I've been given this rather large and heavy AV amp dating from the last
century which is faulty. It will yield a pretty decent mains transformer
even if I scrap the rest.

Basically it started making funny noises from one of the rear channel amps
- and after a few weeks now powers down a couple of seconds after being
switched on. My guess is the speaker DC protection cutting in due to a
faulty output on that amp.

Is it worth attempting a repair?

--
*When cheese gets it's picture taken, what does it say?

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
I've been given this rather large and heavy AV amp dating from the last
century which is faulty. It will yield a pretty decent mains transformer
even if I scrap the rest.

Basically it started making funny noises from one of the rear channel amps


Means it's ****ed.



- and after a few weeks now powers down a couple of seconds after being
switched on.


Means it's double-****ed.



My guess is the speaker DC protection cutting in due to a
faulty output on that amp.


Your amp, your guess is as good as anyone's here....



Is it worth attempting a repair?



And *your* call - but with a seriously decent 4 x HDMI input 7.1 channel
Sony AV amp capable of outputting 80 Watts (somewhere and at some point in
time) costing little over 200 quid *brand spanking new* I would say
definitely not, but then you may have all the parts you need already on your
shelf. Depends what you think your time is worth...??

Anyway, nice to see you attempt to start a thread for once ;-)

Well is it one of those dc coupled all through jobbies, if it is, then the
fault could be anywhere after the volume circuitry!

I had one of those Memorex branded tuneramps like this and it ate power amp
modules until, one day, the fault was in the protection circuit and it
welded up the speaker voice coil and trashed the amp completely.


Moral is, be very careful if you do not exactly know where the intermittent
bit is as something else will blow it all up for you courtesy of Mr Murphy.

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"Dave Plowman (News)" wrote in message
...
I've been given this rather large and heavy AV amp dating from the last
century which is faulty. It will yield a pretty decent mains transformer
even if I scrap the rest.

Basically it started making funny noises from one of the rear channel amps
- and after a few weeks now powers down a couple of seconds after being
switched on. My guess is the speaker DC protection cutting in due to a
faulty output on that amp.

Is it worth attempting a repair?

--
*When cheese gets it's picture taken, what does it say?

Dave Plowman London SW
To e-mail, change noise into sound.

In article , Dave Plowman (News)
wrote:
I've been given this rather large and heavy AV amp dating from the last
century which is faulty. It will yield a pretty decent mains transformer
even if I scrap the rest.

Basically it started making funny noises from one of the rear channel
amps

What sort of 'funny noises'?

- and after a few weeks now powers down a couple of seconds after
being switched on. My guess is the speaker DC protection cutting in due
to a faulty output on that amp.

Is it worth attempting a repair?

Does a scope/meter show an excessive output dc voltage or one that waggles
about along with the noises?

If you can put a current meter in the rail to measure the current (use a
2mic cap to bypass the meter) see if the quiescent jumps about.

Afraid I don't know a thing about the specific model. Hard to say from the
above if the fault is trivial or serious. Might be a loose connection or
fuse. But might be something more costly and hard-to-diagnose.

FWIW One of my power amps a few years ago developed occasional 'rustling'
noises which were accompanied by changes in the output dc level of about
100mV. Freezer spray followed by replacing some pre-driver transistors
fixed this. Turned out to be an intermittent connection inside the pack of
one of the transistors. Replacement device cost about 20p IIRC, but was a
pest to find which one to replace. At least your fault isn't intermittent
so can be relied on to show up when you are trying to nail it down. :-)

I also have encountered cases where the monitor circuits misbehave and the
actual amp is fine. In such cases you can sometimes just disable the
protection. But that obviously is only safe if you know this is the problem
when using it with speakers - as distinct from dummy loads you don't mind
frying. 8-]

TBH I never liked active protection for power amps. Just one more bolt-on
to fail or get in the way. Prefer fuses in the rails.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

"Dave Plowman (News)" wrote in message
...
I've been given this rather large and heavy AV amp dating from the last
century which is faulty. It will yield a pretty decent mains transformer
even if I scrap the rest.

Basically it started making funny noises from one of the rear channel amps
- and after a few weeks now powers down a couple of seconds after being
switched on. My guess is the speaker DC protection cutting in due to a
faulty output on that amp.

Is it worth attempting a repair?

**Probably not. If you want to persevere though. your best move is to obtain
a service manual, so you can interpret the fault codes. The service manual
will also provide the procedure to over-ride the protection system, so you
can fault find. The protection system in those critters is a very
sophisticated arrangement. It will shut the amp down in response to a whole
host of different things, including (but not limited to):

* DC offset.
* Over current in output stage.
* Regulater power supply faults.
* DSP faults.
* Microprocessor fauts.


--
Trevor Wilson
www.rageaudio.com.au

In article ,
Jim Lesurf wrote:
In article , Dave Plowman (News)
wrote:
I've been given this rather large and heavy AV amp dating from the
last century which is faulty. It will yield a pretty decent mains
transformer even if I scrap the rest.

Basically it started making funny noises from one of the rear channel
amps

What sort of 'funny noises'?

Didn't hear them myself but was told they happened with the rear amps not
being fed. Ie, Dolby off.

- and after a few weeks now powers down a couple of seconds after
being switched on. My guess is the speaker DC protection cutting in due
to a faulty output on that amp.

Is it worth attempting a repair?

Does a scope/meter show an excessive output dc voltage or one that
waggles about along with the noises?

I've not even had the cover off yet. But can see it's pretty densely
packed through the grills.

If you can put a current meter in the rail to measure the current (use a
2mic cap to bypass the meter) see if the quiescent jumps about.

Afraid I don't know a thing about the specific model. Hard to say from
the above if the fault is trivial or serious. Might be a loose
connection or fuse. But might be something more costly and
hard-to-diagnose.

FWIW One of my power amps a few years ago developed occasional
'rustling' noises which were accompanied by changes in the output dc
level of about 100mV. Freezer spray followed by replacing some
pre-driver transistors fixed this. Turned out to be an intermittent
connection inside the pack of one of the transistors. Replacement device
cost about 20p IIRC, but was a pest to find which one to replace. At
least your fault isn't intermittent so can be relied on to show up when
you are trying to nail it down. :-)

I also have encountered cases where the monitor circuits misbehave and
the actual amp is fine. In such cases you can sometimes just disable the
protection. But that obviously is only safe if you know this is the
problem when using it with speakers - as distinct from dummy loads you
don't mind frying. 8-]

TBH I never liked active protection for power amps. Just one more
bolt-on to fail or get in the way. Prefer fuses in the rails.

Thanks, Jim. I'll report back when I do some tests.

--
*Plagiarism saves time *

Dave Plowman London SW
To e-mail, change noise into sound.

In article , Trevor Wilson
wrote:


**Probably not. If you want to persevere though. your best move is to
obtain a service manual, so you can interpret the fault codes.

Jings. Sounds like trying to repair such beasts is similar to trying to
sort out modern TVs with their fancy 'menu' systems.

The service manual will also provide the procedure to over-ride the
protection system, so you can fault find. The protection system in those
critters is a very sophisticated arrangement. It will shut the amp down
in response to a whole host of different things, including (but not
limited to):

* DC offset. * Over current in output stage. * Regulater power supply
faults. * DSP faults. * Microprocessor fauts.

That tends to feed my predjudice that the protection circuitry tends to
bring with it a set of additional 'failure modes' and sources of problems.
:-)

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article ,
Jim Lesurf wrote:
In article , Trevor Wilson
wrote:


**Probably not. If you want to persevere though. your best move is to
obtain a service manual, so you can interpret the fault codes.

Jings. Sounds like trying to repair such beasts is similar to trying to
sort out modern TVs with their fancy 'menu' systems.

I've had a glance at the handbook that came with it and microprocessor
control does have its advantages. Like being able to trim the gain on each
and every input.

The service manual will also provide the procedure to over-ride the
protection system, so you can fault find. The protection system in
those critters is a very sophisticated arrangement. It will shut the
amp down in response to a whole host of different things, including
(but not limited to):

* DC offset. * Over current in output stage. * Regulater power supply
faults. * DSP faults. * Microprocessor fauts.

That tends to feed my predjudice that the protection circuitry tends to
bring with it a set of additional 'failure modes' and sources of
problems.
:-)

Indeed. I'm hoping it isn't so clever it won't power up unless it sees
exactly the right load.
I've spoken to the ex-owner who says the noise from one rear speaker was
a loud but intermittent crackle. My hope is it's a (simple) amp fault
causing the DC speaker protection to trip. Anything else and it's likely
scrap.

Doing a 'Google' on it seems it was a well respected amp in its day.

Slainte,

Jim

--
*It sounds like English, but I can't understand a word you're saying.

Dave Plowman London SW
To e-mail, change noise into sound.

In article , Dave Plowman (News)
wrote:
In article , Jim Lesurf
wrote:

That tends to feed my predjudice that the protection circuitry tends
to bring with it a set of additional 'failure modes' and sources of
problems.
:-)

Indeed. I'm hoping it isn't so clever it won't power up unless it sees
exactly the right load. I've spoken to the ex-owner who says the noise
from one rear speaker was a loud but intermittent crackle. My hope is
it's a (simple) amp fault causing the DC speaker protection to trip.

The "intermittent crackle" is the kind of symptom I associate with a poor
joint or a componment degrading and causing the bias levels to be quickly
wiggled about. If you also see an output dc level that jumps about a few
10s or 100s of mV when this happens I'd say that was a candidate.

If so, a quick shuggle (wiggle or poke) of various components or spray with
freezer may show up the culprit. Or threaten them with a close encounter
with a soldering iron. :-) If you are lucky it is just an internal
connector that needs a clean.

FWIW My one annoyance with the Yamaha CT7000 FM tuner is all the
expletive push-on connectors used for links between boards, etc. After a
decade or two these tend to go intermittent and need unplugging, then the
pins and sockets cleaning, then replugging. If you are lucky that is the
cause and will be easy to fix ... until it happens again in X years time.
:-)

If you are unlucky it is an internal connection in a device and be
reluctant to show up with freezer or a shuggle. In the end I only found
this with my amp by replacing one individual device at a time until I found
the little devil.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

"Dave Plowman (News)" wrote in message
...
In article ,
Jim Lesurf wrote:
In article , Trevor Wilson
wrote:


**Probably not. If you want to persevere though. your best move is to
obtain a service manual, so you can interpret the fault codes.

Jings. Sounds like trying to repair such beasts is similar to trying to
sort out modern TVs with their fancy 'menu' systems.

I've had a glance at the handbook that came with it and microprocessor
control does have its advantages. Like being able to trim the gain on each
and every input.



That'll be a) digital attenuation and b) the last vestiges of any 'sound
quality' down the Swannee then?