Toshiba TV29C90 problem; Image fades to black...

[AZ Nomad]

On Thu, 27 Oct 2005 08:16:04 GMT, Rikard Bosnjakovic <bos@REMOVETHIShack.org> wrote:

I have a motherboard with a slightly "roasted" coil that I'm interested in
knowing if it is possible to replace and make the board work again.

Have a look at these two images:

http://www.meradan.se/albums/album45/IMG_2210.sized.jpg (component side)

Forget the coil, look at those caps! They're blown.

There where a gadzillion motherboards made around '99-'00 that had defective
caps. You got one of them. If your time is worth more than a buck an hour
then you should just replace the board. Boards from that era can be had,
and without the defective caps, for under twenty dollars.

 

[B. W. Salt.]

In article <eq08f.18219$Ih5.9890@fe1.news.blueyonder.co.uk>,
iain@wilkie-electronics.co.uk (Iain Wilkie) wrote:

DL000D

That seems to be the Texas Instruments SN74LS00 as a direct replacement.

The others are similarly numbered.

See http://www.elektron-bbs.de/elektronik/tabellen/ddr/digibiic.htm

Seems they might have originated from the old Eastern Germany, perhaps?

 

Hi!

I've often wondered the same thing...also why a $9 alarm clock will have
provision for battery backup, but $200 VCR (back when VCRs were $200)
needed to be rweset with each blip in the mains voltage.

Hmmm...not all of them do. I've got a Panasonic VCR that will hold the
time for a couple of hours after a power failure and a Sony that seems
to be good for a few days. (Of course, both are 'mid-range' machines
and the Sony might qualify as lower high end equipment.)

I also have a Panasonic time-lapse VCR that has a NiCad battery in it.
I know it will the clock for at least two weeks. The manual says it
could last for a month.

William

 

[Iain Wilkie]

Thanks for the link.... that confirms what I was thinking !!




"B. W. Salt." <briansalt@NScix.co.uk> wrote in message
news:memo.20051027122526.42227A@briansalt.compulink.co.uk...

In article <eq08f.18219$Ih5.9890@fe1.news.blueyonder.co.uk>,
iain@wilkie-electronics.co.uk (Iain Wilkie) wrote:

DL000D

That seems to be the Texas Instruments SN74LS00 as a direct replacement.

The others are similarly numbered.

See http://www.elektron-bbs.de/elektronik/tabellen/ddr/digibiic.htm

Seems they might have originated from the old Eastern Germany, perhaps?

 

Hi!

Is that a DS1387 or something else?

I've got some microchannel-based computers that use that module. None
have died yet but I know it is a matter of time.

How did you get the module open? Do you have pictures?

William

 

[Sam Goldwasser]

"kip" <nospam@nospam.com> writes:

Looking at that 1st Jpg it looks like all those filter caps needs changing
they are swollen.

Replace the mainboard. Not worth the time and agony.

--- sam | Sci.Electronics.Repair FAQ: 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 Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
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contact me via the Feedback Form in the FAQs.

kip
"Rikard Bosnjakovic" <bos@REMOVETHIShack.org> wrote in message
news:8108f.149218$dP1.507157@newsc.telia.net...
I have a motherboard with a slightly "roasted" coil that I'm interested in
knowing if it is possible to replace and make the board work again.

Have a look at these two images:

http://www.meradan.se/albums/album45/IMG_2210.sized.jpg (component side)
http://www.meradan.se/albums/album45/IMG_2211.sized.jpg (solder side)

I know it is difficult to give a clear opinion only by looking, but what
would be your guess? Could it be only the coil that's toasted, or could it
be any more components? If the latter, how can I find out if that's the
case?

 

[Ol' Duffer]

In article <7zT7f.19409$Pp1.3037@bignews3.bellsouth.net>,
jakdedert@bellsouth.net says...

FWIW, there are utilities which will update your computer clock from the
National Bureau of Standards over the web.....

They call themselves NIST these days, and they also still have
a dialup service.

 

Hi!

I've always wondered why the batteries in macs run down so quickly. I
rarely see a PC newer than 10 years old with a bad battery, but I
consistently see 3-5 year old macs with totally dead clock batteries.

Yep, I've seen the same thing here. I have a number of old Macs (6100,
6300, LC, 9600, SE/30) that still keep decent time on the
factory-installed batteries. Some of these have gotten to the point
where the machines need to be powered up somewhat often to keep the
settings intact.

By compare I have many a G3 CRT-type iMac around (the 2001 models,
350~500MHz) and almost all of them have had to have their batteries
replaced.

Looking at things I can see one difference. Most PCs new and old power
their CMOS RAM chips from the power supply when they're running. A
great many ATX systems seem to keep the CMOS RAM and clock running from
the ATX standby supply as long as it is running. Some older PCs also
have NiCad or NiMH batteries onboard along with the circuitry to charge
them when powered up.

I've investigated the Macintosh a little bit and it looks like the
clock/NVRAM battery is constantly pulled upon, even when the computer
is on. This could also shorten battery life.

William

 

[James Sweet]

Mark Smith wrote:

Installed new flyback to restore high voltage. Now can't get good focus.
When focus is good in center, it's poor on sides & corners.
When it's good on sides & corners, it's poor in center.
This is the first G810 I've ever repaired. CRT seems good & strong
with great grey scale.

Thanks in advance.

Sounds like you got the two focus leads swapped, check the wires that go
to the neck board, colors can be deceptive, try swapping the two focus
leads and see what happens. Make sure you don't swap the G2 with one of
the focus though.

 

[James Sweet]

bstanton@null.com wrote:

I've inherited my grandfather's shop, and there are boxes of
old components, from transistors in metal cans to rolls of
cotton insulated wire and capacitors that look like wax
sealed rolls of paper and foil. Little to none of it is
actually "new," it's mostly removed from older equipment.
There are also rectifiers that look like multiple square
pieces of metal separated by some rectifying material.

Is any of this worth anything? I'd like to junk anything
without value, but not if it's useful. Do people repair
older equipment with this stuff for "authenticity?" Not
many tubes in the collection. Comments are welcome.

Bits and pieces of it may well be worth something, other bits are junk.
Your best bet is to talk to people who restore old radios, they're the
ones most likely to benefit from it. In a pinch you could just sort it
into boxes of similar looking stuff and post it on ebay.

 

[Asimov]

"tempus fugit" bravely wrote to "All" (27 Oct 05 11:17:42)
--- on the heady topic of "unit hums loudly regardless of volume"

tf> From: "tempus fugit" <toccata@no.spam.ciaccess.com>
tf> Xref: core-easynews sci.electronics.repair:346437

tf> Hey all;

tf> I'm trying to repair an old tube portable record player. When it is
tf> on, it hums really loud, regardless of the volume.

Have you tried turning the ac plug around?

Which way the plug is inserted matters with these. Let the record
player warm up, then insert the plug one way or the other, and then
paint a mark for which was the quietest way. One way: lots of hum, the
other: quiet hiss.

Those old tube units used to get B+ directly from the powerline (or
sometimes a voltage doubler) and used a large value resistor bypassed
by a 0.01uF to RF ground the tone arm shielding to neutral. The power
for the filaments often came from a secondary winding in the motor
coil. Don't use this type of record player near the bathtub. Lethal!

Another possibility is a broken wire at the cartridge.

A*s*i*m*o*v

.... Just a little force field zap.

 

[Asimov]

"do_not_spam_me@my-deja.com" bravely wrote to "All" (27 Oct 05 09:34:24)
--- on the heady topic of "Re: Why aren't computer clocks as accurate as cheap
quartz watches?"

do> From: do_not_spam_me@my-deja.com
do> Xref: core-easynews sci.electronics.basics:145659
do> sci.electronics.repair:346469 alt.comp.hardware.pc-homebuilt:351295



do> w_tom wrote:

Watches have an internal capacitor to adjust for each
crystal. I have never seen that capacitor on motherboards
since (I believe it was) the IBM AT. Furthermore, the PC
clock operates at two significantly different voltages that
will change crystal frequency. Battery voltage and voltage
when PC is powered will cause additional fluctuation. Which
voltage should they adjust the capacitor to? Just easier to
not install and adjust the capacitor.

do> I have an ancient Seiko quartz with a trimmer inside, and by adjusting
do> it I was able to make it accurate to 30 seconds a year. But few cheap
do> watches have them, including none of those I tried in this test.


I bought a cheap $5 lcd watch years ago and noticed the circuit had
the solder pads for a trimmer cap. After adding the timmer and
adjusting, it was the most accurate timepiece in the house. When I
came across another identical watch many years later I did the same
thing to it too.

The adjustment was trial and error using CHU. Starting at the
midpoint, I kept cutting the error in half either side then set it
inbetween. Both keep great time, I never notice a difference even
longterm, perhaps a second per month if that.

How did you adjust yours, with a pickup coil and frequency counter?
I suppose that would be the logical way to do it but then again a
counter could be off a tiny bit too. The NIST over the internet seems
nice too but what are the sources of error with this?

A*s*i*m*o*v

.... I worked hard to attach the electrodes to it.

 

[CJT]

tempus fugit wrote:

Thanks for your reply.

Sorry, here's some more info:

There is a power transformer.
Only 1 diode that I could see.
Measured voltages at cap in question was ~150v.

If the cap had DC on it, the diode is probably ok. The capacitor(s)
could be dried out (although I think you said you checked them, so
that's not too likely). From there, you move toward shielding type
problems as already described elsewhere in the thread.

Only 2 tubes - 12AX7 and can't remember the power tube offhand.

If one of the tubes had an internal heater-to-cathode short (or for

that matter, a short at the tube socket), that could cause a lot of hum.
Such shorts are not uncommon.

At any rate, now you have plenty of ideas to consider.

There was also some small device which I assume was a transformer that hadd
100mA marked on it. It looked like a trasformer with cooling fins.


"CJT" <abujlehc@prodigy.net> wrote in message
news:436100B7.1090008@prodigy.net...

tempus fugit wrote:


Hey all;

I'm trying to repair an old tube portable record player. When it is on,

it

hums really loud, regardless of the volume. I assumed that this must be

a

problem with filter caps, but they test OK for ESR and shorts. 1 of the
problems is that there are 3 or 4 in a can, so I don't know what the

values

are supposed to be.

Is there anything else that may cause this symptom? I suppose I could
parallel some caps across the existing ones, but I don't even know what

the

values are supposed to be.

Thanks




One or more diodes in the power supply (assuming it uses them) is
shorted. If it has a rectifier tube instead of semiconductor diodes,
then either the tube is shorted or, if it has its own filament supply
(e.g. 5U4), then that supply could be shorted inside or outside of the
power transformer (assuming it has a transformer), although there's a
pretty good chance the tube would be glowing bright red if that were
the case. If it's all tube and has no power transformer, then you've
got a potentially lethal hot chassis and you'd better be d*mned careful.
Check for shorted line bypass capacitors if it's this last case.

Or it could be one or more capacitors, as earlier suggested, or a break
in some shielding.

As you can surmise, additional information about the circuit involved
could narrow the possibilities (and possibly suggest others).

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.

 

[jakdedert]

James Sweet wrote:

Joe Waddell wrote:

All,
I have a Leslie Combo Preamp pedal that I use to connect musical
instruments to a Leslie 147 Speaker.

The pedal has a Pilot Light in it that indicates if the Leslie 147
Speaker is rotating at "Fast" speed.

A foot switch on the pedal closed and opened the circuit that
controlled speed. When the circuit was open, the Leslie spun "Fast"
and when the circuit was closed, the Leslie spun "Slow".

There are two wires running to the foot switch. Right before that
switch, the Pilot Light is located, connected to both wires that are
running to the foot switch.

When the footswitch is closed, the current flows through the footswitch
and not the pilot light, and the pilot light is not lit.

When the foot switch is open, the current flows to the pilot light and
causes it to emit light.

Here's the strange thing that I need help with. I noticed that in Fast
mode (with the pilot light lit from the open footswitch), an annoying
noise would come out of the Leslie Speaker. I, just by chance,
discovered that the Pilot Light was the source of this noise.

Some sources on-line talk about needing to ground pilot lights in
electronics, or it can cause a 120Hz buzz.

Has anyone every heard of this before? Could someone explain to me
what a Pilot Light is? Is it like a lightbulb, in that it acts as a
resistor in a circuit?

Thanks,
Joe



A pilot light is nothing but a lightbulb, my guess is that the load of
the lamp is exposing a problem elsewhere in the circuit, probably a bad
connection or a dried out capacitor.

....or else the lightbulb has nothing at all to do with the noise you
experience.

How did the OP determine it to be so? I see nothing in the post to pin
the pilot light as the culprit, except that he says it's so.

The description of the lamp circuit is fairly complete, but how does
this relate to the audio signal path? What is this noise, how does it
sound? Is it a 120 Hz buzz or something else? You (OP) describe this
as a preamp pedal. Does it also contain active electronics to boost the
signal?

jak

 

[CJT]

B. W. Salt. wrote:

In article <lb62m1t57qasrqdrer78qisaq1hs1e02cr@4ax.com>, B Stanton
(ll.com) wrote:


There are also rectifiers that look like multiple square
pieces of metal separated by some rectifying material.


Those are selenium rectifiers. No longer used except as replacements in
very old equipment. Smell like rotten eggs when they fail.

Definitely not a good thing to breathe in.

I still have a

battery charger that uses selenium...


Do people repair
older equipment with this stuff for "authenticity?"


Might well be so in the case of the capacitors, but one would have to be
really dedicated to authenticity, I would think, unless a modern component
doesn't fit the bill.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.

 

[jakdedert]

CJT wrote:

B. W. Salt. wrote:

In article <lb62m1t57qasrqdrer78qisaq1hs1e02cr@4ax.com>, B Stanton
(ll.com) wrote:


There are also rectifiers that look like multiple square
pieces of metal separated by some rectifying material.



Those are selenium rectifiers. No longer used except as replacements
in very old equipment. Smell like rotten eggs when they fail.


Definitely not a good thing to breathe in.

I still have a

battery charger that uses selenium...

If you use it often, replace with silicon. A series resistor is

required to simulate the original voltage drop. As CJT notes, it's NOT
a good thing to breathe...poisonous, I've heard.

The old rectifier 'will' go out...not if, but when.

Do people repair
older equipment with this stuff for "authenticity?"


Often, restorers will use the shell of the old component to hide the

new--for authenticity. OTOH, some of those old wax caps bring high
prices on Ebay, due to a misguided quest for an 'authentic' sound.....

jak

Might well be so in the case of the capacitors, but one would have to
be really dedicated to authenticity, I would think, unless a modern
component doesn't fit the bill.

 

[James Sweet]

...or else the lightbulb has nothing at all to do with the noise you
experience.

How did the OP determine it to be so? I see nothing in the post to pin
the pilot light as the culprit, except that he says it's so.

The description of the lamp circuit is fairly complete, but how does
this relate to the audio signal path? What is this noise, how does it
sound? Is it a 120 Hz buzz or something else? You (OP) describe this
as a preamp pedal. Does it also contain active electronics to boost the
signal?

jak

Well I had simply assumed that he had tried disconnecting the pilot lamp
and the problem went away,if not then that's certainly the obvious next
step.

 

[Clive Tobin]

Joe Waddell wrote:

Here's the strange thing that I need help with. I noticed that in Fast
mode (with the pilot light lit from the open footswitch), an annoying
noise would come out of the Leslie Speaker.

Ah, youngsters and their lack of familiarity with old stuff! (I say,
while stroking my hypothetical long white beard)...

If this is old technology, and if the foot switch is switching line
voltage, the pilot light is probably a small NE-2 type neon lamp and
series ballasting resistor. It does not conduct continuously but just
on peaks of the AC voltage when it is high enough for the lamp to
ionize. The voltage and current through it makes a nasty
spiky-square-ish waveform of about 200 volts p-p which can in fact
easily cause a buzz in nearby sensitive low level circuits. At the end
of each half-cycle it could also be oscillating in its negative
resistance region.

I would look for a shielding or grounding problem. Maybe replace the
neon light with a pair of back-to-back low current rated LEDs and a
series resistor to limit the current to a few milliamps or so.

 

[gb]

"bstanton@null.com" <B Stanton> wrote in message
news:lb62m1t57qasrqdrer78qisaq1hs1e02cr@4ax.com...

I've inherited my grandfather's shop, and there are boxes of
old components, from transistors in metal cans to rolls of
cotton insulated wire and capacitors that look like wax
sealed rolls of paper and foil. Little to none of it is
actually "new," it's mostly removed from older equipment.
There are also rectifiers that look like multiple square
pieces of metal separated by some rectifying material.

Is any of this worth anything? I'd like to junk anything
without value, but not if it's useful. Do people repair
older equipment with this stuff for "authenticity?" Not
many tubes in the collection. Comments are welcome.

Yes, rec.antiques.radio+phone IS the correct group for this posting.

The cloth covered wire is used by some restorers of 1930s; 1940s radios
(authentic, look for restorations).

The transistors may be of value - especially if they are no longer available
(1950s and 1960s transistor radio restorers).

In any event do NOT chuck to the garbage. Find a bright young mind (high
school) that is interested in electronics -- and needs his first "junk box
of components -- there is at least one in every neighborhood

gb

 

[Rick Yerger]

"DBLEXPOSURE" &lt;celstuff@hotmail.com&gt; wrote in message news:VNGdnd0SY9s30PzenZ2dnUVZ_tCdnZ2d@midco.net...

Just in case anybody is interested

http://www.thinkman.com/dimension4/index.htm

And for the record, Tom, is relevant to the OP's question because it
concerns your PC's clock keeping accurate time. It is a solution to the
problem.

That wasn't the question. The OP didn't ask how to solve
the problem.