I have to NAD T762 on the table. Both with burned out (shorted) 5,1V
zenerdiodes (D718).



I have replaces them with a new 5W type instead of the original 2W.



But the diodes is getting extremely hot and I can't figure out if this is ok
(like the way it was designed). They are sitting directly in series with a
7812 from a 22V DC supply. The thought behind the design must bee to divide
the power loss between the zenerdiode and the 7812.

The amplifier is working, but I don't like those hot zeners!



Is there anybody out there that have worked on a NAD T762?



Peter

On Aug 29, 11:57 am, "Peter Andersen"
wrote:
I have to NAD T762 on the table. Both with burned out (shorted) 5,1V
zenerdiodes (D718).

I have replaces them with a new 5W type instead of the original 2W.

But the diodes is getting extremely hot and I can't figure out if this is ok
(like the way it was designed). They are sitting directly in series with a
7812 from a 22V DC supply. The thought behind the design must bee to divide
the power loss between the zenerdiode and the 7812.

The amplifier is working, but I don't like those hot zeners!

Is there anybody out there that have worked on a NAD T762?

Peter

*Shorted* Zeners? Are you sure? Usually they fail open.

Betcha you have a shorted driver transistor, possibly even a shorted
output transistor. What other tests have you done?

Peter Wieck
Wyncote, PA

On Wed, 29 Aug 2007 17:57:08 +0200, "Peter Andersen"
put finger to keyboard and composed:

I have to NAD T762 on the table. Both with burned out (shorted) 5,1V
zenerdiodes (D718).



I have replaces them with a new 5W type instead of the original 2W.



But the diodes is getting extremely hot and I can't figure out if this is ok
(like the way it was designed). They are sitting directly in series with a
7812 from a 22V DC supply. The thought behind the design must bee to divide
the power loss between the zenerdiode and the 7812.

If there is a series resistor, then I'd measure the voltage across it.
That should give you the current, which in turn should give you the
actual dissipation in the zener. A 5V1 zener dissipating 1W would be
passing 200mA. Any more than that and I'd be looking for a culprit.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Peter Andersen wrote:

I have to NAD T762 on the table. Both with burned out (shorted) 5,1V
zenerdiodes (D718).



I have replaces them with a new 5W type instead of the original 2W.



But the diodes is getting extremely hot and I can't figure out if this is ok
(like the way it was designed). They are sitting directly in series with a
7812 from a 22V DC supply. The thought behind the design must bee to divide
the power loss between the zenerdiode and the 7812.

The amplifier is working, but I don't like those hot zeners!



Is there anybody out there that have worked on a NAD T762?



Peter
Well,
I have a theory..
If the Zener is in fact in series with the feed to the 7812
from the 22 volt source? May I suggest that maybe 22 volts isn't
the real voltage it should be? If this is the case, it would place
the zener in a high resistive state and it will get hot!..
The reason say this is because the 7812 (last time I checked) can
handle around 36 volts.
Since your Zener is 5.1 volts, that leaves 2 things in conclusion.

#1.
It really isn't being used in Series but in parallel with a feeder
resistor to be used as a reference! In which case, the feeder as
reduced in size of the load from the circuit has been removed!.

#2
The 5.1 volt zener was picked to bring the Vcc source voltage down
a bit with in the safe operating range.

I would be willing to bet that it's suppose to be more than 22 volts.




--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

"Jamie" t wrote in message
news
Peter Andersen wrote:

I have to NAD T762 on the table. Both with burned out (shorted) 5,1V
zenerdiodes (D718).



I have replaces them with a new 5W type instead of the original 2W.



But the diodes is getting extremely hot and I can't figure out if this is
ok (like the way it was designed). They are sitting directly in series
with a 7812 from a 22V DC supply. The thought behind the design must bee
to divide the power loss between the zenerdiode and the 7812.

The amplifier is working, but I don't like those hot zeners!



Is there anybody out there that have worked on a NAD T762?



Peter
Well,
I have a theory..
If the Zener is in fact in series with the feed to the 7812
from the 22 volt source? May I suggest that maybe 22 volts isn't
the real voltage it should be? If this is the case, it would place
the zener in a high resistive state and it will get hot!..
The reason say this is because the 7812 (last time I checked) can
handle around 36 volts.
Since your Zener is 5.1 volts, that leaves 2 things in conclusion.

#1.
It really isn't being used in Series but in parallel with a feeder
resistor to be used as a reference! In which case, the feeder as reduced
in size of the load from the circuit has been removed!.

#2
The 5.1 volt zener was picked to bring the Vcc source voltage down
a bit with in the safe operating range.

I would be willing to bet that it's suppose to be more than 22 volts.





Well I must say, Jamie, I am having some difficulty following those lines of
reasoning. If the nominal supply is 22v, and a 5v1 zener is glued in series
with that to the input of the 7812, that's going to leave around 17v on the
input to the reg. So why is that a problem in as much as you think that the
starting voltage should be higher than 22v ? I must confess that I don't
really see the point of reducing the input volts by 5 - either 17 or 22
seems like a perfectly valid amount to me, just that at 22v, the reg might
need a bit more heatsinking on it. However, on that point, if the original
zener was rated at 2 watts, then allowing for some margin and derating to
say 1.5 watts, that would allow for a maximum current of 1.5 / 5 or ~330mA,
so that would imply that the designer was not expecting more than this to be
drawn from his 7812, even though these, in their commonest form, are rated
to an amp. Now if that is the case, the 7812 is almost idling anyway with
17v on its input, so I really can't see it caring much, temperature -wise,
about having 22v on it rather than 17v.

However, something else just occured to me. The OP was taking about zeners
in the plural - two I think. So is that two zeners, in series with each
other, and then in series with the input to the reg ? If that is the case,
then the maths certainly doesn't stack up, as 10v will be lost across the
zeners, leaving only 12v on the input to the regulator, which clearly isn't
enough, as Jamie suggests might be the case.

As a matter of interest, as these zeners had apparently failed short
circuit, and we know that the 7812 can take up to 36v on its input, how did
the OP know that there was a problem, given that he says that the amp is
apparently working ok ?

Arfa

Arfa Daily wrote:

"Jamie" t wrote in message
news
Peter Andersen wrote:


I have to NAD T762 on the table. Both with burned out (shorted) 5,1V
zenerdiodes (D718).



I have replaces them with a new 5W type instead of the original 2W.



But the diodes is getting extremely hot and I can't figure out if this is
ok (like the way it was designed). They are sitting directly in series
with a 7812 from a 22V DC supply. The thought behind the design must bee
to divide the power loss between the zenerdiode and the 7812.

The amplifier is working, but I don't like those hot zeners!



Is there anybody out there that have worked on a NAD T762?



Peter

Well,
I have a theory..
If the Zener is in fact in series with the feed to the 7812
from the 22 volt source? May I suggest that maybe 22 volts isn't
the real voltage it should be? If this is the case, it would place
the zener in a high resistive state and it will get hot!..
The reason say this is because the 7812 (last time I checked) can
handle around 36 volts.
Since your Zener is 5.1 volts, that leaves 2 things in conclusion.

#1.
It really isn't being used in Series but in parallel with a feeder
resistor to be used as a reference! In which case, the feeder as reduced
in size of the load from the circuit has been removed!.

#2
The 5.1 volt zener was picked to bring the Vcc source voltage down
a bit with in the safe operating range.

I would be willing to bet that it's suppose to be more than 22 volts.






Well I must say, Jamie, I am having some difficulty following those lines of
reasoning. If the nominal supply is 22v, and a 5v1 zener is glued in series
with that to the input of the 7812, that's going to leave around 17v on the
input to the reg. So why is that a problem in as much as you think that the
starting voltage should be higher than 22v ? I must confess that I don't
really see the point of reducing the input volts by 5 - either 17 or 22
seems like a perfectly valid amount to me, just that at 22v, the reg might
need a bit more heatsinking on it. However, on that point, if the original
zener was rated at 2 watts, then allowing for some margin and derating to
say 1.5 watts, that would allow for a maximum current of 1.5 / 5 or ~330mA,
so that would imply that the designer was not expecting more than this to be
drawn from his 7812, even though these, in their commonest form, are rated
to an amp. Now if that is the case, the 7812 is almost idling anyway with
17v on its input, so I really can't see it caring much, temperature -wise,
about having 22v on it rather than 17v.

However, something else just occured to me. The OP was taking about zeners
in the plural - two I think. So is that two zeners, in series with each
other, and then in series with the input to the reg ? If that is the case,
then the maths certainly doesn't stack up, as 10v will be lost across the
zeners, leaving only 12v on the input to the regulator, which clearly isn't
enough, as Jamie suggests might be the case.

As a matter of interest, as these zeners had apparently failed short
circuit, and we know that the 7812 can take up to 36v on its input, how did
the OP know that there was a problem, given that he says that the amp is
apparently working ok ?

Arfa


Ok, I'll add to that. What if, there were filter caps that reduce the
ripple of the 22 volt source and the cap's were defective? This in turn
wouldn't give you a constant voltage and thus, your meter would not be
giving you the actual where it should be if working caps were in there.

So lets assume for the moment, 22 * 1.414 = 31.108;

Lets say we place a 5.1 in series, net results would be ~25 V
At this level, the zener's resistive path would be much lower
and thus, less heat dissipation. And ofcourse, bringing the input
voltage down a bit for the post regulator will help reduce the
dissipation.

Not knowing exactly what the device is.
May I suggest that it's a small device being operated via an incorrectly
supplied wall wart or a supply unit that has failed caps.

Just an analogy !

Ok, Bye fer now!






--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

On Aug 29, 8:41 pm, "Arfa Daily" wrote:
Well I must say, Jamie, I am having some difficulty following those lines of
reasoning. If the nominal supply is 22v, and a 5v1 zener is glued in series
with that to the input of the 7812, that's going to leave around 17v on the
input to the reg. So why is that a problem in as much as you think that
the starting voltage should be higher than 22v?

I thought he was suggesting that the starting voltage should be ~40V,
and that's why the zener is needed (to get below 36V). Since the amp
is working with 22V as the starting voltage, this doesn't seem likely.

However, something else just occured to me. The OP was taking about
zeners in the plural - two I think. So is that two zeners, in series with
each other, and then in series with the input to the reg?

As I read it, there are two amplifiers, and the diode at location D718
is the zener in question. Or is D718 a part number?

TM

wrote:
On Aug 29, 8:41 pm, "Arfa Daily" wrote:
Well I must say, Jamie, I am having some difficulty following those
lines of reasoning. If the nominal supply is 22v, and a 5v1 zener is
glued in series with that to the input of the 7812, that's going to
leave around 17v on the input to the reg. So why is that a problem
in as much as you think that
the starting voltage should be higher than 22v?

I thought he was suggesting that the starting voltage should be ~40V,
and that's why the zener is needed (to get below 36V). Since the amp
is working with 22V as the starting voltage, this doesn't seem likely.

However, something else just occured to me. The OP was taking about
zeners in the plural - two I think. So is that two zeners, in series
with each other, and then in series with the input to the reg?

As I read it, there are two amplifiers, and the diode at location D718
is the zener in question. Or is D718 a part number?

That is the partnumber on the schematic (if there should be a NAD technichan
out there he would know..)

No, there is only ONE zener in series with the 7812. The supply is 22V. The
7812 can be driven with 22V directly, so I located the _shorted_ zener by
the smell :-) In the other amp the zener is leaking with 300ohm in both
directions.



I got a mail from someone that confirms the theory about the divided heat
dissipation. This 7812 is supplying the tuner and preoutboard (with digital
volumecontrol, a lot of opamps etc.)

The question is now: is there drawn to much current from this zener/7812
circuit or is it normal(bad bad design!). Who knows?



Peter

Arfa Daily wrote:

"Jamie" t wrote

Well,
I have a theory..
If the Zener is in fact in series with the feed to the 7812
from the 22 volt source? May I suggest that maybe 22 volts isn't
the real voltage it should be? If this is the case, it would place
the zener in a high resistive state and it will get hot!..
The reason say this is because the 7812 (last time I checked) can
handle around 36 volts.
Since your Zener is 5.1 volts, that leaves 2 things in conclusion.

#1.
It really isn't being used in Series but in parallel with a feeder
resistor to be used as a reference! In which case, the feeder as reduced
in size of the load from the circuit has been removed!.

#2
The 5.1 volt zener was picked to bring the Vcc source voltage down
a bit with in the safe operating range.

I would be willing to bet that it's suppose to be more than 22 volts.


Well I must say, Jamie, I am having some difficulty following those lines of
reasoning.

The guy is totally clueless about hardware design.

Graham

"Eeyore" wrote in message
...


Arfa Daily wrote:

"Jamie" t wrote

Well,
I have a theory..
If the Zener is in fact in series with the feed to the 7812
from the 22 volt source? May I suggest that maybe 22 volts isn't
the real voltage it should be? If this is the case, it would place
the zener in a high resistive state and it will get hot!..
The reason say this is because the 7812 (last time I checked) can
handle around 36 volts.
Since your Zener is 5.1 volts, that leaves 2 things in conclusion.

#1.
It really isn't being used in Series but in parallel with a feeder
resistor to be used as a reference! In which case, the feeder as
reduced
in size of the load from the circuit has been removed!.

#2
The 5.1 volt zener was picked to bring the Vcc source voltage down
a bit with in the safe operating range.

I would be willing to bet that it's suppose to be more than 22 volts.


Well I must say, Jamie, I am having some difficulty following those lines
of
reasoning.

The guy is totally clueless about hardware design.

Graham

Wot, Jamie or me Graham ?? :-)

Peter. As far as whether there is too much current being drawn, the absolute
maximum, which would take the original zener up to its 2 watt limit, is
400mA, which is obviously well within the capability of the 7812. However,
if I had been designing the thing, I wouldn't really want more than about
1.5 watts going west in that diode, (not that I would even have put it there
in the first place ...) so we're talking around 330mA. That would leave
around 4 watts or so in the 7812. Now that is basically nothing, especially
if a small heatsink is fitted, so I don't really see the point in having the
zener there to split the power dissipation. Maybe the 7812 is running
without a heatsink, and putting in a 2 cent zener was cheaper than a 3 cent
heatsink, but either way, unless we are missing something here, it seems
like a nonsense piece of design work to me.

I still don't really follow Jamies point about the zener being placed in a
"high resistive state". Once the zener 'knee' point on its curve has been
reached, that curve becomes pretty much vertical within a very small span of
reverse current. With the full rail current of 300mA or possibly more
passing through the one in this bit of kit, it should be in it's lowest
resistance fully on condition.

The point about a poor smoother, and excess ripple resulting in a low
average measured starting voltage is ok in principle, but if the cap was
really in that virtually open circuit condition, I would have expected to
have heard hum on the amp's outputs. The OP said that it was working ok.

I'm interested in the failures of these zeners, and how they were detected
by "smell". In the case of the one that had gone short, it can't have been
the diode itself that was smelling, as its dissipation must have dropped to
zero. That must mean that any power that was being 'lost' in it, was passed
on to the 7812 to lose, so was it this that was smelling to give the clue ?
If it was, then I am surprised, because if its dissipation had risen to the
point where it was smelling, I would have expected its SOA thermal foldback
to have kicked in. As for the zener that had gone 300 ohms (both ways)
leaky, it's hard to see how that circuit even carried on working, as all
voltage input for the 7812 would have disappeared across a 'resistor' of
this value placed in series with the regulator input, with just a few 10s of
mA being drawn.

It's all very curious. Given that the zeners have failed in normal service
in two cases, my inclination would be to short them out and let the regs
have the full 22v up 'em, and add a couple of heatsinks. Those circular
crinkly ones actually work very well, when the gap in the circle is forced
down over the devices's tab. I learnt that from a commercial board that I
repair, that has 3 TO220 Darlington motor driver transistors on it, heatsunk
in this way.

Arfa

Peter Andersen wrote:
I have to NAD T762 on the table. Both with burned out (shorted) 5,1V
zenerdiodes (D718).



I have replaces them with a new 5W type instead of the original 2W.



But the diodes is getting extremely hot and I can't figure out if this is ok
(like the way it was designed). They are sitting directly in series with a
7812 from a 22V DC supply. The thought behind the design must bee to divide
the power loss between the zenerdiode and the 7812.

The amplifier is working, but I don't like those hot zeners!



Is there anybody out there that have worked on a NAD T762?



Peter




Peter (and others who have replied),

Unfortunately, some of these diodes do run hot. D716 is also doing the
same thing as D718 in the T762 for a different 12V regulator, so I'd see
how hot that diode (D716) is getting. Of course if the current load is
different on the regulator, the temperature may be different as well. I
don't have a T762 here to look at right now.

I would certainly agree with the other poster that the input capacitor
coming off the bridge rectifier (C704, 3300uf/35V) could be in trouble
and high ripple could cause problems. This can easily be scoped by
looking at the cathode end of either D718 or D716.

I have had problems on this series of NAD's with the bridge rectifier
diodes D701-704, especially if there is the brownish glue on them. They
often have horrible solder joints, and sometimes fail. I replace them
(originally they are 1N4004)with 1N5399 diodes which are rated for 1.5
amps. I also stand them off the board a bit for better cooling. If you
are running with only 3 of these diodes connected, you'll certainly have
higher ripple on the cap.

While you have the board out (lucky you) I'd also check D705-708 in the
same area and maybe replace them as well. Also check soldering in
general of the regulators. You don't want to have to keep removing the
board as it is rather time consuming and annoying.

Many owner's don't realize that surround sound receivers in general run
quite hot inside and need good air flow around them. I suggest at least
3 inches (8cm) of open air above the receiver if on an open shelf, and a
couple of inches (5cm) on either side and rear. The receiver should
also be on a hard surface, not carpet or such.

To other repliers: These supplies that we are discussing are low
voltage regulators for the input switching, digital board and front
panel, just about everything EXCEPT the power amps.

Regards,
Tim Schwartz
Bristol Electronics

On Aug 30, 12:33 am, "Peter Andersen"
wrote:
wrote:
As I read it, there are two amplifiers, and the diode at location D718
is the zener in question. Or is D718 a part number?

That is the partnumber on the schematic (if there should be a NAD technichan
out there he would know..)

Part number, or reference designator?

The question is now: is there drawn to much current from this zener/7812
circuit or is it normal(bad bad design!). Who knows?

You could tack in a low value resistor in front of the zener and
measure it.

TM

"Tim Schwartz" wrote in message
...
Peter Andersen wrote:
I have to NAD T762 on the table. Both with burned out (shorted) 5,1V
zenerdiodes (D718).



I have replaces them with a new 5W type instead of the original 2W.



But the diodes is getting extremely hot and I can't figure out if this is
ok (like the way it was designed). They are sitting directly in series
with a 7812 from a 22V DC supply. The thought behind the design must bee
to divide the power loss between the zenerdiode and the 7812.

The amplifier is working, but I don't like those hot zeners!



Is there anybody out there that have worked on a NAD T762?



Peter




Peter (and others who have replied),

Unfortunately, some of these diodes do run hot. D716 is also doing the
same thing as D718 in the T762 for a different 12V regulator, so I'd see
how hot that diode (D716) is getting. Of course if the current load is
different on the regulator, the temperature may be different as well. I
don't have a T762 here to look at right now.

I would certainly agree with the other poster that the input capacitor
coming off the bridge rectifier (C704, 3300uf/35V) could be in trouble and
high ripple could cause problems. This can easily be scoped by looking at
the cathode end of either D718 or D716.

I have had problems on this series of NAD's with the bridge rectifier
diodes D701-704, especially if there is the brownish glue on them. They
often have horrible solder joints, and sometimes fail. I replace them
(originally they are 1N4004)with 1N5399 diodes which are rated for 1.5
amps. I also stand them off the board a bit for better cooling. If you
are running with only 3 of these diodes connected, you'll certainly have
higher ripple on the cap.

While you have the board out (lucky you) I'd also check D705-708 in the
same area and maybe replace them as well. Also check soldering in general
of the regulators. You don't want to have to keep removing the board as
it is rather time consuming and annoying.

Many owner's don't realize that surround sound receivers in general run
quite hot inside and need good air flow around them. I suggest at least 3
inches (8cm) of open air above the receiver if on an open shelf, and a
couple of inches (5cm) on either side and rear. The receiver should also
be on a hard surface, not carpet or such.

To other repliers: These supplies that we are discussing are low voltage
regulators for the input switching, digital board and front panel, just
about everything EXCEPT the power amps.

Regards,
Tim Schwartz
Bristol Electronics

So how much current do you reckon is being drawn off that rail Tim ? If all
the logic and opamps and whatever are being fed from it, you'd have to
reckon on at least the 330mA that would take the dissipation in that zener
up to 1.6 watts or so. 400mA and we're at its limit. Obviously, you see a
lot of these. Is it common for that zener to fail ? I don't remember ever
having had one, but then if they fail short, I've maybe never had cause to
go looking ?? Seems like a piece of design work of marginal validity to me.
Does it reduce the temperature of the regulator by much ? Is it worth it for
the dissipation created in the zener, and the apparent reliability issues
which ensue ? As one service engineer to another, I would be interested in
your opinions.

Arfa

Arfa Daily wrote:

"Eeyore" wrote
Arfa Daily wrote:
"Jamie" t wrote

Well,
I have a theory..
If the Zener is in fact in series with the feed to the 7812
from the 22 volt source? May I suggest that maybe 22 volts isn't
the real voltage it should be? If this is the case, it would place
the zener in a high resistive state and it will get hot!..
The reason say this is because the 7812 (last time I checked) can
handle around 36 volts.
Since your Zener is 5.1 volts, that leaves 2 things in conclusion.

#1.
It really isn't being used in Series but in parallel with a feeder
resistor to be used as a reference! In which case, the feeder as
reduced
in size of the load from the circuit has been removed!.

#2
The 5.1 volt zener was picked to bring the Vcc source voltage down
a bit with in the safe operating range.

I would be willing to bet that it's suppose to be more than 22 volts.


Well I must say, Jamie, I am having some difficulty following those lines
of
reasoning.

The guy is totally clueless about hardware design.

Graham

Wot, Jamie or me Graham ?? :-)

Jamie.

I've never once seen a post where he 'gets it'. It never stops him pontificating
though. I understand he's a programmer. Explains a lot.

Graham

On Thu, 30 Aug 2007 12:45:34 GMT, Tim Schwartz
put finger to keyboard and composed:

Peter (and others who have replied),

Unfortunately, some of these diodes do run hot. D716 is also doing the
same thing as D718 in the T762 for a different 12V regulator, so I'd see
how hot that diode (D716) is getting. Of course if the current load is
different on the regulator, the temperature may be different as well. I
don't have a T762 here to look at right now.

Why not replace the single 5V1 zener with two series 2V7 zeners? Or
add a resistor in parallel with the zener?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Eeyore wrote:

Arfa Daily wrote:


"Jamie" t wrote


Well,
I have a theory..
If the Zener is in fact in series with the feed to the 7812
from the 22 volt source? May I suggest that maybe 22 volts isn't
the real voltage it should be? If this is the case, it would place
the zener in a high resistive state and it will get hot!..
The reason say this is because the 7812 (last time I checked) can
handle around 36 volts.
Since your Zener is 5.1 volts, that leaves 2 things in conclusion.

#1.
It really isn't being used in Series but in parallel with a feeder
resistor to be used as a reference! In which case, the feeder as reduced
in size of the load from the circuit has been removed!.

#2
The 5.1 volt zener was picked to bring the Vcc source voltage down
a bit with in the safe operating range.

I would be willing to bet that it's suppose to be more than 22 volts.


Well I must say, Jamie, I am having some difficulty following those lines of
reasoning.


The guy is totally clueless about hardware design.

Graham

Get a life asshole.

I most likely knew 10 times your current knowledge before I turned
the age of 18 and left home, where I took up work designing circuits
that you could have used once your self at one time or another.

Worked with an engineering group that placed many of my designs into
production of various things. That was the good old days, the
chinese market killed..

I now work mostly doing industrial designs, upgrades, special
OEM Uc boards etc. Also did some free lance work with Semco
" A capacitor manufacture" designing new automative equipment
in assembling mica chip capacitors using robotics assemblers
that was all done in computer software.

I don't why i'm wasting my time telling you this, it's so far
beyond you it isn't funny.

I've watched you here foaming at the mouth. You must be one the
most arrogant British trash I have ever seen..


Take about some one clue less. You fit the bill.

btw, any more of your solders making mistakes over there and
trying to past the buck along to us?. It seems to be a traditional
past time! if you're an example.




--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

"Jamie" t wrote in message
...
Eeyore wrote:

Arfa Daily wrote:


"Jamie" t wrote


Well,
I have a theory..
If the Zener is in fact in series with the feed to the 7812
from the 22 volt source? May I suggest that maybe 22 volts isn't
the real voltage it should be? If this is the case, it would place
the zener in a high resistive state and it will get hot!..
The reason say this is because the 7812 (last time I checked) can
handle around 36 volts.
Since your Zener is 5.1 volts, that leaves 2 things in conclusion.

#1.
It really isn't being used in Series but in parallel with a feeder
resistor to be used as a reference! In which case, the feeder as
reduced
in size of the load from the circuit has been removed!.

#2
The 5.1 volt zener was picked to bring the Vcc source voltage down
a bit with in the safe operating range.

I would be willing to bet that it's suppose to be more than 22 volts.


Well I must say, Jamie, I am having some difficulty following those lines
of
reasoning.


The guy is totally clueless about hardware design.

Graham

Get a life asshole.

I most likely knew 10 times your current knowledge before I turned the
age of 18 and left home, where I took up work designing circuits that you
could have used once your self at one time or another.

Worked with an engineering group that placed many of my designs into
production of various things. That was the good old days, the
chinese market killed..

I now work mostly doing industrial designs, upgrades, special
OEM Uc boards etc. Also did some free lance work with Semco
" A capacitor manufacture" designing new automative equipment
in assembling mica chip capacitors using robotics assemblers
that was all done in computer software.

I don't why i'm wasting my time telling you this, it's so far
beyond you it isn't funny.

I've watched you here foaming at the mouth. You must be one the
most arrogant British trash I have ever seen..


Take about some one clue less. You fit the bill.

btw, any more of your solders making mistakes over there and
trying to past the buck along to us?. It seems to be a traditional
past time! if you're an example.



Don't start down that path, pal. I object to the British being collectively
described by you as "trash". No one has made any comments about you as "An
American" . And what are you talking about regarding solder and "passing the
buck" along to you ? Lets just try and all get along without starting
another ****ing contest, shall we ?

Graham. Leave Jamie alone, and Jamie, stop your name calling.

Eeyore wrote:


Arfa Daily wrote:


"Eeyore" wrote

Arfa Daily wrote:

"Jamie" t wrote


Well,
I have a theory..
If the Zener is in fact in series with the feed to the 7812
from the 22 volt source? May I suggest that maybe 22 volts isn't
the real voltage it should be? If this is the case, it would place
the zener in a high resistive state and it will get hot!..
The reason say this is because the 7812 (last time I checked) can
handle around 36 volts.
Since your Zener is 5.1 volts, that leaves 2 things in conclusion.

#1.
It really isn't being used in Series but in parallel with a feeder
resistor to be used as a reference! In which case, the feeder as
reduced
in size of the load from the circuit has been removed!.

#2
The 5.1 volt zener was picked to bring the Vcc source voltage down
a bit with in the safe operating range.

I would be willing to bet that it's suppose to be more than 22 volts.


Well I must say, Jamie, I am having some difficulty following those lines
of
reasoning.

The guy is totally clueless about hardware design.

Graham


Wot, Jamie or me Graham ?? :-)


Jamie.

I've never once seen a post where he 'gets it'. It never stops him pontificating
though. I understand he's a programmer. Explains a lot.

Graham

Graham, You better go back to the ****ter and wipe your ass. Something
smells and I know it isn't me.

If only you had a clue, oh wet, you stopped at the birth of
cat whisker diodes and germanium transistors. I understand, to
complicated. Stay with your valves, they suit you fine.

I must say, your so far out of league you make me laugh. That is
the only reason I respond.

Btw, A couple of my engineer friends monitor this area, they think
you're a real peach.

--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Arfa Daily wrote:

"Jamie" t wrote in message
...

Eeyore wrote:

The guy is totally clueless about hardware design.

Graham


Get a life asshole.

I most likely knew 10 times your current knowledge before I turned the
age of 18 and left home, where I took up work designing circuits that you
could have used once your self at one time or another.

Worked with an engineering group that placed many of my designs into
production of various things. That was the good old days, the
chinese market killed..

I now work mostly doing industrial designs, upgrades, special
OEM Uc boards etc. Also did some free lance work with Semco
" A capacitor manufacture" designing new automative equipment
in assembling mica chip capacitors using robotics assemblers
that was all done in computer software.

I don't why i'm wasting my time telling you this, it's so far
beyond you it isn't funny.

I've watched you here foaming at the mouth. You must be one the
most arrogant British trash I have ever seen..


Take about some one clue less. You fit the bill.

btw, any more of your solders making mistakes over there and
trying to past the buck along to us?. It seems to be a traditional
past time! if you're an example.




Don't start down that path, pal. I object to the British being collectively
described by you as "trash". No one has made any comments about you as "An
American" . And what are you talking about regarding solder and "passing the
buck" along to you ? Lets just try and all get along without starting
another ****ing contest, shall we ?

Graham. Leave Jamie alone, and Jamie, stop your name calling.

Oh, should I direct you to post after post of Graham bashing the US?
and everything it stands for?

Until you know who and what Graham is, I'd suggest you sit back and
monitor a bit.
That comment was directed to him not the British as a whole. I feel
sorry for the british that they have people like him they must deal with.
And I feel sorry for you, because he just sucked you into it..
I'm sure he's sitting back now and enjoying this while he's sucking
on his crumpets and tea.

If you don't want to heed my warnings about him so be it, Every one
has a right to make there own choices. To bad Graham doesn't know what
i'm talking about.



--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Jamie wrote:

Eeyore wrote:
Arfa Daily wrote:
"Eeyore" wrote
Arfa Daily wrote:
"Jamie" t wrote

Well,
I have a theory..
If the Zener is in fact in series with the feed to the 7812
from the 22 volt source? May I suggest that maybe 22 volts isn't
the real voltage it should be? If this is the case, it would place
the zener in a high resistive state and it will get hot!..
The reason say this is because the 7812 (last time I checked) can
handle around 36 volts.
Since your Zener is 5.1 volts, that leaves 2 things in conclusion.

#1.
It really isn't being used in Series but in parallel with a feeder
resistor to be used as a reference! In which case, the feeder as
reduced
in size of the load from the circuit has been removed!.

#2
The 5.1 volt zener was picked to bring the Vcc source voltage down
a bit with in the safe operating range.

I would be willing to bet that it's suppose to be more than 22 volts.


Well I must say, Jamie, I am having some difficulty following those lines
of
reasoning.

The guy is totally clueless about hardware design.

Graham


Wot, Jamie or me Graham ?? :-)


Jamie.

I've never once seen a post where he 'gets it'. It never stops him pontificating
though. I understand he's a programmer. Explains a lot.

Graham

Graham, You better go back to the ****ter and wipe your ass. Something
smells and I know it isn't me.

If only you had a clue, oh wet, you stopped at the birth of
cat whisker diodes and germanium transistors. I understand, to
complicated. Stay with your valves, they suit you fine.

I must say, your so far out of league you make me laugh. That is
the only reason I respond.

Btw, A couple of my engineer friends monitor this area, they think
you're a real peach.

They're as thick as you are ?

Your 'theories' above were totally pathetic btw.

Graham

"Jamie" t wrote in message
...
Arfa Daily wrote:

"Jamie" t wrote in
message ...

Eeyore wrote:

The guy is totally clueless about hardware design.

Graham


Get a life asshole.

I most likely knew 10 times your current knowledge before I turned the
age of 18 and left home, where I took up work designing circuits that
you could have used once your self at one time or another.

Worked with an engineering group that placed many of my designs into
production of various things. That was the good old days, the
chinese market killed..

I now work mostly doing industrial designs, upgrades, special
OEM Uc boards etc. Also did some free lance work with Semco
" A capacitor manufacture" designing new automative equipment
in assembling mica chip capacitors using robotics assemblers
that was all done in computer software.

I don't why i'm wasting my time telling you this, it's so far
beyond you it isn't funny.

I've watched you here foaming at the mouth. You must be one the
most arrogant British trash I have ever seen..


Take about some one clue less. You fit the bill.

btw, any more of your solders making mistakes over there and
trying to past the buck along to us?. It seems to be a traditional
past time! if you're an example.




Don't start down that path, pal. I object to the British being
collectively described by you as "trash". No one has made any comments
about you as "An American" . And what are you talking about regarding
solder and "passing the buck" along to you ? Lets just try and all get
along without starting another ****ing contest, shall we ?

Graham. Leave Jamie alone, and Jamie, stop your name calling.

Oh, should I direct you to post after post of Graham bashing the US?
and everything it stands for?

Until you know who and what Graham is, I'd suggest you sit back and
monitor a bit.
That comment was directed to him not the British as a whole. I feel
sorry for the british that they have people like him they must deal with.
And I feel sorry for you, because he just sucked you into it..
I'm sure he's sitting back now and enjoying this while he's sucking
on his crumpets and tea.

If you don't want to heed my warnings about him so be it, Every one
has a right to make there own choices. To bad Graham doesn't know what
i'm talking about.



I know exactly who Graham is - I have been posting on here for a very long
time, so I don't need you to tell me how to sit back and monitor on this
group. He has not sucked me into anything, and I am not defending him, but
in the past, many people have been drawn into endless ****ing contests which
he may or may not have started, but has certainly helped to perpetuate, with
ever-more offensive and sometimes silly retorts. I just didn't want this
particular thread, which up until then had been an interesting one, to
dissolve into yet another such contest, which is why I suggested that you
should *both* STF up, before all of 'the usual suspects' joined in.

Whilst he might have done his fair share of 'America bashing' both on this
group and others, up until this point, he, or no one else had actually done
any in this particular thread. As far as I am concerned, we are all just
service engineers, and except to point out from time to time that the UK and
the US are two countries separated by a common language, which sometimes
gives rise to misunderstandings, I really don't care what nationality you,
or anyone else that talks on here, are. Which is why I object when people
start dragging nationality into it, in an offensive way.

Reading again, I can see that you might have been referring to Graham as a
single example of what you consider to be "trash", but it just as easily
reads that he is a single example of a collective British trash. Anyway, if
you intended it as just him, then I apologise, but you need to watch how you
put things, and remember how easily people from different cultures can read
things not in the way that you intended.

And that's all that I am going to say. If you two want to keep having a pop
at each other, do it by direct e-mail, and let's just keep it friendly on
here, with disagreements being 'robust' rather than spiralling down into
endless tirades of offensive crap. OK with that ?


Arfa

Arfa Daily wrote:
"Tim Schwartz" wrote in message
...
Peter Andersen wrote:
I have to NAD T762 on the table. Both with burned out (shorted) 5,1V
zenerdiodes (D718).



I have replaces them with a new 5W type instead of the original 2W.



But the diodes is getting extremely hot and I can't figure out if this is
ok (like the way it was designed). They are sitting directly in series
with a 7812 from a 22V DC supply. The thought behind the design must bee
to divide the power loss between the zenerdiode and the 7812.

The amplifier is working, but I don't like those hot zeners!



Is there anybody out there that have worked on a NAD T762?



Peter




Peter (and others who have replied),

Unfortunately, some of these diodes do run hot. D716 is also doing the
same thing as D718 in the T762 for a different 12V regulator, so I'd see
how hot that diode (D716) is getting. Of course if the current load is
different on the regulator, the temperature may be different as well. I
don't have a T762 here to look at right now.

I would certainly agree with the other poster that the input capacitor
coming off the bridge rectifier (C704, 3300uf/35V) could be in trouble and
high ripple could cause problems. This can easily be scoped by looking at
the cathode end of either D718 or D716.

I have had problems on this series of NAD's with the bridge rectifier
diodes D701-704, especially if there is the brownish glue on them. They
often have horrible solder joints, and sometimes fail. I replace them
(originally they are 1N4004)with 1N5399 diodes which are rated for 1.5
amps. I also stand them off the board a bit for better cooling. If you
are running with only 3 of these diodes connected, you'll certainly have
higher ripple on the cap.

While you have the board out (lucky you) I'd also check D705-708 in the
same area and maybe replace them as well. Also check soldering in general
of the regulators. You don't want to have to keep removing the board as
it is rather time consuming and annoying.

Many owner's don't realize that surround sound receivers in general run
quite hot inside and need good air flow around them. I suggest at least 3
inches (8cm) of open air above the receiver if on an open shelf, and a
couple of inches (5cm) on either side and rear. The receiver should also
be on a hard surface, not carpet or such.

To other repliers: These supplies that we are discussing are low voltage
regulators for the input switching, digital board and front panel, just
about everything EXCEPT the power amps.

Regards,
Tim Schwartz
Bristol Electronics

So how much current do you reckon is being drawn off that rail Tim ? If all
the logic and opamps and whatever are being fed from it, you'd have to
reckon on at least the 330mA that would take the dissipation in that zener
up to 1.6 watts or so. 400mA and we're at its limit. Obviously, you see a
lot of these. Is it common for that zener to fail ? I don't remember ever
having had one, but then if they fail short, I've maybe never had cause to
go looking ?? Seems like a piece of design work of marginal validity to me.
Does it reduce the temperature of the regulator by much ? Is it worth it for
the dissipation created in the zener, and the apparent reliability issues
which ensue ? As one service engineer to another, I would be interested in
your opinions.

Arfa


Arfa,

I've never measured the current on the rail, and while I've
touched up soldering on the zeners, I've never replaced one. On the
other hand, I've never checked them either, so while I may have let a
shorted one get by, I've certainly not seen an open one. I haven't
worked on that many of these, maybe a dozen or so. But, I've certainly
seen small regulated supplies run what I would call way to hot on any
brand of surround receiver that I've seen.

I can't speak for the design, as I've not analyzed it, though I don't
like any products where the regulators run hot and bake the boards. As
for the bridge diodes failing, it happens most commonly when the factory
manages to spill some of the light brown glue on them, effectively
insulating them. The glue often darkens and becomes brittle. The
solder joints get baked. I've also seen this glue be corrosive and
conductive when it gets baked enough.

Regards,
Tim Schwartz
Bristol Electronics

Arfa Daily wrote:

"Jamie" t wrote in message
...

Arfa Daily wrote:


"Jamie" t wrote in
message ...


Eeyore wrote:

The guy is totally clueless about hardware design.

Graham



I know exactly who Graham is - I have been posting on here for a very long
time, so I don't need you to tell me how to sit back and monitor on this
group. He has not sucked me into anything, and I am not defending him, but
in the past, many people have been drawn into endless ****ing contests which
he may or may not have started, but has certainly helped to perpetuate, with
ever-more offensive and sometimes silly retorts. I just didn't want this
particular thread, which up until then had been an interesting one, to
dissolve into yet another such contest, which is why I suggested that you
should *both* STF up, before all of 'the usual suspects' joined in.

Whilst he might have done his fair share of 'America bashing' both on this
group and others, up until this point, he, or no one else had actually done
any in this particular thread. As far as I am concerned, we are all just
service engineers, and except to point out from time to time that the UK and
the US are two countries separated by a common language, which sometimes
gives rise to misunderstandings, I really don't care what nationality you,
or anyone else that talks on here, are. Which is why I object when people
start dragging nationality into it, in an offensive way.

Reading again, I can see that you might have been referring to Graham as a
single example of what you consider to be "trash", but it just as easily
reads that he is a single example of a collective British trash. Anyway, if
you intended it as just him, then I apologise, but you need to watch how you
put things, and remember how easily people from different cultures can read
things not in the way that you intended.

And that's all that I am going to say. If you two want to keep having a pop
at each other, do it by direct e-mail, and let's just keep it friendly on
here, with disagreements being 'robust' rather than spiralling down into
endless tirades of offensive crap. OK with that ?


Arfa

Well that's fine. You said your peace.

One day, You may find your self suffering from
dashavou. Hope you remember this.

Bye for now.



--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Meat Plow wrote:

On Thu, 30 Aug 2007 21:55:02 -0400, Jamie wrote:


Eeyore wrote:


Arfa Daily wrote:






I've got to say that this reply or yours is one of the most idiotic things
I've ever read in SER. Those like you who have to brag and blow about
what they know usually don't know ****. If you are as smart as you say you
are then at least act like it.

Acting? I really wonder who is?

Think about that.


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

"Jamie" t wrote in message
...
Arfa Daily wrote:

"Jamie" t wrote in
message ...

Arfa Daily wrote:


"Jamie" t wrote in
message ...


Eeyore wrote:

The guy is totally clueless about hardware design.

Graham



I know exactly who Graham is - I have been posting on here for a very
long time, so I don't need you to tell me how to sit back and monitor on
this group. He has not sucked me into anything, and I am not defending
him, but in the past, many people have been drawn into endless ****ing
contests which he may or may not have started, but has certainly helped
to perpetuate, with ever-more offensive and sometimes silly retorts. I
just didn't want this particular thread, which up until then had been an
interesting one, to dissolve into yet another such contest, which is why
I suggested that you should *both* STF up, before all of 'the usual
suspects' joined in.

Whilst he might have done his fair share of 'America bashing' both on
this group and others, up until this point, he, or no one else had
actually done any in this particular thread. As far as I am concerned, we
are all just service engineers, and except to point out from time to time
that the UK and the US are two countries separated by a common language,
which sometimes gives rise to misunderstandings, I really don't care what
nationality you, or anyone else that talks on here, are. Which is why I
object when people start dragging nationality into it, in an offensive
way.

Reading again, I can see that you might have been referring to Graham as
a single example of what you consider to be "trash", but it just as
easily reads that he is a single example of a collective British trash.
Anyway, if you intended it as just him, then I apologise, but you need to
watch how you put things, and remember how easily people from different
cultures can read things not in the way that you intended.

And that's all that I am going to say. If you two want to keep having a
pop at each other, do it by direct e-mail, and let's just keep it
friendly on here, with disagreements being 'robust' rather than
spiralling down into endless tirades of offensive crap. OK with that ?


Arfa
Well that's fine. You said your peace.

One day, You may find your self suffering from
dashavou. Hope you remember this.

Bye for now.



That would be "piece" then ... And dashvou. WTF is that ??? Are you
struggling for the spelling of deja vue ?
(should have accents over the 'e' and 'a')

If you don't know the French, and exactly what it means, don't try to use
it. And if you do understand what it means, with exactly what relevance are
you applying it here ?

Arfa