What do you do when the thermal fuse is blown?
Dennis Bathory-Kitsz
Occasionally we get in units where a transformer's internal thermal fuse
has opened up. For safety reasons, we replace the transformers -- but
it's irritating to have to bill a customer $50-$150 to replace a fuse.
Last week we got in a once-high-end Carver unit whose transformer is no
longer available. We can't find any explanation for the why the fuse
opened; there's no abnormal heat when the fuse is jumpered.
This problem is coming up more frequently as newer units' thermal fuses
fail due to overly conservative design or simply aging fuses. It seems
such a waste to junk an amp like this.
Is there a safe way to replace these internal fuses with external ones
bonded to the transformer? Is there some clever fuse replacement
technique we just don't know about?
(By "safe" I mean both "does it work" and "how many lawsuits have
resulted from shops doing this"?)
Dennis
--
Dennis Báthory-Kitsz
MaltedMedia: http://maltedmedia.com/
The Transitive Empire: http://maltedmedia.com/empire/
Kalvos & Damian's New Music Bazaar: http://kalvos.org/
Xavier van Unen
>Occasionally we get in units where a transformer's internal thermal fuse
>has opened up. For safety reasons, we replace the transformers -- but
>it's irritating to have to bill a customer $50-$150 to replace a fuse.
>
>Last week we got in a once-high-end Carver unit whose transformer is no
>longer available. We can't find any explanation for the why the fuse
>opened; there's no abnormal heat when the fuse is jumpered.
I have encountered this problem numerous times, and I don't even try to get
a replacement transformer anymore, as these are either extremely expensive
or obsolete (as you noticed yourself). I just short the thermal fuse with a
wire, and let the device (usually amps) run hot for a day or two. If it
survives this, well it will last a longer while yet.
I have had no complaints yet, but I do mention to my customers that I give
no guarantee on the repair, and that there is a minor risk involved (the
darn thing _can_ catch fire). But when presented with the low bill as
against the high bill as it would have been when the transformer was
replaced, people are very satisfied.
I must say this is on mainland Europe and not the USofA where people do dumb
things and then sue the heck out of you. So beware over there.
I've alse had a Carver throw its thermal fuse. It was over 10 years old.
These fuses have to pass all primary currents including high inrush currents
when the device switches on. Perhaps these things just age. I dunno.
Sony transformers are notorious too. Sometimes the thermal fuses are blown
when the device is connected to the wrong mains potential (400V instead of
230V or 230V instead of 110V).
Hope this is of any help.
Regards Xavier van Unen.
Steve Bell
Dennis Bathory-Kitsz wrote in message <37A58E...@maltedmedia.com>...
>Hi,
>
>Occasionally we get in units where a transformer's internal thermal fuse
>has opened up. For safety reasons, we replace the transformers -- but
>it's irritating to have to bill a customer $50-$150 to replace a fuse.
>
>Last week we got in a once-high-end Carver unit whose transformer is no
>longer available. We can't find any explanation for the why the fuse
>opened; there's no abnormal heat when the fuse is jumpered.
>
>fail due to overly conservative design or simply aging fuses. It seems
>such a waste to junk an amp like this.
>
>Is there a safe way to replace these internal fuses with external ones
>bonded to the transformer? Is there some clever fuse replacement
>technique we just don't know about?
>
>(By "safe" I mean both "does it work" and "how many lawsuits have
>resulted from shops doing this"?)
>
>Dennis
>
The only time I see this is on a few transformers that have 3 tags on the
primary, 2 are across the thermal fuse. You can buy replacement thermal
fuses in a thin rectangular wire ended format. Simply wire across the tags
and bond to the outer winding. Then soak test, monitor for excessive
current.
Steve Bell
Dennis Bathory-Kitsz
>
> I have had no complaints yet, but I do mention to my customers that I give
> no guarantee on the repair, and that there is a minor risk involved
>
> things and then sue the heck out of you. So beware over there.
Right indeed. I don't want this to come back to haunt me. It's not quite
as simple as warning of a 'minor risk' here! This wasn't a problem where
I am (Vermont) until the past 10 years, but with the influx of folks
from the cities, we've started to get a little more uncomfortable about
giving advice, something we could do with our neighbors.
Bedankt voor uw ideeen. Uitsteked dat Europa is niet nog lawsuit-happy.
(O, o, soory voor krom nederlands ... Ik heb in Amsterdam voor half jaar
gewoon, maar m'n nederlands is erg slecht!)
Groeten,
Dennis Bathory-Kitsz
>
> The only time I see this is on a few transformers that have 3 tags on the
> primary, 2 are across the thermal fuse. You can buy replacement thermal
> fuses in a thin rectangular wire ended format. Simply wire across the tags
> and bond to the outer winding. Then soak test, monitor for excessive
> current.
Yes, I've done the external thermal fuses (only) for myself now & then,
but I wondered if you know about any long-term issues, esp. how
manufacturers view this kind of thing (and why they do it that way to
start with)?
And any experience with the 'legal factor', considering that schematics
often mark these parts with those charming little triangulated
exclamation marks?
Lenny
>
> Xavier van Unen wrote:
> >
> > I have had no complaints yet, but I do mention to my customers that I give
> > no guarantee on the repair, and that there is a minor risk involved
> >
> > I must say this is on mainland Europe and not the USofA where people do dumb
> > things and then sue the heck out of you. So beware over there.
>
> Right indeed. I don't want this to come back to haunt me. It's not quite
> as simple as warning of a 'minor risk' here! This wasn't a problem where
> I am (Vermont) until the past 10 years, but with the influx of folks
> from the cities, we've started to get a little more uncomfortable about
> giving advice, something we could do with our neighbors.
>
> Bedankt voor uw ideeen. Uitsteked dat Europa is niet nog lawsuit-happy.
> (O, o, soory voor krom nederlands ... Ik heb in Amsterdam voor half jaar
> gewoon, maar m'n nederlands is erg slecht!)
>
> Groeten,
>
> --
> Dennis Báthory-Kitsz
> MaltedMedia: http://maltedmedia.com/
> The Transitive Empire: http://maltedmedia.com/empire/
> Kalvos & Damian's New Music Bazaar: http://kalvos.org/
when an output shorts, and I agree it is a senseless waste to discard
the entire unit for this. But I always make sure that the altered
transformer runs cool after the repair, and also that I've installed a
small line fuse if none was present before. I would NEVER give a
customer informational ammunition like this though.
With the completion of a repair done in this fashion I would have no
reason to doubt the safety issues here, but you have to realize that in
this country if you tell someone that their repair might "catch fire",
they will be on the phone with one of those TV lawyers before they even
plug the damn thing in.
You might as well burn your own house down and go live in a cave,
because thats exactly where you'll be after one of those dirtbags
finishes with you anyway.
Lenny Stein.
Wild Bill
hi.. for some of these types of xfmrs, the thermal fuse can be removed and
replaced.. if it's temperature is marked on the device. Sometimes digging
and trimming does more damage though.
If the choice is made by the customer to have you repair a non-serviceable
item, they should be grateful to have that done for them.. but then again,
well it's obvious that many aren't.
Some people do some really stupid stuff to damage their own equipment. Then
they look for someone to blame.. because life has been so unfair to them.
That brings me to a reason why the manufacturers specify a xfmr with
thermal protection, because they understand that physics is the most
misunderstood knowlege of all.. and they'd like to stay in business too.
It's their way of trying to make an idiot-proof product, even though they
know that it's virtually impossible to do.
Right now, there is someone that left home with their 400W stereo system
(with a dust cover on it) in a closed cabinet..blasting to annoy the
neighbors, until they get back.
Adding a circuit breaker and a current fuse would make a reasonably safe
repair if the internal device is bypassed. This method might be easier than
trying to retrofit a different type of thermal device directly to the xfmr.
An alternative would be to send the xfmr to a rebuilder, but that would
cost about the same.. or more, in many instances.
cheers
WB
....................
Dennis Bathory-Kitsz <bat...@maltedmedia.com> wrote in article
<37A58E...@maltedmedia.com>...
> Hi,
>
> Occasionally we get in units where a transformer's internal thermal fuse
> has opened up. For safety reasons, we replace the transformers -- but
> it's irritating to have to bill a customer $50-$150 to replace a fuse.
>
> Last week we got in a once-high-end Carver unit whose transformer is no
> longer available. We can't find any explanation for the why the fuse
> opened; there's no abnormal heat when the fuse is jumpered.
>
> This problem is coming up more frequently as newer units' thermal fuses
> fail due to overly conservative design or simply aging fuses. It seems
> such a waste to junk an amp like this.
>
> Is there a safe way to replace these internal fuses with external ones
> bonded to the transformer? Is there some clever fuse replacement
> technique we just don't know about?
>
> (By "safe" I mean both "does it work" and "how many lawsuits have
> resulted from shops doing this"?)
>
BOB URZ
out, and a bigger pain to re-install them. You have to put a screwdriver or
such down where the
old fuse was to widen the windings so you can get the new one in. Liability
is an issue. I have done this mainly for myself or people I know. Very few
for customers.
It worries me to just bypass the fuse. I have about a 75% success rate doing
this.
I usually get them from MCM.
BOB URZ
Mike Tomlinson
<bat...@maltedmedia.com> writes
>
>And any experience with the 'legal factor', considering that schematics
>often mark these parts with those charming little triangulated
>exclamation marks?
along with wording similar to 'Safety Critical Part - Replace with
Manufacturer's Approved Part Only" or similar, and things start to look
a little shaky legally.
I've repaired xformers in the manner suggested by Steve Bell for stuff
for personal use, but when dealing with customer equipment, I've played
safe and replaced the part or junked the unit.
I seem to remember some Philips monochrome monitors had the thermal fuse
in a clear plastic housing which made it easy to identify and replace -
almost as if they expected it to be a serviceable part.
--
Mike Tomlinson