Toshiba TV29C90 problem; Image fades to black...

[3T39]

Hello, les!
You wrote on Tue, 21 Mar 2006 16:23:25 -0600:

I think the OP was talking about a common or garden laser photocopier
probably A3, with a machine like that, your options are very limited and I
would recommend trying the last posters idea with a camera with a decent mp
count and filters, the scanner has potential, but an A4 scanner would make
it very hard work stitching the parts together. Of course it depends on the
physical size of the schematics but with a camera, that's not as much of an
issue. either way, to get decent results is going to take some effort.
Still, I'm sure that when you have recovered the schematics in some decent
electronic form you will make them available to all your friends here on
sci.electronics.repair, - wont you? :^)
Pete

lWith best regards, 3T39. E-mail: rubbishrat@hotmail.com

 

[JANA]

From experience with these monitors, the fault is caused by either the HV
module is failing, or the CRT is going weak.

I would be out shopping for a new monitor at this time.

--

JANA
_____


"RD" <reddog500@hotmail.com> wrote in message
news:442Uf.876496$xm3.806829@attbi_s21...
The above has 1U8-03700474 MFD SEP 2000 on the tag. It has been an excellent
monitor for about 5 or so years now. Recently, however, it has
intermittently begun to "fuzz" the fonts. I have degaussed it a few times to
no avail. When the monitor is cold, everything looks good, but after about
30 mins or so, the fonts turn fuzzy. I normally run my ATI 9700 Pro @
1024X768 32-bit colour, 85Hz refresh. Is this worth repairing? If so, where
would one begin to look? Thanks!

RD

 

[Wayne]

On Wed, 22 Mar 2006 02:58:44 GMT, adamandevil <adamandevil@nospam.net>
wrote:

I'm looking for a Dell D2026T-HS 21" CRT service manual.

I have lots of manuals to trade, mostly laser and dot-matrix printer
repair manuals for several major manufacturers - but I can probably
get any other kind of service manual you need in exchange.

Thanks,
Adam

Same chassis as Sony GDM-20SE2T

 

[Chuck]

On Tue, 21 Mar 2006 16:13:47 GMT, "Dave" <dspear99ca@yahoo.delete.com>
wrote:

I've identified a bad transistor in the power supply of an audio component,
circa 1981. It's a 2SB527 PNP transistor... I had a bit of a look around on
the net and didn't find any quick easy sources. This transistor's sole
function is to convert -26VDC coming off one side of a bridge rectifier
to -13 volts. It's wired up as follows, and I apologize for not being more
skilled in ascii art or I'd try to draw it.

The collector is the -26VDC input. It is connected to ground via a 100uF
cap.
The emitter is the -13VDC output. It is connected to ground via a 10uF cap.
The base is connected to a series 470-ohm resistor, then a parallel 10uF cap
(to ground), then a parallel zener diode (to ground), then a 5.6K-ohm
resistor, then to the collector.

My question is thus: if my downstream components can get by with -15VDC,
can I just substitute a 7915 15VDC negative voltage regulator? There are no
feedback connections from any other part of my circuit to this transistor,
it's output voltage should not vary under normal conditions. And, by freak
coincidence, the pinout of the regulator matches my circuit perfectly, it'd
be a straight swap and removing a couple of resistors. And perhaps most
importantly, I have one.

We used to sub a 2sb633 which cost about a U.S. dollar. Chuck

 

[GregS]

In article <sgZTf.7433$_Q.4467@edtnps89>, "Dave" <dspear99ca@yahoo.delete.com> wrote:

"GregS" <szekeres@pitt.edu> wrote in message
news:dvplb2$948$1@usenet01.srv.cis.pitt.edu...
In article <ktYTf.7417$_Q.7383@edtnps89>, "Dave"
dspear99ca@yahoo.delete.com> wrote:
I read again with magnifiers, thats TO126 package. Perhaps the orginator
can identify which case?? TO220 or TO126 ??

It's a TO-220 looking at it...

If its a TO220 then its a TO220.
I found my Japanese cross reference book. Here goes. Still a TO126

2SB527 SAN 2SB631 TOS 2SA815 NEC 2SA985 MAT 2SA1110 ROHM 2SB1085

A trouble may reside in you transistor manufacturer. You would have to look
at the manufacturers spec sheet to get exact figures.

If you make a regulator with diodes, put some capacitance across
the diodes.

greg

 

[Mr. Land]

I agree. I don't see how a HV or focus voltage problem would mess up
the focus in only one direction (unless it's some strange interaction
with one of Sony's non-standard shadow masks or something like that,
but that seems unlikely.)

It seems more likely that, if you are somehow losing your video
bandwidth you'd get blurring like this. Something in the video
circuitry could be intermittently limiting bandwidth, so when the fault
is occuring and the electron beam in the tube is about to draw one of
the lines making up the "o" in my example, instead of the video level
jumping "instantaneously" from white to black (which requires good
bandwidth) at the edge of the "o", it rather ramps down to black. So
what you see is a fade (aka blur) from white to black instead of a
nice, sharp, crisp line.

If I've convinced you of this hypothesis, I also have some land for
sale....

 

[Dave]

"G" <skiffing@nbnet.nb.ca> wrote in message
news:44209DDB.7060702@nbnet.nb.ca...

Dave you wouldn't put the diodes from the 7915 output to ground but from
the output to your load in series......being a negative polarity output
you'd put the cathode towards the 7915 (and any additional diodes as
well).

The trick to bumping up the voltage of a 3 terminal fixed regulator is
to insert a diode between the ground pin and ground (keep in mind to
insulate the tab if you do this!). The regulated voltage will now be
pushed up by the junction voltage of the diode or diodes (Diodes placed
as such in a 7912 would have their cathode face the ground pin.....anode
to ground).

Makes sense. One question: why do you say insulate the tab? If the tab is
already connected to ground, and you are just adding a diode, wouldn't you
only have the 1V of potential difference between ground and the pin with a
diode? Would I want to use a mica insulator between the tab and heatsink?

clear as mud?

 

[Dave D]

"Dave" <dspear99ca@yahoo.delete.com> wrote in message
news:d3fUf.1230$K11.421@clgrps12...

Makes sense. One question: why do you say insulate the tab? If the tab
is
already connected to ground, and you are just adding a diode, wouldn't you
only have the 1V of potential difference between ground and the pin with a
diode?

Because the tab is connected to the ground pin internally. If you ground the
tab then the pin is also grounded, bypassing the diode.

Would I want to use a mica insulator between the tab and heatsink?

Yes. You'd need the whole heatsink 'kit', including the plastic insulating
collar which goes on the bolt, or a plastic bolt.

Dave

 

[Scrim]

"Mr. Land" <graftonfot@yahoo.com> wrote in message
news:1143043162.600153.134710@g10g2000cwb.googlegroups.com...

I agree. I don't see how a HV or focus voltage problem would mess up
the focus in only one direction (unless it's some strange interaction
with one of Sony's non-standard shadow masks or something like that,
but that seems unlikely.)

It seems more likely that, if you are somehow losing your video
bandwidth you'd get blurring like this. Something in the video
circuitry could be intermittently limiting bandwidth, so when the fault
is occuring and the electron beam in the tube is about to draw one of
the lines making up the "o" in my example, instead of the video level
jumping "instantaneously" from white to black (which requires good
bandwidth) at the edge of the "o", it rather ramps down to black. So
what you see is a fade (aka blur) from white to black instead of a
nice, sharp, crisp line.

If I've convinced you of this hypothesis, I also have some land for
sale....

Loss of bandwidth! Yes, that would do it! Thank you - new theory. It makes a

lot more sense than my mystery high frequency modulation (which would
require lots of spare bandwidth, so didn't sound likely).
The only other possibility I can think of is if they do have separate
horizontal and vertical focus (cylindrical electron lenses?) - it's just
that I vaguely recollect reading that they do. Anyone know about that?
New:
I just got hold of "Nokia Monitor Test" and checked to see if the effect
varies with the screen resolution set in windows, and it doesn't as far as I
can tell - the physical width of blurring remains fairly constant - but I
think I now have to admit that there is some blurring in the vertical
direction too, although it's not as bad. I guess that points back to the HT?
This morning also, for the first time, I left the screen blurred to let it
warm up. Just as I returned I heard a small 'pop', which coincided with the
screen image momentarily collapsing.
So perhaps the horizontal/vertical variation in blurring is just a
consequence of the aperture grill and there is some kind of HT problem where
charge is building up and that's causing the blur?
I'll leave it blurred and watch it like a hawk tomorrow morning.
Scrim

 

[Glen in Orlando]

We have original 2SB527 in stock for US$1.99 each.

http://www.acme-sales.net

Regards,

Glen Goodwin
ACME Enterprises of Orlando
1-800-575-9833

Dave wrote:

I've identified a bad transistor in the power supply of an audio component,
circa 1981. It's a 2SB527 PNP transistor... I had a bit of a look around on
the net and didn't find any quick easy sources. This transistor's sole
function is to convert -26VDC coming off one side of a bridge rectifier
to -13 volts. It's wired up as follows, and I apologize for not being more
skilled in ascii art or I'd try to draw it.

The collector is the -26VDC input. It is connected to ground via a 100uF
cap.
The emitter is the -13VDC output. It is connected to ground via a 10uF cap.
The base is connected to a series 470-ohm resistor, then a parallel 10uF cap
(to ground), then a parallel zener diode (to ground), then a 5.6K-ohm
resistor, then to the collector.

My question is thus: if my downstream components can get by with -15VDC,
can I just substitute a 7915 15VDC negative voltage regulator? There are no
feedback connections from any other part of my circuit to this transistor,
it's output voltage should not vary under normal conditions. And, by freak
coincidence, the pinout of the regulator matches my circuit perfectly, it'd
be a straight swap and removing a couple of resistors. And perhaps most
importantly, I have one.

 

[Fred McKenzie]

In article <d3fUf.1230$K11.421@clgrps12>, "Dave"
<dspear99ca@yahoo.delete.com> wrote:

"G" <skiffing@nbnet.nb.ca> wrote in message
news:44209DDB.7060702@nbnet.nb.ca...
Dave you wouldn't put the diodes from the 7915 output to ground but from
the output to your load in series......being a negative polarity output
you'd put the cathode towards the 7915 (and any additional diodes as
well).

The trick to bumping up the voltage of a 3 terminal fixed regulator is
to insert a diode between the ground pin and ground (keep in mind to
insulate the tab if you do this!). The regulated voltage will now be
pushed up by the junction voltage of the diode or diodes (Diodes placed
as such in a 7912 would have their cathode face the ground pin.....anode
to ground).


Makes sense. One question: why do you say insulate the tab? If the tab is
already connected to ground, and you are just adding a diode, wouldn't you
only have the 1V of potential difference between ground and the pin with a
diode? Would I want to use a mica insulator between the tab and heatsink?

Dave-

I agree with G for the most part. I prefer the 7912 approach rather then
using the 7915. As someone else suggested, a capacitor from the output to
ground would be a good idea. I think you mentioned having one in the
original circuit.

Another alternative to the 7912 approach would be to use the negative
version of an LM317 with pair of resistors instead of the one diode. One
resistor would be connected from the regulator's output to its common
("adj") terminal. The other would be connected from the common terminal
to ground. Values would be chosen to produce the required output
voltage. The LM317 regulator actually has about 1.2 volts output plus the
voltage dropped by the resistor to ground. I assume there is a negative
version of the LM317, if you wanted to look further.

Of course an exact replacement transistor is the most sure-fire solution.
If you were to use an alternative part, I suggest using one rated for at
least the minimum hfe of the original part, or at least one having an
actual (measured) hfe of that value or higher.

Fred

 

[Dave]

"Glen in Orlando" <nospam.for.me@spamfree.com> wrote in message
news:442189DC.6000708@spamfree.com...

We have original 2SB527 in stock for US$1.99 each.

http://www.acme-sales.net

Holy sh#t, this site is a GOLDMINE! You sell transistors that haven't been

made since 1975! Tons of them!

Thanks, it's in my bookmark file. I already bought a TIP42C (over-rated,
but at $1.99 the price was right) at my local electronics store. BTW, how
much is shipping to Canada?

 

[G]

Looks like you're getting lots of help Dave.
The comment about insulating the tab is so that you DON'T negate the
effect of adding the diode. The tab is common with the ground pin so
you'd be bypassing what you'd be trying to accomplish

Gord

 

[Michael Kennedy]

Yes you can upgrade windows 98 to xp with the xp install disc.

"Mr. Land" <graftonfot@yahoo.com> wrote in message
news:1142965090.668227.279040@v46g2000cwv.googlegroups.com...

You're really in the wrong group for this question, but here's a short
answer: if Windows XP supports "upgrading" from Windows 98, you should
be able to retain most, if not all, of your old applications. Go
search the Windows groups to be sure, tho.

 

[adamandevil]

On Wed, 22 Mar 2006 13:41:50 GMT, whmrs@mrbc.ca (Wayne) wrote:

On Wed, 22 Mar 2006 02:58:44 GMT, adamandevil <adamandevil@nospam.net
wrote:

I'm looking for a Dell D2026T-HS 21" CRT service manual.

I have lots of manuals to trade, mostly laser and dot-matrix printer
repair manuals for several major manufacturers - but I can probably
get any other kind of service manual you need in exchange.

Thanks,
Adam

Same chassis as Sony GDM-20SE2T

Thanks Wayne!

 

[budgie]

On Wed, 22 Mar 2006 00:42:29 GMT, G <skiffing@nbnet.nb.ca> wrote:

(snip)

The trick to bumping up the voltage of a 3 terminal fixed regulator is
to insert a diode between the ground pin and ground (keep in mind to
insulate the tab if you do this!).

Sorry to be a spolier, but according to my data sheets the tab is connected to
pin 2 (whic is INPUT on a 7912 and presumably on other 79XX regulators). So the
O/P is going to have to go the insulated mounting route regardless of the diode.

 

On Tue, 21 Mar 2006 11:50:14 +0100, Jorgen Lund-Nielsen
<jorgen.lund-nielsen@xxxxxxxxdesy.de> wrote:

PE1E wrote:

The data wheel is dead.

Any 8566/8 specialist in the group whom I could explain the relevant
details to ? ( e.g. : marker is not movable/tunable neither in front
panel, nor under HPIB ).

I have ( not yet ) the Serv Ref part 1 ( RF ).


Thanks.
Peter, PE1E

Hi,

ask the people there:

http://groups.yahoo.com/group/hp_agilent_equipment/

AFAIK there are a some owner of those fine analyzer and
they have repaird them.

Jorgen

Just to throw this out there, our 8568b had the card edge connectors
start to break, specifically on the interface boards in the rf section
and power supply boards in the if/display, and weren't making good
contact. The analyzer was acting very funny and erratic. Probably
won't help, for what it's worth.

 

[Wayne Tiffany]

Voltages looked good except for the output. I had already replaced 5 caps
in that area due to high ESR, so I ordered & replaced the vertical output
chip, which was a TDA8172. The set is now up & running. Thanks for the
comments.

WT


"kip" <nospam@nospam.com> wrote in message
news:newscache$unwbwi$wvo$1@newsfeed.niagara.com...

Check Voltage on Pin 2 and 3 ,this is not your
regular Vert IC it has 2 supply voltages.
Maybe one is missing !!! if not change it.
Also change the filter caps associated with it.



kip


"Wayne Tiffany" <waynetiffany(RMVJUNK)@netzero.net> wrote in message
news:dvh6hh$dhp8$1@news3.infoave.net...
Sony KV-24FS100 television
Chassis BA-6

I agreed to look at this set for a friend at work and I am sort of stuck.
She said she was watching it just fine, glanced away, and when she looked
back, the top half of the picture was gone - just black. I fired it up
and find that the top half has collapsed. The bottom half is just fine -
full color, no foldover into that area, etc. I do, however, find that if
I hit the tv/video button on the remote, then in what I presume are the
video modes, the whole screen collapses into a horizontal line at the
middle. Keep pushing the button and when it gets back to the tv mode, the
bottom half returns.

I searched for this issue online (here and otherwise) and not found it
mentioned anywhere, so I started in. I found and downloaded the service
manual, so I have the schematics. The first thing I checked was the
electrolytic caps around the vertical output chip (TDA8172). ESR was way
high on 2, and marginal on 3 more so I replaced all 5. I also checked
all the resistors that attach to that chp and all appeared to pretty well
match the schematic. No change in action.

So, that's where I am now. My next thought is to replace the TDA8172
chip, but I would appreciate the opinion of the more experienced people
here. Any thoughts? Thanks.

WT

 

[Andy Cuffe]

On Wed, 22 Mar 2006 01:14:56 GMT, "Scrim" <nospam@nospam.com> wrote:

Hi,
What kind of tube problem would cause an intermittent blurring in only the
horizontal plane?
Isn't this most likely an intermittent fault somewhere in the electronics?
Scrim

There's a large HV resistor in the electron gun which can fail. This
causes all sorts of strange problems. I saw one that was physically
cracked once. It would go out of focus and snap back into focus.
It's also possible for arcing, or leakage around the focus grids to
cause intermittent focus. These CRTs use separate horizontal and
vertical focusing grids, so it's not unusual for them to go out of
focus in one direction only.
Andy Cuffe

acuffe@gmail.com

 

[Andy Cuffe]

On Wed, 22 Mar 2006 17:26:21 GMT, "Scrim" <nospam@nospam.com> wrote:

The only other possibility I can think of is if they do have separate
horizontal and vertical focus

They do in fact have separate horizontal and vertical focus. The two
interact slightly, so if it goes out of horizontal focus, the vertical
focus will also be affected.

I had a 21" Sony with a CRT that would intermittently go way out of
focus in the horizontal direction. Sometimes it was unusable, but it
often went for weeks without a problem. Normally it would only snap
out of focus for a second or two every few days. I eventually
replaced the CRT with one from a scrap monitor and it's been working
fine for a couple of years.
Andy Cuffe

acuffe@gmail.com