Hi All
My Aleph 5 clone has broken down again....though this time i'm getting quicker at narrowing down the problem area..
This amp has been running faultless ly for nearly a year (i think )since a rebuild.
When it runs heatsinks are at abt 45deg C -fan cooled
This time the neg rail fuse keeps blowing.
I've ripped out all the output mosfets and replace one by one until the last one which causes the problem...
Its not the mosfet as I have tried about 6 in this location and it always blows the fuse . (seems to be ok without this mosfet left out)
The mosfet in question is the one which is fed from the base of Q4 (ztx450 )
When power is applied the 1ohm source resistor for the mosfet also glows (pretty!) along with the fuse till it blows.
Any ideas?
Replace Q4 or something else?
Hard to measure voltages with blown fuse.
Many thanks in advance, as per usual I run out of talent pretty quick
Cheers
My Aleph 5 clone has broken down again....though this time i'm getting quicker at narrowing down the problem area..
This amp has been running faultless ly for nearly a year (i think )since a rebuild.
When it runs heatsinks are at abt 45deg C -fan cooled
This time the neg rail fuse keeps blowing.
I've ripped out all the output mosfets and replace one by one until the last one which causes the problem...
Its not the mosfet as I have tried about 6 in this location and it always blows the fuse . (seems to be ok without this mosfet left out)
The mosfet in question is the one which is fed from the base of Q4 (ztx450 )
When power is applied the 1ohm source resistor for the mosfet also glows (pretty!) along with the fuse till it blows.
Any ideas?
Replace Q4 or something else?
Hard to measure voltages with blown fuse.
Many thanks in advance, as per usual I run out of talent pretty quick
Cheers
OOOOOPPSSS
CORRECTION
Sorry I'm getting tired.
Its a pos rail mosfet
I'll re examine and post correct info
CORRECTION
Sorry I'm getting tired.
Its a pos rail mosfet
I'll re examine and post correct info
yup
agree with AS
throrough check of heatsink surface , (non)continuity test and - in your case as must - measuring temp of all mosfets (at mid pin) , to be sure they're all in 10% bracket
just in case - sure that all (on same rail ) need to be matched
agree with AS
throrough check of heatsink surface , (non)continuity test and - in your case as must - measuring temp of all mosfets (at mid pin) , to be sure they're all in 10% bracket
just in case - sure that all (on same rail ) need to be matched
Hi Guys = you are quick off the mark.
Yes the fets are matched.
No short to heatsink
I attach a diagram indicating the suspect mosfet location.
The diagram is that which was used for earlier trouble shooting (from an Aleph 3 ) (partial circuit only )
but circuit layout is the same in this case.
Any ideas ?
Yes the fets are matched.
No short to heatsink
I attach a diagram indicating the suspect mosfet location.
The diagram is that which was used for earlier trouble shooting (from an Aleph 3 ) (partial circuit only )
but circuit layout is the same in this case.
Any ideas ?
Attachments
Just an update
this seems to be a similar problem to that of last time - see aleph 5 and Dolphin sounds. June /july 2013
Zen mod you assisted last time too
Many thanks
That time the problem was solved by a complete rebuild- cant do that this time (yet)
this seems to be a similar problem to that of last time - see aleph 5 and Dolphin sounds. June /july 2013
Zen mod you assisted last time too
Many thanks
That time the problem was solved by a complete rebuild- cant do that this time (yet)
no reason (change that small bjt whatever - it can be damaged ) except physical ones - bad thermal contact with surface at that particular mosfet position
temp probe would reveal any possible discrepancy between mosfets
temp probe would reveal any possible discrepancy between mosfets
Maybe the 0.47 ohm resistor for that MOSFET has a problem. Maybe there is a bad connection to all the other MOSFET gates in the upper side, so that one is doing all the work.
"Its not the mosfet as I have tried about 6 in this location and it always blows the fuse . (seems to be ok without this mosfet left out)"
"When power is applied the 1ohm source resistor for the mosfet also glows (pretty!) along with the fuse till it blows."
this tells me that there is a huge amount of current going here. and since there is no current with the mosfet out. it tells me that the conection between the mosfet and ground has a role in your trouble. (i doubt it's the mosfet itself since you tried 6 of them).
"When power is applied the 1ohm source resistor for the mosfet also glows (pretty!) along with the fuse till it blows."
this tells me that there is a huge amount of current going here. and since there is no current with the mosfet out. it tells me that the conection between the mosfet and ground has a role in your trouble. (i doubt it's the mosfet itself since you tried 6 of them).
Hi All
I've been a bit distracted and haven't had much of a chance to post.
Anyway
Output mosfets were blown.
I'm awaiting delivery of a new batch for matching and installation.
The suggestion of replacing or at least checking the source resistors is a good pone .
a few of those blown as well - though I never got to see them "glow"
I'll post again when its all repaired.
Many thanks for help so far
Cheers
I've been a bit distracted and haven't had much of a chance to post.
Anyway
Output mosfets were blown.
I'm awaiting delivery of a new batch for matching and installation.
The suggestion of replacing or at least checking the source resistors is a good pone .
a few of those blown as well - though I never got to see them "glow"
I'll post again when its all repaired.
Many thanks for help so far
Cheers
Hi All
I've managed to get back to it.
i ordered some 30 irfp240's off ebay and after receiving them
did the matching bit.
Vgs varied from 3.3v to 4.7 , but in between ended up with about 5-6 sets of 3 mosfets with a variance of under 0.05v per each set.
note my aleph uses 6 output mosfets per channel. 3 upper - 3 lower.
Now the interesting bit.
i started by have 2 mosfets added at a time (1 upper - 1 lower )
and tested for operation and played music through "sacrificial" speak-
all good - offset low. sounded ok.
added another pair and often 1 mosfet would blow (no voltage across the 1ohm source resistor connected to each mosfet.
front end appears fine.
eventually after having repeated the process - I've ended up with what seems to be a working amp again- though i will let it run for a while before connecting to main speakers.
Question.
Why would output mosfets "blow" at turn on?
After blowing - i retested the suspect mosfet for Vgs and found them now to be between 0.1v and 1v...? instead of 3-4v..
what might be happening hear?
is there someway to protect the mosfets at turn-on?
Yes i tested for shorts to heatsink and tested each source resistor after each fail
Any clues?
Thanks in advance.
I've managed to get back to it.
i ordered some 30 irfp240's off ebay and after receiving them
did the matching bit.
Vgs varied from 3.3v to 4.7 , but in between ended up with about 5-6 sets of 3 mosfets with a variance of under 0.05v per each set.
note my aleph uses 6 output mosfets per channel. 3 upper - 3 lower.
Now the interesting bit.
i started by have 2 mosfets added at a time (1 upper - 1 lower )
and tested for operation and played music through "sacrificial" speak-
all good - offset low. sounded ok.
added another pair and often 1 mosfet would blow (no voltage across the 1ohm source resistor connected to each mosfet.
front end appears fine.
eventually after having repeated the process - I've ended up with what seems to be a working amp again- though i will let it run for a while before connecting to main speakers.
Question.
Why would output mosfets "blow" at turn on?
After blowing - i retested the suspect mosfet for Vgs and found them now to be between 0.1v and 1v...? instead of 3-4v..
what might be happening hear?
is there someway to protect the mosfets at turn-on?
Yes i tested for shorts to heatsink and tested each source resistor after each fail
Any clues?
Thanks in advance.
I can think of crooked mosfets only ........ or some mistake made during amp making
even without gate to source protective zenners , with properly made amp , mosfets are more then safe
give us pictures
even without gate to source protective zenners , with properly made amp , mosfets are more then safe
give us pictures
Hi All
I've managed to get back to it.
i ordered some 30 irfp240's off ebay and after receiving them
did the matching bit.
Vgs varied from 3.3v to 4.7 , but in between ended up with about 5-6 sets of 3 mosfets with a variance of under 0.05v per each set.
note my aleph uses 6 output mosfets per channel. 3 upper - 3 lower.
Now the interesting bit.
i started by have 2 mosfets added at a time (1 upper - 1 lower )
and tested for operation and played music through "sacrificial" speak-
all good - offset low. sounded ok.
added another pair and often 1 mosfet would blow (no voltage across the 1ohm source resistor connected to each mosfet.
front end appears fine.
eventually after having repeated the process - I've ended up with what seems to be a working amp again- though i will let it run for a while before connecting to main speakers.
Question.
Why would output mosfets "blow" at turn on?
After blowing - i retested the suspect mosfet for Vgs and found them now to be between 0.1v and 1v...? instead of 3-4v..
what might be happening hear?
is there someway to protect the mosfets at turn-on?
Yes i tested for shorts to heatsink and tested each source resistor after each fail
Any clues?
Thanks in advance.
I've managed to get back to it.
i ordered some 30 irfp240's off ebay and after receiving them
did the matching bit.
Vgs varied from 3.3v to 4.7 , but in between ended up with about 5-6 sets of 3 mosfets with a variance of under 0.05v per each set.
note my aleph uses 6 output mosfets per channel. 3 upper - 3 lower.
Now the interesting bit.
i started by have 2 mosfets added at a time (1 upper - 1 lower )
and tested for operation and played music through "sacrificial" speak-
all good - offset low. sounded ok.
added another pair and often 1 mosfet would blow (no voltage across the 1ohm source resistor connected to each mosfet.
front end appears fine.
eventually after having repeated the process - I've ended up with what seems to be a working amp again- though i will let it run for a while before connecting to main speakers.
Question.
Why would output mosfets "blow" at turn on?
After blowing - i retested the suspect mosfet for Vgs and found them now to be between 0.1v and 1v...? instead of 3-4v..
what might be happening hear?
is there someway to protect the mosfets at turn-on?
Yes i tested for shorts to heatsink and tested each source resistor after each fail
Any clues?
Thanks in advance.
I have a theory...
1. Some the mosfets that have failed at turn on were probably dodgy to start with....that's life I suspect.
2. some of the failed mosfets could be due to assembly error - dodgy sil-pads now replaced with brand new ones (though i did test for shorts to heatsink..).
If not shorted - the thermal bond is now hopefully up to scratch
3. Original cause of failure - these things run hot and I suspect that due to the quality (tolerance) of the source resistors which are not high tolerance that some current hogging of some mosfets has occurred over the years that the amp has been working flawlessly and that the hottest mosfets have basically given up.
Finding higher powered 1% resistors is difficult locally and thanks to the internet i have ordered 100 of them at a reasonable price.
These upon arrival will replace the crappy ones currently installed and hopefully the current hogging will be reduced .
Whilst the measured vgs of the fets is good , is it not great in situ - with enough variance to be possibly attributed to low tolerance source resistors. (i think)
They are very noticeable different in surface temperature during operation.
i'll keep you posted.
One by-product of this whole exercise is that I have hardly used the stereo whilst the aleph has been out of action.
It makes THAT much difference.
Let me make this clear, the yearly breakdown is not the fault of the aleph but rather mine and to some extent probably crappy components.
I have no way of comparing this thing to a supposedly better amp......and as such am a lucky man..it may be an old design...but its a keeper...
Thanks Nelson.
and thanks for the support from others.
1. Some the mosfets that have failed at turn on were probably dodgy to start with....that's life I suspect.
2. some of the failed mosfets could be due to assembly error - dodgy sil-pads now replaced with brand new ones (though i did test for shorts to heatsink..).
If not shorted - the thermal bond is now hopefully up to scratch
3. Original cause of failure - these things run hot and I suspect that due to the quality (tolerance) of the source resistors which are not high tolerance that some current hogging of some mosfets has occurred over the years that the amp has been working flawlessly and that the hottest mosfets have basically given up.
Finding higher powered 1% resistors is difficult locally and thanks to the internet i have ordered 100 of them at a reasonable price.
These upon arrival will replace the crappy ones currently installed and hopefully the current hogging will be reduced .
Whilst the measured vgs of the fets is good , is it not great in situ - with enough variance to be possibly attributed to low tolerance source resistors. (i think)
They are very noticeable different in surface temperature during operation.
i'll keep you posted.
One by-product of this whole exercise is that I have hardly used the stereo whilst the aleph has been out of action.
It makes THAT much difference.
Let me make this clear, the yearly breakdown is not the fault of the aleph but rather mine and to some extent probably crappy components.
I have no way of comparing this thing to a supposedly better amp......and as such am a lucky man..it may be an old design...but its a keeper...
Thanks Nelson.
and thanks for the support from others.
Hi All
After quite a few distractions , The Aleph is singing again,
A couple of blown Mosfets and a dud 9610...
One advantage of the unit being out of commission for an extended period of time is when its hooked into the system and its like getting a brand new amp.
It just plays beautifully ,
Thanks to all for your assistance.
However an interesting problem
All the output mosfets were matched using the method outlined by Nelson on PASS site
They are all within 0.05v Vgs
until installed in situ and fired up, then the Vgs will vary wildly from device to device and even in a different location if i move them around within the same channel...
I don't know why.
Source resistors are at 1%.
What I've ended up doing is matching them in place (takes ages -not fun) and at full operating voltage - and generally the match across the mosfets is now within 0.05v....what gives?
Cheers to all
oh and next task is building another Aleph to power the midrange units ....I have lots of parts to use up..
After quite a few distractions , The Aleph is singing again,
A couple of blown Mosfets and a dud 9610...
One advantage of the unit being out of commission for an extended period of time is when its hooked into the system and its like getting a brand new amp.
It just plays beautifully ,
Thanks to all for your assistance.
However an interesting problem
All the output mosfets were matched using the method outlined by Nelson on PASS site
They are all within 0.05v Vgs
until installed in situ and fired up, then the Vgs will vary wildly from device to device and even in a different location if i move them around within the same channel...
I don't know why.
Source resistors are at 1%.
What I've ended up doing is matching them in place (takes ages -not fun) and at full operating voltage - and generally the match across the mosfets is now within 0.05v....what gives?
Cheers to all
oh and next task is building another Aleph to power the midrange units ....I have lots of parts to use up..
most likely you didn't ensure same temp. conditions for all of them , during matching
in situ they're all on same plank of metal
in situ they're all on same plank of metal
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