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blown fuse on fairly new Yamaha HTR 5790 receiver

One of the two main fuses blows instantly as soon as power is applied
to receiver. I checked the main power supply caps [email protected],000uf and they
were ok. I also checked the bridge rectifier and it was ok. When I
remove the two power leads to the transformer it does not blow fuse.
The main windings of the transformer are 1.0 ohm. The output
transistors are each about 800 ohms at the speaker terminal (prior to
relay).

What else to check?????


Thanks!!
 
H

hr(bob) [email protected]

Jan 1, 1970
0
One of the two main fuses blows instantly as soon as power is applied
to receiver. I checked the main power supply caps [email protected],000uf and they
were ok. I also checked the bridge rectifier and it was ok. When I
remove the two power leads to the transformer it does not blow fuse.
The main windings of the transformer are 1.0 ohm. The output
transistors are each about 800 ohms at the speaker terminal (prior to
relay).

What else to check?????

Thanks!!

Disconnect all loads from the electrolytics, so you just have the
transformer, diodes and capacitors in the circuit and see what
happens. The diodes may test ok but break down under higher voltage
than your tester applies.

H. R. (Bob) Hofmann
 
J

Jamie

Jan 1, 1970
0
One of the two main fuses blows instantly as soon as power is applied
to receiver. I checked the main power supply caps [email protected],000uf and they
were ok. I also checked the bridge rectifier and it was ok. When I
remove the two power leads to the transformer it does not blow fuse.
The main windings of the transformer are 1.0 ohm. The output
transistors are each about 800 ohms at the speaker terminal (prior to
relay).

What else to check?????


Thanks!!

To save your self some fuses and hassles, find
your self a high wattage incandescent lamp rated
for the line voltage your using (120v 200W) for
example. Use that in place of the fuse until you can
removed the solid short.
WHen you say you removed the main windings? I can
only assume you're referring to the primary side of the
xformer?. If so, how about disconnecting the secondary
sides?
You may want to perform a short test to ground to see if you have
a shorted xformer. The preferred method is to use a megga meter.

Usual causes are arc's from lightning storms or over heating of the
enamel if you do find a short to ground.
--
If disconnecting the secondary from the bridge removes the short,
then try disconnecting the output supply that goes from the bridge and
caps into the amp.

Also, you may have a time delayed on or soft start circuit that may not
be soft starting.

P.S.
Because a CAP or bridge test ok at DMM voltage levels does not mean
they are good.
 
A

Arfa Daily

Jan 1, 1970
0
Jamie said:
To save your self some fuses and hassles, find
your self a high wattage incandescent lamp rated
for the line voltage your using (120v 200W) for
example. Use that in place of the fuse until you can
removed the solid short.
WHen you say you removed the main windings? I can
only assume you're referring to the primary side of the
xformer?. If so, how about disconnecting the secondary
sides?
You may want to perform a short test to ground to see if you have
a shorted xformer. The preferred method is to use a megga meter.

Usual causes are arc's from lightning storms or over heating of the
enamel if you do find a short to ground.
--
If disconnecting the secondary from the bridge removes the short,
then try disconnecting the output supply that goes from the bridge and
caps into the amp.

Also, you may have a time delayed on or soft start circuit that may not
be soft starting.

P.S.
Because a CAP or bridge test ok at DMM voltage levels does not mean
they are good.

If you can lay hands on a variac, use that to power the unit. This kind of
fault then becomes a breeze to locate (the basic cause of). If it turns out
to be related to the output stages - and I'm not quite sure of what you are
measuring to come up with your "800 ohms" figure - then how simple or not
the *actual* problem is, is a whole new ball game with DC coupled amps like
this ...

Arfa
 
M

Mark D. Zacharias

Jan 1, 1970
0
Arfa Daily said:
If you can lay hands on a variac, use that to power the unit. This kind of
fault then becomes a breeze to locate (the basic cause of). If it turns
out to be related to the output stages - and I'm not quite sure of what
you are measuring to come up with your "800 ohms" figure - then how simple
or not the *actual* problem is, is a whole new ball game with DC coupled
amps like this ...

Arfa

I'm going to assume the typical.

1. An amp channel is blown.
2. The associated emitter resistor is not blown yet since the fuse blows.
3. You can measure from the center leg of each emitter resistor to the
collector tabs of the associated output transistors.
4. When you find a channel where the emitter is shorted to one or both
collectors, you've found your blown channel.
5. There are often other parts bad as well, though the Yamaha amp channels
are pretty easy. Often there is a resistor between the driver transistors
which is burned - usually 220 ohms, and of course the drivers are suspect,
the bias transistor could be bad OR HAVE BAD SOLDER CONNECTIONS which caused
the failure in the first place, and there could be another resistor bad
which feeds the B+ or B- voltage to a driver - usually 47 ohms.


Mark Z.
 
I'm going to assume the typical.

1. An amp channel is blown.
2. The associated emitter resistor is not blown yet since the fuse blows.
3. You can measure from the center leg of each emitter resistor to the
collector tabs of the associated output transistors.
4. When you find a channel where the emitter is shorted to one or both
collectors, you've found your blown channel.
5. There are often other parts bad as well, though the Yamaha amp channels
are pretty easy. Often there is a resistor between the driver transistors
which is burned - usually 220 ohms, and of course the drivers are suspect,
the bias transistor could be bad OR HAVE BAD SOLDER CONNECTIONS which caused
the failure in the first place, and there could be another resistor bad
which feeds the B+ or B- voltage to a driver - usually 47 ohms.

Mark Z.- Hide quoted text -

- Show quoted text -

I do have a variac, I am not sure how it really helps finds the fault,
though. I have not determined yet whether the short is in the power
supply board or the output transistors.
Thanks
 
Ok, one step closer. I replaced the two 10,000uf 71v power supply
caps with two 12,000uf 80v caps I had and now the fuse does NOT blow
when I push the power button. But, I hear a relay click and the unit
does still not power up.
 
A

Arfa Daily

Jan 1, 1970
0
Ok, one step closer. I replaced the two 10,000uf 71v power supply
caps with two 12,000uf 80v caps I had and now the fuse does NOT blow
when I push the power button. But, I hear a relay click and the unit
does still not power up.

It's hard to say exactly what that implies, other than that one of the two
caps was short circuit. I have to say though, that it is rare for large
electros like those to fail short circuit. Have you tried measuring them to
see if either is short ? Is it the standby relay that is clicking, or is
there a delay before you hear the relay, and it is the output relays that
you are hearing ? If the standby relay, does it drop straight back out ?
This is what commonly happens on Yammies when there is an output fault. If
it looks like there is an output fault, go with the good checking advice
that Mark gave. He does a lot of these AV amps, and is well worth following
for specific advice on them.

Arfa
 
It's hard to say exactly what that implies, other than that one of the two
caps was short circuit. I have to say though, that it is rare for large
electros like those to fail short circuit. Have you tried measuring them to
see if either is short ? Is it the standby relay that is clicking, or is
there a delay before you hear the relay, and it is the output relays that
you are hearing ? If the standby relay, does it drop straight back out ?
This is what commonly happens on Yammies when there is an output fault. If
it looks like there is an output fault, go with the good checking advice
that Mark gave. He does a lot of these AV amps, and is well worth following
for specific advice on them.

Arfa

I believe it is the standby relay which is located on the circuit
board right at the ac mains input. I believe my next step is to find
the output transistor fault.
 
P

PeterD

Jan 1, 1970
0
It's hard to say exactly what that implies, other than that one of the two
caps was short circuit. I have to say though, that it is rare for large
electros like those to fail short circuit. Have you tried measuring them to
see if either is short ? Is it the standby relay that is clicking, or is
there a delay before you hear the relay, and it is the output relays that
you are hearing ? If the standby relay, does it drop straight back out ?
This is what commonly happens on Yammies when there is an output fault. If
it looks like there is an output fault, go with the good checking advice
that Mark gave. He does a lot of these AV amps, and is well worth following
for specific advice on them.

Arfa

The OP may want to check the diodes in the bridge, one (or more?) may
have blown with the bad caps, and the PS now is not delivering enough
voltage to power (up) the unit.
 
M

Mark D. Zacharias

Jan 1, 1970
0
Ok, one step closer. I replaced the two 10,000uf 71v power supply
caps with two 12,000uf 80v caps I had and now the fuse does NOT blow
when I push the power button. But, I hear a relay click and the unit
does still not power up.

Sounds like the emitter resistor has now failed, so the fuse no longer
blows...

Mark Z.
 
M

Mark D. Zacharias

Jan 1, 1970
0
Mark D. Zacharias said:
Sounds like the emitter resistor has now failed, so the fuse no longer
blows...

Mark Z.
Of course, you could have a shorted filter cap, but this would be pretty
unusual on a newer unit.

mz
 
J

James Sweet

Jan 1, 1970
0
If you can lay hands on a variac, use that to power the unit. This kind of
fault then becomes a breeze to locate (the basic cause of). If it turns
out to be related to the output stages - and I'm not quite sure of what
you are measuring to come up with your "800 ohms" figure - then how simple
or not the *actual* problem is, is a whole new ball game with DC coupled
amps like this ...


Use a large incandescent lightbulb wired in series with the unit for
testing. It's cheaper than a variac and in this case is a better solution.
200-300W should do it.
 
Use a large incandescent lightbulb wired in series with the unit for
testing. It's cheaper than a variac and in this case is a better solution.
200-300W should do it.

Ok, I dug a bit deeper and found that the two center channel power
transistors were shorted. I replaced them with the rear channel
devices to see if it would work.
The fuse no longer blows but the standby relay still kicks it out.
The difference is that the display comes on momentarily and no fuse
blowing.
So either I have more issues on the center channel or the protection
circuitry knows that the rear channel transistors are missing.
 
J

James Sweet

Jan 1, 1970
0
Ok, I dug a bit deeper and found that the two center channel power
transistors were shorted. I replaced them with the rear channel
devices to see if it would work.
The fuse no longer blows but the standby relay still kicks it out.
The difference is that the display comes on momentarily and no fuse
blowing.
So either I have more issues on the center channel or the protection
circuitry knows that the rear channel transistors are missing.


There's a good chance the latter is the case.
 
A

Arfa Daily

Jan 1, 1970
0
James Sweet said:
There's a good chance the latter is the case.
Agreed. This is common for Yammies, and is a most frustrating characteristic
when you want to just check that all the other channels work before putting
in a firm quote. I have one sitting up the corner of the workshop waiting
for transistors right now, that does exactly as you describe, with the bad
ones removed. You will be quite lucky if there are no issues other than bad
output transistors on your originally faulty channel.

Arfa
 
Agreed. This is common for Yammies, and is a most frustrating characteristic
when you want to just check that all the other channels work before putting
in a firm quote. I have one sitting up the corner of the workshop waiting
for transistors right now, that does exactly as you describe, with the bad
ones removed. You will be quite lucky if there are no issues other than bad
output transistors on your originally faulty channel.

Arfa- Hide quoted text -

- Show quoted text -

I got it back together tonight. I used the presence transistors and
placed them in the surround channel locations. I substituted an
mjl1302a for the 2sa1492 and a mjl3281a for the 2sc3856.
The case size for the mjl is larger than the original so I figured
they would be ok in the open air since they were not used.
It worked fine for over an hour and then the two mjls burned up. I
could not figure out how to get zone2/zone3 off the display so that is
probably why they failed. I guess I will order the correct ones that
fit and all should be fine.
 
Agreed. This is common for Yammies, and is a most frustrating characteristic
when you want to just check that all the other channels work before putting
in a firm quote. I have one sitting up the corner of the workshop waiting
for transistors right now, that does exactly as you describe, with the bad
ones removed. You will be quite lucky if there are no issues other than bad
output transistors on your originally faulty channel.

Arfa- Hide quoted text -

- Show quoted text -

I disconnected the power to the zone2/zone3 board which I do not plan
on using and now it is working fine again and powering on
 
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