Roland Keyboard Works for 50 seconds... then dies

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melbournesurprise
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Roland Keyboard Works for 50 seconds... then dies

Post by melbournesurprise » Wed Apr 13, 2011 2:27 pm

Hello,

I have a problem that hopefully users of older KBs/synths can shed some light on. I have an Roland HP-300 Piano Plus Keyboard. I bought it used, but I reckon it's at least 20 years old. The current problem appeared suddenly over the last two days.

Once I turn it on, I can play it for around 50 seconds, after which point it makes no more sounds when keys are pressed (the last note that works dies out like any normal note would). Neither is any output sent via MIDI after this point (MIDI works fine for those first 50 seconds). However, all power lights remain on, and if I plug a laptop, ipod etc into the 'line in' connection at the rear of the keyboard, whatever I play off that device comes through the keyboard's speakers.

Now, after it 'dies', if I turn it off and then IMMEDIATELY on again, I can play for only around 5 - 10 seconds before the keys and MIDI output dies once more. Basically it seems like the longer I leave it off, the longer it is playable for, up to a maximum of 50 seconds.

Based on what I paid for it, it's not really worth taking it in to get professionally looked at, but I love the feel of this keyboard, and want to do what I can before giving it up.

My electronics knowledge is fairly limited, but if I could identify the faulty component (if that was the case), I'd be able to remove it and solder a new one into place.

I've had a look inside and nothing immediately jumps out at me as being broken, fried, burnt or leaking.

Any ideas what the problem might be, or what I should be looking for?

Thanks

Dave

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

Post by rhino » Wed Apr 13, 2011 3:46 pm

could not find a schematic online (after a quick search), but I'd suspect the +5 volt regulator that powers the logic.
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Re: Roland Keyboard Works for 50 seconds... then dies

Post by sam » Wed Apr 13, 2011 3:49 pm

Good old dry joint....Also check the power supply.
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Re: Roland Keyboard Works for 50 seconds... then dies

Post by rhino » Wed Apr 13, 2011 4:48 pm

sam wrote:Good old dry joint....
I meant to say THAT !!!! (lol)
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Re: Roland Keyboard Works for 50 seconds... then dies

Post by Stab Frenzy » Wed Apr 13, 2011 5:49 pm

Yeah sounds like a dry joint opening up as the synth powers on. I'd be checking the power supply area first.

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

Post by melbournesurprise » Fri Apr 15, 2011 8:29 am

Thanks for all the help so far.

Note that my electronics knowledge is basic (I mucked around with kits when I was younger) so I may have gone about the following the wrong way...

This is the power supply: Image

Since most of the advice I've received pointed me towards the power supply -- I first replaced the fuses and replaced a suspect capacitor. I then got a voltmeter and took some readings. This keyboard has an internal transformer, from which 3 pairs of AC power wires go to the power supply PCB. There are then 3 pairs of DC voltage wires that leave the PCB, marked -15V, +15V, 5V.

Attaching the negative probe of the voltmeter to a metal grounding point on the inside of the keyboard's case, I measured the voltage on the AC and DC connections. DC, unsurprisingly, came up -15, +15, +5. AC came up 20, 18, 8. There was no voltage change whatsoever between when the keys on my board worked, and when they stopped working.

There were also other wires coming off the power supply in a similar arrangement to the AC and DC connections, but I couldn't get a voltage reading off them (and without a schematic, don't really know what they do).

Does the above mean I can rule out the power supply as the source of the problem?

Thanks again.

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

Post by sam » Fri Apr 15, 2011 9:52 am

It seems the power supply is fine.....Check the other boards for bad connections or dry joints...Esp the Amp section.
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Re: Roland Keyboard Works for 50 seconds... then dies

Post by melbournesurprise » Sun Apr 17, 2011 5:02 pm

Thanks all for the help so far.

Some more info which may help... at the point which the keyboard "dies" (anywhere from a few seconds to a minute, depending on how long the keyboard has been powered off for, as above):

- Whatever sound playing at the time the keyboard dies is left fading out in the speakers.
- I am able to use the front panel controls to change the volume, tone/instrument, and properties of the sound as it fades out.
- If keys are played with the sustain pedal, the notes continue on when the keyboard dies as if the sustain pedal has never been released. The keyboard no longer responds to input from the sustain pedal (releasing it or pressing it again has no effect).
- If I connect the keyboard to a MIDI software synth on my laptop, any MIDI notes sent by the keyboard either fade out or continue to sustain (in the same way as they do in the keyboard's speakers) when the keyboard "dies".

Does this help narrow down where to check? If so, what (in general terms) is the best way to go about searching for the fault?

I don't know if this will help, but here's a more detailed image of the keyboard:

Image

- A is the power supply, expanded at top right
- B is the PCB connecting to the rear input/output jacks
- C is the front panel PCB containing volume, tone selection, etc
- D is a small PCB connecting to the headphone jack
- E is the keyboard; at bottom left is the rear of this. I've had a look underneath this PCB and everything is fine. The keyboard usually attaches to the white connector on the top right of "G".
- F & G are expanded at bottom. I don't know what the specific function of each is. You can read the names of the ICs if you view the full image.

Thanks again,

Dave

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

Post by snod_donkey » Sun Apr 17, 2011 8:52 pm

From the fault it sounds like a problem as the component heats up a little. If you had a can of freezer spray you could try cooling parts until the unit starts to work again..... as it then warms again it should go wrong

this could be an i.c, resistor, cap ???

Its something to try and i have fixed many synths this way

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

Post by th0mas » Sun Apr 17, 2011 9:38 pm

Is there a wall wart power supply for this thing? Don't rule out that it has gone bad.

Also, if you pull the power while the unit is on, does it fail in the same manner?

Good for you trying to fix it yourself. regardless of the outcome you'll learn a lot (even if it is "I shouldn't try to fix synths" ha ha ha)

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

Post by rhino » Sun Apr 17, 2011 10:43 pm

Since the tone continues after shutdown, chances are the CPU is still running. Guess we need a schematic to see where the keyboard is decoded. When it dies, try flexing the mainboard slightly (board G). A fault in the sound generating circuitry would p'bly NOT kill the MIDI OUT...that - as a rule - comes right from the CPU. The time delay (power off longer = plays longer) sure sounds like a thermal problem either in a chip, or a bad joint.
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Re: Roland Keyboard Works for 50 seconds... then dies

Post by th0mas » Mon Apr 18, 2011 1:16 am

rhino wrote:Since the tone continues after shutdown, chances are the CPU is still running.
Just because the CPU is still running doesn't mean power is still applied properly from the powersupply or from the wall wart. Capacitors will keep power supplied for up to a few seconds.

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

Post by melbournesurprise » Mon Apr 18, 2011 2:08 am

Thomas: the power supply/transformer is all internal, in my earlier posts you'll see some simple tests I've done on the power supply, everything appears okay. Powering off the unit cuts off any sound playing, almost immediately. And yes, all my friends are telling me to just quit. Not yet :D

Rhino: I gave it a bit of a flex, no result.

Snod: Going to pick up some freezing spray today. Seems like my best bet right now, besides checking for dry joints (again!)

Cheers

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

Post by melbournesurprise » Mon Apr 18, 2011 1:34 pm

Good news!

I was pointed towards the green board ("G") by a synth repairman, as he was certain board "F" generated the tones.

I noticed one of the ICs (large one second from bottom left on G) was unusually hot to the touch, and became warmer as the synth was left on, to the point of uncomfortable heat.

I measured the voltages on the IC's legs before and after the keyboard failed, and sure enough, there were differences (although the differences were not always uniform).

I also had picked up that can of freezing spray. I tried an experiment where I would let the keyboard fail, turn it off for ten seconds, and then on again. As usual, I only got about 5-10 seconds of operation out of it. I did this two or three times, and got the same result. I then blasted it with freezer, turned it off and on again within 10 seconds, and this time it worked for over a minute.

I think the combination of (1) excessive heat, (2) voltage differences and (3) success of freezing the IC leads to the pretty safe conclusion I've found my problem.

The IC is labelled:
3F1
HD6801S0P
A78

Two final questions:

1. Is it a fairly safe bet to start by changing the IC, rather than seeing if it's something in the circuit that feeds the IC that's causing the problem?

2. If so, are there any "changing ICs for dummies" tutorials on the web? Is it workable to cut the legs off the current one, and solder the new IC to those cut legs, slightly raised above the PCB? Or is this something that really should be done by a pro? All I have is a soldering iron and pliers.

Thanks again for all the help. Much appreciated and very useful, I would've been lost without the help and direction. I'll be sure to post the results of the IC change (if that is the way to go) once it's all done.

Dave

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

Post by rhino » Mon Apr 18, 2011 3:04 pm

Good work ! We LIKE success stories!

Now the bad: IMHO you should not make this project your first attempt at changing a 40-pin IC.

But if you do, you'll need a 25-watt iron with the smallest (1/64) tip, de-soldering braid (I like "Pro-Wick"), a rubber-bulb de-soldering tool. (the spring-loaded ones can be too rough on such narrow copper traces)

It's kinda a rule that when you replace an IC, you install a socket.

You may find this vintage CPU at www.utsource.com

work carefully and you may come out OK.... but maybe this is should be a tech job.

Remember: Solder bridges are your hidden enemy !!
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