sci.electronics.repair@googlegroups.com

Today's topics:

* Blew another damn transformer on my Trane XB80 - 5 messages, 4 authors
http://groups.google.com/group/sci.electronics.repair/t/f883cd09a3a0b791?hl=en
* Thinking and Analysis based on Marxism & Literature - 2 messages, 2 authors
http://groups.google.com/group/sci.electronics.repair/t/a3d52715af04fe0e?hl=en
* Gareth Magennis is xxxxxxxxxxxx - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/aff797bedba2c908?hl=en
* White coating over part of surface mount amp - 2 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/150806fccb06a046?hl=en

==============================================================================
TOPIC: Blew another damn transformer on my Trane XB80
http://groups.google.com/group/sci.electronics.repair/t/f883cd09a3a0b791?hl=en
==============================================================================

== 1 of 5 ==
Date: Sat, Apr 9 2011 6:55 pm
From: Steve Turner

On 4/9/2011 7:29 PM, Jim Yanik wrote:
> "robb"<some@where.on.net> wrote in
> news:WfKdnQOvu_d2bz3QnZ2dnUVZ_uadnZ2d@earthlink.com:
>
>> "Steve Turner" wrote in message news:inoakf$qin$1@dont-email.me...
>>
>>> A continuation of the "Why does the 115V->24V transformer keep
>>> blowing on my Trane XB80?" discussion I started on 04/02/2011.
>>>
>>> Yep, My A/C unit blew another transformer. Pictures (and wiring
>>> diagram) here:
>>>
>>> http://www.flickr.com/photos/bbqboyee/sets/72157626457562742/
>>>
>>> Trane's manual for the unit is here (for perhaps better viewing of
>>> the wiring diagrams that I also copied to my above flickr site as
>>> jpg images):
>>>
>>>
>>>
>> http://www.trane.com/webcache/un/furnaces%20%28furn%29/product/22-1666-
>> 07_04012009.pdf
>>>
>>> As you can probably see in the pictures, there is visible charring
>>> of the 115V leads going into the transformer, and of course the 115V
>>> circuit is open (again). If you didn't see my first thread, this is
>>> the third transformer the unit has blown. In the previous
>>> discussion, it was discussed that perhaps the first one just blew
>>> because of old age (6 years), and the second blew because it wasn't
>>> a proper replacement (poor quality, made in China, etc.). This
>>> third unit is most certainly a proper replacement, and it's most
>>> certainly indicative of a real problem I have somewhere else in the
>>> unit. I didn't see any such charring on the previous two units, at
>>> least not like this.
>>>
>>> I never got a real chance to test out the system after installing
>>> this third transformer. We had cool weather for several days, and I
>>> never tried to force the system to come on so I could monitor it;
>>> that was probably a mistake. Unfortunately, I was also absent from
>>> the premises during the extended times when the unit was most likely
>>> operational, so that didn't help either. However, my family tells me
>>> that it WAS working and cooling the house rather nicely, for at
>>> least a day, perhaps two. I'm getting 115V in all the right places,
>>> so it doesn't look like an over-voltage condition to me. Perhaps
>>> it's an overheating condition? It looks to me like the only real
>>> load on this circuit is the blower motor; could the motor be causing
>>> this? The blower spins freely when I turn it by hand. Start
>>> capacitor on the motor maybe? Relay on the control board perhaps?
>
> a bad start cap would not affect the 24v control transformer,that just
> powers the controller board and relays.
> either something is loading the transformer or a problem with input
> voltage.
>>>
>>
>> Just a thought,
>>
>> When you put the new transformer in does the "Diagnostic Light" LED
>> turn on ?
>> Does the LED blink or flash in one of the patterns indicated in the
>> "diagnostic codes" section that you posted a link to ?
>>
>> The "diagnostic codes" imply that the control board can detect
>> several of the problems mentioned by others.
>> Maybe a good starting point as there is not enough time to test with
>> test equipment.
>>
>> robb
>>
>>
>
> a line voltage monitor may be needed to see if there's some short-term
> overvoltage applied to the transformer,and a oscilloscope may determine if
> the input waveform is sinusoidal or otherwise,because 60hz iron core
> tranformers don't like extreme distortion on their input,it gets converted
> to heat,not output voltage. a DMM will not show line distortion or short
> term overvoltages.
> are the wires burned close to the transformer,or over their entire length?

I peeled the insulation back from the hot and neutral wires and the burning
only occurred right at the terminals, no more than 1/4" into the wiring.

== 2 of 5 ==
Date: Sat, Apr 9 2011 7:06 pm
From: John Robertson

Steve Turner wrote:
> On 4/9/2011 7:29 PM, Jim Yanik wrote:
>> "robb"<some@where.on.net> wrote in
>> news:WfKdnQOvu_d2bz3QnZ2dnUVZ_uadnZ2d@earthlink.com:
>>
>>> "Steve Turner" wrote in message news:inoakf$qin$1@dont-email.me...
>>>
>>>> A continuation of the "Why does the 115V->24V transformer keep
>>>> blowing on my Trane XB80?" discussion I started on 04/02/2011.
>>>>
>>>> Yep, My A/C unit blew another transformer. Pictures (and wiring
>>>> diagram) here:
>>>>
>>>> http://www.flickr.com/photos/bbqboyee/sets/72157626457562742/
>>>>
>>>> Trane's manual for the unit is here (for perhaps better viewing of
>>>> the wiring diagrams that I also copied to my above flickr site as
>>>> jpg images):
>>>>
>>>>
>>>>
>>> http://www.trane.com/webcache/un/furnaces%20%28furn%29/product/22-1666-
>>> 07_04012009.pdf
>>>>
>>>> As you can probably see in the pictures, there is visible charring
>>>> of the 115V leads going into the transformer, and of course the 115V
>>>> circuit is open (again). If you didn't see my first thread, this is
>>>> the third transformer the unit has blown. In the previous
>>>> discussion, it was discussed that perhaps the first one just blew
>>>> because of old age (6 years), and the second blew because it wasn't
>>>> a proper replacement (poor quality, made in China, etc.). This
>>>> third unit is most certainly a proper replacement, and it's most
>>>> certainly indicative of a real problem I have somewhere else in the
>>>> unit. I didn't see any such charring on the previous two units, at
>>>> least not like this.
>>>>
>>>> I never got a real chance to test out the system after installing
>>>> this third transformer. We had cool weather for several days, and I
>>>> never tried to force the system to come on so I could monitor it;
>>>> that was probably a mistake. Unfortunately, I was also absent from
>>>> the premises during the extended times when the unit was most likely
>>>> operational, so that didn't help either. However, my family tells me
>>>> that it WAS working and cooling the house rather nicely, for at
>>>> least a day, perhaps two. I'm getting 115V in all the right places,
>>>> so it doesn't look like an over-voltage condition to me. Perhaps
>>>> it's an overheating condition? It looks to me like the only real
>>>> load on this circuit is the blower motor; could the motor be causing
>>>> this? The blower spins freely when I turn it by hand. Start
>>>> capacitor on the motor maybe? Relay on the control board perhaps?
>>
>> a bad start cap would not affect the 24v control transformer,that just
>> powers the controller board and relays.
>> either something is loading the transformer or a problem with input
>> voltage.
>>>>
>>>
>>> Just a thought,
>>>
>>> When you put the new transformer in does the "Diagnostic Light" LED
>>> turn on ?
>>> Does the LED blink or flash in one of the patterns indicated in the
>>> "diagnostic codes" section that you posted a link to ?
>>>
>>> The "diagnostic codes" imply that the control board can detect
>>> several of the problems mentioned by others.
>>> Maybe a good starting point as there is not enough time to test with
>>> test equipment.
>>>
>>> robb
>>>
>>>
>>
>> a line voltage monitor may be needed to see if there's some short-term
>> overvoltage applied to the transformer,and a oscilloscope may
>> determine if
>> the input waveform is sinusoidal or otherwise,because 60hz iron core
>> tranformers don't like extreme distortion on their input,it gets
>> converted
>> to heat,not output voltage. a DMM will not show line distortion or short
>> term overvoltages.
>> are the wires burned close to the transformer,or over their entire
>> length?
>
> I peeled the insulation back from the hot and neutral wires and the
> burning only occurred right at the terminals, no more than 1/4" into the
> wiring.
>

So the problem is the joint of the transformer wiring to the lugs. They
may have cold solder joints, or the lug may be slightly loose - enough
to crack the solder connection over time. Your transformer may still be
good!

When you are examining the transformer wire make sure it is stripped
enough to get good solder coverage. Burn off the insulation (enamel) -
do not sand, scrape, or try to erode it because if you scratch the wire
it will break at the scratch.

Re-solder the transformer connectors after first making sure the wire
has at least two complete wraps around the solder lug and the solder
makes a good meniscus joint to the wire and lug. Also use a good grade
of solder, not regular 60/40, find some 63/37 solder (Kester is best) -
this solder resists cold solder joints due to movement when cooling by
solidifying very fast.

John :-#)#

--
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

== 3 of 5 ==
Date: Sat, Apr 9 2011 7:22 pm
From: "Phil Allison"

"robb"

>
> Yep, My A/C unit blew another transformer. Pictures (and wiring diagram)
> here:
>
> http://www.flickr.com/photos/bbqboyee/sets/72157626457562742/
>
> http://www.trane.com/webcache/un/furnaces%20%28furn%29/product/22-1666-07_04012009.pdf
>
> As you can probably see in the pictures, there is visible charring of the
> 115V leads going into the transformer, and of course the 115V circuit is
> open (again).

** From the damage to the tranny visible in the photos - the primary has
developed an internal short ( due to insulation failure) and since there is
no fuse link in series, the resulting current was high enough to make an
exposed wire leading to the terminals explode.

An internal short could develop due to heat alone because of an overload on
the tranny - but this requires a fault to exist on the secondary side which
seems not to be the case.

High voltage spikes on the primary could also cause insulation failure
leading to the damage seen in the pics - lightning does this sort of thing.
So also could back emfs from the blower fan if the is a bad connection in
the AC supply feed.

I suggest you provide the next replacement for that vulnerable tranny with
some "protection" - firstly an in-line fuse of say 1/4 amp AND a
capacitor wired across the primary of say 1uF rated for continuous use
across the AC supply.

If there is an overload on the tranny, the fuse will blow.

The 1uF capacitor should suppress spike voltages enough to save the tranny
from harm.

..... Phil

== 4 of 5 ==
Date: Sat, Apr 9 2011 7:54 pm
From: Grant

On Sat, 09 Apr 2011 20:55:37 -0500, Steve Turner <bbqboyee@swtacobell.net.invalid> wrote:

>On 4/9/2011 7:29 PM, Jim Yanik wrote:
>> "robb"<some@where.on.net> wrote in
>> news:WfKdnQOvu_d2bz3QnZ2dnUVZ_uadnZ2d@earthlink.com:
>>
>>> "Steve Turner" wrote in message news:inoakf$qin$1@dont-email.me...
>>>
>>>> A continuation of the "Why does the 115V->24V transformer keep
>>>> blowing on my Trane XB80?" discussion I started on 04/02/2011.
>>>>
>>>> Yep, My A/C unit blew another transformer. Pictures (and wiring
>>>> diagram) here:
>>>>
>>>> http://www.flickr.com/photos/bbqboyee/sets/72157626457562742/
>>>>
>>>> Trane's manual for the unit is here (for perhaps better viewing of
>>>> the wiring diagrams that I also copied to my above flickr site as
>>>> jpg images):
>>>>
>>>>
>>>>
>>> http://www.trane.com/webcache/un/furnaces%20%28furn%29/product/22-1666-
>>> 07_04012009.pdf
>>>>
>>>> As you can probably see in the pictures, there is visible charring
>>>> of the 115V leads going into the transformer, and of course the 115V
>>>> circuit is open (again). If you didn't see my first thread, this is
>>>> the third transformer the unit has blown. In the previous
>>>> discussion, it was discussed that perhaps the first one just blew
>>>> because of old age (6 years), and the second blew because it wasn't
>>>> a proper replacement (poor quality, made in China, etc.). This
>>>> third unit is most certainly a proper replacement, and it's most
>>>> certainly indicative of a real problem I have somewhere else in the
>>>> unit. I didn't see any such charring on the previous two units, at
>>>> least not like this.
>>>>
>>>> I never got a real chance to test out the system after installing
>>>> this third transformer. We had cool weather for several days, and I
>>>> never tried to force the system to come on so I could monitor it;
>>>> that was probably a mistake. Unfortunately, I was also absent from
>>>> the premises during the extended times when the unit was most likely
>>>> operational, so that didn't help either. However, my family tells me
>>>> that it WAS working and cooling the house rather nicely, for at
>>>> least a day, perhaps two. I'm getting 115V in all the right places,
>>>> so it doesn't look like an over-voltage condition to me. Perhaps
>>>> it's an overheating condition? It looks to me like the only real
>>>> load on this circuit is the blower motor; could the motor be causing
>>>> this? The blower spins freely when I turn it by hand. Start
>>>> capacitor on the motor maybe? Relay on the control board perhaps?
>>
>> a bad start cap would not affect the 24v control transformer,that just
>> powers the controller board and relays.
>> either something is loading the transformer or a problem with input
>> voltage.
>>>>
>>>
>>> Just a thought,
>>>
>>> When you put the new transformer in does the "Diagnostic Light" LED
>>> turn on ?
>>> Does the LED blink or flash in one of the patterns indicated in the
>>> "diagnostic codes" section that you posted a link to ?
>>>
>>> The "diagnostic codes" imply that the control board can detect
>>> several of the problems mentioned by others.
>>> Maybe a good starting point as there is not enough time to test with
>>> test equipment.
>>>
>>> robb
>>>
>>>
>>
>> a line voltage monitor may be needed to see if there's some short-term
>> overvoltage applied to the transformer,and a oscilloscope may determine if
>> the input waveform is sinusoidal or otherwise,because 60hz iron core
>> tranformers don't like extreme distortion on their input,it gets converted
>> to heat,not output voltage. a DMM will not show line distortion or short
>> term overvoltages.
>> are the wires burned close to the transformer,or over their entire length?
>
>I peeled the insulation back from the hot and neutral wires and the burning
>only occurred right at the terminals, no more than 1/4" into the wiring.

Is that a dual primary 115V (230V) xformer? Did you wire both primaries
in parallel for 115V operation?

Grant.

== 5 of 5 ==
Date: Sat, Apr 9 2011 11:00 pm
From: "Phil Allison"

"Phil Allison"

> firstly an in-line fuse of say 1/4 amp ....

** Must be a "slo-blo" type fuse.

.... Phil

==============================================================================
TOPIC: Thinking and Analysis based on Marxism & Literature
http://groups.google.com/group/sci.electronics.repair/t/a3d52715af04fe0e?hl=en
==============================================================================

== 1 of 2 ==
Date: Sat, Apr 9 2011 7:12 pm
From: Mukunda Lohani

For getting good knowledge about Marxism and Literature, Marx & his
Opinions to sharpen thinking analytically, don't forget to click on
the website given below:-
www.analyzethink.blogspot.com

== 2 of 2 ==
Date: Sat, Apr 9 2011 11:41 pm
From: "Michael A. Terrell"

Mukunda Lohani wrote:
>
> Grocho Marx & his
> brothers.

--
You can't fix stupid. You can't even put a Band-Aid� on it, because it's
Teflon coated.

==============================================================================
TOPIC: Gareth Magennis is xxxxxxxxxxxx
http://groups.google.com/group/sci.electronics.repair/t/aff797bedba2c908?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Apr 9 2011 8:18 pm
From: "Phil Allison"

"Meat Plow"
>
> I cried the day Hitachi quit manufacturing the 2SK49 / 2SJ135 pairs. I
> have one old SCS 350w/ch power amp that uses them. I acquired it with a
> blow channel back in the late 90's. It wasn't easy back then to find
> replacements. I imagine it's probably a lot easier these days to find NOS
> replacements. Maybe even a sub is made today?

** Finding NOS for those numbers is nigh impossible now.

But the Semelab BUZ900 and BUZ905 lateral mosfets are near identical.

Where devices operate in parallel, best not mix the numbers up -
particularly if there are no source ballast resistors.

.... Phil

==============================================================================
TOPIC: White coating over part of surface mount amp
http://groups.google.com/group/sci.electronics.repair/t/150806fccb06a046?hl=en
==============================================================================

== 1 of 2 ==
Date: Sun, Apr 10 2011 12:27 am
From: "N_Cook"

Jim Yanik <jyanik@abuse.gov> wrote in message
news:Xns9EC292B4E862Bjyaniklocalnetcom@216.168.3.44...
> "N_Cook" <diverse@tcp.co.uk> wrote in news:inph8p$h89$1@dont-email.me:
>
> > The 500 class D amp shown component level on eservice is near enough
> > the same as the 300 with scaling down of ratings of components.
> > Overlay numbering 7... for transistors, 6... for diodes, 5... for
> > inductors. The large lump that looks like a transformer is 30uH output
> > filter choke. Will replace the powerfets with mica'd IRF740 and 0.056R
> > "fuses" with a small piece of resistance wire, previous such repair of
> > this model of amp never bounced back but otherwise unknown .
> > I see the replacement FETs for the 2SK3607 is IRF640 which gives me
> > more confidence.
> > Will try and find from the owner how they knew and why they replaced
> > the output fan. But will do my previous retrofit fudge of bending up
> > the corner of the chassis top cover over the fan ouput and a 5mm
> > nylon standoff under the fixing screw to at least double/halve the
> > "choked" fan . Otherwise the ridiculous air flow design? of this amp
> > is to try and make a compressor out of these little 12V fans.
> > I will assume heat build up was failure mode as quite a bit of dust
> > inside, even under the 1/4 inch sockets etc where air prefers to
> > ingress rather than the designed? row of tiny holes in the chassis
> > cover. The crack in the FET gate solder was just a partial PbF crack ,
> > bending the leg to force the "crack" open failed to do so , so not
> > through to the pad/trace. Plus usaul suspects of PbF dealt with JIC.
> >
> >
> >
>
> the fan may have been replaced because it's bearings wore out and got
> noisy.
>
> --
> Jim Yanik
> jyanik
> at
> localnet
> dot com

T'was a noisey fan. Still I find it suspicious the same fault outcome, both
powerfets shorted all round but just one 0.056R "fuse" blown in the negative
rail supply. The fan must be overloaded as well as poor amp ventilation.
Allowing for central core of fan but not the fan blades themselves, area
across duct within the 2 inch fan is 420 sq mm.
Ignoring aerodynamic braking effects of forcing the outcoming air to
immediately do a confined right angle, a wall 10 mm beyonfd the face of the
fan, and vortexing effects from forcing througth 2mm wide slots, the
combined area of the outlet slots is 170 sq mm. So more like a compressor
than ventilator. Not only will I be lifting the outlet grill to double or
treble the area for the outlet air, but drilling out every other inlet hole
as well perhaps.

== 2 of 2 ==
Date: Sun, Apr 10 2011 1:14 am
From: "N_Cook"

N_Cook <diverse@tcp.co.uk> wrote in message
news:inrm3t$gnq$1@dont-email.me...
> Jim Yanik <jyanik@abuse.gov> wrote in message
> news:Xns9EC292B4E862Bjyaniklocalnetcom@216.168.3.44...
> > "N_Cook" <diverse@tcp.co.uk> wrote in news:inph8p$h89$1@dont-email.me:
> >
> > > The 500 class D amp shown component level on eservice is near enough
> > > the same as the 300 with scaling down of ratings of components.
> > > Overlay numbering 7... for transistors, 6... for diodes, 5... for
> > > inductors. The large lump that looks like a transformer is 30uH output
> > > filter choke. Will replace the powerfets with mica'd IRF740 and 0.056R
> > > "fuses" with a small piece of resistance wire, previous such repair of
> > > this model of amp never bounced back but otherwise unknown .
> > > I see the replacement FETs for the 2SK3607 is IRF640 which gives me
> > > more confidence.
> > > Will try and find from the owner how they knew and why they replaced
> > > the output fan. But will do my previous retrofit fudge of bending up
> > > the corner of the chassis top cover over the fan ouput and a 5mm
> > > nylon standoff under the fixing screw to at least double/halve the
> > > "choked" fan . Otherwise the ridiculous air flow design? of this amp
> > > is to try and make a compressor out of these little 12V fans.
> > > I will assume heat build up was failure mode as quite a bit of dust
> > > inside, even under the 1/4 inch sockets etc where air prefers to
> > > ingress rather than the designed? row of tiny holes in the chassis
> > > cover. The crack in the FET gate solder was just a partial PbF crack ,
> > > bending the leg to force the "crack" open failed to do so , so not
> > > through to the pad/trace. Plus usaul suspects of PbF dealt with JIC.
> > >
> > >
> > >
> >
> > the fan may have been replaced because it's bearings wore out and got
> > noisy.
> >
> > --
> > Jim Yanik
> > jyanik
> > at
> > localnet
> > dot com
>
> T'was a noisey fan. Still I find it suspicious the same fault outcome,
both
> powerfets shorted all round but just one 0.056R "fuse" blown in the
negative
> rail supply. The fan must be overloaded as well as poor amp ventilation.
> Allowing for central core of fan but not the fan blades themselves, area
> across duct within the 2 inch fan is 420 sq mm.
> Ignoring aerodynamic braking effects of forcing the outcoming air to
> immediately do a confined right angle, a wall 10 mm beyonfd the face of
the
> fan, and vortexing effects from forcing througth 2mm wide slots, the
> combined area of the outlet slots is 170 sq mm. So more like a compressor
> than ventilator. Not only will I be lifting the outlet grill to double or
> treble the area for the outlet air, but drilling out every other inlet
hole
> as well perhaps.
>
>

There must be a ventilation problem with these tiny amps
http://www.luthermusic.com/uat/luthermusic_class/prod/765_1_preview.jpg

The outlet grill , on this presumably later version, is under the master
control in the pic orientation.
This pic shows about twice the number of slots as the one I have here, so in
recent years they have punched more slots. This one is just the slots in the
black area of that pic, not the continuation towards the master control. I'm
not in the position to retrofit slots, but can lift that corner with a
standoff.
The inlet holes are a line of 1.5mm holes , directly under the top handle in
that pic, so obscured.

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