Toshiba TV29C90 problem; Image fades to black...

Phil Allison wrote:
clare@snyder.on.ca

The fuse is not being put forward as a solution - just to avoid
blowing the transformer while finding the real problem.


** The fuse will actually help you diagnose the problem.

If the fuse opens soon as AC power is applied - the tranny is being
overloaded.

If the fuse opens after some time because insulation in the primary side has
failed, replacement fuses will open immediately despite the secondary being
disconnected.



...Phil



Hi,
Click to expand...
Another question, does he keep buying same x-former over and over or
something different little havier one? Along with fuse I'd put in series
a low value proper Wattage resistor to lower the primmary voltage little
bit. Crazy thinking but hope the x-former is not put in backward.
 
"Don Klipstein is Full of Bull "

Measure both AC and DC current through the secondary of the transformer.
If putting a multimeter into DC current mode gets a reading around or over
50 milliamps (,05 amp), then something is wrong with the load.
If DC secondary current is near or over 200 milliamps, then,
"Houston, we have a problem"!
Click to expand...

** Simply fitting that DAMN 1/4 amp s-b fuse will tell you immediately if
any such problem exists.

Significant DC in the secondary will causes high current to flow in the
primary ( due to core saturation) and BLOW the fuse !!!

If the 1/4 amp fuse holds and the tranny does not get stinking hot - all is
OK.



..... Phil
 
In <dc989a93-2114-4712-b192-aa6441ae2ce8@r33g2000prh.googlegroups.com>,
trader4@optonline.net wrote:

<SNIP stuff previously said>

After you put it in, measure the current and voltages in both
the primary and secondary. I'd measure them both with the
AC running and with it not running.

Also, not sure if anyone ever covered this, but when the transformers
have failed have they all been in cooling mode, heating, or both?
Click to expand...
Measure both AC and DC current through the secondary of the transformer.
If putting a multimeter into DC current mode gets a reading around or over
50 milliamps (,05 amp), then something is wrong with the load.
If DC secondary current is near or over 200 milliamps, then,
"Houston, we have a problem"! Probably with one of the recently-mentioned
discrete diodes in a board's bridge rectifier.

Ideally, DC current through transformer windings should be zero. With
exception to specialty cases, typically involving special transformers
that use DC-handling means such as gapped cores.

If this tranny is running into problems related to DC, look for DC
through the secondary. If that turns up substantially, then the
already-mentioned 4-discrete-diode bridge rectifier on the board is
likely to be the culprit. Look for solder joints there that need touching
up, or else replace the bad diode if one is found to be bad (or all 4 of
them), or the whole board.

Depending on ability and willingness to use a soldering iron and to
troubleshoot and repair a board to component level, even with pointers
to a suspect identified set of components on the board...
It may be more practical to get a replacement board if the existing one
causes substantial DC to flow through the secondary of the transformer
that is prone to failing.

--
- Don Klipstein (don@misty.com)
 
Measure both AC and DC current through the secondary of the
transformer.
If putting a multimeter into DC current mode gets a reading
around or over
50 milliamps (,05 amp), then something is wrong with the load.
If DC secondary current is near or over 200 milliamps, then,
"Houston, we have a problem"!
Click to expand...
I have been (sort of) following this conversation. I assume this
transformer also drives the contactor for the AC compressor.
Maybe there is a short in that circuit and the transformer
secondary gets shorted when the thermostat calls for cooling.

David
 
On Fri, 15 Apr 2011 14:04:11 +1000, Phil Allison wrote:


"Tony Hwang"


This isunthinkab;e crazy idea but is the x-former being put in
backward?

** You must be totally schizo.
Click to expand...
Ironic statement of the year candidate!



--
Live Fast Die Young, Leave A Pretty Corpse
 
On 4/14/2011 9:52 PM, Tony Hwang wrote:
John Robertson wrote:
Steve Turner wrote:
On 4/14/2011 2:54 PM, trader4@optonline.net wrote:
On Apr 14, 2:37 pm, Steve Turner<bbqbo...@swtacobell.net.invalid
wrote:
On 4/14/2011 12:06 PM, Smitty Two wrote:





In article<io785f$t8...@dont-email.me>,
Steve Turner<bbqbo...@swtacobell.net.invalid> wrote:

On 4/14/2011 12:41 AM, Smitty Two wrote:
In article<io5tea$b6...@dont-email.me>,
Steve Turner<bbqbo...@swtacobell.net.invalid> wrote:

Just mentioned elsewhere that I have a new transformer on order
and I
can't
really do anything until that arrives.

Sure you could. You could open up those other two transformers
and check
for an open thermal fuse. As I recall, you said neither of them
failed
in the same manner as the third. I still say you could have 3
distinct,
unrelated failures.

The design of the first transformer makes it virtually impossible
to open it
up
(remove the tape) without destroying the windings, (which I did)
so there is
no
possibility of "repairing" it by installing a thermal fuse (as some
suggested).
There is evidence of burning at the input contactors just like
there is on
the third transformer (the one I took pictures of), but not quite
as bad. I
wouldn't call it an "explosion". There is no evidence of a thermal
fuse.

On the second transformer (a completely different brand and style)
there was
no
evidence of burning. Again, it too was virtually impossible to
open up with
destroying it, so I didn't bother. However, because everyone has
been so
curious, I just did open it up (destroying it in the process) and
there IS a
thermal fuse on the input side; it is open, which explains why
there is no
burning.

The third transformer is similar to the first in design (except
for the extra
208 and 240 legs, which, per the instructions, I taped off and
ignored). It
is
also virtually impossible to remove the tape to gain access to the
primary
windings without breaking through the wires, but I did, and again
there is no
evidence of a thermal fuse.

I see no reason to conclude there are "3 distinct, unrelated
failures".

Just because you can't fix something, it doesn't mean that failure
analysis is moot. I'd be doing serious exploratory surgery on all
3 of
those transformers to try to understand what the hell happened.

I'm not "concluding" that there are 3 distinct unrelated failures,
I'm
suggesting it as a possibility.

The first, OEM transformer lasted 6 years. The second transformer
lasted
a few days, and by your own admission was a cheap knockoff that may
not
have been suited for your application at all.

Others sorta concluded that for me. It was "Made in China" and has a
bit of a
different form factor, but that's the only evidence I have so say it
might not
have been "suitable". The transformer was similarly rated, and
internally it
doesn't look much different from the others, so I still have no real
reason to
believe it shouldn't have worked.

And the 3rd transformer may well have failed due to improper
wiring, or
a loose connection leading to excessive current leading to insulation
breakdown and a hard short, or as has been suggested repeatedly, a
fault
somewhere on the secondary side.

You've also agreed that there are wire color discrepancies and
several
respondents have opined that both halves of the primary should,
perhaps,
have been wired in parallel to accommodate the current requirements.

I brought the old transformer to a local HVAC supply house, and the
sales
person (whom I perceived to be at least somewhat of an expert), gave
me the
third transformer as a suitable replacment. I chose to connect the
transformer
according to the instructions, and not according to any speculation
"opined" in
this group.

So, I too am curious, have you acquired some appropriate fuses,
figured
out how to monitor the current, and been able to schedule some time
off
from your other responsibilities so that you can actually work
through
this puzzle once the new xformer arrives? Are you equipped to bench
test
the new transformer to verify wiring color scheme before you
install it?
Do you know how to test that bridge rectifier? Seems like you have a
*lot* you could be doing while waiting for the UPS guy.

I'm sorry you feel that I'm not "doing" anything or that I'm leaving
you
hanging, but I'll be making the repairs on my own schedule, as time
permits.
My own place of employ has me working 12 and 16 hour days, so I
can't be
everywhere at once. Plus, the weather here is pleasant and there's
been no
real need to run the air conditioner, and the house has two A/C
units anyway so
I'm in no hurry. I don't have the fuses or fuse holders yet, but the
transformer isn't going in without them, so it will be taken care
of. My
common sense tells me that I really shouldn't *have* to test and
verify the
living daylights out of a new transformer, but I will most certainly
get
bitched out here if I don't, so yes, that will be done. I don't
really recall
the discussion about the bridge rectifier, but I'll look for it. I
will be
reviewing the entire discussion and make a checklist of all the
steps I need to
perform.

Anything else?- Hide quoted text -

- Show quoted text -

After you put it in, measure the current and voltages in both
the primary and secondary. I'd measure them both with the
AC running and with it not running.

Also, not sure if anyone ever covered this, but when the transformers
have failed have they all been in cooling mode, heating, or both?

Yep, I'll do that. It's only in cooling mode that the transformers
have failed, but I'm in Texas and we're long past the point where
we'll be needing the heater for a while, so it's hard to say whether
or not running the heat would also trigger the problem.


Steve, As said before the best thing to do is to fuse both the primary
and secondary windings.

If you have the recommended (original) transformer ratings handy that
should make it easy to figure out. For example, if the secondary (24VAC
as I recall) is rated at 1A, then the primary fuse is 1/5 of that
(24:120 - plus a fudge factor) suggesting that a 0.25A slo-blo should
last fairly well, and a 1A slo-blo on the secondary winding. If the
secondary is rated at 2A, then I'd go with a 0.5A slo-blo on the
primary, along with a 2A slo-blo on the secondary.

Two fuse holders should be fine - one for the 120VAC side and one for
the 24VAC side.

Hope this helps - at least it will reduce the cost of replacing
transformers!

John :-#)#

Hi,
Giving up for real solution? Just band aid fix? VChanging blown x-former
to blown fuse? If I am having problem like that I'd fix it for sure
dragging out all the tools I need. O'scope, clamp ammeter, DVM, etc.
Maybe it is asked already but is happening all of sudden or been like
that since the system got installed? Every symptom has cause.
Click to expand...
It's the first step in determining if the problem is on the primary or
secondary. Ever hear of "divide and conquer"? Fuses will hopefully cut
the troubleshooting in half. That's the first step since he can't
monitor voltage and current for hours or days at a time.
 
On 4/14/2011 11:18 PM, Tony Hwang wrote:
Phil Allison wrote:
clare@snyder.on.ca

The fuse is not being put forward as a solution - just to avoid
blowing the transformer while finding the real problem.


** The fuse will actually help you diagnose the problem.

If the fuse opens soon as AC power is applied - the tranny is being
overloaded.

If the fuse opens after some time because insulation in the primary
side has
failed, replacement fuses will open immediately despite the secondary
being
disconnected.



...Phil


Hmm,
This isunthinkab;e crazy idea but is the x-former being put in backward?
Rgwew i a such thing as current limiting x-formers. One thig I'd try
then I'd put in proper Wattage low value resister to lower the primary
voltage.
Click to expand...
My word, you need sleep or something. Backwards would, oh never mind
you just proved you have no electronics knowledge.
 
Tony Miklos wrote:
OK ;-)
Click to expand...
An example of excessive trimming...

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."
 
Top posted, too!

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"John Robertson" <spam@flippers.com> wrote in message
news:Q5WdnWnG5pyLUTTQnZ2dnUVZ_ridnZ2d@giganews.com...
Tony Miklos wrote:
OK ;-)
Click to expand...
An example of excessive trimming...

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."
 
http://www.gizmodo.com.au/2008/07/simple_hack_turns_usb_charger_units_into_iphone_chargers-2/


+5V ---50k --- D-
|
10k
|
GND ---40K --- D+

Is this safe? Would it work?

--
@~@ Might, Courage, Vision, SINCERITY.
/ v \ Simplicity is Beauty! May the Force and farces be with you!
/( _ )\ (x86_64 Ubuntu 9.10) Linux 2.6.38.4
^ ^ 22:00:02 up 5 days 2:01 1 user load average: 1.10 1.08 1.05
不借貸! 不詐騙! 不援交! 不打交! 不打劫! 不自殺! 請考慮綜援 (CSSA):
http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa
 
+5V ---50k --- D-
|
10k
|
GND ---40K --- D+

Show your work -- why make people duplicate your analysis?
Click to expand...
I dont' wanna kill my iPod Touch... :)

--
@~@ Might, Courage, Vision, SINCERITY.
/ v \ Simplicity is Beauty! May the Force and farces be with you!
/( _ )\ (x86_64 Ubuntu 9.10) Linux 2.6.38.4
^ ^ 23:40:01 up 5 days 3:41 1 user load average: 1.00 1.04 1.05
不借貸! 不詐騙! 不援交! 不打交! 不打劫! 不自殺! 請考慮綜援 (CSSA):
http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa
 
I made an iPod charger to run off 4 AA batteries using a similar divider.
Not sure why you are modifying the example given, but the values are not
especially critical. Any reason you can't measure the output?

..
"Man-wai Chang" <toylet.toylet@gmail.com> wrote in message
news:ipegh4$qd0$1@dont-email.me...
http://www.gizmodo.com.au/2008/07/simple_hack_turns_usb_charger_units_into_iphone_chargers-2/


+5V ---50k --- D-
|
10k
|
GND ---40K --- D+

Is this safe? Would it work?

--
@~@ Might, Courage, Vision, SINCERITY.
/ v \ Simplicity is Beauty! May the Force and farces be with you!
/( _ )\ (x86_64 Ubuntu 9.10) Linux 2.6.38.4
^ ^ 22:00:02 up 5 days 2:01 1 user load average: 1.10 1.08 1.05
???! ???! ???! ???! ???! ???! ????? (CSSA):
http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa
Click to expand...
 
On Apr 29, 7:04 am, Man-wai Chang <toylet.toy...@gmail.com> wrote:
http://www.gizmodo.com.au/2008/07/simple_hack_turns_usb_charger_units...

+5V ---50k --- D-
                |
               10k
                |
GND ---40K --- D+

Is this safe? Would it work?
Click to expand...
Show your work -- why make people duplicate your analysis?
 
On Apr 29, 8:44 am, Man-wai Chang <toylet.toy...@gmail.com> wrote:
+5V ---50k --- D-
                 |
                10k
                 |
GND ---40K --- D+

Show your work -- why make people duplicate your analysis?

I dont' wanna kill my iPod Touch... :)
Click to expand...
Why not just use the two resistor dividers your link claims do work?
 
On 29 abr, 10:04, Man-wai Chang <toylet.toy...@gmail.com> wrote:
http://www.gizmodo.com.au/2008/07/simple_hack_turns_usb_charger_units...

+5V ---50k --- D-
                |
               10k
                |
GND ---40K --- D+

Is this safe? Would it work?

--
   @~@   Might, Courage, Vision, SINCERITY.
  / v \  Simplicity is Beauty! May the Force and farces be with you!
/( _ )\ (x86_64 Ubuntu 9.10)  Linux 2.6.38.4
   ^ ^   22:00:02 up 5 days 2:01 1 user load average: 1.10 1.08 1.05
不借貸! 不詐騙! 不援交! 不打交! 不打劫! 不自殺! 請考慮綜援 (CSSA):http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa
Click to expand...
Seems to me that this mod should work. All that this mod does is to
put some voltage in D- and D+ pins, and that voltage will never be
greater than 5V, so I don´t see why it will not work.

Just give it a try. You won´t fry anything.
 
On 2011-04-29, Man-wai Chang <toylet.toylet@gmail.com> wrote:
http://www.gizmodo.com.au/2008/07/simple_hack_turns_usb_charger_units_into_iphone_chargers-2/


+5V ---50k --- D-
|
10k
|
GND ---40K --- D+

Is this safe? Would it work?
Click to expand...
As you're not putting more than 3.3V on the data lines it looks fine
to me.

There's a standard for power-only USB sockets.
it's basically 5V and some resistors, I'm not sure how close to it
that layout it is, I'd research and try the standard way first.







--
⚂⚃ 100% natural
 
On 2011-04-29, Man-wai Chang <toylet.toylet@gmail.com> wrote:
http://www.gizmodo.com.au/2008/07/simple_hack_turns_usb_charger_units_into_iphone_chargers-2/


+5V ---50k --- D-
|
10k
|
GND ---40K --- D+

Is this safe? Would it work?
Click to expand...
At initial glance it seems good, but I haven't read the whole USB
charging specification.

http://www.usb.org/developers/devclass_docs/Battery_Charging_V1_2.zip
 
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