Laney Cub 12R

P

Phil Allison

Guest
** Ever see one of these ?

An evil mix of EL84s, ECC83s and SMD on the same PCB.

Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
sockets.

But none of these were the problem.

The amp would run OK for about 10 mins and then power itself down - all the
lights go out and the sound fades away.

Turning the power off and waiting a few minutes restored operation, but not
for long.

Who has come across this one?



..... Phil
 
"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:b6qt7rF481jU1@mid.individual.net...
** Ever see one of these ?

An evil mix of EL84s, ECC83s and SMD on the same PCB.

Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
sockets.

But none of these were the problem.

The amp would run OK for about 10 mins and then power itself down - all
the lights go out and the sound fades away.

Turning the power off and waiting a few minutes restored operation, but
not for long.

Who has come across this one?



.... Phil
Click to expand...
I have never seen one of those but a first guess, look for a cracked smd
resistor that opens up with heat.
Maybe you can spray some freeze spray around to see if you can localize the
problem.

Is it RoHS?
 
"tm"
"Phil Allison"

** Ever see one of these ?

An evil mix of EL84s, ECC83s and SMD on the same PCB.

Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
sockets.

But none of these were the problem.

The amp would run OK for about 10 mins and then power itself down - all
the lights go out and the sound fades away.

Turning the power off and waiting a few minutes restored operation, but
not for long.

Who has come across this one?



I have never seen one of those but a first guess, look for a cracked smd
resistor that opens up with heat.
Maybe you can spray some freeze spray around to see if you can localize
the problem.
Click to expand...
** All the clues are there.

The amp powers itself off, valve heaters and the dial light goes out and
will not restart by itself.

A few minutes with the AC off does the trick.



.... Phil
 
"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:b6rn9tF9clcU1@mid.individual.net...
"tm"
"Phil Allison"

** Ever see one of these ?

An evil mix of EL84s, ECC83s and SMD on the same PCB.

Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
sockets.

But none of these were the problem.

The amp would run OK for about 10 mins and then power itself down - all
the lights go out and the sound fades away.

Turning the power off and waiting a few minutes restored operation, but
not for long.

Who has come across this one?



I have never seen one of those but a first guess, look for a cracked smd
resistor that opens up with heat.
Maybe you can spray some freeze spray around to see if you can localize
the problem.

** All the clues are there.

The amp powers itself off, valve heaters and the dial light goes out and
will not restart by itself.

A few minutes with the AC off does the trick.



... Phil
Click to expand...

Sounds like it needs a good squib of WD40 to me, Phil ... :)

But seriously, it's gotta be something to do with either that connector, SK4
that they've put in the way, or the PTC, F1 that follows it ?? Maybe faulty,
maybe hotting more than normal up for some reason ? Maybe had the wrong
pilot lamp fitted, although I would have expected the two 10 ohm Rs to have
taken care of that. Otherwise, apart from a heater in a valve going short to
a cathode maybe, about the only other thing is the hum balance pot, although
I'm not sure in what way practically that it could fail, to place an excess
load on the PTC ...

Arfa
 
Phil Allison wrote:
** Ever see one of these ?

An evil mix of EL84s, ECC83s and SMD on the same PCB.

Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
sockets.

But none of these were the problem.

The amp would run OK for about 10 mins and then power itself down -
all the lights go out and the sound fades away.

Turning the power off and waiting a few minutes restored operation,
but not for long.

Who has come across this one?



.... Phil
Click to expand...
--

I've never seen one of those units, but I'll take a guess that a PTC
resettable fuse is in the power transformer primary. It's clicking the set
off due to an overcurrent condition (bad transformer, filter caps,
rectifiers, etc.).

Dave M
 
"Arfa Daily"
"Phil Allison"

** Ever see one of these ?

An evil mix of EL84s, ECC83s and SMD on the same PCB.

Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
sockets.

But none of these were the problem.

The amp would run OK for about 10 mins and then power itself down - all
the lights go out and the sound fades away.

Turning the power off and waiting a few minutes restored operation, but
not for long.

Who has come across this one?

** All the clues are there.

The amp powers itself off, valve heaters and the dial light goes out and
will not restart by itself.

A few minutes with the AC off does the trick.


Sounds like it needs a good squib of WD40 to me, Phil ... :)
Click to expand...
** LOL !!

But seriously, it's gotta be something to do with either that connector,
SK4 that they've put in the way, or the PTC, F1 that follows it ??
Click to expand...
** Give that man a Kewpie doll.................


? Maybe faulty, maybe hotting more than normal up for some reason ? Maybe
had the wrong pilot lamp fitted, although I would have expected the two 10
ohm Rs to have taken care of that. Otherwise, apart from a heater in a
valve going short to a cathode maybe, about the only other thing is the hum
balance pot, although I'm not sure in what way practically that it could
fail, to place an excess load on the PTC ...
Click to expand...
** For some whacky reason, the Chinese included a PTC ( aka Polyswitch ) in
series with the 6.3 volt AC heater supply - adding to their bad judgement,
they picked one with too low a current rating.

The heater draw in the Cub 12R is a tad over 3 amps ( = 20 watts) and is
the largest load on the AC tranny.

Seems these Polyswitch devices deteriorate with age, if run hot all the
time - until they trip and go high resistance. With no heater supply, the
dial lamp goes out and the amp goes slowly silent and the same scenario can
be repeated indefinitely.

From reading the Laney user's forum, the fault is endemic with the model and
you need to fit a 6 amp rated PTC to fix it for sure.

Or just leave it out.


.... Phil
 
"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:b6rsl4FagogU1@mid.individual.net...
"Arfa Daily"
"Phil Allison"

** Ever see one of these ?

An evil mix of EL84s, ECC83s and SMD on the same PCB.

Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
sockets.

But none of these were the problem.

The amp would run OK for about 10 mins and then power itself down -
all the lights go out and the sound fades away.

Turning the power off and waiting a few minutes restored operation,
but not for long.

Who has come across this one?

** All the clues are there.

The amp powers itself off, valve heaters and the dial light goes out and
will not restart by itself.

A few minutes with the AC off does the trick.


Sounds like it needs a good squib of WD40 to me, Phil ... :)

** LOL !!


But seriously, it's gotta be something to do with either that connector,
SK4 that they've put in the way, or the PTC, F1 that follows it ??

** Give that man a Kewpie doll.................


? Maybe faulty, maybe hotting more than normal up for some reason ? Maybe
had the wrong pilot lamp fitted, although I would have expected the two 10
ohm Rs to have taken care of that. Otherwise, apart from a heater in a
valve going short to a cathode maybe, about the only other thing is the
hum balance pot, although I'm not sure in what way practically that it
could fail, to place an excess load on the PTC ...


** For some whacky reason, the Chinese included a PTC ( aka Polyswitch )
in series with the 6.3 volt AC heater supply - adding to their bad
judgement, they picked one with too low a current rating.

The heater draw in the Cub 12R is a tad over 3 amps ( = 20 watts) and is
the largest load on the AC tranny.

Seems these Polyswitch devices deteriorate with age, if run hot all the
time - until they trip and go high resistance. With no heater supply, the
dial lamp goes out and the amp goes slowly silent and the same scenario
can be repeated indefinitely.

From reading the Laney user's forum, the fault is endemic with the model
and you need to fit a 6 amp rated PTC to fix it for sure.

Or just leave it out.


... Phil
Click to expand...
Interestingly, on the schematic copy that I have, it shows F1 as a linear
thermistor which has the designation "PTC 6.0" by the side of it, which
would imply that it is specced as a 6 amp device. However, a little further
up the schematic in the AC feeds to the opamp supply rectifiers, there are
two more devices, this time shown as fuses with the component references F2
and F3, and designated as "PolySW0.3" which would imply to me that these are
300mA opening-current devices, and that Laney believe them to be a different
thing altogether from a PTC ?? Although polyswitches are of course PTCs,
they are designed to be very fast. On the other hand, there are positive
temperature coefficient thermistors that are similarly 'slow' to NTC ones.
There are plenty of characteristic graphs on the web showing 'slow' linear
PTC thermistor action, and others showing fast PTC polyswitch action.

Although that said, I don't really know why Laney would have designed one
into there anyway. An NTC thermistor to mitigate heater surge when they are
cold, maybe, but a PTC - linear characteristic or polyswitch
characteristic - seems altogether 'wrong' in that position, and I agree with
you that it's probably best just bypassed ...

Arfa
 
On 08/11/2013 06:48 PM, Phil Allison wrote:
** Ever see one of these ?

An evil mix of EL84s, ECC83s and SMD on the same PCB.

Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
sockets.

But none of these were the problem.

The amp would run OK for about 10 mins and then power itself down - all the
lights go out and the sound fades away.

Turning the power off and waiting a few minutes restored operation, but not
for long.

Who has come across this one?



.... Phil
Click to expand...
If you can't afford freeze spray a Q-tip with 91% alcohol will chill
components.
 
"dave" <ricketzz@earthlink.net> wrote in message
news:Z8-dnfT6KM-tYpXPnZ2dnUVZ_vOdnZ2d@earthlink.com...
On 08/11/2013 06:48 PM, Phil Allison wrote:
** Ever see one of these ?

An evil mix of EL84s, ECC83s and SMD on the same PCB.

Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
sockets.

But none of these were the problem.

The amp would run OK for about 10 mins and then power itself down - all
the
lights go out and the sound fades away.

Turning the power off and waiting a few minutes restored operation, but
not
for long.

Who has come across this one?



.... Phil


If you can't afford freeze spray a Q-tip with 91% alcohol will chill
components.
Click to expand...
In the case of the amount of heat involved in this problem, IPA would
vapourise pretty instantly, and the Q-Tip would likely scorch ! :)

Arfa
 
On Mon, 12 Aug 2013 19:13:29 +1000, Phil Allison wrote:

"tm"
"Phil Allison"

** Ever see one of these ?

An evil mix of EL84s, ECC83s and SMD on the same PCB.

Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
sockets.

But none of these were the problem.

The amp would run OK for about 10 mins and then power itself down -
all the lights go out and the sound fades away.

Turning the power off and waiting a few minutes restored operation,
but not for long.

Who has come across this one?



I have never seen one of those but a first guess, look for a cracked
smd resistor that opens up with heat.
Maybe you can spray some freeze spray around to see if you can localize
the problem.

** All the clues are there.

The amp powers itself off, valve heaters and the dial light goes out and
will not restart by itself.

A few minutes with the AC off does the trick.



... Phil
Click to expand...

That sounds like it could easily be a dying polyfuse.

?-)
 
"josephkk" <joseph_barrett@sbcglobal.net> wrote in message
news:520c3f47$0$58621$c3e8da3$12bcf670@news.astraweb.com...
On Mon, 12 Aug 2013 19:13:29 +1000, Phil Allison wrote:

"tm"
"Phil Allison"

** Ever see one of these ?

An evil mix of EL84s, ECC83s and SMD on the same PCB.

Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
sockets.

But none of these were the problem.

The amp would run OK for about 10 mins and then power itself down -
all the lights go out and the sound fades away.

Turning the power off and waiting a few minutes restored operation,
but not for long.

Who has come across this one?



I have never seen one of those but a first guess, look for a cracked
smd resistor that opens up with heat.
Maybe you can spray some freeze spray around to see if you can localize
the problem.

** All the clues are there.

The amp powers itself off, valve heaters and the dial light goes out and
will not restart by itself.

A few minutes with the AC off does the trick.



... Phil

That sounds like it could easily be a dying polyfuse.

?-)
Click to expand...

You must have Phil's personal posts blocked ?

Arfa
 
"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:b73q3cF1bjoU1@mid.individual.net...
"Arfa Daily"
"josephkk"
You must have Phil's personal posts blocked ?


** Errr - he just answered one ...




... Phil
Click to expand...

Well, yes, but I wondered in that case why he did not see the detailed
response that you gave to my reply, telling all about the polyfuse.
Sometimes, people that have blocked you see your posts as a result of the
original text appearing within someone else's post that's not blocked, but
again, I guess that he could have seen your reply in the response that I
posted after, without cutting any of your text ...

Life's full of mysteries ... :)

Arfa
>
 
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