"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

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

"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