Prev: Simple Hack To Get $2500 To Your PayPal Account.
Next: Paralleled Amplifier Wiring
From: N_Cook on 21 Jul 2010 06:51
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.


From: N_Cook on 21 Jul 2010 10:09
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.


From: Gareth Magennis on 21 Jul 2010 17:15


"N_Cook" <diverse(a)tcp.co.uk> wrote in message
news:i26v0g$l9b$1(a)news.eternal-september.org...
> 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.

From: Arfa Daily on 21 Jul 2010 19:46


"Gareth Magennis" <sound.service(a)btconnect.com> wrote in message
news:urJ1o.2844$FM1.1896(a)hurricane...
>
>
> "N_Cook" <diverse(a)tcp.co.uk> wrote in message
> news:i26v0g$l9b$1(a)news.eternal-september.org...
>> 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.

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

From: N_Cook on 22 Jul 2010 03:13
Gareth Magennis <sound.service(a)btconnect.com> wrote in message
news:urJ1o.2844$FM1.1896(a)hurricane...
>
>
> "N_Cook" <diverse(a)tcp.co.uk> wrote in message
> news:i26v0g$l9b$1(a)news.eternal-september.org...
> > 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.
>

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.


 |  Next  |  Last
Pages: 1 2 3
Prev: Simple Hack To Get $2500 To Your PayPal Account.
Next: Paralleled Amplifier Wiring