Frozen Microprocessor in Yamaha HTR-5440 A/V Receiver

[Mark]

As a favor to my son's friend, we are trying to repair his Yamaha HTR-5440
Receiver. The symptom for the past few weeks was that the unit would play
for a while and then stop responding to all front panel buttons and the
remote; then the only way to turn the receiver off was to unplug it.
Re-plugging it in would restore operation until the next time that the unit
froze up.

When we brought the unit into our shop, it wouldn't work at all. The low
voltage power is present (+5V, +15V and -15V), but the power-on relay won't
activate, so the display and everything else is dead.

Probing around, I find a clock signal on the microprocessor, running at 10
MHz. I can see the signal from the power-on switch; it goes into a pin on
the microprocessor (+5V when the button is pressed, 0V otherwise). The
output from the microprocessor that is supposed to drive the power-on relay
is always low regardless of the state of the power-on button. Other than the
clock, there is only one other signal on one other pin of the processor that
isn't +5V or ground, and it is a square wave with a 40 msec period. I would
have expected to see other lines transitioning from data transfers, but
nothing.

I don't see any obvious signs of damage, and all of the solder joints look
good. Does anyone have any experience servicing this receiver or ones like
it? Can anyone shed any light on the problem?

 

[Leonard Caillouet]

Invest in a service manual from Yamaha ($18, $12 if you are a dealer) and
look to the reset circuit.

Leonard Caillouet

"Mark" <MarkWharton@NOSPAM.Hotmail.com> wrote in message
news:msDmb.129680$qj6.8488135@news1.news.adelphia.net...

As a favor to my son's friend, we are trying to repair his Yamaha HTR-5440
Receiver. The symptom for the past few weeks was that the unit would play
for a while and then stop responding to all front panel buttons and the
remote; then the only way to turn the receiver off was to unplug it.
Re-plugging it in would restore operation until the next time that the
unit
froze up.

When we brought the unit into our shop, it wouldn't work at all. The low
voltage power is present (+5V, +15V and -15V), but the power-on relay
won't
activate, so the display and everything else is dead.

Probing around, I find a clock signal on the microprocessor, running at 10
MHz. I can see the signal from the power-on switch; it goes into a pin on
the microprocessor (+5V when the button is pressed, 0V otherwise). The
output from the microprocessor that is supposed to drive the power-on
relay
is always low regardless of the state of the power-on button. Other than
the
clock, there is only one other signal on one other pin of the processor
that
isn't +5V or ground, and it is a square wave with a 40 msec period. I
would
have expected to see other lines transitioning from data transfers, but
nothing.

I don't see any obvious signs of damage, and all of the solder joints look
good. Does anyone have any experience servicing this receiver or ones like
it? Can anyone shed any light on the problem?

 

[Mark D. Zacharias]

If it freezes up and is still playing whatever source, I think I'd look at
the crystal maybe being bad. Of course one could also try resoldering the
micro.

If it helps, Yamahas of recent vintage don't, for example, scan the
key-matrix with data, the key matrix is part of a resistive ladder
arrangement. I believe this also applies to other functions of the
microprocessor.

Mark Z.


"Leonard Caillouet" <lcailloNOSPAM@devoynet.com> wrote in message
news:vbGmb.102000$AH4.152@lakeread06...

Invest in a service manual from Yamaha ($18, $12 if you are a dealer) and
look to the reset circuit.

Leonard Caillouet

"Mark" <MarkWharton@NOSPAM.Hotmail.com> wrote in message
news:msDmb.129680$qj6.8488135@news1.news.adelphia.net...
As a favor to my son's friend, we are trying to repair his Yamaha
HTR-5440
Receiver. The symptom for the past few weeks was that the unit would
play
for a while and then stop responding to all front panel buttons and the
remote; then the only way to turn the receiver off was to unplug it.
Re-plugging it in would restore operation until the next time that the
unit
froze up.

When we brought the unit into our shop, it wouldn't work at all. The low
voltage power is present (+5V, +15V and -15V), but the power-on relay
won't
activate, so the display and everything else is dead.

Probing around, I find a clock signal on the microprocessor, running at
10
MHz. I can see the signal from the power-on switch; it goes into a pin
on
the microprocessor (+5V when the button is pressed, 0V otherwise). The
output from the microprocessor that is supposed to drive the power-on
relay
is always low regardless of the state of the power-on button. Other than
the
clock, there is only one other signal on one other pin of the processor
that
isn't +5V or ground, and it is a square wave with a 40 msec period. I
would
have expected to see other lines transitioning from data transfers, but
nothing.

I don't see any obvious signs of damage, and all of the solder joints
look
good. Does anyone have any experience servicing this receiver or ones
like
it? Can anyone shed any light on the problem?

 

[Mark]

Thanks for your suggestions Leonard and Mark. The idea that the processor
may being held in a RESET state makes sense, and is consistent with the
observed symptoms. So, I found the components associated with the reset
circuit and by implication, the reset pin of the processor (pin 63 if I'm
counting them correctly). Pin 63 is normally held high by 100k-ohm pullup
resistor R921, and is pulled low by npn reset transistor Q909. When the unit
is unplugged, then reconnected to the AC line, pin 63 goes low for a few
hundred milliseconds, then high again. So it would appear that the reset
circuit is working correctly (darn!).

I can also reset the processor by grounding pin 63 directly. When I do this,
the 25 Hz square wave (40 ms period) on pin 34 stops for the duration of the
reset, and resumes when the reset is finished. Again, this appears to be
normal behavior. However, once in a while the waveform at pin 63 will change
to a narrower pulse after the reset, and when it does, the power-on relay
kicks in and momentarily turns the unit on (for only tenths of a second,
however).

So, it appears that sometimes after reset the processor attempts to execute
the proper set of code, and other times it gets lost or hung up or
something.

And yes, Mark, you are correct. This model does not scan the front-panel
keys. It uses a voltage-encoding scheme like you describe that requires only
2 wires to connect 10 pushbuttons. Very clever.

Anyway, I'll keep plugging away. If anyone has any suggestions, please pass
them on.

Mark

 

[James Sweet]

"Mark" <MarkWharton@NOSPAM.Hotmail.com> wrote in message
news:My_mb.132465$qj6.8869548@news1.news.adelphia.net...

Thanks for your suggestions Leonard and Mark. The idea that the processor
may being held in a RESET state makes sense, and is consistent with the
observed symptoms. So, I found the components associated with the reset
circuit and by implication, the reset pin of the processor (pin 63 if I'm
counting them correctly). Pin 63 is normally held high by 100k-ohm pullup
resistor R921, and is pulled low by npn reset transistor Q909. When the
unit
is unplugged, then reconnected to the AC line, pin 63 goes low for a few
hundred milliseconds, then high again. So it would appear that the reset
circuit is working correctly (darn!).

I can also reset the processor by grounding pin 63 directly. When I do
this,
the 25 Hz square wave (40 ms period) on pin 34 stops for the duration of
the
reset, and resumes when the reset is finished. Again, this appears to be
normal behavior. However, once in a while the waveform at pin 63 will
change
to a narrower pulse after the reset, and when it does, the power-on relay
kicks in and momentarily turns the unit on (for only tenths of a second,
however).

So, it appears that sometimes after reset the processor attempts to
execute
the proper set of code, and other times it gets lost or hung up or
something.

And yes, Mark, you are correct. This model does not scan the front-panel
keys. It uses a voltage-encoding scheme like you describe that requires
only
2 wires to connect 10 pushbuttons. Very clever.

Anyway, I'll keep plugging away. If anyone has any suggestions, please
pass
them on.

Mark

Have a look at the power supply, I've seen a lot of stuff lately with bad
output filter capacitors, often they're even bulging, this causes severe
ripple on the output which causes all sorts of random problems.

 

[Mark]

James:

Thanks for the suggestion. The power supply filter capacitor is fine,
unfortunately. I checked it by substitution.

Mark

"James Sweet" <jamessweet@hotmail.com> wrote in message
news:se%mb.38912$e01.84768@attbi_s02...

Have a look at the power supply, I've seen a lot of stuff lately with bad
output filter capacitors, often they're even bulging, this causes severe
ripple on the output which causes all sorts of random problems.