´t remove the AC-leakage you will need to replace the voltage regulators and or the diodbridge.

WT

Re: Roland Keyboard Works for 50 seconds... then dies

Posted: Mon May 30, 2011 9:30 am
by melbournesurprise
Hello again!

Not surprisingly, the problem's reared its head again. This time it fails much quicker, within 5 seconds, and there's no real way to 'trick' it into working again.

I took waveterm's advice and looked for AC voltage (should have thought of this earlier!), and sure enough, there's about 10VAC on the 5V DC rail, and roughly 33VAC on the 15V DC rail. None on the DC -15V.

I've checked for dry joints before; there's none that I can see, and I touched up anything that was suspect.

So it comes down to the capacitors. To be frank, for someone (me) with only basic soldering skills, there is an intimidating amount of caps on this thing, particularly ones closely bunched together and/or glued to the PCB and surrounding components. I also have no idea which are the critical ones, so I would have to replace them all. And as waveterm said, the problem may extend beyond the caps.

I was thinking: is it possible to buy a 3rd party power supply and stick that inside instead? I've seen some units listed for around 50 bucks on ebay. However, my uneducated guess is the keyboard needs a specifically regulated and smoothed DC supply, and a run-of-the-mill 5V/+15V/-15V power supply that comes in a little box just won't cut it.

Is this the case?

Also: a while ago, just in case, I ordered a replacement Hitachi IC chip for the suspect one I had identified. I plan on replacing that IC now anyway, but don't want to be replacing it in vain if the AC leakage is going to cause problems again. So something has to be done about this power supply.

In case you're all wondering, this is not my only keyboard, but fixing it has turned into a bit of a challenge/obsession! Onwards...

Re: Roland Keyboard Works for 50 seconds... then dies

Posted: Mon May 30, 2011 10:47 am
by Stab Frenzy
Replace the big electrolytic caps in the power supply section, that should get rid of the AC on the DC lines. They'll probably be glued together for structural support if anything is, but shouldn't be hard to get them off.

Re: Roland Keyboard Works for 50 seconds... then dies

Posted: Mon May 30, 2011 5:12 pm
by waveterm
Ok, I see that the piano has built in speakers so that leads me to believe that the original powersupply must deliver some power. Replacing the original powersupply with a new modern one shouldn´t be impossible as it is only 3 voltages. One would have to check how much Ampere it should be able to supply to each voltage.

To see which caps to swap I would try to get the servicemanual from Roland and trace from the powerinlet through the transformer(s) to the rectifier. After that it should go to three voltage regulators and around there it should be big caps attached. One for each voltage. There might also be a number of smaller caps but those are not the primary concern. The big ones are.

WT