C Audio Pulse 2x 1100 watt amp

[N_Cook]

Goes into protect mode at switch on.
Useful info and schema on these G class amps
http://www.reptips.dk/Reptips/CAUDIO.pdf
as well as schema only, on e-service
One smps supplies both amps and 4 rails, each rail supplies both ch, I've
cut the "overdrive" rails temporarily and running on +/- 60V.
Output has about +18V on ch1 for about a second before dropping down to 0,
so o/p DCsense line to the PIC tells it to go into protect, of whole amp.
With 15R load then op jump is to about 10V. The other ch2 is fine , no more
than 0.5V on output loaded or not.
Same 2 (4 in full operation) rails supply both amps. All electrolytics check
out ok. Problem fault tracing is 3/4 of the active in this amp shows the
same 18V or so jump at power-up.
Disabling the protect line, so the amp powers up, shows nothing amiss after
2 seconds, on all main transistors, running at +/-25 V rails anyway. I will
repeat this now at +/-60 V but as no 1 to 1 correspondence of device
numbering or posistioning between ch1 and ch2 a bit awkward and I don't
expect to see any substantial DC differences as has settled down after the
first couple of seconds. How to zero-in to the problem device . Nothing
untoward at the pa input but I will tie to ground the next time of powering
up just to confirm.

 

[N_Cook]

Looks like all 4 off 1M , need replacing, all those matching operational
position of R182.
Has 80 V in normal use over 1/3W 1Meg and used in dampish conditions is
enough to make it go high or even o/c., not removed it yet. In an area of
circuit not easy to measure or even compare ch for ch. Hooking another 1M
across it is enough to give amp operation without disabling the DCsense
error protection.
Its this R that takes the central biasing section low at power up before the
Tr25+C53 section becomes operational.

 

[Gareth Magennis]

Looks like all 4 off 1M , need replacing, all those matching operational
position of R182.
Has 80 V in normal use over 1/3W 1Meg and used in dampish conditions is
enough to make it go high or even o/c., not removed it yet. In an area of
circuit not easy to measure or even compare ch for ch. Hooking another 1M
across it is enough to give amp operation without disabling the DCsense
error protection.
Its this R that takes the central biasing section low at power up before
the
Tr25+C53 section becomes operational.

You're a braver man that I am Mr Cook. I've seen 2 of these and decided on
both occasions not to touch it with a barge pole.


Perhaps that's a sign of getting older and wiser. - some jobs you really do
need to refuse for your own personal well being.

Good luck,

Gareth.

 

[Arfa Daily]

You're a braver man that I am Mr Cook. I've seen 2 of these and decided
on both occasions not to touch it with a barge pole.


Perhaps that's a sign of getting older and wiser. - some jobs you really
do need to refuse for your own personal well being.

Good luck,

Gareth.

Don't know about you, but I'm finding more and more that these big power
amps are not worth repairing, due to the low cost of replacements. The shop
that I do a lot of work for will often tell me not to spend more than half
an hour making sure that it's not a really simple problem, as a replacement
can be had for a couple of hundred quid or less. Suits me just fine as I
still get an examination fee, without the thought of all the potential grief
of replacing a bunch of output transistors, and trying to ensure that it
doesn't all go bang again when you've finished. As you say, perhaps a case
of getting older and wiser. Not so many years back, I was up for any repair,
just for the challenge of not being defeated. These days, it's about making
a living, and if a repair does defeat me, it's just san fairy ann and on to
the next one ...

Arfa

 

[N_Cook]

You're a braver man that I am Mr Cook. I've seen 2 of these and decided on
both occasions not to touch it with a barge pole.


Perhaps that's a sign of getting older and wiser. - some jobs you really do
need to refuse for your own personal well being.

Good luck,

Gareth.

At least the schema are around. Some notes in passing, you have to be
careful how you pick up that large pcb , by the heatsinks and front
metalwork not by the edge or rear as those large piercings make it weak.
Discharging the rectified mains DC cap of course. Maybe all component
oles( certainly the 4 off 1Meg Rs) are the size for power transistor legs or
IC-pin eyelets so although plated through holes , minor components like 1/3W
Rs have a lot of solder around the leads so libility to cracking I would
think.

 

[N_Cook]

Not actually the 1meg failed it was the TO92 over the complementary 1meg
gone 35uA leaky, pulling the zero point upwards

 

[Arfa Daily]

Not actually the 1meg failed it was the TO92 over the complementary 1meg
gone 35uA leaky, pulling the zero point upwards

So, how did your lead-free lecture turn out last week ? Well received ? Did
you video it ?

Arfa

 

[N_Cook]

So, how did your lead-free lecture turn out last week ? Well received ? Did
you video it ?

Arfa

outline from the .ppt here
http://www.divdev.fsnet.co.uk/scicaf2.htm
interested enough to have 3/4 hour of Q&A afterwards.
Someone from one of the PbF exempted industries there saying they were
having horrendous problems specifying and actually obtaining lead-free-free
components , there is a lot of fraudulent specification paperwork around
apparently.

And someone else from gas-fitting, no problem there as such, they just
charge the customers £250 for a new controller board when it is just PbF
solder failings on the not so old previous board, subjected to normal
in-service conditions but too much heat for pbf.

 

[Meat Plow]

So, how did your lead-free lecture turn out last week ? Well received ?
Did you video it ?

Arfa

Arrrrgggg!

I just repaired a 600 watt Coolmax PC PSU that had defective PBf
soldering. Don't -ever- buy that brand, they are very poorly assembled.

 

[Arfa Daily]

outline from the .ppt here
http://www.divdev.fsnet.co.uk/scicaf2.htm
interested enough to have 3/4 hour of Q&A afterwards.
Someone from one of the PbF exempted industries there saying they were
having horrendous problems specifying and actually obtaining
lead-free-free
components , there is a lot of fraudulent specification paperwork around
apparently.

And someone else from gas-fitting, no problem there as such, they just
charge the customers £250 for a new controller board when it is just PbF
solder failings on the not so old previous board, subjected to normal
in-service conditions but too much heat for pbf.

Yes, I've come across this one. Apparently, there's quite a lot of problems
caused on these PbF boards, by relay hammer, which leads to the joints on
those devices fracturing. The real bummer on this though, is that the boards
have been manufactured in lead-free to help the environment (according to
the green mist eco-bollox brigade, anyway) but what's actually happening is
the things are failing *because* of the lead-free solder, and then a
perfectly otherwise serviceable board, which could easily be repaired, is
being replaced as a service spare, much like a faulty gas valve or pump
motor or whatever, because the person who calls out to fix the fault is a
plumber, and has little or no electronic savvy. A person who I know that is
a plumber, says that his garage is full of scrap boards, and that every now
and then, he just collects them all up and takes them to the tip. How green
and eco friendly is that ? I've been trying to persuade him to collect a big
bag of them up for me to take off his hands, but no luck so far ... I
wonder if the control boards from other appliances like washing machines and
dishwashers suffer the same because of lead-free construction. Actually
there is a little domestic electrical sales and repair shop next to one of
our cafes. Next time I'm down there, I will pop in and see the owner and ask
him. There might be some mileage in this. I'm thinking purely from the
business angle and wads in my pocket of course, rather than the green issues
....

Arfa

 

[N_Cook]

Have you repaired the amp yet?
I sent you a couple of off list messages but they bounced.
I have repaired a few of this type of amplifier and may be able to
help troubleshoot it.
Contact me off list at IFixAudio at GMail.com.

Jim

reply

No valid emails used on usenet
The one with leaky TO92 repaired and waiting for owner to return from
holiday.
Second one initially looked at , problems again in a TO02 device in a
different area of one amp, gone B-C-E shorted so more obvious a problem.
Waiting for owner to return before progressing on that one. Third one not
looked at other than also goes into protect and no obvious problems with the
TO3s , perhaps so well protected that rarely do the YO3s get a chance to
fail.

I will use a valid email account to contact you