Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Yamaha XM6150

While waiting for some more TA7317P devices for my previous replair I was
handed a Yamaha XM6150 six channel power amplifier with the channel C
protection light on.

After removing the top cover I was curious what the four huge inductors were
for and wondered if I was dealing with a class D system. Some of the mystery
was cleared up by googling EEEngine:
http://www.yamahacommercialaudio.com...ine/index.html

I'm not sure I fully understand how it does what is claimed. I've never seen
anything like it before in an audio amplifier.

Next I obtained the service manual. There doesn't seem to be a direct link
but if you google yamaha_xm4220_xm6150.pdf the elektrotanya site will
provide it.

The power amp schematic is the one at the top of the last page with the
darlington output transistors.

I quickly found +55V on the orange wire to the relay board (CN806) and
further tests showed, unsurprisingly, that both darlington output
transistors (2SD2560 and 2SB1647) for that channel are short circuit.

Under a bright light I don't see any burned components or other damage. The
D2560 has obviously been very hot as it has toasted the board a little.

I'm thinking of trying a TIP122/127 pair to see if everything works properly
at low power before I blow up a new pair of correct devices.

Any other suggestions are welcome.

Old guy


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Default Yamaha XM6150

In amps with the output taken off the emitters I used to use like ~100
ohm resistors from E to B and see how it runs with no load. The
problem is that with Darlington outputs disabled like that it may not
have enough current to even drive the feedback network.

But at quiescence there should be no offset and the collector voltages
should be quite low. Not sure how low but they should obviously track
the input signal. It can't be really detected at the output with that
configuration. You should be able to watch the audio on a scope. I
would think that if the voltage control uses the same feedback loop as
the main audio it might just clip up to max with low output, but you
can still ascertain if the regulators are working. If the voltages are
railed with no input, the failure was likely caused by a fault in the
regulator control.

This configuration cannot be a real class AB because for efficiency it
must turn the non driven end of the output stage fully off or very
close. In the linked article it claims a better damping factor than
class D, which I believe, but I don't think it is going to be as good
as good class AB.

All they have really done is take the final SESAPP stage out of the
class D domain. The "output transistors" actually operate as active
filters, as well as polarity switches. I figured someone would come up
with this sooner or later, and it's not much more (operationally) than
using a commutating power supply, except that there are a near
infinite number of commutators.

Since there is a limit as to just how fast this power supply can
respond to the input, I imagine that sustained high output at high
frequencies are hard on the outputs.

Personally I'll just stick with my Phase Linear 400 II and put a fan
on it, but business is business.

J
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Default Yamaha XM6150

John Smith wrote in message
...
While waiting for some more TA7317P devices for my previous replair I was
handed a Yamaha XM6150 six channel power amplifier with the channel C
protection light on.

After removing the top cover I was curious what the four huge inductors

were
for and wondered if I was dealing with a class D system. Some of the

mystery
was cleared up by googling EEEngine:

http://www.yamahacommercialaudio.com...30_power_ampli
fier/product_index/50_eeengine/index.html

I'm not sure I fully understand how it does what is claimed. I've never

seen
anything like it before in an audio amplifier.

Next I obtained the service manual. There doesn't seem to be a direct link
but if you google yamaha_xm4220_xm6150.pdf the elektrotanya site will
provide it.

The power amp schematic is the one at the top of the last page with the
darlington output transistors.

I quickly found +55V on the orange wire to the relay board (CN806) and
further tests showed, unsurprisingly, that both darlington output
transistors (2SD2560 and 2SB1647) for that channel are short circuit.

Under a bright light I don't see any burned components or other damage.

The
D2560 has obviously been very hot as it has toasted the board a little.

I'm thinking of trying a TIP122/127 pair to see if everything works

properly
at low power before I blow up a new pair of correct devices.

Any other suggestions are welcome.

Old guy




I'm only familiar with Yamaha Stagepas 300
If your one is made with lightness in mind and 2 channel, check whether the
audio outputs are antiphase, ie one has "tip" contact to ground, and ground
contact is hot


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Default Yamaha XM6150

"John Smith" wrote in message
...
While waiting for some more TA7317P devices for my previous replair I was
handed a Yamaha XM6150 six channel power amplifier with the channel C
protection light on.

I tried a TIP122/127 pair and The DC conditions then seemed fine.

There's a new 2SD2560 and 2SB1647 in there now.

The protection light is off and all six outputs are only mV from ground.

However the channel C clip light is permanently on (It was on previously
with the shorted output transistors but I didn't thnk much of it at the
time.)

I haven't tried a signal yet.

The schematic is in yamaha_xm4220_xm6150.pdf whcih I got from electrotanya.

The channel C clip signal is at pin 3 of CN602 (page 59) and I found 21.6V
there but 25V on the other channels.

Tracing back this comes from R454 on the driver board (also page 59).

There's 0.8V across D410 (cathode +Ve) but only 0.3V across the equivalent
component in an adjacent channel. Q426 has Vbe 0.56V so no surprise it's
turning on. D409 has 0.23V across it (anode +Ve).

Relative to ground both diodes are -60V but that is also true of an adjacent
channel.

R457 has 0.340V across it and R460 has 0.343V across it.

moving to Q424/427, Q427 base is 46mV and Q424 base is 35mV.

So now I'm wondering what the quickest way to pinpointing the bad component
is.

Thanks in advance if anyone else would like to have a look at the schematic.

Old guy


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