Anyone got the schematics for a Crown XLS5000 ? I'm most interested in the
board that the mains comes in to. There's a bloody great disc something
inside a big lump of heatshrink, and serious flames shoot out of it before
every trip and fuse in the workshop goes out ...

If I bring it up on the variac, I can't get beyond about 20 volts before the
poor thing is jumping off the bench, so there's a good short on there
somewhere. I initially thought that the disc might be a big VDR that was
short, but looking up the part number on the second one that's on there for
the other half of the amp, it appears to be an inrush thermistor, so I guess
whatever is short, must be south of that ...

Arfa

You can send an email to the Crown Technical department, the usually send the schematics to you.

Dan

wrote in message
...
You can send an email to the Crown Technical department, the usually send
the schematics to you.

Dan


Cheers Dan. I'll give it a go. I have to say though that over the years,
I've only had quite limited success prying schematics out of them ...

Arfa

"Arfa Daily" wrote in message
...


wrote in message
...
You can send an email to the Crown Technical department, the usually send
the schematics to you.

Dan


Cheers Dan. I'll give it a go. I have to say though that over the years,
I've only had quite limited success prying schematics out of them ...

Arfa


Well I never ! I asked, I got. Good call, Dan ! :-)

Arfa

Arfa Daily wrote:

Anyone got the schematics for a Crown XLS5000 ? I'm most interested in the
board that the mains comes in to. There's a bloody great disc something
inside a big lump of heatshrink, and serious flames shoot out of it before
every trip and fuse in the workshop goes out ...

If I bring it up on the variac, I can't get beyond about 20 volts before the
poor thing is jumping off the bench, so there's a good short on there
somewhere. I initially thought that the disc might be a big VDR that was
short, but looking up the part number on the second one that's on there for
the other half of the amp, it appears to be an inrush thermistor, so I guess
whatever is short, must be south of that ...

** I found a nice pic:

http://www.musiker-board.de/attachme...005-jpg.84415/

The XLS series of amps use large, 240VAC rated PTCs for inrush limiting AND fault protection. Room temp resistance is a few ohms rising to over 12kohms when hot. Normally, the relay next door bridges it out soon as the DC rails come up.

The example I saw late last year was an XLS602 that would simply not switch on while the PTC was getting very hot. Like yours, you could variac it up to some extent, then the PTC detected a fault and went high.

Problem turned out to be the toroidal transformer, enamel insulation had failed in the primary winding creating shorted turns.



BTW:

Very sad to hear of George Cole's passing.



..... Phil

"Phil Allison" wrote in message
...
Arfa Daily wrote:

Anyone got the schematics for a Crown XLS5000 ? I'm most interested in
the
board that the mains comes in to. There's a bloody great disc something
inside a big lump of heatshrink, and serious flames shoot out of it
before
every trip and fuse in the workshop goes out ...

If I bring it up on the variac, I can't get beyond about 20 volts before
the
poor thing is jumping off the bench, so there's a good short on there
somewhere. I initially thought that the disc might be a big VDR that was
short, but looking up the part number on the second one that's on there
for
the other half of the amp, it appears to be an inrush thermistor, so I
guess
whatever is short, must be south of that ...

** I found a nice pic:

http://www.musiker-board.de/attachme...005-jpg.84415/

The XLS series of amps use large, 240VAC rated PTCs for inrush limiting
AND fault protection. Room temp resistance is a few ohms rising to over
12kohms when hot. Normally, the relay next door bridges it out soon as the
DC rails come up.

The example I saw late last year was an XLS602 that would simply not
switch on while the PTC was getting very hot. Like yours, you could variac
it up to some extent, then the PTC detected a fault and went high.

Problem turned out to be the toroidal transformer, enamel insulation had
failed in the primary winding creating shorted turns.



BTW:

Very sad to hear of George Cole's passing.



.... Phil


Yeah, I was very sad too, but he did have a good innings lasting until he
was 90. Dennis Waterman was still good friends with him as well. He's
looking a bit rough now, though ...

I saw every episode of Minder that was ever made. They all had very clever
'play on words' titles, and the first two series were actually quite dark
stories. They didn't think it was going to last beyond that, but the comedy
element was deliberately ramped up in the third series by the interaction
between Cole and Waterman, and it became an overnight success. I just loved
the character Arthur Daley for the wicked sense of comic timing and the
malapropism he employed. And of course, it was made by Euston Films, the
absolute kings of drama made in London.

Back to the crown. The transformers in this 5000 model are truly massive
torroidals, and I'm leaning towards suspecting shorted turns on the primary
of the one on the bad channel. The inrush thermistors are the size of penny
toffees - the biggest I've ever seen. From the sheet of flame that shot out
of this one and the number of bench fuses that blew, the short must be right
on top of the thermistor. The fact that you can only get to about 20 v of AC
input before the variac is jumping off the bench, also makes me think
shorted primary.

Unfortunately, it's not an easy task to get to the secondary side of the
PSU, as it's one of those two-board constructions, where one power amp is
stacked on top of the other, and all of the bridges and filter caps for both
amps are, needless-to-say, on the bottom board where you can't get to
anything.

Before going to all of the trouble to get the top board out to see if I can
unplug the tranny secondaries, I'm waiting on the shop getting in touch with
the owner to give him an estimate of what it might cost, depending on what I
find. I'm not sure what the spares position for Crown stuff is like here in
the UK, if it needed a tranny ...

Arfa

Arfa Daily wrote:



I just loved
the character Arthur Daley for the wicked sense of comic timing and the
malapropism he employed.


** Like: " The world is your lobster... "


Unfortunately, it's not an easy task to get to the secondary side of the
PSU, as it's one of those two-board constructions, where one power amp is
stacked on top of the other, and all of the bridges and filter caps for both
amps are, needless-to-say, on the bottom board where you can't get to
anything.

* You could snip the leads for the main secondary ( leaving the CT) and join them again if the tranny proves OK.


Before going to all of the trouble to get the top board out to see if I can
unplug the tranny secondaries, I'm waiting on the shop getting in touch with
the owner to give him an estimate of what it might cost, depending on what I
find. I'm not sure what the spares position for Crown stuff is like here in
the UK, if it needed a tranny ...

** Out of curiosity, I stripped down the tranny from that XLS602. Internal shorts in large toroidals are very rare, especially with no other fault.

The whole thing was rough as guts, with a wound core made from dozens of off- cuts of steel strip tacked welded together and bits of cloth tape covering the edges. Normal toroidal cores are precison made and have moulded plastic covers covering all sharp edges, where the primary is wound.

The twin 120/240 primary was bi-filar wound placing 120VAC between every adjacent turn, a dodgy practice at best and fatal if the enamel coating ever gets damaged.


.... Phil

"Phil Allison" wrote in message
...
Arfa Daily wrote:



I just loved
the character Arthur Daley for the wicked sense of comic timing and the
malapropism he employed.


** Like: " The world is your lobster... "


Unfortunately, it's not an easy task to get to the secondary side of the
PSU, as it's one of those two-board constructions, where one power amp is
stacked on top of the other, and all of the bridges and filter caps for
both
amps are, needless-to-say, on the bottom board where you can't get to
anything.

* You could snip the leads for the main secondary ( leaving the CT) and
join them again if the tranny proves OK.


Hadn't thought of that. I've got schematics for the thing, so shouldn't be
too hard to identify which wires are what. The primary is on a plug that's
easy to get to, and all is well with that pulled off, so nothing else on the
input board is the problem.




Before going to all of the trouble to get the top board out to see if I
can
unplug the tranny secondaries, I'm waiting on the shop getting in touch
with
the owner to give him an estimate of what it might cost, depending on
what I
find. I'm not sure what the spares position for Crown stuff is like here
in
the UK, if it needed a tranny ...

** Out of curiosity, I stripped down the tranny from that XLS602. Internal
shorts in large toroidals are very rare, especially with no other fault.

The whole thing was rough as guts, with a wound core made from dozens of
off- cuts of steel strip tacked welded together and bits of cloth tape
covering the edges. Normal toroidal cores are precison made and have
moulded plastic covers covering all sharp edges, where the primary is
wound.

That's interesting. If this turns out to be the tranny, and the owner goes
ahead - assuming we can get one, of course - I will try to find the time to
have a look. Over the last couple of years, I've had probably three or four
large toroidals with shorted primaries, so maybe there's some Chinese
factory churning out cheapies like the one you saw, virtually made from
scrap ...


The twin 120/240 primary was bi-filar wound placing 120VAC between every
adjacent turn, a dodgy practice at best and fatal if the enamel coating
ever gets damaged.

Yes, not a good practice for sure. I suppose though that it's hard to find a
way to wind a twin primary on a toroidal core where you're trying to keep
the profile low, and a similar level of core coupling from both windings.
Much easier when you have a traditional E-I core and can have two primaries
stacked on top of one another, I guess

Arfa


... Phil

Arfa Daily wrote:


** Out of curiosity, I stripped down the tranny from that XLS602. Internal
shorts in large toroidals are very rare, especially with no other fault.

The whole thing was rough as guts, with a wound core made from dozens of
off- cuts of steel strip tacked welded together and bits of cloth tape
covering the edges. Normal toroidal cores are precison made and have
moulded plastic covers covering all sharp edges, where the primary is
wound.

That's interesting. If this turns out to be the tranny, and the owner goes
ahead - assuming we can get one, of course - I will try to find the time to
have a look. Over the last couple of years, I've had probably three or four
large toroidals with shorted primaries, so maybe there's some Chinese
factory churning out cheapies like the one you saw, virtually made from
scrap ...


** The transformer maker used in the XLS series is:

" NRE Electrical Manufacturing Co Ltd ".

www.fsnre.com


( I posted the same details here on December 10,2014 )

BTW:

Is it possible the company is being run by a Mr Dai Lee ??




.... Phil

google images


https://www.google.com/search?site=i...ring+schematic

"Phil Allison" wrote in message
...
Arfa Daily wrote:


** Out of curiosity, I stripped down the tranny from that XLS602.
Internal
shorts in large toroidals are very rare, especially with no other
fault.

The whole thing was rough as guts, with a wound core made from dozens
of
off- cuts of steel strip tacked welded together and bits of cloth tape
covering the edges. Normal toroidal cores are precison made and have
moulded plastic covers covering all sharp edges, where the primary is
wound.

That's interesting. If this turns out to be the tranny, and the owner
goes
ahead - assuming we can get one, of course - I will try to find the time
to
have a look. Over the last couple of years, I've had probably three or
four
large toroidals with shorted primaries, so maybe there's some Chinese
factory churning out cheapies like the one you saw, virtually made from
scrap ...


** The transformer maker used in the XLS series is:

" NRE Electrical Manufacturing Co Ltd ".

www.fsnre.com


( I posted the same details here on December 10,2014 )

BTW:

Is it possible the company is being run by a Mr Dai Lee ??




... Phil


Today, having pulled all of the cabling out of the way, It was possible to
see where the secondary wires spaded onto the lower PCB, and there was just
enough room between the board stack and the cabinet side to mark them, and
pull them with a pair of long-nose pliers. I then shorted the blown-out
thermistor, and hooked up the variac again. Same as before. 20 volts of
input, and the variac is grunting fit to bust, so it does look like the
transformer primary is shorted turns, as that's now the only thing
connected. So now a case of seeing if we can get the tranny and inrush
thermistor, and more to the point, at what price ...

Arfa

On Saturday, August 8, 2015 at 1:11:53 PM UTC-4, wrote:
google images


https://www.google.com/search?site=i...ring+schematic

oooooooooooooooooooooooooooo


https://www.google.com/search?site=i...lCki_FhustM%3A

Arfa Daily wrote:


Today, having pulled all of the cabling out of the way, It was possible to
see where the secondary wires spaded onto the lower PCB, and there was just
enough room between the board stack and the cabinet side to mark them, and
pull them with a pair of long-nose pliers. I then shorted the blown-out
thermistor, and hooked up the variac again. Same as before. 20 volts of
input, and the variac is grunting fit to bust, so it does look like the
transformer primary is shorted turns, as that's now the only thing
connected.


** Just as I suspected, those NRE toroidals are time bombs.


So now a case of seeing if we can get the tranny and inrush
thermistor, and more to the point, at what price ...


** Farnell have some 240V rated PTC thermistors that might do the job:

http://uk.farnell.com/epcos/b59810c0...65?ost=9753265

Check the one on the other tranny to see what cold resistance value you need, probably something around 4 ohms.



.... Phil

"Phil Allison" wrote in message
...
Arfa Daily wrote:


Today, having pulled all of the cabling out of the way, It was possible
to
see where the secondary wires spaded onto the lower PCB, and there was
just
enough room between the board stack and the cabinet side to mark them,
and
pull them with a pair of long-nose pliers. I then shorted the blown-out
thermistor, and hooked up the variac again. Same as before. 20 volts of
input, and the variac is grunting fit to bust, so it does look like the
transformer primary is shorted turns, as that's now the only thing
connected.


** Just as I suspected, those NRE toroidals are time bombs.


So now a case of seeing if we can get the tranny and inrush
thermistor, and more to the point, at what price ...


** Farnell have some 240V rated PTC thermistors that might do the job:

http://uk.farnell.com/epcos/b59810c0...65?ost=9753265

Check the one on the other tranny to see what cold resistance value you
need, probably something around 4 ohms.



... Phil


It's inside a piece of heatshrink sleeve bigger than I've got to replace it
with, but on the blown out one, you can still read "4R7" so I guess 4.7 ohms
which would be about right. Assuming that they have it done, I suppose I
will have to get a length of suitable heatshrink in so that it's restored to
the insulation levels that it came out of the factory with. I was able to
just about get my meter across the bridges after the tranny wires had been
pulled, just to make sure that there were no issues with them or anything
south of them, but all looks ok, so I think that it is just the tranny
primary short circuit for no good reason other than it felt like it ...

Arfa

Arfa Daily wrote:


** Just as I suspected, those NRE toroidals are time bombs.



It's inside a piece of heatshrink sleeve bigger than I've got to replace it
with, but on the blown out one, you can still read "4R7" so I guess 4.7 ohms
which would be about right. Assuming that they have it done, I suppose I
will have to get a length of suitable heatshrink in so that it's restored to
the insulation levels that it came out of the factory with.


** The shrink cover is there to retain bits if the PTC explodes and nearby wiring away when it "trips" - cos its gets so damn hot.

Be far better to slip a piece of silicone tube over the thing, as is often done with NTCs.


I was able to
just about get my meter across the bridges after the tranny wires had been
pulled, just to make sure that there were no issues with them or anything
south of them, but all looks ok, so I think that it is just the tranny
primary short circuit for no good reason other than it felt like it ...


** You gotta hope the new one does not get that same feeling, or the other one in the amp.

For my XLS602, I used a "pre-loved" toroidal tranny that was on hand, with a similar main secondary winding and added a small 18-0-18 E-core for the low voltages.

Might be smart to get a quote for a replacement tranny made to suit that Crown.



.... Phil

"Phil Allison" wrote in message
...
Arfa Daily wrote:


** Just as I suspected, those NRE toroidals are time bombs.



It's inside a piece of heatshrink sleeve bigger than I've got to replace
it
with, but on the blown out one, you can still read "4R7" so I guess 4.7
ohms
which would be about right. Assuming that they have it done, I suppose I
will have to get a length of suitable heatshrink in so that it's restored
to
the insulation levels that it came out of the factory with.


** The shrink cover is there to retain bits if the PTC explodes and nearby
wiring away when it "trips" - cos its gets so damn hot.

Be far better to slip a piece of silicone tube over the thing, as is often
done with NTCs.


Thinking about it, you're probably right about the reason for the sleeve.
I'm sure I'll find something suitable.



I was able to
just about get my meter across the bridges after the tranny wires had
been
pulled, just to make sure that there were no issues with them or anything
south of them, but all looks ok, so I think that it is just the tranny
primary short circuit for no good reason other than it felt like it ...


** You gotta hope the new one does not get that same feeling, or the other
one in the amp.


Yes, that's what bothers me. I never like high cost repairs to older items
like this. It often seems to be the case that once they start failing, they
just carry on with a different problem each time, just inside the 3 month
warranty ...


For my XLS602, I used a "pre-loved" toroidal tranny that was on hand, with
a similar main secondary winding and added a small 18-0-18 E-core for the
low voltages.

Might be smart to get a quote for a replacement tranny made to suit that
Crown.

We got onto the people who handle Crown here today. They said that they
didn't do spare parts, but they did have a transformer. £100 plus shipping
plus tax. I suppose that's not a lot of money when you consider that it's a
custom four-winding thing the size of a baby's head, but still a lot to
shell out up front for a spare part. Considering the power output and
replacement value of this amp, even if the final repair bill weighs in
around the £200 mark, I suppose it has probably still got to be worth doing.

The customer has been given an estimate now by the shop, so we'll see what
he decides in the next few days, I expect ...

Arfa



... Phil

"Arfa Daily" wrote in message ...

Anyone got the schematics for a Crown XLS5000 ? I'm most interested in the
board that the mains comes in to. There's a bloody great disc something
inside a big lump of heatshrink, and serious flames shoot out of it before
every trip and fuse in the workshop goes out ...

If I bring it up on the variac, I can't get beyond about 20 volts before the
poor thing is jumping off the bench, so there's a good short on there
somewhere. I initially thought that the disc might be a big VDR that was
short, but looking up the part number on the second one that's on there for
the other half of the amp, it appears to be an inrush thermistor, so I guess
whatever is short, must be south of that ...

Arfa






Hey guess what? Today I received a Crown XLS 602. (a baby by comparison)
And guess what? The mains Transformer is open circuit.

This TX is marked "NRE Electronics Manufacturing Co Ltd.
08/2006"

Dunno if that makes it from the same source or not.



Cheers,


Gareth.

"Gareth Magennis" wrote in message
...


"Arfa Daily" wrote in message ...

Anyone got the schematics for a Crown XLS5000 ? I'm most interested in the
board that the mains comes in to. There's a bloody great disc something
inside a big lump of heatshrink, and serious flames shoot out of it before
every trip and fuse in the workshop goes out ...

If I bring it up on the variac, I can't get beyond about 20 volts before
the
poor thing is jumping off the bench, so there's a good short on there
somewhere. I initially thought that the disc might be a big VDR that was
short, but looking up the part number on the second one that's on there
for
the other half of the amp, it appears to be an inrush thermistor, so I
guess
whatever is short, must be south of that ...

Arfa






Hey guess what? Today I received a Crown XLS 602. (a baby by
comparison)
And guess what? The mains Transformer is open circuit.

This TX is marked "NRE Electronics Manufacturing Co Ltd.
08/2006"

Dunno if that makes it from the same source or not.



Cheers,


Gareth.



Certainly the same as Phil's one. I don't know who made the one in my '5000.
There's nothing I can immediately see to identify it, but there may be
something when it's out - if of course the owner goes ahead. It's going to
need a pair of spanners big enough to take off tractor wheel nuts ... :-)

Arfa

"Arfa Daily" wrote in message ...



"Gareth Magennis" wrote in message
...


"Arfa Daily" wrote in message ...

Anyone got the schematics for a Crown XLS5000 ? I'm most interested in the
board that the mains comes in to. There's a bloody great disc something
inside a big lump of heatshrink, and serious flames shoot out of it before
every trip and fuse in the workshop goes out ...

If I bring it up on the variac, I can't get beyond about 20 volts before
the
poor thing is jumping off the bench, so there's a good short on there
somewhere. I initially thought that the disc might be a big VDR that was
short, but looking up the part number on the second one that's on there
for
the other half of the amp, it appears to be an inrush thermistor, so I
guess
whatever is short, must be south of that ...

Arfa






Hey guess what? Today I received a Crown XLS 602. (a baby by
comparison)
And guess what? The mains Transformer is open circuit.

This TX is marked "NRE Electronics Manufacturing Co Ltd.
08/2006"

Dunno if that makes it from the same source or not.



Cheers,


Gareth.



Certainly the same as Phil's one. I don't know who made the one in my '5000.
There's nothing I can immediately see to identify it, but there may be
something when it's out - if of course the owner goes ahead. It's going to
need a pair of spanners big enough to take off tractor wheel nuts ... :-)

Arfa





The customer said it had been in storage the past 2 years. He fired it up
today and it blew all the main fuses in his gaff.
So sounds like it may have been short like yours and Phil's, then blew open.



Gareth.

"Gareth Magennis" wrote in message ...



"Arfa Daily" wrote in message ...



"Gareth Magennis" wrote in message
...


"Arfa Daily" wrote in message ...

Anyone got the schematics for a Crown XLS5000 ? I'm most interested in the
board that the mains comes in to. There's a bloody great disc something
inside a big lump of heatshrink, and serious flames shoot out of it before
every trip and fuse in the workshop goes out ...

If I bring it up on the variac, I can't get beyond about 20 volts before
the
poor thing is jumping off the bench, so there's a good short on there
somewhere. I initially thought that the disc might be a big VDR that was
short, but looking up the part number on the second one that's on there
for
the other half of the amp, it appears to be an inrush thermistor, so I
guess
whatever is short, must be south of that ...

Arfa






Hey guess what? Today I received a Crown XLS 602. (a baby by
comparison)
And guess what? The mains Transformer is open circuit.

This TX is marked "NRE Electronics Manufacturing Co Ltd.
08/2006"

Dunno if that makes it from the same source or not.



Cheers,


Gareth.



Certainly the same as Phil's one. I don't know who made the one in my '5000.
There's nothing I can immediately see to identify it, but there may be
something when it's out - if of course the owner goes ahead. It's going to
need a pair of spanners big enough to take off tractor wheel nuts ... :-)

Arfa





The customer said it had been in storage the past 2 years. He fired it up
today and it blew all the main fuses in his gaff.
So sounds like it may have been short like yours and Phil's, then blew open.



Gareth.





Er, except customers tend to lie a lot.

He may have tried to boot several times with various size fuses/paper clips
etc.


Gareth.

The customer said it had been in storage the past 2 years. He fired it up
today and it blew all the main fuses in his gaff.
So sounds like it may have been short like yours and Phil's, then blew
open.



Gareth.





Er, except customers tend to lie a lot.

He may have tried to boot several times with various size fuses/paper
clips etc.


Gareth.


That would be my feeling. It would seem that when these trannies fail on the
primary, they do it in style. The one in this 5000 is *so* short-circuit, it
blew the fuse in the mains lead plugtop, the fuse in the bench input lead
where it plugs into the heavy duty extension cable, and the fuse in the
extension plugtop. Oh yes, and it popped the breaker in the consumer unit as
well. I've had a few mains shorts over the years, but I can't remember one
that has ever taken out three mains fuses in series, *and* the breaker. Just
goes to show how slow the breaker is though, compared to the cartridge fuses
in the plugs. But then I suppose it is over twice their rating, at 30 amps
....

Arfa

Gareth Magennis wrote:



Hey guess what?
Today I received a Crown XLS 602.
And guess what?
The mains Transformer is open circuit.

This TX is marked "NRE Electronics Manufacturing Co Ltd.
08/2006"

Dunno if that makes it from the same source or not.


** It's exactly the same as the one I described as "rough as guts".



.... Phil

Gareth Magennis wrote:



The customer said it had been in storage the past 2 years. He fired it up
today and it blew all the main fuses in his gaff.
So sounds like it may have been short like yours and Phil's, then blew open.


** Hmmm - that should not happen.

However, if the amp worked even for a few seconds, the chunky relay next to the PTC closes and bridges it out. If the primary shorted out after that, it is possible the relay contacts became instantly welded closed.

The fault current could then trip the breaker in the 30A ring mains and easily blow any fuse fitted inside power plug.

A subsequent attempt to switch on the amp would result another huge surge and maybe make a track on the PSU board vaporise.

BTW:

IIRC, the secondary voltages and currents are printed on the side of the tranny. The tranny is about 800VA and it ought to be possible to have one made that is close to the same size and ratings for an acceptable cost.


.... Phil

On Thursday, August 13, 2015 at 5:51:55 AM UTC+1, Phil Allison wrote:
Gareth Magennis wrote:



The customer said it had been in storage the past 2 years. He fired it up
today and it blew all the main fuses in his gaff.
So sounds like it may have been short like yours and Phil's, then blew open.


** Hmmm - that should not happen.

However, if the amp worked even for a few seconds, the chunky relay next to the PTC closes and bridges it out. If the primary shorted out after that, it is possible the relay contacts became instantly welded closed.

The fault current could then trip the breaker in the 30A ring mains and easily blow any fuse fitted inside power plug.

A subsequent attempt to switch on the amp would result another huge surge and maybe make a track on the PSU board vaporise.

BTW:

IIRC, the secondary voltages and currents are printed on the side of the tranny. The tranny is about 800VA and it ought to be possible to have one made that is close to the same size and ratings for an acceptable cost.


... Phil



They are. 74/0/74 and 18.3/0/18.3


Cheers,


Gareth.

wrote:


They are.

74/0/74 and 18.3/0/18.3


** The 74-0-74 winding is rated at about 6 amps.

The 18.3-0-18.3 needs only 0.6 amp but is in fact tapped off the main winding.


.... Phil

"Phil Allison" wrote in message
...
Gareth Magennis wrote:



Hey guess what?
Today I received a Crown XLS 602.
And guess what?
The mains Transformer is open circuit.

This TX is marked "NRE Electronics Manufacturing Co Ltd.
08/2006"

Dunno if that makes it from the same source or not.


** It's exactly the same as the one I described as "rough as guts".



... Phil


The owner has decided to 'go for it' so the owner of the shop that it came
in through has gone ahead and ordered in the replacement that was offered at
100 GBP. Should be here this week sometime. While we're on slave amps,
anyone following this thread got the schematic for an Alto Mac 2.2 ? Very
odd fault. Both channels work just fine for a while, then all of a sudden,
one channel starts to indicate 'clip' with the level control just a gnat's
bollock above zero. There seems to be a dual opamp involved in the clip
detect circuit, but before going round in circles trying to see what's
happening and why, it would be handy to have a schematic to see how the clip
detect circuit is designed and what its inputs are. I'll put a new post up
as well to catch anyone that's not following this discussion.

Arfa

Just start a new thread Arf. Itt is damn hard enough for peopple to keep track of **** without having two separate isssues in threads not specificallty named hat they should be named. If =you do, I won't rip you a new ******** hole, we got Phil to take care of that.

but seriously seriously here, I almost NEVER had an actual bad power traansformer almost in my life. I had one in a Zenith TV that started getting open connections. First was to the CRT filamentm whichg I fixed by wrapping a wire around the flyback core to get about 22 volts peak to peak which is about 6 volts RMS. Then another linee come loose and it was tjhe center tap for the +/- 24V or whatever fed the vertical, and was on th same wire as the return for the 130 volt lin. It sent the picture offf ceneter and the centering control of course did not work. ALL the currnet pulled by the 130 volt line was going through one of the vertical output transistors. this was another of the myriad of TVs that nobody else could fix. That was my specialty.

But that sounds interesting. Question is, is it distorting ? There are a couple of different ways to implement a clipping detector. If it is actually detecting a ifference between the input and output of the power amp there are several possibilities. High frequency oscillation is possible. Loss of bias couldd do it.

Start a thread, I am not going to **** this all up. This thread is for this, make that thread for that. See you there.

Arfa Daily wrote:


While we're on slave amps,
anyone following this thread got the schematic for an Alto Mac 2.2 ? Very
odd fault. Both channels work just fine for a while, then all of a sudden,
one channel starts to indicate 'clip' with the level control just a gnat's
bollock above zero. There seems to be a dual opamp involved in the clip
detect circuit, but before going round in circles trying to see what's
happening and why, it would be handy to have a schematic to see how the clip
detect circuit is designed and what its inputs are.


** The schem of the 2.3 should be very close:

http://www.mediafire.com/view/bmotmj..._manual+8.jpg#

The Alto MAC amps have basically copied early QSC models like the USA850 and 900. Changes include use of a toroidal transformer, flat pack output transistors and SMD for all the small signal stuff.

The topology is very odd with output transistor collectors all tied to chassis ground while the DC rails swing with output signal. Speaker drive comes from the PSU centre points for each channel and the usual driver transistors have simply been eliminated. The short circuit protection scheme is weird too.

Advantages are a low parts count, cheap to make and will not pass DC current into a speaker under fault conditions.

The clip LED is driven by U2-B (half an NE5532 supplying drive to the output stage) via a diode bridge and also triggers the clipping limiter (U1A) via R26 to ground.


.... Phil

"Phil Allison" wrote in message
...
Arfa Daily wrote:


While we're on slave amps,
anyone following this thread got the schematic for an Alto Mac 2.2 ? Very
odd fault. Both channels work just fine for a while, then all of a
sudden,
one channel starts to indicate 'clip' with the level control just a
gnat's
bollock above zero. There seems to be a dual opamp involved in the clip
detect circuit, but before going round in circles trying to see what's
happening and why, it would be handy to have a schematic to see how the
clip
detect circuit is designed and what its inputs are.


** The schem of the 2.3 should be very close:

http://www.mediafire.com/view/bmotmj..._manual+8.jpg#

The Alto MAC amps have basically copied early QSC models like the USA850
and 900. Changes include use of a toroidal transformer, flat pack output
transistors and SMD for all the small signal stuff.

The topology is very odd with output transistor collectors all tied to
chassis ground while the DC rails swing with output signal. Speaker drive
comes from the PSU centre points for each channel and the usual driver
transistors have simply been eliminated. The short circuit protection
scheme is weird too.

Advantages are a low parts count, cheap to make and will not pass DC
current into a speaker under fault conditions.

The clip LED is driven by U2-B (half an NE5532 supplying drive to the
output stage) via a diode bridge and also triggers the clipping limiter
(U1A) via R26 to ground.


.... Phil


Thanks for that, Phil. Much appreciated. Odd how it works for a short while.
Before having the schematic, I gave everything in the area a good dousing
with freezer when it failed, but nothing really that I would say was very
positive. Maybe - and it *was* a maybe - the 5532 was a bit sensitive, but
it was inconclusive. I did notice that when it was wrong, the waveform on
pin 7 I think it was, was much bigger than 'normal' and the output TRs on
that side got quite hot quite quickly.

I'll try and find time to get another look today or tomorrow with the
benefit of your schematic. Thanks again

Arfa

Arfa Daily wrote:


** The schem of the 2.3 should be very close:

http://www.mediafire.com/view/bmotmj..._manual+8.jpg#



Thanks for that, Phil. Much appreciated. Odd how it works for a short while.
Before having the schematic, I gave everything in the area a good dousing
with freezer when it failed, but nothing really that I would say was very
positive. Maybe - and it *was* a maybe - the 5532 was a bit sensitive, but
it was inconclusive. I did notice that when it was wrong, the waveform on
pin 7 I think it was, was much bigger than 'normal' and the output TRs on
that side got quite hot quite quickly.


** Is there a dummy load connected ?

The clip indicator is probably just showing the channel is being overloaded, as is the rapid heating. Could there be an intermittent short in the output wiring ?

Also, I see there are two PCBS, small signal and power stuff, interconnected by some kind of multi-pin. You must know how reliable they all are...


I'll try and find time to get another look today or tomorrow with the
benefit of your schematic. Thanks again.


** I found the Alto schem on a net forum, it looked terribly familiar.

Have you not seen the QSC's USA models or the MX700 ?



... Phil

"Phil Allison" wrote in message
...
Arfa Daily wrote:


** The schem of the 2.3 should be very close:

http://www.mediafire.com/view/bmotmj..._manual+8.jpg#



Thanks for that, Phil. Much appreciated. Odd how it works for a short
while.
Before having the schematic, I gave everything in the area a good dousing
with freezer when it failed, but nothing really that I would say was very
positive. Maybe - and it *was* a maybe - the 5532 was a bit sensitive,
but
it was inconclusive. I did notice that when it was wrong, the waveform on
pin 7 I think it was, was much bigger than 'normal' and the output TRs
on
that side got quite hot quite quickly.


** Is there a dummy load connected ?

The clip indicator is probably just showing the channel is being
overloaded, as is the rapid heating. Could there be an intermittent short
in the output wiring ?

Also, I see there are two PCBS, small signal and power stuff,
interconnected by some kind of multi-pin. You must know how reliable they
all are...


I'll try and find time to get another look today or tomorrow with the
benefit of your schematic. Thanks again.


** I found the Alto schem on a net forum, it looked terribly familiar.

Have you not seen the QSC's USA models or the MX700 ?



... Phil


Yes, and embarrassingly, I was even working on one last week ... :-\
Funny how just a different name on the front blinkers you to the obvious. I
was even discussing that odd output topology with a colleague.

Back to the problem in hand. I only had a few minutes to look further today.

In answer to your questions, yes, there was a dummy load on the end that has
a built in power meter. Yes, there are two main boards, each of which has a
power amp and power supply, and one of which also has the driver / clip
sense circuitry for both channels. Initially today, it was giving its
problem. Couple or three volts RMS going in, transformer balanced into the
channel 2 XLR input. As soon as the front panel level control is advanced
just a gnat's cock, on comes the clip light, very solid. The amp still has
output, but it's pretty strangled, as you would expect if the clip limiter
is genuinely coming in. When looking at the output of the opamp on pin 7,
when it's wrong, it's massive, and asymmetric, so I guess that's the reason
for the clip circuit to come in and the light to come on. It's as though the
opamp has suddenly attained 10 times its normal gain. I thought at one point
that maybe the level control was going intermittently open at its groundy
end, but when it's working, with that level of input signal, you can wind
the level pot full up, and not make it clip. It's as though a feedback
resistor is going open intermittently. Trouble is, all of the resistors
around the opamp are those tiny tiny sm devices that are so small you can
barely see them.

Actually, a thought now occurs to me. I wonder if the level control is
actually nothing of the (conventional) sort, but rather a variable feedback
resistor for the opamp, as they sometimes are in some amps. If that went
open, it might allow the opamp to go to full open loop gain. I don't
remember the level control being shown on the section of schematic that you
linked for me. I'll maybe have a look tomorrow if I get time, but today, a
****load of work has poured in the door, including four Technics SL1210s
that are needed by the weekend, an Evans tape echo, two Voxs and a Marshall
....

As I finished checking around the opamp today, it came back right, and
wouldn't go bad again, with the control as smooth as you like from zero to
flat out, so at that point, it got flung off the bench again to make room
for something else.

Oh yes, and the ribbon. There is one of about ten or twelve ways that links
the two boards, and I have had problems in the past I seem to remember, but
in this case, it seems quite solid, as do all the other connectors. In fact
I haven't found a way to provoke the problem into either coming or going. It
just does it, as and when it feels like it.

Thanks for your input. Any and all suggestions and insights are welcome with
problems like this

Arfa

Arfa Daily wrote:


Actually, a thought now occurs to me. I wonder if the level control is
actually nothing of the (conventional) sort, but rather a variable feedback
resistor for the opamp, as they sometimes are in some amps.

** The volume pot is connected in the usual way between the output of the input balancing stage ( U2A ) and the input of U2B.

FYI:

The QSC model that is near identical to your Alto is the RMX1450.

You will find a much more readable schem in the RMX850,1450&2450 manual from Elektrotanya and without the little errors I see in the Alto one.

http://elektrotanya.com/qsc_rmx_850_.../download.html



..... Phil