** I have a Line 6 " Spider II " amp in the workshop (this is the head only
version and removing the chassis seems impossible until you discover the
trick with the front panel). It came in completely dead with both power ICs
blown.

The amp has dual power channels rated at 75W each by the makers and uses a
pair of TDA7293s - with 15 leads to remove from a double sided PCB with
some very fine traces, replacement is tedious to say the least.

There is a quite a decent looking heatsink and the TDAs are clamped with
steel brackets that apply lotsa force to hold the packages against silicone
thermal pads which are stuck onto the heatsink.

When re-assembled and tested, each channel delivered 90W clean into an 8 ohm
load - which is rather a LOT for an IC that only has slightly more heat
tab area than a *single* TO3P !!

A finger test revealed that each TDA was getting very hot after only a few
seconds while the heatsink was still essentially at room temp. Tested with a
K type thermocouple, the mounting tab reached 90C in just over 1 minute and
would clearly soon exceed 100C as the heatsink warmed. This is not good.

Being suspicious of the stick-on thermal pads, I decided to remove them and
fit mica ones instead, aided by silicone grease. ( Pealing off the original
pads revealed a thick film of adhesive on the heatsink which had to be
scraped off and rubbed clean with solvent).

When re-assembled, I tested again and it was a very different story. The
temp reading on the mounting tabs reached only 56C in the first two minutes
and then stabilised at just under 60C.

Is there any need to mention the amp was made in China ??

BTW:

The reason for the dual channel failure is almost certainly that the owner
plugged both outputs into the same speaker cab.


.... Phil

Phil Allison wrote:
** I have a Line 6 " Spider II " amp in the workshop (this is the head only
version and removing the chassis seems impossible until you discover the
trick with the front panel). It came in completely dead with both power ICs
blown.

The amp has dual power channels rated at 75W each by the makers and uses a
pair of TDA7293s - with 15 leads to remove from a double sided PCB with
some very fine traces, replacement is tedious to say the least.

There is a quite a decent looking heatsink and the TDAs are clamped with
steel brackets that apply lotsa force to hold the packages against silicone
thermal pads which are stuck onto the heatsink.

When re-assembled and tested, each channel delivered 90W clean into an 8 ohm
load - which is rather a LOT for an IC that only has slightly more heat
tab area than a *single* TO3P !!

A finger test revealed that each TDA was getting very hot after only a few
seconds while the heatsink was still essentially at room temp. Tested with a
K type thermocouple, the mounting tab reached 90C in just over 1 minute and
would clearly soon exceed 100C as the heatsink warmed. This is not good.

Being suspicious of the stick-on thermal pads, I decided to remove them and
fit mica ones instead, aided by silicone grease. ( Pealing off the original
pads revealed a thick film of adhesive on the heatsink which had to be
scraped off and rubbed clean with solvent).

When re-assembled, I tested again and it was a very different story. The
temp reading on the mounting tabs reached only 56C in the first two minutes
and then stabilised at just under 60C.

Bergquist mentions that their 'Gap Pad' products can be reused but they
can't decide if their Hi-Flow material is 'reworkable' or not.

One section of the catalog recommends Hi-Flow pad replacement every time
a component is replaced and another section of the catalog specifically
calls the Hi-Flow 225 product 'reworkable'. They offer a non-answer
about reworkability of their 'Gap Filler' product and remain mum about
the reworkability of the old Sil-Pads we've used for years.

I assume this means that they would recommend replacing Sil-Pads at
each component replacement.

--Winston

"Winston the Troll "

Bergquist mentions that their 'Gap Pad' products can be reused but they
can't decide if their Hi-Flow material is 'reworkable' or not.


** Complete red herring !!!!!!!!!!!!

The pads used here were not of that kind or brand.

These consisted of a thin plastic film, coated in silicone on both sides,
with a clear adhesive layer on one side.

When the blown TDAs were removed, there was no mark or indentation on the
pads AT ALL.

The pads measured a tiny 0.15mm thick, which is similar to some 3M products.


I assume this means that they would recommend replacing Sil-Pads at
each component replacement.


** Guarantee it would not have helped one bit, the pads were performing
exactly as per usual - ie crap.

Thin mica and thermal grease have 2 to 3 times less temp drop for the same
power throughput than any of the low cost pads.

In this particular amp, it is critical that such temp drops be minimised.


.... Phil

On Jun 29, 7:02*pm, "Phil Allison" wrote:
** I have a Line 6 " Spider II " amp in the workshop (this is the head only
version and removing the chassis seems impossible until you discover the
trick with the front panel). It came in completely dead with both power ICs
blown.

....
A finger test revealed that each TDA was getting very hot after only a few
seconds while the heatsink was still essentially at room temp. Tested with a
K type thermocouple, the mounting tab reached 90C in just over 1 minute and
would clearly soon exceed 100C as the heatsink warmed. This is not good.

Being suspicious of the stick-on thermal pads, I decided to remove them and
fit mica ones instead, aided by silicone grease. ( Pealing off the original
pads revealed a thick film of adhesive on the heatsink which had to be
scraped off and rubbed clean with solvent).

Was this adhesive meant to be thermally conductive? Or did the
assembly house just use whatever was on hand to get the work out?



BTW:

The reason for the dual channel failure is almost certainly that the owner
plugged both outputs into the same speaker cab.


Forgive my ignorance of musical instrument speakers, but why would the
cabinet have been designed to make this possible, given that Murphy's
Law is in full force?

"spamtrap1888"
"Phil Allison"

Being suspicious of the stick-on thermal pads,

Was this adhesive meant to be thermally conductive? Or did the
assembly house just use whatever was on hand to get the work out?

** The pads were "self adhesive " = like stamps.


The reason for the dual channel failure is almost certainly that the owner
plugged both outputs into the same speaker cab.


Forgive my ignorance of musical instrument speakers, but why would the
cabinet have been designed to make this possible,


** What cabinet is that ?

" I have a Line 6 " Spider II " amp in the workshop (this is the head only
version .. "


..... Phil

BTW:

The reason for the dual channel failure is almost certainly that the owner
plugged both outputs into the same speaker cab.


... Phil




I'm not sure how this is easily achievable, even by the most Numpty of all
Numptys.


More likely IMHO that said Numpty connected the amp to a speaker where
either the speaker cable or the speaker itself was shorted.
He then did it again with the other side.

Or possibly he was otherwise exceeding the specs of amp and speakers, and
that one side blew ages ago, and he only brought the amp to you when the
other side also gave up the ghost.

Or it could have been not due to Numptyism at all, e.g. the manufacturers
had put some sort of substandard silicon pad between Power device and
Heatsink that did not perform as it should.
Again, one side blew ages ago, he only brought it to you when the other side
blew, rendering the amp useless.



Gareth.

"Gareth Magennis"

The reason for the dual channel failure is almost certainly that the
owner plugged both outputs into the same speaker cab.


I'm not sure how this is easily achievable,

** It is very easily achieved.

Lotsa speaker cabs have twin, parallel wired sockets.

Imbecile.


More likely IMHO that said Numpty connected the amp to a speaker where
either the speaker cable or the speaker itself was shorted.
He then did it again with the other side.

** So you have no clue that TDA7293s fail short ?

Guess what instantly follows ?


Or it could have been not due to Numptyism at all, e.g. the manufacturers
had put some sort of substandard silicon pad between Power device and
Heatsink that did not perform as it should.
Again, one side blew ages ago, he only brought it to you when the other
side blew, rendering the amp useless.

** So you have no clue how TDA7293s fail short ?

Guess what instantly follows ?

The AC fuse blows of course.

So if you find *both* ICs on a common DC supply have failed short, they
must have done so simultaneously.

BTW:

TDA7293 have over temp protection, which generally saves them from an
inadequate heatsink but not from, sudden massive over dissipation.

Do you know anything about amplifiers at all ?


..... Phil

So if you find *both* ICs on a common DC supply have failed short, they
must have done so simultaneously.




Er, no.


Gareth.

"Gareth Magennis = ****"

So if you find *both* ICs on a common DC supply have failed short, they
must have done so simultaneously.


Er, no.


** My god you are one, pig arrogant pommy **** head.

**** off.

"Phil Allison" wrote in message
...

"Gareth Magennis = ****"

So if you find *both* ICs on a common DC supply have failed short, they
must have done so simultaneously.


Er, no.


** My god you are one, pig arrogant pommy **** head.

**** off.





Thank you very much.

Goodbye.




Gareth.

"Gareth Magennis = ****"

So if you find *both* ICs on a common DC supply have failed short,
they must have done so simultaneously.


Er, no.


** My god you are one, pig arrogant pommy **** head.

**** off.



Thank you very much.


** Get cancer and DIE you criminal POS.

On Friday, June 29, 2012 10:02:41 PM UTC-4, Phil Allison wrote:

Sili pads are not the greatest to begin with, some be'n better than others. The mfgr's of the sili pads don't recommend they be reused. I replace them with mica most of the time. Chip amps need all the help they can get attempting to dissipate heat from that small of a package. The cheap fans used in the Mar$hall Mode Four and AVT series always take a **** and the chip amps go with them.

Just a note on those 7293s, make *damn* sure the rail filter caps are well discharged before reconnecting the repaired board (or inserting a replacement chip). Charged caps will likely damage the chip and render it useless.

Phil Allison wrote:

Sili pads are not the greatest to begin with, some be'n better than others.
The mfgr's of the sili pads don't recommend they be reused.


** The pads used here were not of the regular kind - these consisted of a
thin plastic ( Kapton) film, coated in silicone on both sides, with a clear
adhesive layer on one side. The pads measured a tiny 0.15mm thick.

When the blown TDAs were removed, there was no mark or indentation on the
pads AT ALL.


I replace them with mica most of the time.


** Good.


..... Phil