Yamaha DSP A2070
 

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.

Yamaha DSP A2070
 

"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 ;-)

Yamaha DSP A2070
 

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.

Yamaha DSP A2070
 

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

Yamaha DSP A2070
 

"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

Yamaha DSP A2070
 

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.

Yamaha DSP A2070
 

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

Yamaha DSP A2070
 

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.

Yamaha DSP A2070
 

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

Yamaha DSP A2070
 

"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?

Yamaha DSP A2070
 

"Jim Lesurf" wrote in message
...
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.

**Worse. MUCH worse. If the fault is a catastrophic one (ie: Shorted output
devices) then it is usually not possible to ove-ride the protection system
anyway. I do understand the reasons why these guys (Yamaha is not the only
company) build these protection systems into their units though. You'll
typically find 5, 7 or 9 channels of amplification, upwards of a dozen
regulated power supplies, another half dozen CPUs, etc, etc. Failure of any
one can cause the whole amp to function poorly, damage speakers or no
function at all. As an aid to fault-finding it makes some sense to tie the
whole lot into a CPU and allow the display of the appropriate error 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.

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.
:-)

**Yes, indeedy. I worked on several early Sony surround sound units a few
years back. The fault was quite odd. Every single output stage had failed.
In some cases, catastrophically. The PCB had been burned completely through
in a few places. I obtained a service manual to ascertain what was going on.
IT seems that all the output stages were linked together for over-current
sensing. For some reason, when one output stage failed, it caused the
failure of all the others. I assumed it was a freak, until I worked on two
more units with the same fault.


--
Trevor Wilson
www.rageaudio.com.au

Yamaha DSP A2070
 

In article , Trevor Wilson
wrote:

"Jim Lesurf" wrote in message
...
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.

**Worse. MUCH worse. If the fault is a catastrophic one (ie: Shorted
output devices) then it is usually not possible to ove-ride the
protection system anyway. I do understand the reasons why these guys
(Yamaha is not the only company) build these protection systems into
their units though. You'll typically find 5, 7 or 9 channels of
amplification, upwards of a dozen regulated power supplies, another
half dozen CPUs, etc, etc. Failure of any one can cause the whole amp
to function poorly, damage speakers or no function at all. As an aid to
fault-finding it makes some sense to tie the whole lot into a CPU and
allow the display of the appropriate error codes.

Maybe the designers need to look up the word 'fuse' in a technical
directory and think a bit more carefully about the overall design approach
they use!

In a way it reminds me of the undergrad who decided to use an ADC and a DAC
to divide a voltage by 2, by wiring them together with the bits shifted by
one place. He seemed not to have heard of using a couple of resistors.

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

Yamaha DSP A2070
 

"Jim Lesurf" wrote in message
...
In article , Trevor Wilson
wrote:

"Jim Lesurf" wrote in message
...
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.

**Worse. MUCH worse. If the fault is a catastrophic one (ie: Shorted
output devices) then it is usually not possible to ove-ride the
protection system anyway. I do understand the reasons why these guys
(Yamaha is not the only company) build these protection systems into
their units though. You'll typically find 5, 7 or 9 channels of
amplification, upwards of a dozen regulated power supplies, another
half dozen CPUs, etc, etc. Failure of any one can cause the whole amp
to function poorly, damage speakers or no function at all. As an aid to
fault-finding it makes some sense to tie the whole lot into a CPU and
allow the display of the appropriate error codes.

Maybe the designers need to look up the word 'fuse' in a technical
directory and think a bit more carefully about the overall design approach
they use!

**Well, they do. It's just that when the fuse blows, the resultant
non-Voltage is monitored by the protection system. Again: You'll typically
find upwards of a dozen fuses in a modern surreund sound receiver. Space
constraints (or, more likely, cost constraints) mean that the fuses will
look like a TO92 transistor with two leads. Difficult to fault find
visually.


In a way it reminds me of the undergrad who decided to use an ADC and a
DAC
to divide a voltage by 2, by wiring them together with the bits shifted by
one place. He seemed not to have heard of using a couple of resistors.

**Oh, we've all seen that kind of thing. Back when I was a trainee tech
officer, I was posted to the newest exchange operated by OTC (The Overseas
Telecommunications Commission). It was an all-electronic affair (not a relay
in sight). I pestered the STO for some work, so he showed me a troublesome
rack of equipment that had been designed by an in-house engineer (most of
the rest of the floor used equipment from Hasler or Siemens and functioned
perfectly). Here's a short list of things the guy had managed to do and my
suggested changes:

* The use of 7 linear regulators, dropping 24 Volts down to 12 @ around 8
Amps per card. 3 RU high. The heat generated was ridiculous. I suggested
switch mode regulators be used.
* Instead of using 'rat-trap' fuses (which have been around for many
decades) that are cheap, reliable, simple and compact, the engineer chose
3AG fuses.
* To identify the blown fuse (which is automatic with rat-trap fuses), the
engineer chose to use an opto-isolator to sense a fault. The system never
worked, because the engineer did not understand what 'current transfer
ratio' was. My solution was to install a BC108 to sort out the problem. I
was not allowed to do the job. I was not allowed to speak to the engineer to
explain how he got it wrong.
* The installation of several 30cm X 30cm PCBs, packed with sufficient
components generating approximately 140 Watts.


--
Trevor Wilson
www.rageaudio.com.au

Yamaha DSP A2070
 

"Trevor Wilson" wrote

**Oh, we've all seen that kind of thing. Back when I was a trainee tech
officer, I was posted to the newest exchange operated by OTC (The Overseas
Telecommunications Commission). It was an all-electronic affair (not a
relay in sight).

There has never been a public telephone exchange with "not a relay in
sight". Even in current digital exchanges relays are used for such functions
as test access.

I pestered the STO for some work, so he showed me a troublesome rack of
equipment that had been designed by an in-house engineer.

A whole rack of equipment that was designed solely by one engineer?, I don't
think so, especially if he was half as incompetent as you suggest.

Your whole anecdote sounds like a load of bull to me.

David.

Yamaha DSP A2070
 

On Mon, 16 Nov 2009 22:00:50 -0000, "David Looser"
wrote:

There has never been a public telephone exchange with "not a relay in
sight".

NEVER? Careful with such sweeping statements!
http://www.britannica.com/EBchecked/...e-19th-century

Though I suppose the girls could be considered to be relays. Command
received, contact made. That's a relay isn't it? :-)

Yamaha DSP A2070
 

"Laurence Payne" wrote in message
...
On Mon, 16 Nov 2009 22:00:50 -0000, "David Looser"
wrote:

There has never been a public telephone exchange with "not a relay in
sight".

NEVER? Careful with such sweeping statements!
http://www.britannica.com/EBchecked/...e-19th-century

Though I suppose the girls could be considered to be relays. Command
received, contact made. That's a relay isn't it? :-)

An exchange like the one illustrated would have had electromechanical relays
in it. The CB system, introduced in 1899, and which rapidly became the
system of choice for all but the very smallest exchanges, had so many it was
sometimes known as "the relay system".

But yes, I stand corrected, some *very* early manual exchanges had only
"human powered" relays. But electromechanical relays used for signalling
purposes began appearing within a very few years of the start. At first they
were as likely to appear in the telephone as in the exchange, switching
current from a local battery to ring the call-bell in response to DC applied
to the line.

David.

Yamaha DSP A2070
 

"David Looser" wrote in message
...
"Trevor Wilson" wrote

**Oh, we've all seen that kind of thing. Back when I was a trainee tech
officer, I was posted to the newest exchange operated by OTC (The
Overseas Telecommunications Commission). It was an all-electronic affair
(not a relay in sight).

There has never been a public telephone exchange with "not a relay in
sight". Even in current digital exchanges relays are used for such
functions as test access.

**I was engaged in hyperbole. The exchange was digital. There probably were
a few relays. They were, on the whole, inaudible over the air conditioning
system.


I pestered the STO for some work, so he showed me a troublesome rack of
equipment that had been designed by an in-house engineer.

A whole rack of equipment that was designed solely by one engineer?

**One rack. All designed by one engineer. Correct. The rack was a
freestanding one. Standard 19 inch wide, around 7 feet high.

, I don't
think so, especially if he was half as incompetent as you suggest.

**You thought wrong. I obtained the blueprints, so I could fault find the
thing.


Your whole anecdote sounds like a load of bull to me.

**That it may. It is, nonetheless, quite true.


--
Trevor Wilson
www.rageaudio.com.au

Yamaha DSP A2070
 

In article , Trevor Wilson
wrote:

"Jim Lesurf" wrote in message
...


Maybe the designers need to look up the word 'fuse' in a technical
directory and think a bit more carefully about the overall design
approach they use!

**Well, they do. It's just that when the fuse blows, the resultant
non-Voltage is monitored by the protection system.

That is the thing I find strange. The fuse blowing tells you there is may
be a fault. Having the 'protection system' then get in the way of
diagnosing it seems crazy to me. But I guess I am old-fashioned. :-)


In a way it reminds me of the undergrad who decided to use an ADC and
a DAC to divide a voltage by 2, by wiring them together with the bits
shifted by one place. He seemed not to have heard of using a couple of
resistors.

**Oh, we've all seen that kind of thing. Back when I was a trainee tech
officer, I was posted to the newest exchange operated by OTC (The
Overseas Telecommunications Commission). It was an all-electronic
affair (not a relay in sight). I pestered the STO for some work, so he
showed me a troublesome rack of equipment that had been designed by an
in-house engineer (most of the rest of the floor used equipment from
Hasler or Siemens and functioned perfectly). Here's a short list of
things the guy had managed to do and my suggested changes:

[snip list]

My biggest error when I ran a research group was to arrange to do some work
jointly with another organisation on the basis that I thought they had a
clue. They built the main part of the equipment to my functional spec as
they had access to special parts I could not otherwise use.

I should have realised something was wrong when I had to re-explain the way
the system was to operate *four times* to them during the their 'design and
assemble' phase. The people building it didn't really understand how it
worked. However I decided that was because the measurement technique it
used was a novel and unusual one. One my group had developed but most other
people hadn't encountered. But they had a long track record in microwave
kit, so I assumed they'd build something that worked OK.

When the box came we tried using it and it simply didn't work reliably. So
a postdoc and I opened it up. I'm not sure if the best phrase is "bag of
nails" or "can of worms"...

The person who assembled it clearly had zero understanding of things like
signal and ground paths. And no idea of how to power things. For example,
items that required 5V or 9V or 12Vdc rails were powered via a series
dropper resistor from a 15V stabiliser. The result was that power rails
seen by items wandered all over the place and were hidiously noisy, etc.
More than one costly item was damaged by this allowing an over-voltage to
be applied.

Took months to rebuild properly. They main guy who built it left for a job
elsewhere.

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