Toshiba TV29C90 problem; Image fades to black...

[Wayne]

Search the monitor repair forum here
http://www.network54.com/Forum/87612
Common problem usually easily remedied by a simple hardware mod

Wayne

On 21 Oct 2004 09:38:41 -0700, lynx@vogan.dynip.com (erik vogan)
wrote:

Hello,

I am hoping that someone can help me identify the problem(s) with
a Sony G400 19" CRT that I recently was given. After connecting and
powering on the G400, the display showed these symptoms:

1) The picture was far too bright. Black displays as a light gray.
Adjusting the brightness through the onscreen menu makes no
difference.

2) Vertical retrace lines are clearly visible (white or very light
gray) as a zig zag pattern. From the bottom left of the monitor a
line will go diagonally to about an inch above the bottom on the
right, then go straight back to the left side, etc. Repeats about
twelve times. The retrace lines get closer together as they get to
the top of the monitor.

3) There are very bright lines on both edges of the picture. If I
reduce the horizontal picture size (by decreasing the horizontal size
in the onscreen menu), the bright lines move with the picture. Could
these be the horizontal retrace lines ?

4) The display seems a bit fuzzy. Text is hard to read at 1280x1024
on a monitor that should support 1600x1200. This could easily be due
to point 1), but I decided to mention it in case it is a important
detail.

5) All of the onscreen menu options work, with the exception of the
horizontal position slider. Varying that slider does not change the
picture in any way. The vertical position slider does work, as do both
horizontal and vertical size sliders.

6) Leaving the monitor on for 45 minutes did not improve any of the
symptoms.


After reading the Monitor repair FAQ (
http://repairfaq.ece.drexel.edu/sam/monfaq.htm ), I think that this is
probably a failure of the blanking system (misadjustment, a power
supply or connection issue, or a failure of the blanking circuit).
However I can't find a mention of anything like 5) in the FAQ (which
could be due more to reader error rather than absence of the
information), and I think it is probably telling me something
important.

Has anyone seen these symptoms, either alone or together ? I am
fairly certain that 1) to 4) form a group caused by a single defect,
but I hope that 1) to 5) can narrow the failed (loose) or misadjusted
component a bit more. Can anyone tell me how best to proceed with an
attempted repair on this monitor ? In addition, I don't know how long
the monitor has been in this state. Is there likely to be permenant
damage if the monitor was run this way for an extended period of time
?

Thanks very much for any help or suggestions.

 

[Charles Schuler]

1. Semiconductor junctions have a leakage current that is temperature
dependent.
2. Solder joints that are intermittent can be thermally sensitive.
3. A hairline crack in a circuit board can be thermally sensitive.

Others will no doubt add more.

 

[LASERandDVDfan]

1. Semiconductor junctions have a leakage current that is temperature
dependent.
2. Solder joints that are intermittent can be thermally sensitive.
3. A hairline crack in a circuit board can be thermally sensitive.

Others will no doubt add more.

I don't think there is anything more to add.
As you said in a fantastically detailed fashion, it is likely a problem in the
drive electronics which has made one or more critical components thermal
sensitive.

What is important now is determining how the drive sustained such damage to
allow this condition in the first place.

For instance, if it was the result of an overheating problem in the computer
itself, this would be an issue that requires effective ventilation to prevent
it from occuring again. - Reinhart

 

[LASERandDVDfan]

It is not good to unplug your units from the AC line. Some of these
types depended on the standby power to maintain their set-ups and
configurations.

Furthermore, if you have any items that use a linear power supply, constantly
unplugging and plugging in the device could strain various parts in that power
supply, including the bridge rectifier module or rectifier diodes. - Reinhart

 

[Jerry G.]

There is a problem with the colour demodulator circuits. There are
probably come some components that have become thermo sensitive. This is
impossible to service over an email, but an experienced TV tech with the
proper setup can troubleshoot the demodulator, and locate the defective
component(s). This can be anything from a cap to the reference crystal.

--

Jerry G.
======

"Willem van der Berg" <noone@here.com> wrote in message
newsan.2004.10.21.19.49.05.246000@here.com...
Hi all,

I`ve got a Sony Trinitron Colour 4:3 PAL TV (KV-X2141D), purchased in
1993. It`s hooked up to cable TV. Lately I have been experiencing a very
odd problem, which I totally cannot explain. Perhaps someone here can
help
me.

My display will all of a sudden `lose` the ability to show colour. The
image will only output black & white on every channel. The problem
begins
after 30-60 minutes of use and therefore makes watching TV almost
impossible. Switching the TV off and back on again does not help. If I
wait an hour or so I get my colour back. But then my TV only takes
minutes
to revert back into black & white. If I wait a day before turning it on
again the old pattern returns: black & white after 30-60 minutes of use.

Although my television is hooked up through a video with the cable
signal,
I have confirmed that the problem is definitely my TV. When I use tv-out
on my computer (with a direct connection to the television) the same
problem occurs. That rules out both my video-recorder and my cable
signal.
Which couldn`t have been the problem in the first place, as de signal
downstairs comes through in colour.

Here`s a twist: teletext always shows in colour, even when the tv signal
has dropped into black & white mode. I`m not an expert, but to me that
means that the screen itself is still working. I`m guessing something is
heating up and failing, but I can`t understand why the damage would not
be
permanent or instantly occur.

Can anyone shed some light on this? Based on the symptoms, which is the
most likely place to look for the solution? Is it the TV or some cable
or
something?

Any help appreciated.

Regards,
Willem van der Berg

 

[Tom MacIntyre]

On Fri, 22 Oct 2004 01:15:45 -0400, "techdrive" <mikeinpa@suscom.net>
wrote:

Hi Again, We had another CTC203AX with a Bad Pip board that caused it too:
(F2PIP board) Try pulling the pip board out and turn the set on. It if
comes on the pip board is defective. -Mike

Doesn't the 203 fail to turn on (except to the Service Menu) is any
I2C device is defective or missing? Is there anything on the PIP board
that is in the communications loop? It's been awhile here, folks.

I know I worked on one that the tuner was bad. I removed the tuner, it
refused to come on. I consulted the manual, and determined that it
would turn on to the Service Menu if a communication-required device
was disabled or missing.

Tom

 

[Mike Kennedy]

It could be a mechanical problem. Have you ever taken apart a hdd? The read
head is very small and very sensitive. The drive has to compensate for
heating and cooling off in normal operation. If it didnt, it wouldnt work
once the drive started to heat up. I think it may have gotten a out of
alginment from getting too hot and freezing it was just enough to get it
back inside specs.

- Mike

"Ken" <user@domain.invalid> wrote in message
news:QOsed.750782$Gx4.671534@bgtnsc04-news.ops.worldnet.att.net...

LASERandDVDfan wrote:
1. Semiconductor junctions have a leakage current that is temperature
dependent.
2. Solder joints that are intermittent can be thermally sensitive.
3. A hairline crack in a circuit board can be thermally sensitive.

Others will no doubt add more.



I don't think there is anything more to add.
As you said in a fantastically detailed fashion, it is likely a problem
in the
drive electronics which has made one or more critical components thermal
sensitive.

What is important now is determining how the drive sustained such damage
to
allow this condition in the first place.

For instance, if it was the result of an overheating problem in the
computer
itself, this would be an issue that requires effective ventilation to
prevent
it from occuring again. - Reinhart

Thanks to all who replied. One thing I did NOT mention in my original
post was that I had acquired an identical HD with the same firmware so
that if the logic board was the cause of failure, I could get the data
off the disk. Swapping out the logic board did not improve the
situation. My reason for suspecting the logic board was that the HD
appeared not to get up to speed fast enough. Upon powering up the HD,
the computer bios would NOT initially detect it. If I did a warm reboot
while still powered up, it would detect the drive as being present on
the second attempt. This logic board swap DID NOT improve the ability
to read the drive, but I thought the motor drive might not be getting
the disk up to the proper RPM's fast enough. When this did not solve my
problem, I went into desperation mode and froze the drive.

Myself, I tend to agree that some connection or the IC inside the disk
was being effected by the cold enough to allow an otherwise weak signal
to be read. It is hard to understand how a mechanical function could be
effected by the cold that would give the same results. However, I am
always willing to learn new things.

---
Outgoing mail is certified Virus Free.
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"keepcold" <keepcold@comcast.net> wrote:

I have a about 100 different bags of sony factory sealed circuits used for
repair of tv's dvd players...ect
Most of these bags have like 4 or 5 of the same part..
There are too many part #s to post but if anyone is intrested i will post
them.... Make me an offer

I'll give you a dollar for all of them.

Pig in a poke, eh? "If you can guess how many chickens I've got in
this bag, I'll give you all five of them."

 

"keepcold" <keepcold@comcast.net> wrote:

Make me an offer

I'll give you all the cash currently in my wallet. 8*)

 

[Jim Adney]

On Fri, 22 Oct 2004 23:54:04 +0200 Willem van der Berg
<noone@here.com> wrote:

BTW, tonight it worked for two hours. Yesterday it worked for 20 minutes.
Does that make any sense?

Was it cooler last night than it was the night before? Your problem
sounds temperature related, so if the set starts out cooler, then it
will take it longer to warm up to the failure temp.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------

 

[Henry Markov]

It's been a while since I've dealt with DOS but here's my idea. I would guess
that you can't run your programs properly when booting from floppy because you
need both the DblSpace drivers to access your HD files and you need a LoadHigh
type capability to put some of your drivers and other DOS components into the
640-1000K region in order to free enough of the base 640K for your
applications. You should be able to configure a config.sys and autoexec.bat on
your floppy boot disk to accomplish both. Of course you will also need to have
the Dbl drivers and QEMM components on your boot floppy. If you configure the
floppy properly there is no reason that you cannot create the same run time
environment that enables your programs to run when you boot from a HD.

For an entirely different approach take a look at BartPE and/or Knoppix which
you can find easily by googling. These are Windows XP and Linux systems
respectively that boot entirely from a CD. Assuming you either have or are
willing and able to install a CD drive and network card in your machine you
should be able to boot these systems and then you would have a networked
computer from which you could transmit your files. If your 386/25 only has ISA
slots and you have no compatible network card, I have some old 3COM cards that
would work. If you wish to communicate by mail, reverse all the letters in the
user name part of my email address.

Roger

Lenny wrote:

snip
It uses Qemm ... "Optimize"
.. <snip
I would rather just get it to boot normally one more time and then do
some kind of a complete transfer. If anyone has any suggestions about
this I would be extemely grateful. Whew, I miss carbon paper. It never
crashed... Thanks, Lenny Stein, Barlen Electronics.

 

[tempus fugit]

Thanks Ben.

Rather than spend time on your present machine which will possibly
need a schematic and test equipment to rectify completely, it may be
simpler to get a decent , tested, quality 3 head machine from a
reputable dealer if you really want a good spec cassette machine.

Ya, I know that, but I hate to throw something away that I might be able to
fix (it's a little "problem" I have). Also, if I can do it, it would be cool
to learn how, especially in light of your above comment - if I screw
something up irreparably, I can always pick up a used cheapie (hell, I've
pulled decks out of the garbage that were working fine), and I have another
one lying around anyway.



"b" <reverend_rogers@yahoo.com> wrote in message
news:1cfa6663.0410231713.78c4b925@posting.google.com...

"tempus fugit" <toccata@no.spam.ciaccess.com> wrote in message
news:<BJted.2147$57.1813@fe51.usenetserver.com>...
Hey all;

I've got a Technics tape deck (RS-B18) that is about 20 years old. I had
some problems with intermittent channels (rec and play) and took it
apart to
see what I could do. I found a cold solder joint in the signal path and
resoldered it, which (so far, anyway) has fixed the problem.

However, there are a few things I'm wondering about. First, the levels
(as
indicated on the meters) are lower in playback than record. IOW, if I
record
a cassette with the levels reading around 0, the tape will play back
with
the levels at, say -3 or so. It also varies depending on how the noise
reduction and bias is set:

1. No Dolby, CrO2 - levels are pretty much the same
2. Dolby B, Cr02 - levels slightly lower on playback
3. dbx, Cr02 - levels considerably (3 - 6 db) lower on playback
4. any or no noise reduction, Metal - no playback at all (this has been
a
problem since I got the deck)

I can post more combinations if need be, but I hope that this will give
the
general idea. I also cannot remember if this was the way things were
going
before the repair (I think it was though).
Are these type of discrepencies normal, or can/should I adjust things to
equal them out?

I also noticed that the playback was a little dull after the repair (to
be
honest, I hadn't used the deck in quite a while, so it may be the way it
always sounded). Would this be a bias setting that I may have
inadvertently
moved while repairing? or perhaps it needs some adjustment in another
area?

Thanks

I sympathise with all the above, but when all's said and done we are
talking about a 20 year old machine using a format which is rapidly
growing obsolete. there must come a point at which one asks: is this
worth spending time and money on?
Second hand markets are full of cassette decks, even hi-spec ones,
going for ridiculously low prices (seeing as CD-R has occupied the
mainstream for home recording.)

Rather than spend time on your present machine which will possibly
need a schematic and test equipment to rectify completely, it may be
simpler to get a decent , tested, quality 3 head machine from a
reputable dealer if you really want a good spec cassette machine.
Ben

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.775 / Virus Database: 522 - Release Date: 08/10/2004

 

[Tom MacIntyre]

On 18 Oct 2004 09:23:14 -0700, captainvideo462002@yahoo.com (Lenny)
wrote:

This post is partly a message which I posted the other day, however
now the problem has gotten more serious.
I'm running a 386/25 with Dos 6.2 for billing. The unit has two
Seagate MFM 40Meg drives that are doublespaced. It uses Qemm as a
manager, and the high memory area is being used. I use "Optimize" to
configure the memory. Scandisk found a problem on the E drive that it
can't fix and I hesitate to use Norton as this could make things
worse. Recently it has been having problems with bad sectors on the
drive showing, and refusing to boot unless you boot off a floppy and
do a sys c: from the A drive. Of course if you boot off the floppy and
then try to access programs they will either not run properly or there
isn't enough memory to operate them possibly due to doublespace not
loading? Anyway, now it will only boot if I'm lucky. Luckily I copied
my customer files on two floppies last time I got it to boot. But
there is alot of other stuff I would like to get off it. We are going
to try to get it to boot one more time and if it does I should assume
that it may be the last time. So if we're sucessful, I would like to
be ready to transfer everything on it to another drive. Is it possible
to do some kind of a transfer perhaps through the parallel port to a
Windows 2000 machine. We also have an old hard card which in theory
could be installed and it would boot my machine, but this other stuff
that presently has to load to make my machine come up and run properly
has me perplexed. If I can get in with my hard card is my data
accessible without doublespace being invoked? Of course
I would rather just get it to boot normally one more time and then do
some kind of a complete transfer. If anyone has any suggestions about
this I would be extemely grateful. Whew, I miss carbon paper. It never
crashed... Thanks, Lenny Stein, Barlen Electronics.

Man, this is nostalgic! I had an identical, or next to it, setup a few
years back.

Doublespace had its share of difficulties, although Drivespace was
scarier.

Can you boot from another Doublespaced HDD, and transfer the data?
Just because a drive won't boot doesn't mean you can't retrieve data.
The bad sectors may be somewhat confined to the boot sector area.

I have never tried it myself, but I have heard that sometimes you can
put a drive in a zip bag with as much air as possible removed, put it
in the freezer overnight, and then you may have a shot at getting more
data from it.

Good luck.

Tom

 

[Andy Cuffe]

On Tue, 19 Oct 2004 16:57:53 GMT, Me <special4mrmeval@earthlink.net>
wrote:

Inside mounted on the metal plate covering the CRT is a red block. It has
a knob on it to adjust horizontal static convergence. Try that.

The blocks in those like to crack so before doing that take an insanely
bright light and look at the body of it.

I've repaired many cracked ones by sealing the cracks with RTV
silicone. The other failure mode I've seen is on the ones that are
also used for HV regulator feedback. The voltage divider networks
tend to fail causing intermittent shutdown.
Andy Cuffe
baltimora@psu.edu

 

[Franc Zabkar]

On Sat, 23 Oct 2004 16:50:56 GMT, "Mike Kennedy"
<mikek400@R3MOVE.earthlink.net> put finger to keyboard and composed:

It could be a mechanical problem. Have you ever taken apart a hdd? The read
head is very small and very sensitive. The drive has to compensate for
heating and cooling off in normal operation. If it didnt, it wouldnt work
once the drive started to heat up. I think it may have gotten a out of
alginment from getting too hot and freezing it was just enough to get it
back inside specs.

Modern HDDs use an embedded servo, so I can't understand how alignment
could be an issue.

- Mike

"Ken" <user@domain.invalid> wrote in message
news:QOsed.750782$Gx4.671534@bgtnsc04-news.ops.worldnet.att.net...
LASERandDVDfan wrote:
1. Semiconductor junctions have a leakage current that is temperature
dependent.
2. Solder joints that are intermittent can be thermally sensitive.
3. A hairline crack in a circuit board can be thermally sensitive.

Others will no doubt add more.



I don't think there is anything more to add.
As you said in a fantastically detailed fashion, it is likely a problem
in the
drive electronics which has made one or more critical components thermal
sensitive.

What is important now is determining how the drive sustained such damage
to
allow this condition in the first place.

For instance, if it was the result of an overheating problem in the
computer
itself, this would be an issue that requires effective ventilation to
prevent
it from occuring again. - Reinhart

Thanks to all who replied. One thing I did NOT mention in my original
post was that I had acquired an identical HD with the same firmware so
that if the logic board was the cause of failure, I could get the data
off the disk. Swapping out the logic board did not improve the
situation. My reason for suspecting the logic board was that the HD
appeared not to get up to speed fast enough. Upon powering up the HD,
the computer bios would NOT initially detect it. If I did a warm reboot
while still powered up, it would detect the drive as being present on
the second attempt. This logic board swap DID NOT improve the ability
to read the drive, but I thought the motor drive might not be getting
the disk up to the proper RPM's fast enough. When this did not solve my
problem, I went into desperation mode and froze the drive.

Myself, I tend to agree that some connection or the IC inside the disk
was being effected by the cold enough to allow an otherwise weak signal
to be read. It is hard to understand how a mechanical function could be
effected by the cold that would give the same results. However, I am
always willing to learn new things.


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.782 / Virus Database: 528 - Release Date: 10/22/04

- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Jerry G.]

The standby power of a typical TV set is about 5 to 7 Watts. It is the
about the same for most cable boxes, VCR
and etc. At about this amount, the power usage meter from the power
company may not even respond. It is when you get many of these 5 Watt
loads around the house, they can add up. Having 10 units that work at 5
Watts, adds to about 50 Watts. Then this is noticed. Even a small
electric alarm clock can consume about 3 to 5 Watts.

It is not good to unplug your units from the AC line. Some of these
types depended on the standby power to maintain their set-ups and
configurations. If you have a pay TV cable box, it will probably have to
re-initialize itself each time the power us cut off. As for the
lifespan, it is best to not have a complete shutdown each time it is
used. In many industrial centres, they leave their equipment on 24/7,
and generally get a better lifespan out of it.

I have a cable TV pay box at home. It has been sitting on top of the TV
for about 3 years now, and has never failed. It is never unplugged from
the power. The TV is from 1993, and it is still going strong. The TV is
in standby all the time when not used. It is used about 6 to 10 hours
per week to watch the odd thing.

I have computers at some locations that are running 24/7, and rarely
have failures. I simply blow the dust out of them every year in the
spring time. I have a few machines that are going in to their 5th year
with a zero failure. I never had a hard disk fail. I did however in one
machine have a sound card failure, and in another one, I had to change
the power supply. This is a good average.

--

Jerry G.
======

"Sam" <ymailus@yahoo.com> wrote in message
news:a5df5561.0410201011.1bf0a214@posting.google.com...
i was horrified when after reading here that the standby mode of most
tv/vcr/cable boxes is around 4-10w.
if an 80w tv is on 2 hrs a day and standby 22, then you have standby
consumption which approaches that of usage!

my question is, does standby mode prolong the life of the device? if i
add a timer to cut off power from the wall socket during the night
will it theoretically shorten the life of the tube/vcr or cable box?

i will pay much more attn to the standby wattage specifications next
time.

thanks,
Sam

 

[Craig Hart]

At a guess, your monitor simply has multiple faults in the power supply
area.

The faults simply mainfest differently at different refresh rates.

Either junk it, or have it professionally fixed.


"Wizard of Ozz" <easytoremember123@email.com> wrote in message
news:fbcc7457.0410232240.7e6f903d@posting.google.com...

I just bought a Samsung Syncmaster 793s 17" monitor. I'm using a very
old computer, with a very old video card, a SiS 6326 (Silicon
Integrated Systems) from 1997. I'm using Windows 98.

I installed the appropriate driver that came with the monitor CD.

I have read the entire FAQ at www.repairfaq.org and my problem didn't
come up.

When I had the display at 800*600 with 75 Hz refresh rate, there was a
linearity problem. The 2 inches closest to the right and left of the
screen were slightly compressed. Barely noticeable by the naked eye.
By measuring the distances using a gif image with evenly spaced lines,
I calculated the difference (from the center screen) to be between
5-10 %. In the FAQ it says that cheap monitors can be expected to have
up to a 2 % difference in linearity (I take this monitor to be on the
cheapo side). But I solved this problem by changing the Hz rate. And
that's where my real problem comes in.

After reading the monitor CD manual to make sure I wasn't doint
something I would regret, I manually changed the refresh rate to 85 Hz
(always at 800*600). Perfect! Beautiful image. Except...

There are these evenly spaced vertical lines, just noticeable, across
the screen. Others might not complain about them. I'm a perfectionist
(there's a bit about perfectionists in the FAQ). There's 7 of them.
They weren't there at 75 Hz. Very evenly spaced, about 4.2 cm apart
(1.65 inches). They are each 1 mm thick (0.04 inches). They seem to be
slightly brighter than the sorrounding picture. On a black image they
don't appear, but on a uniform image of white, red, blue, or green,
they do. When viewing text, I can't notice them, though they still
appear in the blank parts of the text screen. They stretch from top to
bottom. The 2 closest to the left and right side of the screen are
about 2 and 3 cm respectively from the edge of the screen.

If I move the screen using the controls on the side of the monitor,
the lines move with the screen.

The image, otherwise, is absolutely perfect, beautiful, perfect
linearity, colors absolutely perfect, no strange noises, no problem
anywhere whatsoever.

One possible factor I noticed in the FAQ which might apply: most video
cards and monitors use 75 ohms, but older stuff might use 50 ohms, and
this could cause an impedance mismatch. The video card is old, from
1997.

Thanks in advance for any help.

P.S.: one final off topic query while I'm at it. The specifications on
the CD manual said the monitor had presert timing modes for vertical
frequency of 75000 Hz at VESA 640*480, and 85000 Hz at VESA 800*600
and VESA 1024*768. Sorry for the stupid question, but does this mean
the monitor will blow up if I change the desktop screen resolution
from 800*600 to 640*480 without first reducing the refresh rate to 75
Hz? I read in the FAQ that modern monitors automatically block any
signal which is incompatible with their hardwired specs. As I read
this I couldn't help but wonder: what a brilliant tactical move,
allowing your clients to live so they can shop again another day !
Pure genius! And it only took them 20 years to think of this! [Irony
off]

 

[Sam Goldwasser]

easytoremember123@email.com (Wizard of Ozz) writes:

I just bought a Samsung Syncmaster 793s 17" monitor. I'm using a very
old computer, with a very old video card, a SiS 6326 (Silicon
Integrated Systems) from 1997. I'm using Windows 98.

You think that's old?

I installed the appropriate driver that came with the monitor CD.

I have read the entire FAQ at www.repairfaq.org and my problem didn't
come up.

Well, at least one person in the Universe has done so!

When I had the display at 800*600 with 75 Hz refresh rate, there was a
linearity problem. The 2 inches closest to the right and left of the

They probably didn't do much to optimze the design for a resolution
and scan rate that no one uses anymore except you. Oops, sorry. ;-)

screen were slightly compressed. Barely noticeable by the naked eye.
By measuring the distances using a gif image with evenly spaced lines,
I calculated the difference (from the center screen) to be between
5-10 %. In the FAQ it says that cheap monitors can be expected to have
up to a 2 % difference in linearity (I take this monitor to be on the
cheapo side). But I solved this problem by changing the Hz rate. And
that's where my real problem comes in.

After reading the monitor CD manual to make sure I wasn't doint
something I would regret, I manually changed the refresh rate to 85 Hz
(always at 800*600). Perfect! Beautiful image. Except...

There are these evenly spaced vertical lines, just noticeable, across
the screen. Others might not complain about them. I'm a perfectionist
(there's a bit about perfectionists in the FAQ). There's 7 of them.
They weren't there at 75 Hz. Very evenly spaced, about 4.2 cm apart
(1.65 inches). They are each 1 mm thick (0.04 inches). They seem to be
slightly brighter than the sorrounding picture. On a black image they
don't appear, but on a uniform image of white, red, blue, or green,
they do. When viewing text, I can't notice them, though they still
appear in the blank parts of the text screen. They stretch from top to
bottom. The 2 closest to the left and right side of the screen are
about 2 and 3 cm respectively from the edge of the screen.

If I move the screen using the controls on the side of the monitor,
the lines move with the screen.

So the lines stay with the picture? Are they aligned perfectly with
the pixels?

The image, otherwise, is absolutely perfect, beautiful, perfect
linearity, colors absolutely perfect, no strange noises, no problem
anywhere whatsoever.

One possible factor I noticed in the FAQ which might apply: most video
cards and monitors use 75 ohms, but older stuff might use 50 ohms, and
this could cause an impedance mismatch. The video card is old, from
1997.

Not likely. 50 ohms has never been used recent times.

You should check the monitor with another video card or PC as it may indeed
be the video card as someone else suggested. Ignore that guy who didn't
bother to pay attention to what you wrote and said to junk the monitor.

Thanks in advance for any help.

P.S.: one final off topic query while I'm at it. The specifications on
the CD manual said the monitor had presert timing modes for vertical
frequency of 75000 Hz at VESA 640*480, and 85000 Hz at VESA 800*600
and VESA 1024*768. Sorry for the stupid question, but does this mean
the monitor will blow up if I change the desktop screen resolution
from 800*600 to 640*480 without first reducing the refresh rate to 75
Hz? I read in the FAQ that modern monitors automatically block any
signal which is incompatible with their hardwired specs. As I read
this I couldn't help but wonder: what a brilliant tactical move,
allowing your clients to live so they can shop again another day !
Pure genius! And it only took them 20 years to think of this! [Irony
off]

Unlikely but no way to know for sure. It really shouldn't blow up.

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Unlikely but no way to know for sure. It really shouldn't blow up.

 

[Norm Dresner]

SEE ANSWERS INLINE
"mike" <spamme0@juno.com> wrote in message news:417B65C6.1080909@juno.com...

Norm Dresner wrote:
Background: I'm repairing a non-working Tek FG501 function generator
plug
in. So far I've determined that the voltage in the regulated +20V
circuit
is zero. I'm assuming -- for the moment -- that this is caused by a
failure
in the regulator section which consists of a reference diode, an Op Amp
and
a transistor booster (with a second transistor for current limiting)
(and a
suitable number of passive components). All of this is very simple
circuitry and should be easy to debug.


First, are you sure it's the op-amp?

Well, I've measured the voltages at just about every point in that part of
the circuit. I can explain every one except that the non-inverting input to
the Op Amp is 6.2 volts, the inverting input is ~8.2 and the output is ~27.2
volts. Since the voltages on the pass transistor Q410 are consistent with a
normal diode drop from collector to base and a reasonably saturated
transistor between collector and emitter, I've ruled out failure of this
transistor. Similarly, the voltages on the current limiting transistor Q415
also indicate a good unit. Based on the conclusions that the transistors
and the resistors in the circuit are okay, that leaves only the Op Amp which
is clearly misbehaving. BTW, I've checked with a 'scope and the Op Amp is
definitely not oscillating; the output shows pretty much the same ripple as
the input power.

If it is, can you swap it for another that's running on 20V and use the
commercial grade replacement at 20V? Even tho they're selected
differently, they may have in fact put the same part in all places.

I think what I might do is to lift the lower leg of the pass transistor's
emitter resistor (also the current limit sensing resistor) and inject +20V
from a known good supply at this point. If the unit still doesn't work, I'd
be tempted to scrap it because there may be who-know-how-many consequent
failures in the remainder of the circuit.

What's not totally obvious to me from a very, very cursory inspection of the
circuit diagram is what would not work with the higher "regulated"
voltage -- unless something else has failed from that higher voltage,
perhaps a tantalum capacitor as you've suggested -- though I don't "see"
anything that's broken or burned.

Check what's written on each part.
It's clearly different than the other "741" Op Amps in the circuit.

Have you tried ordering one from TEK factory service?
No, I've just started working on this unit.

Can I assume you've tried it in a different hole to rule out the
possibility of a mainframe transistor failure or failure in a solder
joint on one of the transformer windings?
Yes. I've also looked at and measured the AC input and its rectified and

filtered version and they look fine.

Since you didn't mention any of the other supplies being down, one might
rightly or wrongly assume that they're ok and the reference is working.
Look for shorted tantalum caps. Sometimes they short so bad they don't
even get warm.
I haven't even tried to measure the other voltages -- I think that they're

all set "proportional" to this one.

I'd worry about the op amp specs after you determine it's bad.
I'm pretty sure it's bad.

mike

--
Return address is VALID.
500MHz Tek DSOscilloscope TDS520
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Bunch of stuff For Sale and Wanted at the link below.
http://www.geocities.com/SiliconValley/Monitor/4710/

 

[Tom MacIntyre]

On Sat, 23 Oct 2004 20:10:04 -0500, Jim Adney <jadney@vwtype3.org>
wrote:

On Fri, 22 Oct 2004 23:54:04 +0200 Willem van der Berg
noone@here.com> wrote:

BTW, tonight it worked for two hours. Yesterday it worked for 20 minutes.
Does that make any sense?

Was it cooler last night than it was the night before? Your problem
sounds temperature related, so if the set starts out cooler, then it
will take it longer to warm up to the failure temp.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------

Bad solder connection on the colour oscillator?

Tom