I have a Zenith Sentry 2 TV thats broken. It's model number SLS2049S
made in 1993.
When it's turned on there is only a white horizontal line across the
screen.

I've looked at the circuit board and I don't see and obvious bad solder
connections.
How can I fix it?
Since I'm inexperienced with soldering and electronic parts, please be
specific.

Do you know how to troubleshoot a vertical circuit, use test equipment
etc? I could give you some information such as to check for VCC at the
vertical output chip. If its not there follow that line back to the
flyback. You may have a shorted high speed diode that opened a small
value fuse resistor in series with it. Common on some Zeniths. I'm
sorry that I can't tell you specifically what and where but we don't
usually work from schematics. Now If this does not make any sense to
you, with all due respect put the set back together and take it to a TV
repairman. Lenny Stein, Barlen Electronics.

Thanks for your reply. No I don't know how to troubleshoot a vertical
circuit, but I'd like to know how.
I have a voltmeter, but I assume I need more than that. What do I
need? I would like to be able to do troubleshooting so I would
consider buying more test equipment..
I don't have a schematic, so I don't know where the vertical circuit
is. Would it help to have one? If so, where can I get one?
I would expect I could buy a new 25 inch TV cheaper than I would pay to
repair this 20 inch one; so it's either fix it myself or throw it out.

Barry

On 21 Sep 2005 01:38:54 -0700, "Barry" wrote:

I have a Zenith Sentry 2 TV thats broken. It's model number SLS2049S
made in 1993.
When it's turned on there is only a white horizontal line across the
screen.

I've looked at the circuit board and I don't see and obvious bad solder
connections.
How can I fix it?
Since I'm inexperienced with soldering and electronic parts, please be
specific.


These sets had a resistor in series with the power supply to the
vertical circuit that tended to open. A lot of the time it was the
only thing wrong. Bad soldering on the vertical IC was also common.

These sets also had very poor CRT life. I wouldn't bother paying
anyone to look at it because it will probably not last long.

Zenith Sentry 2 and System 3 TVs went way downhill in the mid 80s through
early 90s. The CRTs only lasted about 5 years on average under normal use.
I'd just go out and buy a new set. Don't know how many of these TVs I've
seen playing in thrift stores with a nice white horizontal line across them.

If the CRT alternates now and then between a good full picture and white
horizonal line, then like the other poster said it's a bad resistor in the
vertical circuits... but many TV repair shops don't want to check or mess
with this problem and tell the owner it's still due to a bad CRT.

"Barry" wrote in message
ups.com...

I have a Zenith Sentry 2 TV thats broken. It's model number SLS2049S
made in 1993.
When it's turned on there is only a white horizontal line across the
screen.

Barry:
It would be very much SAFER for you to learn electronics troubleshooting on
equipment less dangerous than your television. Starting at square one like
you would be... you would be wise to get some books and other reading
material and put together and build some basic and simple electronics
projects to hone your soldering skills and electronics knowledge.... then
you can graduate to more intricate battery operated and eventually AC power
line operated devices that use low B+ voltages such as portable radios,
stereo equipment, tape decks, CD players, etc...... then when you know
better what you are doing then you might want to tackle much more
complicated circuitry in things like your television which has very high
voltages with very dangerous and lethal electrical shock hazards inside....
note that these hazards can be present even when the AC Power is
disconnected... be very careful.
You might want to go to the website for this newsgroup at
http://www.repairfaq.org/
there, with some searching, you will find lots of good repair and safety
information regarding a plethora of electronics and electrical equipment.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -



"Barry" wrote in message
oups.com...
Thanks for your reply. No I don't know how to troubleshoot a vertical
circuit, but I'd like to know how.
I have a voltmeter, but I assume I need more than that. What do I
need? I would like to be able to do troubleshooting so I would
consider buying more test equipment..
I don't have a schematic, so I don't know where the vertical circuit
is. Would it help to have one? If so, where can I get one?
I would expect I could buy a new 25 inch TV cheaper than I would pay to
repair this 20 inch one; so it's either fix it myself or throw it out.

Barry

If I bend the circuit board the picture comes back.
I've examined and probed the solder connections on the bottom of the
board, but I can't find any that are obviously bad.
Because the picture comes back when I bend the board, am I right to
assume that it is a bad solder connection or could it still be a bad
resistor in the vertical circuit.
Can any one give me some tips to find the problem?
I can I locate the vertical IC?

If I bend the circuit board the picture comes back.
I've examined and probed the solder connections on the bottom of the
board, but I can't find any that are obviously bad.
Because the picture comes back when I bend the board, am I right to
assume that it is a bad solder connection or could it still be a bad
resistor in the vertical circuit.
Can any one give me some tips to find the problem?
How can I locate the vertical IC?

"Barry" wrote in message
ups.com...
If I bend the circuit board the picture comes back.
I've examined and probed the solder connections on the bottom of the
board, but I can't find any that are obviously bad.
Because the picture comes back when I bend the board, am I right to
assume that it is a bad solder connection or could it still be a bad
resistor in the vertical circuit.
Can any one give me some tips to find the problem?
How can I locate the vertical IC?


It's very likely a solder connection, the vertical IC is usually a small
8-10 pin chip mounted to a heatsink, though sometimes it's separate
transistors. You can follow the traces from the vertical yoke winding back
to the output circuit. Try poking at parts with a plastic or wooden stick
and see if you can narrow down the problem.

Thank you.
I can't find a chip, so maybe the vertical IC is separate resistors.
I followed the traces back from the vertical yoke and poked at the
parts with a wooden stick, but I didn't find anything.
Should I be able to trace the vertical circuit back to the power
supply?
I'm not getting that far, so maybe I'm tracing it wrong.
How would I go about testing each soldered connection?
Can I do a continuity check? With the power off naturally.

Barry

Barry ha escrito:

Thank you.
I can't find a chip, so maybe the vertical IC is separate resistors.
I followed the traces back from the vertical yoke and poked at the
parts with a wooden stick, but I didn't find anything.
Should I be able to trace the vertical circuit back to the power
supply?
I'm not getting that far, so maybe I'm tracing it wrong.
How would I go about testing each soldered connection?
Can I do a continuity check? With the power off naturally.

Barry

well it 's almost certainly not a resistor if the picture comes back.
Don't overlook the possibility that the yoke cables could be loose and
this may cause the problem, especially if there are not obvious bad
solder joints on the pcb.

Ben

On 29 Sep 2005 10:55:21 -0700, "Barry" wrote:

If I bend the circuit board the picture comes back.
I've examined and probed the solder connections on the bottom of the
board, but I can't find any that are obviously bad.
Because the picture comes back when I bend the board, am I right to
assume that it is a bad solder connection or could it still be a bad
resistor in the vertical circuit.
Can any one give me some tips to find the problem?
How can I locate the vertical IC?

The vertical IC is a on a heat sink near the edge of the board on most
of those sets. As someone else said, it will have 8-10 pins, probably
in a single row. It's definitely there somewhere, you just need to
find it and resolder it. Those sets often had bad soldering on this
IC. Don't run the set until it's fixed because the IC will probably
fail.
Andy Cuffe

-- Use this address until 12/31/2005

-- Use this address after 12/31/2005

"Barry" wrote in message
oups.com...
Thank you.
I can't find a chip, so maybe the vertical IC is separate resistors.
I followed the traces back from the vertical yoke and poked at the
parts with a wooden stick, but I didn't find anything.
Should I be able to trace the vertical circuit back to the power
supply?
I'm not getting that far, so maybe I'm tracing it wrong.
How would I go about testing each soldered connection?
Can I do a continuity check? With the power off naturally.

Barry


Transistors, not resistors, and no it shouldn't go back to the power supply,
it should go back to a pair of transistors mounted on heatsinks, might be a
capacitor in series with it too.

Thank you all for your help.
I think I found the vertical IC.
The reason I couldn't find it before was because I didn't recognize the
heatsink for what it was and I wasn't expecting the vertical IC to be
mounted in a vertical position.
The number on the board next the chip is IC2100; that makes sense.
I think it has 7 pins.
I tested the pins by connecting them with a wire to the next connection
on the trace.
Nothing happened to the picture so I figured the soldering job was OK.
Unfortunately, now I can't get the picture to come back when I bend the
board.
Maybe I did burn the IC out by running the set while I was testing it.
Do I need to replace the IC in order to find out?

Barry

"Barry" wrote in message
oups.com...
Thank you all for your help.
I think I found the vertical IC.
The reason I couldn't find it before was because I didn't recognize the
heatsink for what it was and I wasn't expecting the vertical IC to be
mounted in a vertical position.
The number on the board next the chip is IC2100; that makes sense.
I think it has 7 pins.
I tested the pins by connecting them with a wire to the next connection
on the trace.
Nothing happened to the picture so I figured the soldering job was OK.
Unfortunately, now I can't get the picture to come back when I bend the
board.
Maybe I did burn the IC out by running the set while I was testing it.
Do I need to replace the IC in order to find out?

Barry


What's the part number on the IC? If you can find a datasheet then it'll be
easy to check for a complete circuit between the IC and the vertical yoke
winding, power at the IC, and a few other things. Usually when the IC fails
it blows a fusible resistor that supplies power to it so it makes the fault
fairly obvious.

On 30 Sep 2005 12:52:24 -0700, "Barry" wrote:

Thank you all for your help.
I think I found the vertical IC.
The reason I couldn't find it before was because I didn't recognize the
heatsink for what it was and I wasn't expecting the vertical IC to be
mounted in a vertical position.
The number on the board next the chip is IC2100; that makes sense.
I think it has 7 pins.
I tested the pins by connecting them with a wire to the next connection
on the trace.
Nothing happened to the picture so I figured the soldering job was OK.
Unfortunately, now I can't get the picture to come back when I bend the
board.
Maybe I did burn the IC out by running the set while I was testing it.
Do I need to replace the IC in order to find out?

Barry

There's a resistor (around 10 ohms, or less) in series with the power
supply to the vertical IC that tends to open on those sets. If you're
lucky, that's all that's wrong. Get the number off the IC and someone
will be able to tell you which pin to trace back. You may have to
remove a metal clip that holds the IC on the heat sink to be able to
see the number.

As a general rule, resolder anything that there's any doubt about.
Trying to pinpoint the exact pin that's causing the problem is a waste
of time. Pretty much every TV I've ever worked on has had at least a
hand full of bad solder connections (sometimes dozens). Even if they
weren't causing problems yet, it's good to inspect the entire board
and resolder everything that looks questionable.
Andy Cuffe

-- Use this address until 12/31/2005

-- Use this address after 12/31/2005

R3209 and was 2ohm, Zenith later changed it to a 1ohm resistor for
greater reliability on many models.

Thank you.
There are 2 lines of number on the chip somwhat like this
LA7830
2C 4

Pardon my ignorance.
Should I completely remove the old solder before resoldering?
I'm relutant to do a lot of soldering for fear I'll mess up more than I
fix, but if necessary I'll do some practicing.
I can't locate the resistor R3209.
There is a space on the board labeled R3207, but there isn't a resistor
there.

"Barry" wrote in message
ups.com...
Thank you.
There are 2 lines of number on the chip somwhat like this
LA7830
2C 4

Pardon my ignorance.
Should I completely remove the old solder before resoldering?
I'm relutant to do a lot of soldering for fear I'll mess up more than I
fix, but if necessary I'll do some practicing.
I can't locate the resistor R3209.
There is a space on the board labeled R3207, but there isn't a resistor
there.


Here's the datasheet
http://pdf.alldatasheet.com/datashee...YO/LA7830.html


Removing the old solder isn't really nessesary in most cases, but it can't
hurt to do so if you have the tools. You will probably get better joints in
the end if you do. Oh and make sure you're using rosin core solder for
electronics, not acid core plumbing stuff.

Thank you. How would you remove the old solder?

Solder sucking braid or vacuum pump.


kip
"Barry" wrote in message
oups.com...
Thank you. How would you remove the old solder?

"Barry" wrote in message
oups.com...
Thank you. How would you remove the old solder?


My favorite cheap way is the desoldering iron Radio Shack sells for about 10
bucks, it's one of the few useful things you can still buy there.

Barry wrote:
Thank you. How would you remove the old solder?

get some old tv coax 75ohm cable, cut off the outer plastic insulation,
(carefully, so you dont cut the copper braiding), then gently peel back
the copper braiding exposing the plastic centre with 1 central wire.
cut this plastic off leaving the braiding clear. apply this to your
heated solder joints when uysing your iron and it should absorb the
solder. coating it in fluxite (solder paste) helps.
-b.

On 1 Oct 2005 05:44:01 -0700, "Barry" wrote:

Thank you.
There are 2 lines of number on the chip somwhat like this
LA7830
2C 4

Pardon my ignorance.
Should I completely remove the old solder before resoldering?


That's the vertical IC. You don't need to remove the old solder. It
sounds like you may cause more harm than good by trying. You only
need to remove the old solder in cases of extreme heat damage which
crystallizes the old solder. In this case just applying a little new
solder will work fine.
Andy Cuffe

-- Use this address until 12/31/2005

-- Use this address after 12/31/2005