C - Audio slave amp ...

A

Arfa Daily

Guest
Anybody by any remote chance have a schematic copy for a C - Audio RA 1001
slave amp ? Drawn a blank from all the usual places.

Looks as though it has been stored somewhere cold and damp, although dry
enough now. Basically, it won't come out of 'protect' although there seems
to be nothing wrong fundamentally with either channel. Both channels have
good output, with no DC offset, as far as the output relays. There is
another relay over at the mains input side of things that looks like it
shorts a bloody great resistor, so inrush limiting I guess. All three relays
remain stubbornly off, and the protect light stays on. I can't read any
volts at any of the three relay coils, and none of the pins appears to be
grounded, so they are not high-side switched. So may be something as simple
as a missing rail, but hard to follow print around as it's double sided, and
fairly crowded ...

Arfa
 
Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:eek:e0ut.39678$Gx7.36621@fx08.am4...
Anybody by any remote chance have a schematic copy for a C - Audio RA 1001
slave amp ? Drawn a blank from all the usual places.

Looks as though it has been stored somewhere cold and damp, although dry
enough now. Basically, it won't come out of 'protect' although there seems
to be nothing wrong fundamentally with either channel. Both channels have
good output, with no DC offset, as far as the output relays. There is
another relay over at the mains input side of things that looks like it
shorts a bloody great resistor, so inrush limiting I guess. All three
relays
remain stubbornly off, and the protect light stays on. I can't read any
volts at any of the three relay coils, and none of the pins appears to be
grounded, so they are not high-side switched. So may be something as
simple
as a missing rail, but hard to follow print around as it's double sided,
and
fairly crowded ...

Arfa
Click to expand...
If the C is for Crest then sounds like my experience of a pile of
Crest Audio Pulse 2 1100 , amps stored in a Dutch barn
schema available out there
repair briefs on
http://www.divdev.fsnet.co.uk/repair2a.htm
IIRC all the problems were condensation/corossion inside minor TO92
owner thought draping a tarpaulin over them in the barn was sufficient
protection in the UK
 
"Arfa Daily" wrote in message news:eek:e0ut.39678$Gx7.36621@fx08.am4...

Anybody by any remote chance have a schematic copy for a C - Audio RA 1001
slave amp ? Drawn a blank from all the usual places.

Looks as though it has been stored somewhere cold and damp, although dry
enough now. Basically, it won't come out of 'protect' although there seems
to be nothing wrong fundamentally with either channel. Both channels have
good output, with no DC offset, as far as the output relays. There is
another relay over at the mains input side of things that looks like it
shorts a bloody great resistor, so inrush limiting I guess. All three relays
remain stubbornly off, and the protect light stays on. I can't read any
volts at any of the three relay coils, and none of the pins appears to be
grounded, so they are not high-side switched. So may be something as simple
as a missing rail, but hard to follow print around as it's double sided, and
fairly crowded ...

Arfa



Check for corroded tracks around the fan area of the PCB, it was a common
failure, allegedly from corrosive smoke machine smoke.
Folow the relay coil tracks back to the protect circuit at the front of the
amp (I think) as ISTR it was often a break in this circuit that kept it in
protect.



That bloody great resistor is in fact inrush limiting shorted out by a
relay, (47 ohms?), and these often failed.

I might have a RA3000 schematic at work, will look tomorrow.
It is not a Crest.


Gareth.
 
"Arfa Daily" wrote in message news:eek:e0ut.39678$Gx7.36621@fx08.am4...

Anybody by any remote chance have a schematic copy for a C - Audio RA 1001
slave amp ? Drawn a blank from all the usual places.

Looks as though it has been stored somewhere cold and damp, although dry
enough now. Basically, it won't come out of 'protect' although there seems
to be nothing wrong fundamentally with either channel. Both channels have
good output, with no DC offset, as far as the output relays. There is
another relay over at the mains input side of things that looks like it
shorts a bloody great resistor, so inrush limiting I guess. All three relays
remain stubbornly off, and the protect light stays on. I can't read any
volts at any of the three relay coils, and none of the pins appears to be
grounded, so they are not high-side switched. So may be something as simple
as a missing rail, but hard to follow print around as it's double sided, and
fairly crowded ...

Arfa




One corroded track I found was actually underneath one of the relays!

You could be right and it might just be the low voltage supply for the
protect/relays.
If the inrush relay doesn't click in, the output relays won't either,
otherwise the inrush resistor would go bang once the amp delivered any
power.

Gareth.
 
" Nutcase Kook"
If the C is for Crest
Click to expand...

** No way.

"C-Audio" is a British maker.

Weird contraptions with a mix of Hitachi power mosfets and Motorola TO3s in
the output stages.

The fan routinely caused amps to fail since it blew directly onto a bunch of
high voltage TO92s and covered them in dust and moisture.


.... Phil
 
"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:b1sjq9F17b2U1@mid.individual.net...
" Nutcase Kook"


If the C is for Crest


** No way.

"C-Audio" is a British maker.

Weird contraptions with a mix of Hitachi power mosfets and Motorola TO3s
in the output stages.

The fan routinely caused amps to fail since it blew directly onto a bunch
of high voltage TO92s and covered them in dust and moisture.


... Phil
Click to expand...
Yes indeed. C-Audio were based in Cambridge, and their offerings were quite
well regarded in the pro audio field. They are, however, long gone now. This
one has only mosfets in the output stages, no TO3s at all. Considering how
long they were around, I was very surprised to not find any schematics on
the usual sites.

Arfa
 
"Gareth Magennis" <gareth.magennis@ntlworld.com> wrote in message
news:Zm2ut.37568$YV.25656@fx33.am4...
"Arfa Daily" wrote in message news:eek:e0ut.39678$Gx7.36621@fx08.am4...

Anybody by any remote chance have a schematic copy for a C - Audio RA 1001
slave amp ? Drawn a blank from all the usual places.

Looks as though it has been stored somewhere cold and damp, although dry
enough now. Basically, it won't come out of 'protect' although there seems
to be nothing wrong fundamentally with either channel. Both channels have
good output, with no DC offset, as far as the output relays. There is
another relay over at the mains input side of things that looks like it
shorts a bloody great resistor, so inrush limiting I guess. All three
relays
remain stubbornly off, and the protect light stays on. I can't read any
volts at any of the three relay coils, and none of the pins appears to be
grounded, so they are not high-side switched. So may be something as
simple
as a missing rail, but hard to follow print around as it's double sided,
and
fairly crowded ...

Arfa




One corroded track I found was actually underneath one of the relays!

You could be right and it might just be the low voltage supply for the
protect/relays.
If the inrush relay doesn't click in, the output relays won't either,
otherwise the inrush resistor would go bang once the amp delivered any
power.

Gareth.
Click to expand...
Pretty much as I was figuring then. I'm sure it will be a simple problem
when I get to the bottom of it. Just depends how much time the owner is
prepared to pay for ...

If you have any schematics that are at least similar, it would be
appreciated. Most of these amp manufacturers don't reinvent the wheel, and
the relay circuitry is quite likely to be similar between models

TIA

Arfa
 
"Arfa Daily"

If you have any schematics that are at least similar, it would be
appreciated. Most of these amp manufacturers don't reinvent the wheel, and
the relay circuitry is quite likely to be similar between models
Click to expand...
** Decades ago, I managed to extract some schems for C-Audio from the Aussie
importer ( same people who now make Rode Microphones). Not like normal
schems, these were large scale drawings with each part of an amp on a new
page - so very had to use in servicing. Chucked them a long while ago.

IIRC, the relay system was full of BF422 and BF423 transistors, all sitting
right in the fan blast, with badly corroded legs. Check and replace these if
needed and that may be all you have to do.



.... Phil
 
"Phil Allison" wrote in message news:b1soo9F24stU1@mid.individual.net...


"Arfa Daily"

If you have any schematics that are at least similar, it would be
appreciated. Most of these amp manufacturers don't reinvent the wheel, and
the relay circuitry is quite likely to be similar between models
Click to expand...
** Decades ago, I managed to extract some schems for C-Audio from the Aussie
importer ( same people who now make Rode Microphones). Not like normal
schems, these were large scale drawings with each part of an amp on a new
page - so very had to use in servicing. Chucked them a long while ago.

IIRC, the relay system was full of BF422 and BF423 transistors, all sitting
right in the fan blast, with badly corroded legs. Check and replace these if
needed and that may be all you have to do.



.... Phil





It was on one of these amps that I replaced BC182's with BC182L,s not
realising the pinout was different.
It was a week before I worked out what the f**k was going on there.


Gareth.
 
"Gareth Magennis"
"Phil Allison"
** Decades ago, I managed to extract some schems for C-Audio from the
Aussie
importer ( same people who now make Rode Microphones). Not like normal
schems, these were large scale drawings with each part of an amp on a new
page - so very had to use in servicing. Chucked them a long while ago.

IIRC, the relay system was full of BF422 and BF423 transistors, all
sitting
right in the fan blast, with badly corroded legs. Check and replace these
if
needed and that may be all you have to do.

It was on one of these amps that I replaced BC182's with BC182L,s not
realising the pinout was different.
It was a week before I worked out what the f**k was going on there.
Click to expand...
** The BF423 and MPSA92 differ only slightly in specs, but have different
pin outs.

The BF number having the collector in the middle while the MPSA has the
base there.



.... Phil
 
"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:Fa9ut.53617$Gm5.50918@fx11.am4...
"Gareth Magennis" <gareth.magennis@ntlworld.com> wrote in message
news:Zm2ut.37568$YV.25656@fx33.am4...


"Arfa Daily" wrote in message news:eek:e0ut.39678$Gx7.36621@fx08.am4...

Anybody by any remote chance have a schematic copy for a C - Audio RA
1001
slave amp ? Drawn a blank from all the usual places.

Looks as though it has been stored somewhere cold and damp, although dry
enough now. Basically, it won't come out of 'protect' although there
seems
to be nothing wrong fundamentally with either channel. Both channels have
good output, with no DC offset, as far as the output relays. There is
another relay over at the mains input side of things that looks like it
shorts a bloody great resistor, so inrush limiting I guess. All three
relays
remain stubbornly off, and the protect light stays on. I can't read any
volts at any of the three relay coils, and none of the pins appears to be
grounded, so they are not high-side switched. So may be something as
simple
as a missing rail, but hard to follow print around as it's double sided,
and
fairly crowded ...

Arfa




One corroded track I found was actually underneath one of the relays!

You could be right and it might just be the low voltage supply for the
protect/relays.
If the inrush relay doesn't click in, the output relays won't either,
otherwise the inrush resistor would go bang once the amp delivered any
power.

Gareth.


Pretty much as I was figuring then. I'm sure it will be a simple problem
when I get to the bottom of it. Just depends how much time the owner is
prepared to pay for ...

If you have any schematics that are at least similar, it would be
appreciated. Most of these amp manufacturers don't reinvent the wheel, and
the relay circuitry is quite likely to be similar between models

TIA

Arfa
Click to expand...
Just a thought - I have seen on many older amps, a small value electrolytic
used to provide a hold-off for the sharp cutoff at power-off.
Power shut off, DC (usually 1/2 wave recified) dies very quickly, and
protect relay cuts off before the amp can "pop".
Usually 1uF, 2.2uF, 4.7uF etc associated with a single diode in the power
supply.

This is especially common if a TA7317P or similar protect IC is used.

Later!

Mark Z.
 
Hi,

I've emailed you the 1001/2001/3001 schematics. Sorry for delay, but hours
of major outage of BT Internet this morning.

Maybe you could post them somewhere when you have time and post a link here,
I'm sure there will be a few interested here in having them.
I'm not very good at that sort of thing. ;)


Note what I said about the 'L' suffix - I got it the wrong way round, but
C-Audio used BC184L and BC214L in these designs, and these are a different
pinout to BC 184 and BC214.





Cheers,


Gareth.
 
I did look at uploading the schematics to eserviceinfo, but they want far
too many personal details for registration for my liking.



Gareth.
 
"Gareth Magennis" <sound.service@btconnect.com> wrote in message
news:aLudnf0ELbZvKCTMnZ2dnUVZ8uKdnZ2d@bt.com...
I did look at uploading the schematics to eserviceinfo, but they want far
too many personal details for registration for my liking.



Gareth.
Click to expand...
All received, thanks. I'll try and look into it again by the weekend, and
post back.

Phil. Did you have a good birthday ? :)

Arfa
 
"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:krjut.61734$y63.2896@fx25.am4...
"Gareth Magennis" <sound.service@btconnect.com> wrote in message
news:aLudnf0ELbZvKCTMnZ2dnUVZ8uKdnZ2d@bt.com...
I did look at uploading the schematics to eserviceinfo, but they want far
too many personal details for registration for my liking.



Gareth.

All received, thanks. I'll try and look into it again by the weekend, and
post back.

Phil. Did you have a good birthday ? :)

Arfa
Click to expand...
OK. It's fixed. The three relay coils are in series and are switched by Q45.
There was good volts at its emitter, but bugger all at its collector.
Conditions at its base were wrong, but not because of it sensing DC offset
or over-temp condition, so had to be a component around the transistor.
Turned out that the base ground return resistor R148 39k was completely
open. No signs of any distress or corrosion, just open. Put a new one in,
and away it went, so I was a happy bunny as I reached for the pen to write
the bill out ... :)

Cheers for the help with the schems Gareth. It just makes the job so much
easier !

Arfa
 
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