Toshiba TV29C90 problem; Image fades to black...

[Alan Harriman]

On 28 Jul 2003 18:50:28 -0700, captainvideo462002@yahoo.com (Lenny) wrote:

My son who works with me in my electronics service business is
presently enrolled in an Electronics Technology course at the local
College. I introduced him to test equipment by getting him a used 260
and a new cheapo hand held digital from Harbor Freight, just so that
he could "get his feet wet". He's a hard worker, and a good boy and
now I would like to do something special for him. He has asked for a
Fluke portable meter with a case for his birthday.

The Fluke 87 III is an excellent meter. Especially useful is its peak hold
feature, a must for troubleshooting shutdown circuits. They retail for about
$350, but can often be found on ebay for $200 or less. See
http://search.ebay.com/search/search.dll?MfcISAPICommand=GetResult&SortProperty=MetaEndSort&ht=1&query=fluke+87+III

Alan Harriman

 

[Dave D]

"A E" <aeisenhut@videotron.ca> wrote in message
news:3F26EC29.19262042@videotron.ca...

dave's theory was that a diode was more 'efficient'
than a resistor, which doesn't compute.

OK, cheerfully withdrawn! Maybe it was a bad choice of words. Let's just say
IMO a diode is a cleaner way of dropping voltage because a 0.6V drop
(approx) can be predicted, and all available current is still available,
unlike a resistor. I'm well aware of the maths regarding dissipation, on
reflection I didn't really say what I meant.

Dave

 

[Marko]

BG: Your post is very well written and I do understand it. Nevertheless, I
will read it several times until I am sure that I have it all understood.

I am currently working on something else which may not be finished for
several days. You probably visit this NG often so I will post a message for
you when I am done. It is not uncommon for something to come along that may
delay this for a few weeks.

I don't think this deck has a zenith adjustment unless it is the play in the
azimuth adjustment. Sounds to me that what makes a low end deck sound
"inexpensive" is partially due to the poor alignment of the heads.

I have done XY plots before so I follow you on the circles and lines on the
CRT. I built a quadraphonic decoder years ago which utilized a broadband
all-pass filter, so I was looking at circles with the 90 degree shift. I
have also determined that the 10KHz tone on the test tape gives the most
accurate adjustment of azimuth.


I'll have to think about the statement you made about the test tape being
full track.

I have been picking up $5 cassette decks and scrapping them if I couldn't
get them going. If the tires were melted all over the transport I scrapped
them. Sometimes the heads and capstan were so coated with oxide that they
were literally ruined from corrosion.

I have a Teac and a Technics here that are totally functional, but they
don't have good speed accuracy.



When I did manage to get belts etc. on it I used the alignment tape to get
both channels to record and play strong in the car. I have a bunch of $3
soft heads I got from MCM that are fine for only recording tapes. When I
aligned these heads there would be one strong track and on weak one if the
azimuth was off.

My point is that it will take a while to understand why the azimuth affects
each track differently (I hope I haven't totally confused you). It usually
hits me a few days later.

If I had your e-mail address I would tell you what happens, but it is
understandable that some people don't like to pass it around. Therefore I
will post a message on this NG when I know something.

Also, concerning your comments about setting EQ etc. I have noticed that
the Dolby is way off when using a tape from another deck. I have started
recording with Dolby off and get much better results.

The adjustment pots on this Fisher are labeled on the board. I don't know
what to do with them though. Possibly after I get these heads aligned you
will help me with the electronics.

Thanks a lot BG, even if this deck turns out to be a scrapper I have learned
a lot. Sincerely, Mark


"bg" <bg@nospam.com> wrote in message
news:bg7a7i$ivb$1@terabinaries.xmission.com...

It sounds as though you have enough guides to make it work.
Alignment tapes are usually full track. You can't set tracking with it but
you can use it for azimuth. Hopefully the fixed guides are in the right
position. My gut feel is that the azimuth would be the only adjustment you
need to make unless the guides were moved somehow.
The normal method for setting the head height is to record a tone on the
tape and then measure the track positions with a toolmakers microscope.
I'm
sure you don't have this equipment, so the next best thing would be to
record a 1000 hz tone on a known good cassette deck and use that tape as
your tracking standard. As you play the tape back in the Fisher deck,
lightly push or lift the playback head to see if the playback level
increases. If the guide on your playback head hasn't been moved, your
tracking should be OK. Flip the tape over and check the levels again. For
every .001 inch that the tracking is off, you lose about .4db of signal
level. If the levels are within 1/2 to 1 db from side one, you probably
won't be able to improve the tracking by moving the playback head guide.
Moving it that small amount would be very difficult, and the guides have
to
be wider than the tape by about .001 inch to allow the tape to fit thru it
anyway. So .001 of tape movement is perfectly normal.
To set azimuth on the playback head, use the 10 khz tone on your alignment
tape. There's two ways to do this. One way is to simply adjust your
playback
head azimuth for maximum output at 10 khz. The other method is to measure
the phase between the left and right tracks. (lissajous patterns)
Set up your scope for X-Y mode. Plug the left line out into one channel
and
the right line out into the other channel. When the two tracks are in
perfect phase alignment, the scope trace should make a line angled at 45
degrees . It looks like this -- (/) .
If the phase alignment is out by 180 degrees the line is angled like
this ---- (\). Between 0 and 180 degrees the line changes to an oval or a
circle. Multiples of 360 degrees will look like it's in phase alignment,
but
the length of the line will get shorter. So what you want is the longest
line possible angled like (/). Note that when the azimuth is off, the
level
of the 10 khz tone drops off. Lower frequencies are barely affected by bad
azimuth, that's why it is set using a higher frequency tone. If the 45
degree line fluctuates rapidly, there is a problem with the tape moving up
and down. This might be due to the guides not all being at the same height
or bad zenith. Your alignment tape might be stretched also. It doesn't
take
very much abuse to stretch a tape. If the tape seems to be bad , try
recording a 10k tone on a good cassette deck and use that for your
alignment
tape.
Now that the playback head is in correct azimuth and height. You can align
your record head to your playback head. Check the height of the record
head
by recording a 1000 hz tone. Move the record head up or down until you get
maximum output from the playback head. Again, if you flip the tape over,
the
levels should playback within about 1db. seeing as the record head has a
guide welded to it , there should be no reason for the record head
tracking
to be incorrect. Set the azimuth by recording a 10khz tone and adjust the
record head azimuth for maximum output from the playback head or 0 degree
phase shift between left and right outputs.
You might need to set levels, EQ, bias, and calibrate the VU meters. This
would be hard to do unless the adjustment pots are marked on the circuit
board, but not impossible to figure out.
Let me know how you make out.


Marko wrote in message ...
BG: OK let's give it a try. This time I will get it right about where
the
guides are

Originally this machine had four guides:
(1) one solidly affixed to left of erase head
(2) one on left of record head, but affixed to the transport frame
(3) One spot welded to the right side of the record head
(4) One affixed (with miniature screw) to left side of PB head

The one on the right side of the record head is less than a cm from the
guide on the left of the PB head (PB head guide is effectively missing,
not
repairable, mangled)

As far as stability of the tape going across the heads goes, I feel that
the 3 remaining guides will be enough, if they are aligned

The two problems are as follows:

(1) The guide to the left of the record head is affixed to frame and all
other guides must correspond to this one or the tape will not ride
smoothly
on the heads.

(2) Seems like the guide to the right of the record head should not
effect
the path of the tape over the PB head because it is over the screw that
is
not for adjustment (the mounting screw that is tightened and not
adjustable). BUT, it does because I didn't notice the 3rd head when I
was
adjusting the azimuth for the record head (I thought it was the playback
head at the time). Turning the azimuth adjustment for the record head
affects the path of the tape over the PB head. I recall seeing the PB
amplitude vary on a scope as the azimuth screw for Rec head was turned.

I hope I have written this in a readable manner.

All I can see is that I should adjust the Rec and PB heads over and over
until hopefully they are aligned.

Any ideas or warnings, BG? Thanks for your help. Your advice has given
me
a much needed understanding of this situation. Mark
"bg" <bg@nospam.com> wrote in message
news:bg68j6$bkg$1@terabinaries.xmission.com...
Just about every deck I've ever seen has a guide on the ingoing side of
the
erase head and a guide on the outgoing side of the playback head, with
no
other guides in between. It is also common practise to affix the guides
to
the heads, not the chassis. On the chassis there will be posts that
hold
the shell in place, they are not tape guides.
I have plenty of time . If you are ready to continue let me know
bg
Marko wrote in message ...
BG: I have reread your post several times and now realize that
without
the
guide on the PB head then it is up to me and luck to get it going
right.

Unless you have some more advice, thanks much, you've been a great
help.
Sincerely, Mark

"bg" <bg@nospam.com> wrote in message
news:bg3s50$qi0$1@terabinaries.xmission.com...
The heads from left to right are, the erase head, the record head
and
the
playback head. Any cassette I've ever seen has a guide attached to
the
playback head. If possible, bend the damaged guide back into place.
Usually
this guide is spot welded, therefore the height of the guide might
not
have
changed. This guide sets the tracking which usually is not
adjustable
because the guide is fixed to the playback head at the factory. On
rare
occasions this guide is adjustable.
The tilt of the head sets azimuth which is adjustable on all decks.
You
will
have to examine the record and playback heads to see if there is
azimuth
adjustments for both heads. I would expect there is. Head height
raises
or
lowers the position of the head gaps on the tape. Azimuth rotates
the
gaps
so that they are aligned perpendicular (90 degrees) to the tape.
Azimuth
will have a slight effect on the head height. Another head
adjustment
you
might have is zenith. Usually located at the rear of the head, it
tilts
the
face of the head, so that the head is parallel to the tape. This
adjustment
if incorrect, would tilt the top of the head either closer or
further
from
the tape than the bottom of the head. It causes uneven head wear and
it
causes the tape to scew up and down. As the tape scews, the azimuth
and

tracking will also be out of adjustment. The erase head should also
have
a
non adjustable guide affixed to it.
Check to see that you have these guides in place, the azimuth and
zenith
adjustments, and that the adjustments will move the heads. If you
can't
physically align the heads, or the guides are bad, there is no sense
in
going any further. you will have to replace whatever mechanics are
bad.
You might want to sacrafice an old cassette by cutting away the
plastic
shell in the area where the heads contact the tape. This will give
you
the
abiltiy to see how the tape rides over the heads. If the tape is
visibly
moving up or down, you will have to correct this. It is impossible
to
align
a head to tape that moves all over the place. The basic concept is
to
set
all guides at the same height so that the tape enters the shell and
leaves
the shell at the same height. Any guides in between should not raise
or
lower the tape as it travels thru the shell.
Post back here with your results and we'll determine the next step.
bg


Marko wrote in message ...
BG: I thought I would check for replies just one more time before
I
stopped
NG activity for awhile. Glad I did.


I have a signal generator, alignment tape, scope, and HP5210 freq
meter
that
I have used to set the motor RPM with 1KHz test tone.

I haven't checked yet, but I am hoping that

(1) the head on the far right is the play head
(2) the tape monitor switch will allow me to record a test tone (I
will
use
10KHz) and then monitor it with the play head so that I can align
the
record
head.
(3) that the tape guide on the PB head (which has been bent out of
the
tape
path) is not necessary for proper tape transfer over the heads.

What worries me is that the tape guide is on the record head and I
must
align the playback head first.

I didn't notice the third head at first and aligned the playback
with
the
record head adjustment screw. This worked because the tape guide
is
on
the
record head.

How do I start out with proper alignment of the two tape guides
before
aligning the heads? One guide, the first one, is affixed to the
transport
frame and the second guide is affixed to the record head. I think
this
problem may have been encountered by
whoever worked on it before it was sent to a resale shop. I could
see
that
they had disturbed the paint on the screws. It also had two
stretched
belts
and a very dirty rec/play switch on the board, so I'm not sure.
The
belts
may have stretched and the grease in the switch may have dried from
sitting
on the shelf for years after they encountered the alignment
problem.

What do you suggest? Sincerely, Mark (this is a top post)






----- Original Message -----
From: "bg" <bg@nospam.com
Newsgroups: sci.electronics.repair
Sent: Sunday, July 27, 2003 11:46 PM
Subject: Re: Fisher cassette heads


You need an audio generator, and an AC audio voltmeter with a DB
scale.
If
you have this equipment I'll steer you through it.
bg
Marko wrote in message ...
I have a Fisher cassette deck with separate record and playback
heads.
I
assume that the one in the middle, the large one, is the record
head.

I have a professional alignment tape. How does one align the
record
head?
There is a tape monitor switch which probably is used to compare
input
to
output.

These are ferrite heads with no visible wear, new belts,
switches
cleaned
thoroughly: this deck is worth an alignment as opposed to the
trash
can
(mabey).

Also, one tape guide (the one on the far left, just to the left
of
the
record head) is affixed to the transport frame. The second
guide
is
affixed
to the record head. The third tape guide on the playback head
is
bent
over
to the side, obviously bent intentionally to get it out of the
way.
The
adjustment screw to this bent guide is not accessable for
adjustment
(sloppy
design). The third tape guide is probably not necessary since
it
is
only
about a cm from the guide on the record head. This transport
may
be
a
piece
of junk due to lousy design.

Any helpful hints will be appreciated Thanks, Mark





"bg" <bg@nospam.com> wrote in message
news:bg29k2$6ia$1@terabinaries.xmission.com...
You need an audio generator, and an AC audio voltmeter with a DB
scale.
If
you have this equipment I'll steer you through it.
bg
Marko wrote in message ...
I have a Fisher cassette deck with separate record and playback
heads.
I
assume that the one in the middle, the large one, is the record
head.

I have a professional alignment tape. How does one align the
record
head?
There is a tape monitor switch which probably is used to compare
input
to
output.

These are ferrite heads with no visible wear, new belts,
switches
cleaned
thoroughly: this deck is worth an alignment as opposed to the
trash
can
(mabey).

Also, one tape guide (the one on the far left, just to the left
of
the
record head) is affixed to the transport frame. The second
guide
is
affixed
to the record head. The third tape guide on the playback head
is
bent
over
to the side, obviously bent intentionally to get it out of the
way.
The
adjustment screw to this bent guide is not accessable for
adjustment
(sloppy
design). The third tape guide is probably not necessary since
it
is
only
about a cm from the guide on the record head. This transport
may
be
a
piece
of junk due to lousy design.

Any helpful hints will be appreciated Thanks, Mark

 

[Andre]

Sam Goldwasser <sam@saul.cis.upenn.edu> wrote in message news:<6wd6fslxyd.fsf@saul.cis.upenn.edu>...

One thing to note: In order to guarantee that the fan starts with a series
resistor, a large electrolytic cap (e.g., 500 uF) should be placed across
the resistor or diode(s). Then, power will initially be applied at
full voltage long enough to get it going.

A typical 12 V 3-1/2" fan will run just above stall speed with a 200 ohm
resistor in series to 12 V. I've built regulated temperature controllers
by using the speed range from this to full speed in a feedback loop.

Hi Sam,

That's interesting, thanks !

Putting a capacitor across a constant current diode (LM317 + resistor)
might work also, for the same reason .

BTW, thanks everyone for your suggestions so far, most useful !

-A

Next problem . How to delay turn-on long enough to charge a fairly
hefty capacitor to boost start the fan ?

I'm thinking some type of MOSFET, and a capacitor/resistor combination
to get the 5 second or so delay . Possibly also a zener diode .

e.g. it waits until the voltage is more than say 3.6V and start
charging the capacitor . When the voltage hits the MOSFET's turn on
voltage it starts, dumping the charge stored in the main reservoir
capacitor into the motor .

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work. To
contact me, please use the Feedback Form at repairfaq.org. Thanks.

 

[Bill Webb]

If you have a spent ink cartridge lying around, you could cut it open
and use one of the sponges from the cartridge (1 in black, 3 smaller
ones in a color cartridge). It may be advisable to wash any residual ink
out of the sponge first, preferably someplace where it will not make a
mess

 

[Mark D. Zacharias]

Probably wasted advice. This fellows obviously not a tech; the chances of
him fixing it himself are remote. Probably just too cheap to pay to get it
fixed.

Mark Z.


<pj1108_no_spam_@telus.net> wrote in message
news:3F277B45.E7E2B11E@telus.net...

mechprof1@yahoo.com wrote:

Hi,

Today I turned on the Sansui 9090 and the flashing red protector light
next to
the power button continuously flashed and the stereo never did go on.
The tuner
seemed to be picking up signals, as evidenced by the signal meter, but
the
sound output meters registered zero and no sound came from the speakers.
Usually
the light flashes red for a few seconds, turns green and then the tuner
and
stereo activates. Can someone tell me what the cause might be and if
there is a
simple fix?


The protector is detecting excessive DC voltage from at least one of the
power amplifier output stages. It could be a leaky transistor, open
resistor, etc. on one of the channels or its the protector itself. It's
not likely that both channels will fail at the same time so your best
bet is measure for unusually high DC voltage on the relay protector's
power amp side. Once the faulty channel is isolated you can do voltage
comparison with the good one but before that check for physical signs,
see my last paragraph below.

I assume that you've checked for normal power supply voltages. Without a
schematic, the DC voltage across the big filter capacitors should be
less but not half the quoted working voltage marking.

With the receiver's age of ~1977, I strongly suggest you to check for
cold/cracked solder joints on hot spots like diodes, high power
resistors and transistors. Usually a darkened PCB would indicate hot
spots. Check for high ESR or dried up capacitors near this area as well.
Doing this will save you a lot of headaches later on any recurring
faults.

I don't have a manual for the unit, and have no idea what the protector
light is
for. Can someone tell me where to obtain a manual?

Thanks.
George

 

[Frank de Lange]

Can anyone with access to EURAS look up the description(s) for this
problem? It might be under the headings

- Bright screen with flyback lines.
- ...?

Thanks//Frank

 

[Jim Dobsin]

Sorry for the lack of info. It is a 13" GE TV, model # 13GP701,
Chassis # TX808H. I am still looking for a place to measure the main
PS without having to remove the main circuit board from the set. Is
there a common point that this could be picked off at ? I basically
have a digital voltmeter as my measuring device.

 

[Sofie]

"Jim Dobsin" <booboojimd@yahoo.com> wrote in message
Sorry for the lack of info. It is a 13" GE TV, model # 13GP701,
Chassis # TX808H. I am still looking for a place to measure the main
PS without having to remove the main circuit board from the set. Is
there a common point that this could be picked off at ? I basically
have a digital voltmeter as my measuring device.
--------------------------------------------

Jim Dobsin
If you are going to troubleshoot the circuitry you NEED to remove the
circuit board from the set..... or more precisely you need to slide it out
so you can access the top and bottom to make test measurements, component
tests, and observations.
If you are going to be able to perform a successful repair you really should
know WHERE to "pick off" points to do some basic measurements. Do you know
exactly WHAT you are going to "measure" with your digital voltmeter and do
you know what readings to expect??
You might be best advised to go to the website for this newsgroup at
http://www.repairfaq.org/
There, with some searching, you will find a wealth of troubleshooting tips,
repair procedures, component testing methods and IMPORTANT safety
information that will help you to stay away from dangerous and lethal
electrical shock hazards inside your television.... note that these hazards
may still be present even when the television is turned off and unplugged
from the AC power... be very careful.
You can also do a google groups archival search for your television's
chassis number.... there will be a lot of specific repair information
regarding the "TX" chassis. Spend some time doing research before you
blindly stick meter probes inside the television.
If, after reading through the repairfaq, you still are not certain where to
start or how to proceed, you maybe should take your television to a repair
shop for a safe and proper repair or at the very least a repair cost
estimate so you can make and intelligent repair decision with facts instead
of internet guesses. While this is not a very expensive television and
maybe not worth a big repair bill, what if the repair shop gives you a
fairly inexpensive and reasonable repair quote???..... get the facts.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
---------------------

 

[Sofie]

George:
Based on your original posting, a manual and a schematic are NOT going to be
much help to you...... it will only be of most use to an experienced and
knowledgeable tech with the proper test equipment, tools, replacement parts,
etc. In fact, most techs will repair this kind of problem without the
manual and schematic.
The Sansui 9090 is a very nice old and powerful receiver and is worth
repairing. Take it to a repair shop BEFORE any failed, botched or aborted
home repair attempts and at the very least get a repair cost estimate so you
can make an INTELLIGENT repair decision with facts instead of internet
guesses.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
-----------------------------------

Today I turned on the Sansui 9090 and the flashing red protector light
next to
the power button continuously flashed and the stereo never did go on.
The tuner
seemed to be picking up signals, as evidenced by the signal meter, but
the
sound output meters registered zero and no sound came from the speakers.
Usually
the light flashes red for a few seconds, turns green and then the tuner
and
stereo activates. Can someone tell me what the cause might be and if
there is a
simple fix> > I don't have a manual for the unit, and have no idea what
the protector light is
for. Can someone tell me where to obtain a manual?
Thanks.
George

 

[Dave D]

"Andre" <testing_h@yahoo.com> wrote in message

Next problem . How to delay turn-on long enough to charge a fairly
hefty capacitor to boost start the fan ?

I'm thinking some type of MOSFET, and a capacitor/resistor combination
to get the 5 second or so delay . Possibly also a zener diode .

e.g. it waits until the voltage is more than say 3.6V and start
charging the capacitor . When the voltage hits the MOSFET's turn on
voltage it starts, dumping the charge stored in the main reservoir
capacitor into the motor .

No need for that. The cap is in _series_ with the motor, and in _parallel_
with the resistor or diodes or LM317. On startup, the cap acts as a very low
resistance shunting the resistor to apply full voltage to the fan. When it
charges up its resistance goes high and it is effectively no longer there,
so the resistor does its job. When the fan is powered off, the resistor
discharges the cap so it's ready to go again. Great idea, so simple like the
best of them!

Dave

 

[Frank de Lange]

Some more info...

As I do not have a schematic diagram (something I'd like to have, so
if you do...), I do not know which voltages are to be found where (the
silkscreen does not give any hints whatsoever... I long for the 'good
old days' where the silkscreen contained most you needed to know...),
but I can make some educated guesses.

Connector M315 on the CRT board (rightmost connector when viewed from
solder side, as mounted on CRT), right to left:

+195V (B+?)
+75V
GND
GND
+6V (heater?)
-20V, spikes down to -42V (G1)
+5V
+12V

As stated, monitor does show picture when G2 (SCREEN) has been turned
down all the way. Turn G2 up, and the background gets lighter, turn it
up above ca. +80V and the picture blooms (washes out, gets bigger).

Levels of R, G and B on tube socket with maximum contrast are between
+3V and ca. -24V.

 

[Ken]

On Wed, 30 Jul 2003 13:19:08 +0000 (UTC), "Dave D"
<someone@somewhere.com> wrote:

No need for that. The cap is in _series_ with the motor, and in _parallel_
with the resistor or diodes or LM317. On startup, the cap acts as a very low
resistance shunting the resistor to apply full voltage to the fan. When it
charges up its resistance goes high and it is effectively no longer there,
so the resistor does its job. When the fan is powered off, the resistor
discharges the cap so it's ready to go again. Great idea, so simple like the
best of them!

It's the best annd it works perfect!
I use it since many years ago.

--

+ Ken +

 

[Philip Pemberton]

In message <bg1d7g$c1s$1@titan.btinternet.com>
"Dave D" <someone@somewhere.com> wrote:

Yes, but be careful where you ground the croc clip!
ISTR you put the grounding clip on the "dag ground" -- the metal grounding

strip around the CRT. The screwdriver goes under the anode cap.

http://rv6llh.rsuh.ru/shema.htm
Well, now I've got some schematics. A manual would have been nice, but I

guess I'll have to work out how to unclip the case and remove the PSUB
myself. The troubleshooting guides in Sony manuals are also usually quite
good IME.

Later.
--
Phil. | Acorn RiscPC600 Mk3, SA202, 64MB,
philpem@despammed.com (valid address)| 6GB, video mods, 8xCD, framegrabber,
http://www.philpem.dsl.pipex.com/ | Ethernet (i3 Etherlan600), Teletext
Error: Keyboard not found. Press F1 to continue or F2 to enter SETUP.

 

[Andre]

"Dave D" <someone@somewhere.com> wrote in message news:<bg8gkc$90f$1@hercules.btinternet.com>...

"Andre" <testing_h@yahoo.com> wrote in message
Next problem . How to delay turn-on long enough to charge a fairly
hefty capacitor to boost start the fan ?

I'm thinking some type of MOSFET, and a capacitor/resistor combination
to get the 5 second or so delay . Possibly also a zener diode .

e.g. it waits until the voltage is more than say 3.6V and start
charging the capacitor . When the voltage hits the MOSFET's turn on
voltage it starts, dumping the charge stored in the main reservoir
capacitor into the motor .


No need for that. The cap is in _series_ with the motor, and in _parallel_
with the resistor or diodes or LM317. On startup, the cap acts as a very low
resistance shunting the resistor to apply full voltage to the fan. When it
charges up its resistance goes high and it is effectively no longer there,
so the resistor does its job. When the fan is powered off, the resistor
discharges the cap so it's ready to go again. Great idea, so simple like the
best of them!

Yeah, should work well . With a few tweaks of my own (to take into
account a slowly rising supply voltage) . Email direct for more
information .

-A

Dave

 

[Fred Abse]

On Tue, 29 Jul 2003 21:40:06 +0100, Tom Jacobs wrote:

Does anyone know what the taco'
bit is for ?.

Something to do with the Taco Bell?

Sorry, dunno what made me say that

--
Then there's duct tape ...
(Garrison Keillor)
nofr@sbhevre.pbzchyvax.pb.hx

 

[LASERandDVDfan]

I didn't know people could see infrared..
People cannot see infrared light. That small red dot of light on the lens is

not the actual beam. The actual beam in the IR range is much more intense.
While the laser is working, take a CCD video camera and look at how the camera
sees the light.

There is a small red light

on, but that's just an indicator to tell you NOT TO LOOK at the
laser... and the difference between the cd and dvd laser isn't
intensity, it's size.

The BIGGEST and correct difference is wavelength. DVD lasers operate at a
shorter wavelength/higher frequency in the electromagnetic spectrum. It's high
enough to be visible. CD lasers operate at a longer wavelength/lower frequency
below the visible spectrum.

The tighter pit density is actually made possible by the fact that the beam
frequency is higher. The higher the frequency of the laser beam, the more
information it can carry at once. This is translated physically on a CD-sized
disc as more pits per centimeter, and more pits for a CD-sized DVD consequently
means a tighter track width to accomodate the higher pit density on the disc.

What happens upon powerup, or interlock close. is the laser starts out with
a weak beam for CD, and tries to focus, and then it gets bright and tries to
focus. The brightness of the beam lights all of the parts surrounding the
lens. like a laser pointer brightness. then CD brightness is typical.

Some players have the lasers go into DVD mode first, then CD mode. Others do
it vice versa.

If when in DVD detecting mode, and the laser is dim, or is not there at all,
but only there on CD, the diode, or driver circuitry is bad.

Just because the pickup cannot read a DVD doesn't mean that the laser is dim or
not there at all. In many cases when the pickup goes south, the actual laser
may still be functional but the photo sensor that is supposed to translate the
light into electrical signals goes bad. There are situations, however, where
the laser does become marginal, usually through wear, either premature or
through normal use. Other times a failure can occur through dust accumulation
inside the pickup. Then there are times where the optical pickup isn't at
fault, but someone makes the mistake in thinking that the pickup is bad purely
from the symptoms they observe, like the symptoms arising from a blown
microfuse with the DSP laser focus servo in the Sony DVP-S350, DVP-S360, and
DVP-S560. - Reinhart

 

[Tom]

Andre,

There are current regulator diodes.
http://www.vishay.com/docs/70711/70711.pdf
and there are others. These range from .43 ma to 4.7 ma. May not be
enough to keep your fan going, but you could put a few in parallel to
adjust.

Tom

 

[Mark D. Zacharias]

OK, I've been waiting to post this. Here it goes:

First, learn some electronic theory and fundamentals, so that you will not
injure or kill yourself, and so you will know a bad part when you find one.
It is critically important to understand theory of operation and signal-flow
if you are to have any hope of repairing most equipment.
Buy a relatively inexpensive digital multimeter, probably at Radio Shack.
An oscilloscope would also be most useful; a decent used one can usually be
found for 100.00 or less.
Learn the appropriate safety considerations for using the tester and 'scope.
There are special considerations for working on most televisions and other
equipment not using a built-in isolation transformer. Most servicers use an
isolation transformer for any AC-powered unit under test.
Learn how to use the multimeter to measure resistance, voltage, and current.
Learn how to use the oscilloscope to observe and analyze waveforms.
Buy a soldering iron, solder, and desoldering equipment.
Learn how to solder and unsolder without damaging the circuit board.
Find a source for replacement parts. Most suppliers have about a 15.00
minimum order.
Order the replacement parts and install them.
Clean the circuit board where you were soldering. Treat the job as if it
were going to be inspected afterwards and graded for neatness.
Visually inspect the piece for any other problems or safety issues.

NOTE:
You are personally responsible for any safety problems you cause, or those
which you
SHOULD have noticed and failed to correct. So if you work on a TV and it
burns down your friend's house in the middle of the night because
of something you missed or that you caused, they can sue you, even years
later.
At this point you can just replace a blown fuse, if any, plug the unit in,
and hope your new parts don't just fail again because you missed something
or installed a part incorrectly. (Or you could use an AC variac to bring up
the line voltage slowly while measuring voltages etc. MCM sells one for
90.00)

Check for normal operation. Watch for any signs of overheating, hum, smoke,
etc and be prepared to shut down quickly.
Test for longer-term operational stability, check for neatness of lead
dress, re-assemble the rest of the way, making sure not to pinch any wires
etc. Make up your mind to re-assemble the piece exactly as it was. If there'
s screws left over, you did a sloppy job.
Final test the piece, and satisfy yourself that there is no possibility of
leakage current between any exposed metal and the AC line. There are several
ways of doing this. Please refer to the manufacturers' service data or your
textbooks.

Decide how to politely tell friends, family, freeloaders and cheapskates
that you must charge appropriately for your work.

Welcome to the exciting world of electronics repair.

Mark Z.



"Sofie" <sofie@olypen.com> wrote in message
news:vifo44ljlkra66@corp.supernews.com...

George:
Based on your original posting, a manual and a schematic are NOT going to
be
much help to you...... it will only be of most use to an experienced and
knowledgeable tech with the proper test equipment, tools, replacement
parts,
etc. In fact, most techs will repair this kind of problem without the
manual and schematic.
The Sansui 9090 is a very nice old and powerful receiver and is worth
repairing. Take it to a repair shop BEFORE any failed, botched or
aborted
home repair attempts and at the very least get a repair cost estimate so
you
can make an INTELLIGENT repair decision with facts instead of internet
guesses.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
-----------------------------------


Today I turned on the Sansui 9090 and the flashing red protector
light
next to
the power button continuously flashed and the stereo never did go on.
The tuner
seemed to be picking up signals, as evidenced by the signal meter,
but
the
sound output meters registered zero and no sound came from the
speakers.
Usually
the light flashes red for a few seconds, turns green and then the
tuner
and
stereo activates. Can someone tell me what the cause might be and if
there is a
simple fix> > I don't have a manual for the unit, and have no idea
what
the protector light is
for. Can someone tell me where to obtain a manual?
Thanks.
George

 

[Mike]

ha, ha, i know better than that.

SCRs arnt images, its a virus i know it



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news:bg9u23$osn$846@news.doit.wisc.edu...

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