Trying to volume pot replacement for JVC Rx-6000 receiver

[Andrew]

Hello,
I have a JVC RX-6000 which works well except for the volume control,
which behaves pretty oddly. If I turn the volume down slowly,
everything works fine. If I turn the volume down quickly, the volume
often ends up higher than it was. I assume the pot has some problems,
though I cannot imagine what would make it behave like this. So I
have the unit open, and there are no identifying marks on the pot.
Its square, top mounted with a metal bushing 3/8" long. The pot stem
stick out another 3/8" past the bushing. I think its 10k, but I can't
be sure until I pull it out. I have looked all over for this pot,
and I can't find anything. Does anyone know how I can identify the
pot, and where I can find a replacement?

thanks,

 

[N_Cook]

Hello,
I have a JVC RX-6000 which works well except for the volume control,
which behaves pretty oddly. If I turn the volume down slowly,
everything works fine. If I turn the volume down quickly, the volume
often ends up higher than it was. I assume the pot has some problems,
though I cannot imagine what would make it behave like this. So I
have the unit open, and there are no identifying marks on the pot.
Its square, top mounted with a metal bushing 3/8" long. The pot stem
stick out another 3/8" past the bushing. I think its 10k, but I can't
be sure until I pull it out. I have looked all over for this pot,
and I can't find anything. Does anyone know how I can identify the
pot, and where I can find a replacement?

thanks,

How to renovate worn pots, on my tips files, off URL below.

 

[Arfa Daily]

How to renovate worn pots, on my tips files, off URL below.

Are you sure it's a pot, and not a rotary encoder ? Does it have end stops
at anticlock and clock ends ? If it goes round and round without stops, then
it is an encoder, not a pot.

The symptoms you describe are very typical of the 'stirring treacle' grease
that they put in the shaft, having migrated down onto the encoder disc and
contacts. If it is one of these, they are cleanable, but you need to
carefully dismantle it, to do so.

Arfa

 

[Andy]

Are you sure it's a pot, and not a rotary encoder ? Does it have end stops
at anticlock and clock ends ? If it goes round and round without stops, then
it is an encoder, not a pot.

The symptoms you describe are very typical of the 'stirring treacle' grease
that they put in the shaft, having migrated down onto the encoder disc and
contacts. If it is one of these, they are cleanable, but you need to
carefully dismantle it, to do so.

Arfa

Thanks. I will look into this. As you describe, the pot has no
stops. I cannot imagine what would cause a pot to behave this way, so
it makes more sense that it is the encoder. Would the encoder be
inside the pot housing?

thanks
Andy

 

[Franc Zabkar]

Hello,
I have a JVC RX-6000 which works well except for the volume control,
which behaves pretty oddly. If I turn the volume down slowly,
everything works fine. If I turn the volume down quickly, the volume
often ends up higher than it was.

I have an amp with a rotary encoder that doesn't respond correctly if
I turn it too quickly. I suspect this reflects the processing speed of
the uP, and is not a deficiency in the encoder. If it's a mechanical
rather than optical encoder, maybe there are time delays to allow for
debouncing. If so, could the uP be confused if a new contact is made
before the previous one has been debounced?

- Franc Zabkar

 

[Mark D. Zacharias]

I have an amp with a rotary encoder that doesn't respond correctly if
I turn it too quickly. I suspect this reflects the processing speed of
the uP, and is not a deficiency in the encoder. If it's a mechanical
rather than optical encoder, maybe there are time delays to allow for
debouncing. If so, could the uP be confused if a new contact is made
before the previous one has been debounced?

- Franc Zabkar

Nah, it's the encoder. I've taken them apart. The contacts are tarnished.

Mark Z.

 

[Arfa Daily]

Nah, it's the encoder. I've taken them apart. The contacts are tarnished.

Mark Z.

Agreed. It is very very common. I would guess that on average, I do one
every couple of weeks. Lots of different makes use them, but they are almost
always the same type with the green square body, 3 electrical legs, and two
mechanical stability pins, one at either side in the middle. ALPS make, I
think.

Arfa

 

[Mark D. Zacharias]

Crikey - thought the whole idea of a shaft encoder was to get rid of any
mechanical contacts. I assumed they were all optical etc devices.

--
*If work is so terrific, how come they have to pay you to do it?

Dave Plowman [email protected] London SW
To e-mail, change noise into sound.

Yeah - they don't produce noise as such, just unreliable, erratic operation.

Mark Z.

 

[Arfa Daily]

Crikey - thought the whole idea of a shaft encoder was to get rid of any
mechanical contacts. I assumed they were all optical etc devices.

--

The one that's commonly found in many hifis Dave, comprises a printed
circuit disc with broken rings of (gold plated?) print on it. This is
attached to the shaft. The plastic body of the encoder has a set of contacts
on it which I think are also gold plated. The whole thing puts out Gray code
or some such, that can be used to derive a rate and direction of rotation.
The system control micro then looks after turning this into an I2C data
stream to work the digital pot IC for volume control, and the display
decoder so that it can put up a pseudo dB display. The useful thing about
using such an encoder, is that it can be used to control other functions
too, such as tone and radio tuning and so on. It's also cheap compared to
optical devices.

As far as problems with them go, I don't think it is so much that they are
unreliable by design, more that their problems have been caused by the
manufacturers being a bit enthusiastic about giving them a high-end 'feel'
in use. To give them this 'stirring treacle' feel, they fill the shaft with
some kilopoise type grease, and this seems to migrate down onto the disc and
contacts, where it wreaks havoc with the operation. Once it has been
carefully cleaned off chemically, the contacts and disc are usually bright
shiny clean, as you would expect gold-plated contacts to be. I usually
finish off before reassembly and refitting, with a small drop of
cleaner/lubricant on the disc. They always work perfectly after this
treatment, and I can't remember ever having had one fail to be recovered.

Arfa

 

[Andy]

The one that's commonly found in many hifis Dave, comprises a printed
circuit disc with broken rings of (gold plated?) print on it. This is
attached to the shaft. The plastic body of the encoder has a set of contacts
on it which I think are also gold plated. The whole thing puts out Gray code
or some such, that can be used to derive a rate and direction of rotation..
The system control micro then looks after turning this into an I2C data
stream to work the digital pot IC for volume control, and the display
decoder so that it can put up a pseudo dB display. The useful thing about
using such an encoder, is that it can be used to control other functions
too, such as tone and radio tuning and so on. It's also cheap compared to
optical devices.

As far as problems with them go, I don't think it is so much that they are
unreliable by design, more that their problems have been caused by the
manufacturers being a bit enthusiastic about giving them a high-end 'feel'
in use. To give them this 'stirring treacle' feel, they fill the shaft with
some kilopoise type grease, and this seems to migrate down onto the disc and
contacts, where it wreaks havoc with the operation. Once it has been
carefully cleaned off chemically, the contacts and disc are usually bright
shiny clean, as you would expect gold-plated contacts to be. I usually
finish off before reassembly and refitting, with a small drop of
cleaner/lubricant on the disc. They always work perfectly after this
treatment, and I can't remember ever having had one fail to be recovered.

Arfa

Arfa, what do you clean the encoder wheels with?

 

[Mark D. Zacharias]

The one that's commonly found in many hifis Dave, comprises a printed
circuit disc with broken rings of (gold plated?) print on it. This is
attached to the shaft. The plastic body of the encoder has a set of
contacts on it which I think are also gold plated. The whole thing puts
out Gray code or some such, that can be used to derive a rate and
direction of rotation. The system control micro then looks after turning
this into an I2C data stream to work the digital pot IC for volume
control, and the display decoder so that it can put up a pseudo dB
display. The useful thing about using such an encoder, is that it can be
used to control other functions too, such as tone and radio tuning and so
on. It's also cheap compared to optical devices.

As far as problems with them go, I don't think it is so much that they are
unreliable by design, more that their problems have been caused by the
manufacturers being a bit enthusiastic about giving them a high-end 'feel'
in use. To give them this 'stirring treacle' feel, they fill the shaft
with some kilopoise type grease, and this seems to migrate down onto the
disc and contacts, where it wreaks havoc with the operation. Once it has
been carefully cleaned off chemically, the contacts and disc are usually
bright shiny clean, as you would expect gold-plated contacts to be. I
usually finish off before reassembly and refitting, with a small drop of
cleaner/lubricant on the disc. They always work perfectly after this
treatment, and I can't remember ever having had one fail to be recovered.

Arfa

I've had one or two that didn't clean quite so well. One was on a JVC shelf
system which caused a BUNCH of extra labor to re-do, which involved
replacement rather than cleaning the second time around. I wasn't going to
risk another re-do.

BTW I don't think it's grease migration. I think it's silver content in the
switch tarnishing like a VCR mode switch. A good cleaning with De-Oxit and a
fiberglass nick-sander brush usually gets it but the parts are actually
pretty cheap, and there's only a couple types in common use. I get them from
Onkyo.

Mark Z.