Hi everyone

I have a problem with my television set. It's a Daewoo 2594ST model
using the CP775 chassis. Service manual can be downloaded for free
from he http://www.eserviceinfo.com by entering the
model or chassis number in the datasheet search field, or I can email
the whole manual or just the schematics in PDF format upon request.

There's a 1cm vertical band which is lighter than the rest of the
screen at the right-hand edge. It tapers slightly as it gets toward
the bottom. Also the top-right corner has a couple of columns of
pixels not lighting as though corner adjustment is off, and the same
towards the middle of this right-hand edge, as though pincushion
needs adjusting, although this goes when the overall screen
brightness increases and the picture 'breathes'.

I thought maybe the corner and pincushion might need adjusting, or
since it tapers slightly, maybe even the trapezium adjustment, but I
can't do geometry adjustments without a "Remocon" service
remote according to the service manual, and I've never seen this
lighter band effect when geometry is out before. I have seen
something like it when horizontal linearity was over-adjusted on a
set, as though the picture was folding over at the edge or horizontal
centering was adjusted too far over to one side causing that side to
have a siilar effect to this, but all that seems ok - channel logos
are in the correct positions.

Only one thing in the sci.electronics.repair FAQ sounds slightly
similar but the cause (electrolytic decoupling the 205V supply to CRT
base amps) isn't the case in this set as substitution today of the
10uF, 250V one with a known good replacement made no difference. Two
more caps on the same feed on the CRT base itself are also good.

Anyone got any ideas please?

Regards,
James

Rather do adjustments, it would be more intelligent to find the
defective parts that are causing the problem. Most of the time, it is
capacitors that are going high in ESR, that cause these types of faults.
Do an ESR test of all the caps in the scan and pin amplifier areas. I am
sure you will probably find a number of them that have to be changed.

--

Jerry G.


"JamesQB" wrote in message
...
Hi everyone

I have a problem with my television set. It's a Daewoo 2594ST model
using the CP775 chassis. Service manual can be downloaded for free
from he http://www.eserviceinfo.com by entering the
model or chassis number in the datasheet search field, or I can email
the whole manual or just the schematics in PDF format upon request.

There's a 1cm vertical band which is lighter than the rest of the
screen at the right-hand edge. It tapers slightly as it gets toward
the bottom. Also the top-right corner has a couple of columns of
pixels not lighting as though corner adjustment is off, and the same
towards the middle of this right-hand edge, as though pincushion
needs adjusting, although this goes when the overall screen
brightness increases and the picture 'breathes'.

I thought maybe the corner and pincushion might need adjusting, or
since it tapers slightly, maybe even the trapezium adjustment, but I
can't do geometry adjustments without a "Remocon" service
remote according to the service manual, and I've never seen this
lighter band effect when geometry is out before. I have seen
something like it when horizontal linearity was over-adjusted on a
set, as though the picture was folding over at the edge or horizontal
centering was adjusted too far over to one side causing that side to
have a siilar effect to this, but all that seems ok - channel logos
are in the correct positions.

Only one thing in the sci.electronics.repair FAQ sounds slightly
similar but the cause (electrolytic decoupling the 205V supply to CRT
base amps) isn't the case in this set as substitution today of the
10uF, 250V one with a known good replacement made no difference. Two
more caps on the same feed on the CRT base itself are also good.

Anyone got any ideas please?

Regards,
James

very nice and helpful Larry Z. at daewoo technical (1-800-323-9668)


Daewoo part number DECAKIT011 Picture shift kit
can be ordered from Fox International 800-321-6993

The main issue: pix shifted to right leaving black bar on left side:
Variable resistor R516 is open and/or D504 open due to excess current.
Repair: The below is the mod kit called: decakit011.
Change value of R420,C505, replace damaged R516,D504.
Repair:
R420: 240 ohm/ 1W --- 1.8K ohm 1W # RS01Z182JF
C505 2200PF 50V Mylar - 1000PF 50V Mylar # CMXB1H102K
R516 10 K ohm VR R semi fixed--- #RV5426103P
D504 1N4148 # D1N4148---
Order From:
Fax 201-935-5004 or call 1-800-323-9668.


r 516 open d504 defective.
change r 420 to 1.8k one watt.
change c 505 to 1000pf@ 50 volt.(mylar)
r516 to 10 k pot. d504 = 1n4148

Dani, thank you very much for the info, however this set has the
trouble on the right of the screen. The picture still seems to be
centered okay, just this trouble at the right-hand edge. It affects
from the middle of the edge to the right corner and is pulled in at
any point along the vertical depending on brightness level in picture
to left of it, leaving unlit pixels.

I will try to do an illustration of it and include it.

Jerry, of course it's more intelligent to find defective parts if any
are, however I got given this set and it had cramped frame affecting
top half of frame, cure was new frame IC and replacement of two high
ESR caps in its feed lines. Also, one O/C dried-up cap was found by
accident which was in circuitry associated with the HT feed to the
line-output transistor - it was a 2.2uF 160V type and was also
replaced. Thing is, I don't know if this problem on the right edge
was always there and the other owners didn't really notice it, as it
isn't that bad, it's just I've got a keen eye and don't like it, or
if it's new. Others have told me before that they don't notice most
picture problems till I point them out.

I have already checked all caps in the line stage and amp area. Those
that had even slightly high ESR were replaced. All others were fine in
ESR and capacitance value. Also checked for any resistors that may
have gone high, none have of those I tested. Also checked all diodes
for any leakage but all read fine.

Here is illustration:

http://img163.imageshack.us/img163/2057/daewoo3qy.png

May want to do some testing of diodes and resistors while the set is
running. I would replace all the caps in the horizontal and drive
section because one may show good but can be bad. I would also
replace those parts that was mentioned in one of the previous post
for parts sometimes test good but can be bad. But it does look like
it may have a B+ problem. Is your B+ at the proper voltage ? Also may
want to replace your horizontal output if you have a spare one there.
What happens when you turn the screen control on the flyback down
does it still show the line on that one side ? This problem can also
be caused by a bad yoke. I will take a look the schematic over the
weekend and see what I may come up with. But check your B+ line.

May want to do some testing of diodes and resistors while the set is
running.
Do you mean checking voltages from them? Or checking voltage drops
across them? All voltages marked on the schematics are reading
correct for chopper and line stages.

I would replace all the caps in the horizontal and drive section
because one may show good but can be bad.
I've now done that (used new ones), but to no avail. I've even checked
the non-electrolytics.

I would also replace those parts that was mentioned in one of the
previous post for parts sometimes test good but can be bad.
Also done, but still no joy I'm afraid.

But it does look like it may have a B+ problem. Is your B+ at the
proper voltage ?
Yep, spot on at 132V when set is running.

Also may want to replace your horizontal output if you have a spare
one there.
Unfortunately I don't have the necessary 2SD1880. I have a 2SD1887 but
it doesn't have the internal damper diode or base-emitter resistor.
The datasheets don't say what the resistance should be of the
internal resistor, but I'm getting 50 Ohms. I have many variations of
BU2508s and BU4808s but the ones with internal damper diodes and
resistors measure 30 Ohms B-E.

What happens when you turn the screen control on the flyback down
does it still show the line on that one side ?
Yes, it does. I am really starting to think this is a line linearity
problem. There is no adjustment in the service mode for line
linearity, so at least my lack of "remocon" may not be
important since it might not be simply an adjustment needed.

This problem can also be caused by a bad yoke. I will take a look
the schematic over the weekend and see what I may come up with. But
check your B+ line.
Did you have a look over it?

Thanks again,
James