JCM2000 DSL100

P

Phil Allison

Guest
Hi,

just put a Marshall JCM2000, DSL100 on the bench.

Looks nice .....

3 output valves installed, 6CA7EH ( Electro-Harmonix, 02/12), only one of
which works.

Two, large mirror burn marks on the glass of one of the dead ones, but the
OT and rest of amp seem OK.

Pulled all the 6CA7s and checked the bias voltage on pin 5 of all 4 sockets
= -43V at max setting.

Played hot air onto the PCB near the octal sockets for about 20 seconds and
re-checked.

Pin 5 voltages had dropped to between 28V & 14 V.

Oh shit !!!!!

How did this amp ever survive for this long with such massive PCB leakage
???

The grid feed resistors are all 220kohms too !!!!

Do Marshall actually have spare PCBs for this god awful POS any more ??

What sort of cost delivered to Sydney Australia ?


..... Phil
 
"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:bltu0uF63k6U1@mid.individual.net...
Hi,

just put a Marshall JCM2000, DSL100 on the bench.

Looks nice .....

3 output valves installed, 6CA7EH ( Electro-Harmonix, 02/12), only one of
which works.

Two, large mirror burn marks on the glass of one of the dead ones, but the
OT and rest of amp seem OK.

Pulled all the 6CA7s and checked the bias voltage on pin 5 of all 4
sockets = -43V at max setting.

Played hot air onto the PCB near the octal sockets for about 20 seconds
and re-checked.

Pin 5 voltages had dropped to between 28V & 14 V.

Oh shit !!!!!

How did this amp ever survive for this long with such massive PCB leakage
???

The grid feed resistors are all 220kohms too !!!!

Do Marshall actually have spare PCBs for this god awful POS any more ??

What sort of cost delivered to Sydney Australia ?


.... Phil

There is no reason why Marshall would not have these PCB's for sale.
The last one I bought cost me just short of Ł50 including VAT and carriage.

I guess if you could persuade them to ship to Sydney, the VAT would be
deducted and you would pay VAT/import duty in Australia instead.

They did have a policy of only selling things that might kill people to bone
fide engineers who wouldn't kill themselves or others with High Voltage, so
you might also have to prove you are not a numpty.


If you're really stuck I have one here I could ship you, but with carriage
and import taxes and already paid VAT @20% now, its going to end up bloody
expensive.



Cheers,


Gareth.
 
On 11/02/2014 10:04, Gareth Magennis wrote:
"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:bltu0uF63k6U1@mid.individual.net...
Hi,

just put a Marshall JCM2000, DSL100 on the bench.

Looks nice .....

3 output valves installed, 6CA7EH ( Electro-Harmonix, 02/12), only one of
which works.

Two, large mirror burn marks on the glass of one of the dead ones, but the
OT and rest of amp seem OK.

Pulled all the 6CA7s and checked the bias voltage on pin 5 of all 4
sockets = -43V at max setting.

Played hot air onto the PCB near the octal sockets for about 20 seconds
and re-checked.

Pin 5 voltages had dropped to between 28V & 14 V.

Oh shit !!!!!

How did this amp ever survive for this long with such massive PCB leakage
???

The grid feed resistors are all 220kohms too !!!!

Do Marshall actually have spare PCBs for this god awful POS any more ??

What sort of cost delivered to Sydney Australia ?


.... Phil




There is no reason why Marshall would not have these PCB's for sale.
The last one I bought cost me just short of Ł50 including VAT and carriage.

I guess if you could persuade them to ship to Sydney, the VAT would be
deducted and you would pay VAT/import duty in Australia instead.

They did have a policy of only selling things that might kill people to bone
fide engineers who wouldn't kill themselves or others with High Voltage, so
you might also have to prove you are not a numpty.


If you're really stuck I have one here I could ship you, but with carriage
and import taxes and already paid VAT @20% now, its going to end up bloody
expensive.



Cheers,


Gareth.

Or you could get sculpting on what you have. Possible with small conical
cintride/diamond bits but I now have a set of cintride tile-hole cutters
for a quick neat job.
Explained on a couple of M, on my file
http://www.divdev.fsnet.co.uk/repair2l.htm
IIRC one was thermally-kicked-off conductive pcb problem at a preamp
valve and the other for output valves. Neither have bounced back to me
and one of the owners I'm in regular contact with.
You have to wonder if the replacement M boards are old stock from the
original salt? contaminated board production run
 
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ldct6l$no1$1@dont-email.me...
On 11/02/2014 10:04, Gareth Magennis wrote:
"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:bltu0uF63k6U1@mid.individual.net...
Hi,

just put a Marshall JCM2000, DSL100 on the bench.

Looks nice .....

3 output valves installed, 6CA7EH ( Electro-Harmonix, 02/12), only one
of
which works.

Two, large mirror burn marks on the glass of one of the dead ones, but
the
OT and rest of amp seem OK.

Pulled all the 6CA7s and checked the bias voltage on pin 5 of all 4
sockets = -43V at max setting.

Played hot air onto the PCB near the octal sockets for about 20 seconds
and re-checked.

Pin 5 voltages had dropped to between 28V & 14 V.

Oh shit !!!!!

How did this amp ever survive for this long with such massive PCB
leakage
???

The grid feed resistors are all 220kohms too !!!!

Do Marshall actually have spare PCBs for this god awful POS any more ??

What sort of cost delivered to Sydney Australia ?


.... Phil




There is no reason why Marshall would not have these PCB's for sale.
The last one I bought cost me just short of Ł50 including VAT and
carriage.

I guess if you could persuade them to ship to Sydney, the VAT would be
deducted and you would pay VAT/import duty in Australia instead.

They did have a policy of only selling things that might kill people to
bone
fide engineers who wouldn't kill themselves or others with High Voltage,
so
you might also have to prove you are not a numpty.


If you're really stuck I have one here I could ship you, but with
carriage
and import taxes and already paid VAT @20% now, its going to end up
bloody
expensive.



Cheers,


Gareth.



Or you could get sculpting on what you have. Possible with small conical
cintride/diamond bits but I now have a set of cintride tile-hole cutters
for a quick neat job.
Explained on a couple of M, on my file
http://www.divdev.fsnet.co.uk/repair2l.htm
IIRC one was thermally-kicked-off conductive pcb problem at a preamp valve
and the other for output valves. Neither have bounced back to me and one
of the owners I'm in regular contact with.
You have to wonder if the replacement M boards are old stock from the
original salt? contaminated board production run


No they are new boards, different colour, different screen printing.
Nobody in their right mind would comtemplate such a thing. Surely.



Gareth.
 
"Gareth Magennis"

No they are new boards, different colour, different screen printing.

** I absolutely hope that IS the case.


Nobody in their right mind would comtemplate such a thing. Surely.

** Right mind ?? "Nutcase Kook" ??

Surely you jest ...........

FYI:

Years ago, I established beyond all doubt that the PCB leakage problem with
these models extends waaaay beyond the octal vales back into the phase
splitter and earlier stages. PCB modifications and/or the use of fans are a
dodge at best and I will never try them again.

In this case, I'm gonna make the OWNER buy the new PCB and supply it to
me.

Soooo, if it turns out to be the wrong one OR has any kind of other
problem - I can just hand it back.

There are for too many *complete idiots* involved in the chain from
Marshall in the UK to me.

Just like the smug pommy bullshitter in these videos:

https://www.youtube.com/watch?v=WeerxAO3oRU

https://www.youtube.com/watch?v=rhe7qXP08qw


Fair makes my skin crawl .......




..... Phil
 
"Gareth Magennis"

There is no reason why Marshall would not have these PCB's for sale.

** Double negatives like that are mind numbing.


The last one I bought cost me just short of Ł50 including VAT and
carriage.

** Was that long ago ?



They did have a policy of only selling things that might kill people to
bone fide engineers who wouldn't kill themselves or others with High
Voltage, so you might also have to prove you are not a numpty.

** Now, that is funny.

So * I * have to prove to Marshall that * I * know what I am doing ?????

They have SFA chance of ever proving the reverse.



If you're really stuck I have one here I could ship you, but with carriage
and import taxes and already paid VAT @20% now, its going to end up bloody
expensive.

** Thanks for the offer.

Is there anything special about ordering such a PCB ?

Or is the amp model number and serial number enough ?



.... Phil
 
"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:bluhqbFa5vuU1@mid.individual.net...
"Gareth Magennis"


There is no reason why Marshall would not have these PCB's for sale.


** Double negatives like that are mind numbing.


The last one I bought cost me just short of Ł50 including VAT and
carriage.

** Was that long ago ?



They did have a policy of only selling things that might kill people to
bone fide engineers who wouldn't kill themselves or others with High
Voltage, so you might also have to prove you are not a numpty.


** Now, that is funny.

So * I * have to prove to Marshall that * I * know what I am doing
?????

They have SFA chance of ever proving the reverse.



If you're really stuck I have one here I could ship you, but with
carriage and import taxes and already paid VAT @20% now, its going to end
up bloody expensive.

** Thanks for the offer.

Is there anything special about ordering such a PCB ?

Or is the amp model number and serial number enough ?



... Phil

Nothing special, just ask for a DSL 100 board.

Just for confirmation, both are marked JCM2-60-00.
The new board has two extra connectors, Con 15 and Con16, as well as a relay
which the old board does not. (Also Con 4 is not in the same orientation)
This is probably so it can be used in the TSL 100 as well, the 3 channel
version.
Definitely not the same PCB at all.

I think the DSL 50 also uses the same PCB, but with only 2 output valve
sockets populated, but don't quote me on that cos my memory is a bit shit
when it comes to things like that.


Cheers,


Gareth.
 
"Gareth Magennis"
"Phil Allison"
"Gareth Magennis"


There is no reason why Marshall would not have these PCB's for sale.


** Double negatives like that are mind numbing.


The last one I bought cost me just short of Ł50 including VAT and
carriage.

** Was that long ago ?



They did have a policy of only selling things that might kill people to
bone fide engineers who wouldn't kill themselves or others with High
Voltage, so you might also have to prove you are not a numpty.


** Now, that is funny.

So * I * have to prove to Marshall that * I * know what I am doing
?????

They have SFA chance of ever proving the reverse.



If you're really stuck I have one here I could ship you, but with
carriage and import taxes and already paid VAT @20% now, its going to
end up bloody expensive.

** Thanks for the offer.

Is there anything special about ordering such a PCB ?

Or is the amp model number and serial number enough ?


Nothing special, just ask for a DSL 100 board.

Just for confirmation, both are marked JCM2-60-00.
The new board has two extra connectors, Con 15 and Con16, as well as a
relay which the old board does not. (Also Con 4 is not in the same
orientation)
This is probably so it can be used in the TSL 100 as well, the 3 channel
version.
Definitely not the same PCB at all.

I think the DSL 50 also uses the same PCB, but with only 2 output valve
sockets populated, but don't quote me on that cos my memory is a bit shit
when it comes to things like that.

** Thanks again.

I found this page that details the many problems techs have found with these
Marshalls.

http://www.lynx.net/~jc/TSL122.html

Quote from Malcolm:

" I have just been visiting your web site and had a look at your attempts
to deal with one of the most diabolical amps ever to see the light of day.

My advice to anyone given one of these thing to fix - drop it like a hot
potato and run in the opposite direction. These things were doomed the
moment they left the factory " .

Says it all really.



..... Phil
 
"Phil Allison" wrote in message news:bm01okFk9obU1@mid.individual.net...


"Gareth Magennis"
"Phil Allison"
"Gareth Magennis"


There is no reason why Marshall would not have these PCB's for sale.


** Double negatives like that are mind numbing.


The last one I bought cost me just short of Ł50 including VAT and
carriage.

** Was that long ago ?



They did have a policy of only selling things that might kill people to
bone fide engineers who wouldn't kill themselves or others with High
Voltage, so you might also have to prove you are not a numpty.


** Now, that is funny.

So * I * have to prove to Marshall that * I * know what I am doing
?????

They have SFA chance of ever proving the reverse.



If you're really stuck I have one here I could ship you, but with
carriage and import taxes and already paid VAT @20% now, its going to
end up bloody expensive.

** Thanks for the offer.

Is there anything special about ordering such a PCB ?

Or is the amp model number and serial number enough ?


Nothing special, just ask for a DSL 100 board.

Just for confirmation, both are marked JCM2-60-00.
The new board has two extra connectors, Con 15 and Con16, as well as a
relay which the old board does not. (Also Con 4 is not in the same
orientation)
This is probably so it can be used in the TSL 100 as well, the 3 channel
version.
Definitely not the same PCB at all.

I think the DSL 50 also uses the same PCB, but with only 2 output valve
sockets populated, but don't quote me on that cos my memory is a bit shit
when it comes to things like that.

** Thanks again.

I found this page that details the many problems techs have found with these
Marshalls.

http://www.lynx.net/~jc/TSL122.html

Quote from Malcolm:

" I have just been visiting your web site and had a look at your attempts
to deal with one of the most diabolical amps ever to see the light of day.

My advice to anyone given one of these thing to fix - drop it like a hot
potato and run in the opposite direction. These things were doomed the
moment they left the factory " .

Says it all really.






Well, what it says is what we already know, that a batch of faulty circuit
boards were manufactured.
Marshall have since redesigned it and the replacement seems to have sorted
the problem out.

What it also points out is that any bodge is likely to cost far more in
labour than simply replacing the board.
Unless you happen to live in Sydney perhaps.
(Last one I bought was something around Ł35 +carriage +tax, that was 2 or 3
years ago now)

And you would still be charging the customer a load of money for leaving a
faulty board in the amp.


Of course you could argue that Marshall should be offering a free exchange
replacement on such boards, but that is a different debate.



Cheers,


Gareth.
 
http://imageshack.com/a/img845/570/o62e.jpg


The old PCB is the top one.

Note Con15 below the bridge rectifier, it is connected to + and - of
rectifier.
Con 16 is below Con 8 and is just wired in paralell with it.

The old PCB has an LDR, the new one a relay.


There may be more differences, I haven't bothered to check thoroughly.



Gareth.
 
"Gareth Magennis"
"Phil Allison"

** Thanks again.

I found this page that details the many problems techs have found with
these
Marshalls.

http://www.lynx.net/~jc/TSL122.html

Quote from Malcolm:

" I have just been visiting your web site and had a look at your attempts
to deal with one of the most diabolical amps ever to see the light of day.

My advice to anyone given one of these thing to fix - drop it like a hot
potato and run in the opposite direction. These things were doomed the
moment they left the factory " .

Says it all really.



Well, what it says is what we already know, that a batch of faulty circuit
boards were manufactured.

** Wot - a single batch ??

1. How about 20 or 30 batches over a period of 5 or 6 years ?

2. How about publishing schems AND making many thousands of PCBs with 5.6k
grid suppressors substituted for 220k ?

3. Have about never informing any of their overseas agents about it ?

4. How about 10s of thousands of EL34s ( and OTs) destroyed by the stupid
problem ?

5. How about the hefty repair bills paid by Marshall owners and consequent
bad will generated against hard working amp techs who were deliberately NOT
informed of the REAL problem by the culprits - ie Marshall.


Marshall have since redesigned it and the replacement seems to have sorted
the problem out.

** You ARE fucking joking !!!!

You must be sucking those cunt's cocks so hard.


Of course you could argue that Marshall should be offering a free exchange
replacement on such boards, but that is a different debate.

** No it fucking is not.

It is nothing short of gross consumer fraud.



..... Phil
 
On 12/02/2014 10:20, Gareth Magennis wrote:
http://imageshack.com/a/img845/570/o62e.jpg


The old PCB is the top one.

Note Con15 below the bridge rectifier, it is connected to + and - of
rectifier.
Con 16 is below Con 8 and is just wired in paralell with it.

The old PCB has an LDR, the new one a relay.


There may be more differences, I haven't bothered to check thoroughly.



Gareth.

It would be nice to nail down exactly what the problem was with the pcb
manufacture. As China made, probably affects other makes, which at lower
voltages perhaps would take longer to emerge as a problem. I posited
NaCl salt contamination to the filler material as it seems to give the
right sort of temperature / conduction graph. The problem does not
require the amps to be stored in sheds or garages, ie dampish, to induce
the fault condition.
 
"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:bm142iFqv1lU1@mid.individual.net...
"Gareth Magennis"
"Phil Allison"

** Thanks again.

I found this page that details the many problems techs have found with
these
Marshalls.

http://www.lynx.net/~jc/TSL122.html

Quote from Malcolm:

" I have just been visiting your web site and had a look at your
attempts
to deal with one of the most diabolical amps ever to see the light of
day.

My advice to anyone given one of these thing to fix - drop it like a hot
potato and run in the opposite direction. These things were doomed the
moment they left the factory " .

Says it all really.



Well, what it says is what we already know, that a batch of faulty
circuit boards were manufactured.


** Wot - a single batch ??

1. How about 20 or 30 batches over a period of 5 or 6 years ?

2. How about publishing schems AND making many thousands of PCBs with
5.6k grid suppressors substituted for 220k ?

3. Have about never informing any of their overseas agents about it ?

4. How about 10s of thousands of EL34s ( and OTs) destroyed by the stupid
problem ?

5. How about the hefty repair bills paid by Marshall owners and
consequent bad will generated against hard working amp techs who were
deliberately NOT informed of the REAL problem by the culprits - ie
Marshall.


Marshall have since redesigned it and the replacement seems to have
sorted the problem out.

** You ARE fucking joking !!!!

You must be sucking those cunt's cocks so hard.


Of course you could argue that Marshall should be offering a free
exchange replacement on such boards, but that is a different debate.

** No it fucking is not.

It is nothing short of gross consumer fraud.



.... Phil

I'm not going to respond to that, it is disingenous on far too many levels.




Gareth.
 
On 12/02/2014 10:20, Gareth Magennis wrote:
http://imageshack.com/a/img845/570/o62e.jpg


The old PCB is the top one.

Note Con15 below the bridge rectifier, it is connected to + and - of
rectifier.
Con 16 is below Con 8 and is just wired in paralell with it.

The old PCB has an LDR, the new one a relay.


There may be more differences, I haven't bothered to check thoroughly.



Gareth.

Knowing how precious some guitarists are, I'd rather mechanically adapt
the original board rather than swap out to what may or may not be a
sound-wise eqivalent replacement board. I've been there before, having
spent out large spondulics for (not Marshall) a manufacturer's
replacemnt board and ended up in a god-awful slanging match with an
owner because the "sound" was all wrong and resulting with me being the
time and money loser.
 
As a matter of interest, how old is this amplifier?

It'll be part of the serial number.



Gareth.
 
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ldflvg$5tj$1@dont-email.me...
On 12/02/2014 10:20, Gareth Magennis wrote:
http://imageshack.com/a/img845/570/o62e.jpg


The old PCB is the top one.

Note Con15 below the bridge rectifier, it is connected to + and - of
rectifier.
Con 16 is below Con 8 and is just wired in paralell with it.

The old PCB has an LDR, the new one a relay.


There may be more differences, I haven't bothered to check thoroughly.



Gareth.



It would be nice to nail down exactly what the problem was with the pcb
manufacture. As China made, probably affects other makes, which at lower
voltages perhaps would take longer to emerge as a problem. I posited NaCl
salt contamination to the filler material as it seems to give the right
sort of temperature / conduction graph. The problem does not require the
amps to be stored in sheds or garages, ie dampish, to induce the fault
condition.

In this case the problem may have been exacerbated by incorrect value and
possibly temperature co-efficient type of resistors fitted, if Phil's link
is to be believed, so possibly a combination of problems, not a single one.

It would be unwise, IMHO, to assume ALL PCBs in the faulty batches ended up
suffering from this problem. Any contamination/faults may have been quite
clumpy in distribution, and/or down to a single individual during their
shift.

Who knows.




Cheers,


Gareth.
 
"Gareth Magennis"
"Phil Allison"

I found this page that details the many problems techs have found with
these Marshalls.

http://www.lynx.net/~jc/TSL122.html

Quote from Malcolm:

" I have just been visiting your web site and had a look at your
attempts
to deal with one of the most diabolical amps ever to see the light of
day.

My advice to anyone given one of these thing to fix - drop it like a
hot
potato and run in the opposite direction. These things were doomed the
moment they left the factory " .

Says it all really.



Well, what it says is what we already know, that a batch of faulty
circuit boards were manufactured.


** Wot - a single batch ??

1. How about 20 or 30 batches over a period of 5 or 6 years ?

2. How about publishing schems AND making many thousands of PCBs with
5.6k grid suppressors substituted for 220k ?

3. Have about never informing any of their overseas agents about it ?

4. How about 10s of thousands of EL34s ( and OTs) destroyed by the
stupid problem ?

5. How about the hefty repair bills paid by Marshall owners and
consequent bad will generated against hard working amp techs who were
deliberately NOT informed of the REAL problem by the culprits - ie
Marshall.


Marshall have since redesigned it and the replacement seems to have
sorted the problem out.

** You ARE fucking joking !!!!

You must be sucking those cunt's cocks so hard.


Of course you could argue that Marshall should be offering a free
exchange replacement on such boards, but that is a different debate.

** No it fucking is not.

It is nothing short of gross consumer fraud.


I'm not going to respond to that, it is disingenous on far too many
levels.

** It is all simple fact, you lying pommy cunt.

Points 1,2 & 3 are detailed in the link I posted - which I seriously
doubt you bothered to read.

Points 4 & 5 are the unavoidable consequential outcomes.

You have no response because you have been caught lying.

Again.

Fuck you.




..... Phil
 
"Gareth Magennis = Liar"
In this case the problem may have been exacerbated by incorrect value and
possibly temperature co-efficient type of resistors fitted,

** Regular carbon film types were fitted to early examples and later metal
film - neither were the culprits.

The first and worst case I saw ( a TSL 122 ) used metal film types.

FYI, fuckwit:

NTC resistors in the bias feed would have HELPED the problem.


.... Phil
 
On 02/11/2014 05:40 PM, Phil Allison wrote:
"Gareth Magennis"
"Phil Allison"
"Gareth Magennis"


There is no reason why Marshall would not have these PCB's for sale.


** Double negatives like that are mind numbing.


The last one I bought cost me just short of Ł50 including VAT and
carriage.

** Was that long ago ?



They did have a policy of only selling things that might kill people to
bone fide engineers who wouldn't kill themselves or others with High
Voltage, so you might also have to prove you are not a numpty.


** Now, that is funny.

So * I * have to prove to Marshall that * I * know what I am doing
?????

They have SFA chance of ever proving the reverse.



If you're really stuck I have one here I could ship you, but with
carriage and import taxes and already paid VAT @20% now, its going to
end up bloody expensive.

** Thanks for the offer.

Is there anything special about ordering such a PCB ?

Or is the amp model number and serial number enough ?


Nothing special, just ask for a DSL 100 board.

Just for confirmation, both are marked JCM2-60-00.
The new board has two extra connectors, Con 15 and Con16, as well as a
relay which the old board does not. (Also Con 4 is not in the same
orientation)
This is probably so it can be used in the TSL 100 as well, the 3 channel
version.
Definitely not the same PCB at all.

I think the DSL 50 also uses the same PCB, but with only 2 output valve
sockets populated, but don't quote me on that cos my memory is a bit shit
when it comes to things like that.


** Thanks again.

I found this page that details the many problems techs have found with these
Marshalls.

http://www.lynx.net/~jc/TSL122.html

Quote from Malcolm:

" I have just been visiting your web site and had a look at your attempts
to deal with one of the most diabolical amps ever to see the light of day.

My advice to anyone given one of these thing to fix - drop it like a hot
potato and run in the opposite direction. These things were doomed the
moment they left the factory " .

Says it all really.



.... Phil
Or read the article you showed us, which doesn't really say to give up,
after all.
 
On 02/12/2014 05:29 AM, Gareth Magennis wrote:
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ldflvg$5tj$1@dont-email.me...
On 12/02/2014 10:20, Gareth Magennis wrote:
http://imageshack.com/a/img845/570/o62e.jpg


The old PCB is the top one.

Note Con15 below the bridge rectifier, it is connected to + and - of
rectifier.
Con 16 is below Con 8 and is just wired in paralell with it.

The old PCB has an LDR, the new one a relay.


There may be more differences, I haven't bothered to check thoroughly.



Gareth.



It would be nice to nail down exactly what the problem was with the pcb
manufacture. As China made, probably affects other makes, which at lower
voltages perhaps would take longer to emerge as a problem. I posited NaCl
salt contamination to the filler material as it seems to give the right
sort of temperature / conduction graph. The problem does not require the
amps to be stored in sheds or garages, ie dampish, to induce the fault
condition.


In this case the problem may have been exacerbated by incorrect value and
possibly temperature co-efficient type of resistors fitted, if Phil's link
is to be believed, so possibly a combination of problems, not a single one.

It would be unwise, IMHO, to assume ALL PCBs in the faulty batches ended up
suffering from this problem. Any contamination/faults may have been quite
clumpy in distribution, and/or down to a single individual during their
shift.

Who knows.
Read the last 2 letters on Phil's link. The bias problem is on the
Overdrive board.
 

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