Hi NG,
hi Franc,
After my two day business travel I start my next repair attempt on
Saturday morning taking your friendly hints into account.
First of all I was very lucky to find some bad solder pads (at pin 2 and
5 of the TLP580 opto coupler), hoping thats the reason of the malfunction.
But after mounting all boards in the tv case, I get the same black
screen as mentioned before.
I think thanks good its weekend and I have plenty time to find the buggy
part(s).
I start again to solder all suspect looking pads in the belief that
one more is cold ant try to bring the psu to running outside the tv case.
But as Murphy is always not far away it will become a longer story to tell.
As I verified that pin 2 of IC501 (STR58041) gets a high sig from the
opto transistor (about 1.3V) as told me by Franc I create a 500Ohm/100W
dummy load for the 110V line of the psu and connected it to CP508 gnd -
main b+.
I connected pin 1 of CP504 to pin 1 CP505 and pin 3 of CP505 to pin 2
of CP504 together (bridge the POWER-ON switch) and connected pin 1 and 2
of CP502 and in addition supply 0-3V to pin 1 and 2 of CP503 to simulate
a power on sig of the mcu.
After some few trays increasing the voltage over 1,7V at pin 2 of CP503
I hear the switching sound of the psu and measure 113V at my load.
All looks fine and I was lucky and reinstall the psu in the tv case
being convinced that now all will work ok and only a bad solder
connection was the reason for the drop out as so often be the case.
During the Saturday evening tw was running stable, wife was lucky and I
too. Unfortunately after two hours the same black screen scenario
occurred as the two previous times before.
Becoming a bit angry I decide to continue my repair session on Sunday
morning after breakfast with a relaxed brain ;-).
I decide to change all diodes from the primary side except the from the
power rectifier D501 to D504 as this diodes are general purpose diodes
and looks ok as I measured them with a simple ohm meter.
The other diodes looks good too, but are fast recovery diodes and
probably makes trouble when voltage revers, as some of them are located
nearby hot resistors and the pcb is already of a dark color at this
place so that these diodes are exposed to intensive heat too.
I replaced them all (D505,D506,D507,D508,D510) by a 1N4937 (fast
recovery 600V diode found in my boxes) as well the D515 (which looks
different to the changed EU1A, EU1Z). The Marking code is a big B and T
and a smaller 8F and two rings at the kathode side. I'm not sure if this
is a zener diode, but don't looks so according the schematic which is
not in a best quality as mentioned before.
Despite this replacement the psu don't start when applying a 2V voltage
to the power/on pin of CP503 as in my first attempt to repair it.
After this replacement of the mentioned diodes I replaced some resistors
(R509 by 33Ohm/3W), (R504,R507 by 470k || 470k + 390k || 390k all 1/4W
as not having a suitable 2x 220k), (R521, R524 by a new 100k resistor)
and measured R510 as 180k, R507 as 56k R511 as 33Ohm R501 as 1Ohm.
Furthermore I check all tree Transistors Q502/Q503 (2SD863) and Q504
(2SC945) and they looks good when measuring the NP and PN doides.
Now I belief that the IC 501 was blown by my last attempt watching
tv despite the fuse is ok.
When measuring at all five pins I get 313V DC at pin 3, near GND at pin
4, 0V at pin 1 & 5 despite the schematic show -32 or -39 V at pin 1 & 5
and about 1.3V at pin 2 when injecting 2V to CP503 at pin 2.
When I look at pin 3 via the scope I don't see any oscillation attempt.
Today I will buy a new STR58041 (IC501) in the hope that this ic is
defective otherwise I will dispose the tv to the local junk dealer.
Any new suggestion for my last repair attempt.
Greetings
Markus
Franc Zabkar schrieb:
On Tue, 22 Jul 2008 10:05:11 +0200, markus wolfgart
put finger to keyboard and composed:
The tv don't respond to the channel keys but display the last channel
number from the previous run.
Today I had found some datasheet from parts located on the mainboard.
(2SD1878, 2SC2621E, TDA4940, TDA4944, AN5836, AN5860, LA7210, LA7220 and
LA4445) for my later on investigation.
Unfortunately the parts named uPC1488H, ...
That's a vertical output. I wouldn't be looking there.
... TA8659AN Toshiba, OEC8024B Orion,
... and ?K1006? Sony IC102 had no positive hit by my search query :-(.
CXK1006L Serial Electrically-Erasable PROM (EEPROM) - With
Seq/Controller
http://www.datasheetarchive.com/specsheet/CXK1006L.html (specs)
I had already found and download the schematic, but its hard to read it
as it is a very poor quality scan.
No chance to read the voltage levels and even the part id.
If you have a better scan or pdf doc, please sent it to me, if possible.
These look similar:
http://www.eserviceinfo.com/download...rion_5150.html (5150)
http://www.eserviceinfo.com/download...lor%20513.html
http://www.eserviceinfo.com/download...lor%20513.html
I had not yet measured the supply voltages as after the replacement of
all power supply caps located nearby a heat causing part the tv was
running the whole evening like usually. After power down and power on
the next day I got a black screen again and only the channel LED was on.
(no audio tone, no noise on the screen). No respond on pushing the
channel keys at the front panel.
I had checked the remote control transmitter led with a digital camera,
looks fine, ir led is flashing the RC5 patterns when pushing a key.
In addition you right my tv model has to be started by the remote
control main button when powered on starting on the last channel selected.
I hope to have more luck today to find the reason for malfunction,
but its more complicated when I had to check signals on a running tv
bacause of missing service manual.
Greetings
Markus
DL8MBY
I'd be looking for an open "startup" resistor. As you say, the
circuits are hard to read, but these resistors are usually around 100K
or more, and are often connected to the base of the chopper
transistor. In your case the chopper is inside a 5-pin STR regulator.
I would check R503 and R504 (220K) at pin 2 of this IC.
Check that the OEC8024B microcontroller is attempting to switch on the
PSU by monitoring the "POWER ON/OFF" signal (pin #2 of 5-pin
connector). If that signal is toggling, then you can confine your
troubleshooting to the PSU (and the loads on the secondary side).
- Franc Zabkar