250W amp - Mark Bass , Little Mark 250, of 2008, Italy

N

N_Cook

Guest
Mains fuse blew in the middle of normal use.
No mention of PbF anywhere but it is. Unlikely the problem though. Seems bad
thermal design as audio-out vaned heatsink has cooling air through it but
the non-vaned SMPS one does not have, as that intended? air will go through
the path of least resistance over the uncluttered preamp . I can see a
baffle going in here to direct air over this plain block heatsink. Anyone
experience of these little amps?
Both SMPS powerFETs s/c all round. Each has a discoloured patch on the
mounting-plate where the die overlies. No burning/blow-holes of these
powerFET encapsulations or 10R SMD gate droppers or anything else found
suspect from cold testing/close inspection, nor suspect looking PbF. The
SMPS supervisor IC ident is ground off and a schematic for a similar amp
has no ident. I could find details of any 8 pin 0.1 inch pitch package with
push/pull drive in 1991 DATA linear colated listing- any suggestions for
this sort of search?
p1 supply low side
p3 probably Enable
p4 Vcc
p5 and p7 hi/lo outputs
p6 mid connection to both output powerFET
Does not seem to be any thermal shutdown for the SMPS section
 
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:jotrpv$pg1$1@dont-email.me...
Mains fuse blew in the middle of normal use.
No mention of PbF anywhere but it is. Unlikely the problem though. Seems
bad
thermal design as audio-out vaned heatsink has cooling air through it but
the non-vaned SMPS one does not have, as that intended? air will go
through
the path of least resistance over the uncluttered preamp . I can see a
baffle going in here to direct air over this plain block heatsink. Anyone
experience of these little amps?
Both SMPS powerFETs s/c all round. Each has a discoloured patch on the
mounting-plate where the die overlies. No burning/blow-holes of these
powerFET encapsulations or 10R SMD gate droppers or anything else found
suspect from cold testing/close inspection, nor suspect looking PbF. The
SMPS supervisor IC ident is ground off and a schematic for a similar amp
has no ident. I could find details of any 8 pin 0.1 inch pitch package
with
push/pull drive in 1991 DATA linear colated listing- any suggestions for
this sort of search?
p1 supply low side
p3 probably Enable
p4 Vcc
p5 and p7 hi/lo outputs
p6 mid connection to both output powerFET
Does not seem to be any thermal shutdown for the SMPS section
Click to expand...

I've got one of those here I gave up on. Life's too short and doesn't pay
enough for this kind of palaver.

Good luck!


Gareth.
 
Gareth Magennis <sound.service@btconnect.com> wrote in message
news:B86dncP9u4kp5C_SnZ2dnUVZ8hednZ2d@bt.com...
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:jotrpv$pg1$1@dont-email.me...
Mains fuse blew in the middle of normal use.
No mention of PbF anywhere but it is. Unlikely the problem though. Seems
bad
thermal design as audio-out vaned heatsink has cooling air through it
but
the non-vaned SMPS one does not have, as that intended? air will go
through
the path of least resistance over the uncluttered preamp . I can see a
baffle going in here to direct air over this plain block heatsink.
Anyone
experience of these little amps?
Both SMPS powerFETs s/c all round. Each has a discoloured patch on the
mounting-plate where the die overlies. No burning/blow-holes of these
powerFET encapsulations or 10R SMD gate droppers or anything else found
suspect from cold testing/close inspection, nor suspect looking PbF. The
SMPS supervisor IC ident is ground off and a schematic for a similar
amp
has no ident. I could find details of any 8 pin 0.1 inch pitch package
with
push/pull drive in 1991 DATA linear colated listing- any suggestions for
this sort of search?
p1 supply low side
p3 probably Enable
p4 Vcc
p5 and p7 hi/lo outputs
p6 mid connection to both output powerFET
Does not seem to be any thermal shutdown for the SMPS section




I've got one of those here I gave up on. Life's too short and doesn't pay
enough for this kind of palaver.

Good luck!


Gareth.
Click to expand...

So what was the failure on your one?
 
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:jou0av$nff$1@dont-email.me...
Gareth Magennis <sound.service@btconnect.com> wrote in message
news:B86dncP9u4kp5C_SnZ2dnUVZ8hednZ2d@bt.com...

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:jotrpv$pg1$1@dont-email.me...
Mains fuse blew in the middle of normal use.
No mention of PbF anywhere but it is. Unlikely the problem though.
Seems
bad
thermal design as audio-out vaned heatsink has cooling air through it
but
the non-vaned SMPS one does not have, as that intended? air will go
through
the path of least resistance over the uncluttered preamp . I can see a
baffle going in here to direct air over this plain block heatsink.
Anyone
experience of these little amps?
Both SMPS powerFETs s/c all round. Each has a discoloured patch on the
mounting-plate where the die overlies. No burning/blow-holes of these
powerFET encapsulations or 10R SMD gate droppers or anything else found
suspect from cold testing/close inspection, nor suspect looking PbF.
The
SMPS supervisor IC ident is ground off and a schematic for a similar
amp
has no ident. I could find details of any 8 pin 0.1 inch pitch package
with
push/pull drive in 1991 DATA linear colated listing- any suggestions
for
this sort of search?
p1 supply low side
p3 probably Enable
p4 Vcc
p5 and p7 hi/lo outputs
p6 mid connection to both output powerFET
Does not seem to be any thermal shutdown for the SMPS section




I've got one of those here I gave up on. Life's too short and doesn't
pay
enough for this kind of palaver.

Good luck!


Gareth.




So what was the failure on your one?
Click to expand...
Both Power amp and Power supply.
Couldn't get a replacement for a blown PSU Mosfet, (Farnell had a one year
waiting list) so subbed in the highest spec one I could find, but it still
didn't power up, (amp disconnected) so I gave up.

If I come across something like this where schematics and parts are not
available, I am not about to spend 6 difficult hours on it, and only be able
to charge 3, so I now cut my losses and refuse.
This, together with muting all TV adverts the past 5 years, has improved my
life immeasurably.


Gareth.
 
From digeykey filter search , these are 8 pin SMPS ICs , now to see if dual
drive

LTC1041

NJM2103

TDA4605

FAN7680

SG6203
 
On Tue, 15 May 2012 16:12:10 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

a schematic for a similar amp ...
Click to expand...
Could we see it?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 
Franc Zabkar <fzabkar@iinternode.on.net> wrote in message
news:m6j5r79lob3innh1brlfjrctmg46ampm84@4ax.com...
On Tue, 15 May 2012 16:12:10 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

a schematic for a similar amp ...

Could we see it?

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

different powerFET pair but overlay device numbers/types etc correcpond in
the SMPS area otherwise
http://www.eserviceinfo.com/download.php?fileid=51892
 
Will jury-rig with a couple of IRF740 in there at 70 percent mains to check
if the supervisor is working.
Can "totem pole" types be used as dual drive? A TDA8130 would go in there
pinning-wise, with 6 of the 8 pins rewired, no idea if correct operational
parameters though. Before trying a pair of 20 amp/600V powerFETs.
Is there any point in roughing the surface of a flat shiney aluminium block
heatsink or painting black for better heat transfer, not really space to add
vanes to the block
 
Different heatsink types and different layout to the pics shown in that pdf
 
The SG6203 in that list is totem-pole but the source/sink split is not
available at the output unlike the TDA8130, so none suitable from that
sub-set
 
On Wed, 16 May 2012 08:27:42 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

Franc Zabkar <fzabkar@iinternode.on.net> wrote in message
news:m6j5r79lob3innh1brlfjrctmg46ampm84@4ax.com...
On Tue, 15 May 2012 16:12:10 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

a schematic for a similar amp ...

Could we see it?

different powerFET pair but overlay device numbers/types etc correcpond in
the SMPS area otherwise
http://www.eserviceinfo.com/download.php?fileid=51892
Click to expand...
If I use the following search parameters ...

http://www.google.com/search?q=vb+vs+en+vcc+rt+com+filetype%3Apdf

.... I get several promising leads, but all of them have the Vcc and
Ground pins interchanged.

http://www.datasheetcatalog.org/datasheet/irf/ir2151.pdf
http://www.irf.com/product-info/datasheets/data/ir2153z.pdf
http://www.irf.com/product-info/datasheets/data/irs27951s.pdf
http://www.dianyuan.com/bbs/u/83/3675811258537068.pdf
http://bbs.dianyuan.com/bbs/u/70/2970761224726220.pdf

.... and lots more.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 
Franc Zabkar <fzabkar@iinternode.on.net> wrote in message
news:3gv6r7homglogkluobf2t4bcqc4981uipj@4ax.com...
On Wed, 16 May 2012 08:27:42 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

Franc Zabkar <fzabkar@iinternode.on.net> wrote in message
news:m6j5r79lob3innh1brlfjrctmg46ampm84@4ax.com...
On Tue, 15 May 2012 16:12:10 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

a schematic for a similar amp ...

Could we see it?

different powerFET pair but overlay device numbers/types etc correcpond
in
the SMPS area otherwise
http://www.eserviceinfo.com/download.php?fileid=51892

If I use the following search parameters ...

http://www.google.com/search?q=vb+vs+en+vcc+rt+com+filetype%3Apdf

... I get several promising leads, but all of them have the Vcc and
Ground pins interchanged.

http://www.datasheetcatalog.org/datasheet/irf/ir2151.pdf
http://www.irf.com/product-info/datasheets/data/ir2153z.pdf
http://www.irf.com/product-info/datasheets/data/irs27951s.pdf
http://www.dianyuan.com/bbs/u/83/3675811258537068.pdf
http://bbs.dianyuan.com/bbs/u/70/2970761224726220.pdf

... and lots more.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
Click to expand...
I tried googling "switch mode" "8 pin" "totem pole"
"switch mode" "8 pin" "hi output" "low output" and similar and found nothing
suitable
 
"Franc Zabkar"

If I use the following search parameters ...

http://www.google.com/search?q=vb+vs+en+vcc+rt+com+filetype%3Apdf

... I get several promising leads, but all of them have the Vcc and
Ground pins interchanged.

http://www.datasheetcatalog.org/datasheet/irf/ir2151.pdf
http://www.irf.com/product-info/datasheets/data/ir2153z.pdf
http://www.irf.com/product-info/datasheets/data/irs27951s.pdf
http://www.dianyuan.com/bbs/u/83/3675811258537068.pdf
http://bbs.dianyuan.com/bbs/u/70/2970761224726220.pdf
Click to expand...

** The Italian schem may well contain a drawing error re pins 1 and cos
the IR2151 certainly looks the part.

Also, the amplifier output stage is NOT well protected from a short -
those 6.2 V zeners are not gonna save any of the IRFP mosfets, which BTW
need to be matched sets in order to share current.

PLUS, once the power amp fails short from rail to rail - the PSU has got
only one option.

It blows up.

Wot a dago piece of shit.



.... Phil
 
Franc Zabkar <fzabkar@iinternode.on.net> wrote in message
news:3gv6r7homglogkluobf2t4bcqc4981uipj@4ax.com...
On Wed, 16 May 2012 08:27:42 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

Franc Zabkar <fzabkar@iinternode.on.net> wrote in message
news:m6j5r79lob3innh1brlfjrctmg46ampm84@4ax.com...
On Tue, 15 May 2012 16:12:10 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

a schematic for a similar amp ...

Could we see it?

different powerFET pair but overlay device numbers/types etc correcpond
in
the SMPS area otherwise
http://www.eserviceinfo.com/download.php?fileid=51892

If I use the following search parameters ...

http://www.google.com/search?q=vb+vs+en+vcc+rt+com+filetype%3Apdf

... I get several promising leads, but all of them have the Vcc and
Ground pins interchanged.

http://www.datasheetcatalog.org/datasheet/irf/ir2151.pdf
http://www.irf.com/product-info/datasheets/data/ir2153z.pdf
http://www.irf.com/product-info/datasheets/data/irs27951s.pdf
http://www.dianyuan.com/bbs/u/83/3675811258537068.pdf
http://bbs.dianyuan.com/bbs/u/70/2970761224726220.pdf

... and lots more.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
Click to expand...
I checked the pcb traces and pins 1 and 4 are swapped over on that schematic
, the 270K dropper agrees but ground and supply are swapped so pinning
agreement with those IR... ones
 
Would you trust amp repair to a company where they pull knobs away with
carpenter's pliers?
I assume that is the reason for the ground off ident, to lock into their
repair shop
 
"N_Cook"
I checked the pcb traces and pins 1 and 4 are swapped over on that
schematic
, the 270K dropper agrees but ground and supply are swapped so pinning
agreement with those IR... ones
Click to expand...

** Told ya ....



..... Phil
 
With 2x IRF740 in there and 60 percent mains there is high current draw,
some smps type oscillator start up noise and mains draw current drops right
back with 180V over the main bridge rect , switch off and that 180V takes a
long time dropping to 150V with some low level audible osc type noise . No
led or fan tries turning , perhaps needs more than 60 percent for this or
something else wrong, will have to try monitoring SMPS output before
venturing higher
 
On Wed, 16 May 2012 12:34:31 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

I checked the pcb traces and pins 1 and 4 are swapped over on that schematic
, the 270K dropper agrees but ground and supply are swapped so pinning
agreement with those IR... ones
Click to expand...
If you measure the Vcc of the IC, then that should narrow down the
suitable candidates. Vcc is determined by an internal zener, not by
the external components. It doesn't sound like this IC is the problem,
though.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 
Franc Zabkar <fzabkar@iinternode.on.net> wrote in message
news:7va8r75vncka6v2ugat269epqk99avu8bd@4ax.com...
On Wed, 16 May 2012 12:34:31 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

I checked the pcb traces and pins 1 and 4 are swapped over on that
schematic
, the 270K dropper agrees but ground and supply are swapped so pinning
agreement with those IR... ones

If you measure the Vcc of the IC, then that should narrow down the
suitable candidates. Vcc is determined by an internal zener, not by
the external components. It doesn't sound like this IC is the problem,
though.

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

When I get back to it I will try a 72V zener over one of the Brown-out?
zener chain of 220/200V zeners, while srill trying with 60 percent mains (2
x200V caps across the main DC - reminder to myself to find a workaday
formula for "Vz" of zeners at 1/10 to 1/10000 of rated current )
 
On Thu, 17 May 2012 08:13:30 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

When I get back to it I will try a 72V zener over one of the Brown-out?
zener chain of 220/200V zeners ...
Click to expand...
I would think that 420VDC would be required to "turn on" the series
connected zener pair. A 240VAC source would produce 350VDC, so ISTM
that these zeners would be sensing an overvoltage rather than a
brownout. That said, the overvoltage would have to be an extremely
large one (+20%).

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