Roland HP-860 electronic piano has HUM

[Josh9.0]

Hi.
I recently bought a 2nd-hand Roland HP-860 electronic piano (88-key,
analogue).
It has a louder hum than the piano notes.

I'd like to fix it myself. I have been learning electronics most of my
life & I'm in the 3rd year of Electronics Trades at TAFE NSW
(Australia).

I've removed the plug from the final stage PCB (Revo board), and the
amplifier is quiet. This makes me think that somewhere before the amp,
there is hum being made.
I could poke around with my CRO, but I wouldn't know what to look for.

This piano has heaps of boards, for which I've worked out most of the
features.

I could try replacing all the aluminum electrolytic caps, but that
could just be a waste of time.
It was made some where between the late 70's and early 80's.

I looked for date codes, and only found 1, I think.

This piano uses a wiring loom design, with some PCBs using plugs, but
most are wired up (soldered).

To see pics of it, search Google images for
"roland hp-860"
use quotes and thaisecondhand.com has the pictures.
NOTE: I have the 240VAC version.

Please help!
TIA

 

[Gareth Magennis]

Hi.
I recently bought a 2nd-hand Roland HP-860 electronic piano (88-key,
analogue).
It has a louder hum than the piano notes.

I'd like to fix it myself. I have been learning electronics most of my
life & I'm in the 3rd year of Electronics Trades at TAFE NSW
(Australia).

I've removed the plug from the final stage PCB (Revo board), and the
amplifier is quiet. This makes me think that somewhere before the amp,
there is hum being made.
I could poke around with my CRO, but I wouldn't know what to look for.

This piano has heaps of boards, for which I've worked out most of the
features.

I could try replacing all the aluminum electrolytic caps, but that
could just be a waste of time.
It was made some where between the late 70's and early 80's.

I looked for date codes, and only found 1, I think.

This piano uses a wiring loom design, with some PCBs using plugs, but
most are wired up (soldered).

To see pics of it, search Google images for
"roland hp-860"
use quotes and thaisecondhand.com has the pictures.
NOTE: I have the 240VAC version.

Please help!
TIA

Have you looked at the power supplies with your scope? Here's your chance
to put those 3 years of education to good use.




Gareth.

 

[Josh9.0]

No I haven't!
Thanks for the tip, and thanks for the quick reply!
I'll go and try it now.
It has a bunch of different voltages out, and they're labelled on the
PCB!
I guess I should look for ripple on what should be DC, right??
Then trace it back to the offending cap(s).
Then go buy some new ones of those only.

BTW: It has a main voltage going to all the keys of 46V which measures
43V.

 

[Gareth Magennis]

No I haven't!
Thanks for the tip, and thanks for the quick reply!
I'll go and try it now.
It has a bunch of different voltages out, and they're labelled on the
PCB!
I guess I should look for ripple on what should be DC, right??
Then trace it back to the offending cap(s).
Then go buy some new ones of those only.

BTW: It has a main voltage going to all the keys of 46V which measures
43V.

You seem to be jumping to lots of conclusions for no apparent reason.
This is not going to help you.


What's with this "offending caps" businsess? You seem to have decided there
is a cap problem and replacing them will be the solution.
Stop guessing, it will get you nowhere.

You need to investigate and gather information. You start with the power
supplies, If they are OK then you look elsewhere.



Gareth.

 

[PeterD]

No I haven't!
Thanks for the tip, and thanks for the quick reply!
I'll go and try it now.
It has a bunch of different voltages out, and they're labelled on the
PCB!
I guess I should look for ripple on what should be DC, right??

Sounds good.

Then trace it back to the offending cap(s).
Then go buy some new ones of those only.

BTW: It has a main voltage going to all the keys of 46V which measures
43V.

Ba-ding... Now I wonder why that voltage is low? Could it be, oh,
maybe... A bad filter cap?

 

[Archon]

You seem to be jumping to lots of conclusions for no apparent reason.
This is not going to help you.


What's with this "offending caps" businsess? You seem to have decided there
is a cap problem and replacing them will be the solution.
Stop guessing, it will get you nowhere.

You need to investigate and gather information. You start with the power
supplies, If they are OK then you look elsewhere.



Gareth.

Thats because searching for any electronics problem on google comes up
with "check all the electrolytics", ESR is the new religion. I get so
many people bringing stuff to me saying, hey its probably a cap, you got
an ESR meter?, can't be more than 10 bucks to fix. Yeah right. A little
bit of knowledge can be dangerous. Good luck to the OP, with a scope
should be an easy fix.

 

[Gareth Magennis]

Sounds good.


Ba-ding... Now I wonder why that voltage is low? Could it be, oh,
maybe... A bad filter cap?

Er, what exactly is this 46 volts supposed to be doing? I doubt there is
anything like 46 volts anywhere near the keyboard.

Please try again.



Gareth.

 

[Josh9.0]

Er, what exactly is this 46 volts supposed to be doing? I doubt there is

anything like 46 volts anywhere near the keyboard.

Please try again.

Gareth.

Yes... I checked it again. it's a common to all keys. No... there's
little chance of electric shock, as there is a lot of plastic between
the user and the switches.

Sorry for jumping to conclusions. It's what I do, sometimes.
And... as you will know, aluminum electrolytics are prone to going dry
given a few decades (or less) !

 

[Gareth Magennis]

Yes... I checked it again. it's a common to all keys. No... there's
little chance of electric shock, as there is a lot of plastic between
the user and the switches.

Sorry for jumping to conclusions. It's what I do, sometimes.
And... as you will know, aluminum electrolytics are prone to going dry
given a few decades (or less) !

Your measurement is incorrect. No way is there 46 volts around the
keyboard. Possibly 4.6 volts, a slight but possibly acceptable drop from
the 5 volt supply.


You are still wanting to find the answer in dry aluminium electrolytics or
something else. Stop trying to make the symptoms fit your conjoured up
answer. This is not the best way to fault find. You need to establish some
facts. So far you have virtually none at all. Go get some and stop
guessing. Really.


Gareth.

 

[Josh9.0]

You need to establish some

facts. So far you have virtually none at all. Go get some and stop
guessing.

OK, How do I do that?
Thanks.

 

[Josh9.0]

You need to establish some

facts. So far you have virtually none at all. Go get some and stop
guessing.

OK, How do I do that?
Thanks.

 

[Josh9.0]

You need to establish some

facts. So far you have virtually none at all. Go get some and stop
guessing.

OK, How do I do that?
Thanks.

 

[Arfa Daily]

Thats because searching for any electronics problem on google comes up
with "check all the electrolytics", ESR is the new religion. I get so many
people bringing stuff to me saying, hey its probably a cap, you got an ESR
meter?, can't be more than 10 bucks to fix. Yeah right. A little bit of
knowledge can be dangerous. Good luck to the OP, with a scope should be an
easy fix.

ESR is not a religion, it's a fact of life which, if you are a professional
repair technician as your post suggests you might be, you must very well
know ...

Although of course not all, many faults these days are indeed due to
electrolytic caps with a poor ESR. They are the single component which I,
and everybody else I know in the business, change more of per week, than any
other.

That said, in this OP's case, the problem could easily be a leaky diode in
the PSU, or something which may be a deal more difficult to pin down, such
as a bad inter-board ground. The age of it would suggest a cap might be a
firm first favourite though.

Arfa

 

[Arfa Daily]

OK, How do I do that?
Thanks.

Well, for a start, do as was suggested - and which you seemed to
understand - and check each of the rails for ripple with your 'scope ...

Arfa

 

[Josh9.0]

Well, for a start, do as was suggested - and which you seemed to
understand - and check each of the rails for ripple with your 'scope ...

Arfa

Thanks Afra. I checked the rails and they look clean.
The hum has a certain "spike up, down, noise, spike up, down, silence"
pattern.
I'm off to Jaycar now, to buy some tantalums, as it can't hurt, and I
don't like aluminium electros if tantalums are available.

Where can I get a STK025 datasheet ?
I find pages on Google saying such, but when I go there, it's just
datasheets on STK0025 or STK0250.
Even Sanyo's (mfg) site can't help me.

 

[Franc Zabkar]

Where can I get a STK025 datasheet ?

My vrt databook lists the following:

STK025(G) = STK036: +/-30V, 20W (+22V/8 ohms)
STK032 = STK036: +/-33V, 25W (+24V/8 ohms)
STK036 audio amp +/-35V, 30W (+27V/8 ohms)

http://pdf1.alldatasheet.co.kr/datasheet-pdf/view/90354/ETC/STK032/datasheet.pdf

- Franc Zabkar

 

[Arfa Daily]

Thanks Afra. I checked the rails and they look clean.
The hum has a certain "spike up, down, noise, spike up, down, silence"
pattern.
I'm off to Jaycar now, to buy some tantalums, as it can't hurt, and I
don't like aluminium electros if tantalums are available.

Where can I get a STK025 datasheet ?
I find pages on Google saying such, but when I go there, it's just
datasheets on STK0025 or STK0250.
Even Sanyo's (mfg) site can't help me.

If the rails look clean, and the sound you are hearing has the described
waveshape, then it is more likely that it is a buzz rather than a hum
(subtle difference to the experienced ear) and not a power supply issue at
all. It could be a grounding problem, but really, you need to know where the
offending noise is actually getting in to the amplification chain. With
items such as synths, where there are triangle and square wave generators
running all the time, a simple bad ground can allow all sorts of nasty
ground voltages to start appearing in amplification stages.

Try here for your data sheet

http://www.alldatasheet.com/view.jsp?sSearchword=STK025

Arfa

 

[Josh9.0]

If the rails look clean, and the sound you are hearing has the described

waveshape, then it is more likely that it is a buzz rather than a hum
(subtle difference to the experienced ear) and not a power supply issue at
all. It could be a grounding problem, but really, you need to know where the
offending noise is actually getting in to the amplification chain. With
items such as synths, where there are triangle and square wave generators
running all the time, a simple bad ground can allow all sorts of nasty
ground voltages to start appearing in amplification stages.

OK, I could take a photo from the CRO, but how could I post it here ?
I'm using Google. I could upload it to my site, and put a link, I
suppose.
Yes, a buzz it may be.

All grounding wires look intact.

If only I had another one of the same model, I could swap boards to
determine where the problem is.
Although, most are wired in place, it'd be a start, at least.

BTW: I replaced the caps next to one of the STK025's and it didn't
help, but I'm glad I did, because these caps should last another 30
years or so.

Try here for your data sheet
http://www.alldatasheet.com/view.jsp?sSearchword=STK025

Thanks, but I've been there b4 and all I find is other parts. EG: a 3
pin MOSFET.

Is there a sci.electronics.organ.repair or similar group?

 

[propman]

Is there a sci.electronics.organ.repair or similar group?

Might want to try persuing some of the vintage synth sites such as the
following for information etc:

http://www.vintagesynth.com/local/links.shtml

 

[Franc Zabkar]

Thanks, but I've been there b4 and all I find is other parts. EG: a 3
pin MOSFET.

Is there a sci.electronics.organ.repair or similar group?

Did you see my other post?

The datasheet for the STK032 should be appropriate. The STK032 appears
to be a higher power pin compatible version of the STK025.

http://pdf1.alldatasheet.co.kr/datasheet-pdf/view/90354/ETC/STK032/datasheet.pdf

BTW, I would disconnect the input to the STK025, before the coupling
capacitor (negative terminal), and ground it. That should confirm
whether the noise is being generated in an earlier stage.

If you need to purchase an STK025/STK032/STK036 (unlikely, IMHO), then
they are available from "sales at starcomponents dot com dot au". Cost
is AU$27.50 plus $3.30 postage (the STK036 is actually $1 cheaper). It
may be an idea to buy a spare anyway, as Sanyo has obsoleted these
devices long ago.

- Franc Zabkar