Roland Keyboard Works for 1 min... then dies

[melbournesurprise]

Hello,

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 signal 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 die 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 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? I've attached a picture (blurry, I'm afraid) to give a rough idea of my keyboard, with the front panel lifted up.

Thanks

Dave

 

[(*steve*)]

I would start by measuring the power supply voltage, both as you turn it on, but also over the next minute or so, and then while you power off briefly and back on again.

I would also be looking for any signs that anyone has tipped any liquid through ventilation holes or speaker grills.

 

[melbournesurprise]

Thanks for 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:

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.

 

[(*steve*)]

Fault finding is a process, and one where one wants to be fairly sure of what is backing up one's decisions.

In this case, the power supply is a good starting point because it is clearly working to some extent (thus meaning that things like the transformer, fuses, power switch, power cord, etc., are at least somewhat functional. If we can confirm that the power supply is working then the problem lies further in, if we see problems then we need to track them down.

From your measurements it appears that the PSU is working (you have not been able to check if there is excess ripple on the output, but the faults are not really suggestive of that.

The next step is to form some working model of what the unit does, and from that consider where faults could occur which would cause this type of problem. Naturally this step is aided by service manuals, block diagrams and/or circuit diagrams.

Given that we currently don't have any of these, then we need to make stuff up

So here is my conceptual block diagram:

I imagine that there is a keyboard, a decoder, a synthesiser and an amplifier. And there is a power supply connected to them all.

We've checked the power supply, and you tell us that even after the keys on the keyboard stop responding, any sustained sound still plays. And you also make no mention of distorted sound or other issues pointing directly to the amplifier.

This pretty much tells us that the amplifier is working. Now, you could test that by injecting a signal into the input of the amplifier and seeing if it was heard through the speakers. But I assume you do not have a signal source, so let's leave that for the moment. (EDIT: You have effectively injected a sound into the amp, confirming that it is working)

The keys a re mechanical devices. And I can't see any reason why they (all) would suddenly fail after a few seconds, only to start working after the power is removed and reapplied. So I would likewise discount the keys themselves.

There is a possibility that the problem could be caused by power to or scanning of the keyboard. If you have a mode where keys are sustained as long as they are pressed, does the note continue to sound even while other keys are not responding? Or does it seem like the key has been released when the fault starts? If the unit is behaving like the key is still pressed, does it respond correctly to the release of the key?

This is pretty much leading us into the key decoder. This is the part of the unit which determines what key is pressed and/or released, and passes it on to the synthesiser which makes the sounds. It is certainly possible that the decoder is stopping, or failing and that this is causing the problem. Indeed many of the questions above actually will point more to the decoder than he actual keyboard (depending whether the scanning of the keys is separate from the decoding of the keypresses) .

I would be initially suspecting the decoder as a location which needs to be closely looked at.

The next stage is the synthesiser itself. This is likely to be a board with a very large IC on it. It is also likely to have the pitch and/or tuning controls on, or wired to it.

If the unit has any sort of "beat" controls that create a continuous percussive background, then turn this on and see if it also stops when the sound does. It is possible that the synthesiser stops responding to the decoder, and continues with what it was doing, without further input. The synth probably controls setting of voices (although the decoder could be doing this too). Do other (non-keyboard) functions also become unresponsive when the keys stop responding?

That's probably enough for now

 

[melbournesurprise]

Hi Steve,

Thanks for the help so far, very detailed (and very much appreciated!)

Some more info for you, in answer to your questions.

At the point which the keyboard "dies":

- 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".

There are no beat or rhythm functions.

You seem to be right in that the signs point towards a failure somewhere in the decoding of the notes.

Once I sort out what area of the keyboard is responsible for decoding, 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:

- 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 they do; I suspect as you said, one is the synth and one is the decoder.

Thanks again,

Dave

 

[(*steve*)]

It is likely that the PCB under the keyboard is decoding the keys. You say that the keys and pedals are affected, but that the various function buttons are not. This means that the fault is possibly common to the former two and not the latter. Are the pedals connected through to the PCB under the keyboard?

Boards F and G seem to be connected with the synthesiser functions (and possibly other stuff)

I would be taking a closer look at the PCB under the keyboard, although I can't imagine at the moment how this fault may occur.

Some random stuff I might be looking for are inhibit pins of IC's being asserted at the time the keyboard goes dead, or clock signals which disappear. If there are a limited number of signals leading between this board and the others, you could try to determine if any change at the time the fault appears. The problem then is to determine if it is cause or effect though.

Sorry, I'm not sure if I'm going to be of much help, and I can't even be sure that the fault is where I'm pointing you to. I'm really just telling you the thoughts which would go through my head if I were in your position.

 

[melbournesurprise]

Good news!

I was pointed towards the green board ("G") by a synth repairman, as he was certain board "F" generated the tones. This confirmed what you mentioned about the decoder being the source of the problem.

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.

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 a 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'll be sure to post the results of the IC change (if that is the way to go) once it's all done.

Dave

 

[(*steve*)]

Yes, in retrospect I should have asked if something was getting hot. I dropped that ball

I would be careful in jumping in to replace the IC. The problem could quite easily be something that is causing an excessive load.

I would look around the chip and see if there is anything also showing signs of heat, or even some small piece of metal that has managed to wedge in somewhere and short something.

You may have a problem getting a new HD6801S0P.

You can remove the chip the way you suggest, but it destroys the chip whether or not there is anything wrong with it. An alternative method is to use a solder sucker or solder wick to remove the solder from all of the leads and let it just fall out (can you tell it's not really that easy?). Then you could solder in a socket and try the new chip.

The chip is the processor by the way. It's hard to think of how you could load down a signal without it preventing the processor from working in some way.

It may be time for photographs of both sides of the board around this chip.

 

[melbournesurprise]

Well, things keep getting stranger.

As you warned, 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?

Here are pics as you requested. The point I usually use to "reset" the keyboard is the leg of R24 closest to the centre of IC 6801 (the hot one).

 

[(*steve*)]

OK, you're going to have to define "hot". It may just be "warm"

What does it score on the finger test:

0: Feels cool (cooler than if I touch my own arm)
1: Feels very slightly warm (about the same as touching my arm)
2: Feels warm, but not hot
3: Feels very warm, but I could leave my finger there indefinitely without any fear.
4: Feels hot. I can leave my finger there for a while, but I'd prefer not to.
5: Feels quite hot. I can leave my finger on it for a few seconds, but that's about all
6: Feels really hot. I can touch it, but I can't leave my finger resting on it.
7: Extremely hot. I can touch it, but I have to check my finger for burn marks afterwards
8: Superlatively hot. It feels really hot before I get my finger near it, and I don't want to leave flesh behind.
9: Glowingly hot. The device is smoking, in flames, or glowing with radiated heat. Fingers are well away.
10: House on fire. Not going in to check. Fingers dialling fire brigade.

4 or below is almost certainly OK. 5 or 6 are OK in some cases. 7 is generally only seen in devices obviously made to get hot. 8 or above are almost certainly signs of faults. (This is obviously a very rough guide)

It is possible that part of the shield was touching something that increased current flow to a point where the processor got too hot, or maybe that the shield underneath came into contact with stuff as it heated up.

If you can ensure that the shield is kept away from the board -- and typically you might find a layer of clear plastic, or cardboard between them -- then your fault may be cured.

I'm concerned that if minor flexing of the board is an issue that the problem may recur (and may be worse next time) if you don't place some fairly tough insulating layer between them.

 

[melbournesurprise]

I like this scale!

It depends where I place my finger on the chip. At either the top or bottom of the chip, it's a 4. If I place my finger in the centre of the chip, it's between 5 and 6. I have to remove my finger after 5 seconds.

This after the keyboard has been on for a good couple of hours. Keys are working.

 

[(*steve*)]

The actual chip is under the centre of the package, so that will be the warmest.

You're probably seeing (feeling) a temperature of around 60-70C. I'm thinking it's a bit on the high side.

 

[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.

Although I may have 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 last-resort "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 as you suggested, Steve.

If the problem recurs, I will 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.

Thanks again for all the help Steve, much appreciated. Would've been lost without a lot of the advice.

 

[(*steve*)]

If you're planning to add a reset, I would suggest you look at the specifications for the chip and determine how to reset it correctly. A random grounding of a pin may work, but I would not recommend it.

Before you cut the chip out, make sure that you have an exact replacement. If you remove a working (if possibly damaged) device, and a new one fails, then you are in a worse place.

 

[p_wats]

Hey guys,

I've been reading this thread intently, as I had a similar problem with an electric piano recently (ended up scrapping it...long story).

Glad to hear it's almost working!

I have the opportunity to get an HP-300 locally for $100...think I should grab it? We've got a bunch of synths and midi controllers, but nothing that's just an electric piano/nice looking piece of furniture...

Unfortunately, I can't help much with your current situation...but good luck!

Paul

 

[melbournesurprise]

Hey Paul,

Depends what you're going to use it for really -- I bought mine for a bit less than that on eBay, I planned to use it as something to mess about on while I saved up for a new keyboard, but I've ended up really liking it and sticking with it.

95% of the time I use it as a MIDI controller. What I personally really like is the feel of the keyboard. Since I originally learned classical piano growing up, I find a lot of keyboard keys to be way too light and flimsy for my liking. This one's got a solid feel about it, without being as tiring to play as a piano. The wooden case is pretty rugged as well.

I play in a band occasionally, and when I stick it on stage (I only have the top part, not the wooden stand) I always get a comment or two about its retro looks. Only downside is that's it's bloody heavy to move!

So yeah, that's why I like it. Depends what you have and what you're going to use it for I'd say. I doubt I'd still be using it as much without the MIDI.

 

[p_wats]

Thanks for the advice (I don't know of anyone else who actually has one of these...)! I picked it up on the weekend complete with stand and bench for $100 in great shape.

As, expected, the piano sounds are underwhelming, but I have to say I love the "e.piano" setting. Very usable in my book. I also had it controlling an Alesis NanoSynth module through a Mooger Fooger Murph filter and got some crazy sounds! Very fun.

I think there might be something loose inside mine, as every now and then I get farty sounds depending on if I've moved it around. That said, I plan on opening it up anyway to see what mods might be available to the chorus section (add a depth pot maybe).

How is yours doing?

 

[melbournesurprise]

Mine's still going strong, no complaints so far. If you want to open it up, the quickest way to to do is take out the two screws on each side of the unit, and the five smaller screws that run in a straight line under the jacks and power on the back. Then the top panel should, after some wiggling, fold back.

Then if you want to take the keys out, there's a row of five screws and a row of three screws that run the length of the underside of the unit, take those out and the keys will lift off as a whole. I only found this out after extensive trial and error

 

[p_wats]

Then if you want to take the keys out, there's a row of five screws and a row of three screws that run the length of the underside of the unit, take those out and the keys will lift off as a whole. I only found this out after extensive trial and error

Ha. Thanks! Saves me the same trial and error. I can't count the number of times I've taken a synth apart and undid the wrong/too many screws.

 

[Deigh]

A quick check....can you test the power input? if the voltage dropper has been replaced with one of lower amperage than the genuine one then the result can be exactly as you are getting.
Regards
Deigh