Need guidance on SMPS repair

[BFriedl]

Hi...me again. So I've got this Mitsubishi VS-6015R V10 chassis tv that
has a bad power supply. I broke it into two parts, since there are two
switching IC's. Got the first part done (STR-S6301) and get +130v with a
75w load. Yay! Now that I understand how switch-mode supplies work, the
second part is a bit confusing because there is no feedback control. It
seems that the STR-S5041G is not switching?? Correct me if I am wrong. I
have uploaded a scan of the schematics with some modifications done in
mspaint. Each component with a blue square next to it has been replaced.
The section not working is surrounded with a large red square.
<A
HREF=http://www.acbow.com:8080/v10Power.jpg>http://www.acbow.com:8080/v10Power.jpg</A>
http://www.users.qwest.net/~wfriedl/v10Power.jpg

Sorry in advance for the long post, but here go the questions, starting
at the top of the schematic:
1. What is the difference between the two grounding
types shown at the right corner? The one with ///
seems to be used the most.

2. Im a bit confused as to the function of the cap in the yellow circle.
Through troubleshooting, I noticed that the ground on connector PA and
PK is not the same as ground on connectors PC. Could this be because the
circuit that feeds connector PC also feeds PF? (PF is always on, and
ground from PF is same ground as PC.) I noticed that the cap circled is
what bridges these two grounds together.

3. How do i troubleshoot this half of the supply? Heres what I've gotten
with a 25w load:
Connector PA
Pins 1 & 2: +26V; should be +24V
Pins 3 & 2: -24V; good
Connector PK
Pins 1 & 2: +29V; should be +28V (good?)
It appears that pin 3 does not ground with pin 2 here, but when
connected to pin 2 of PC, I get -16V; should be -12.
Connector PC
Pins 1 & 2: +16V; good
Pins 3 & 2: -17V; should be -16V (good?)

4. Now that ive broken it down that way, it seems that everything is
running correctly except for pin 3 of connector PK. Also noticed that
voltages for PF at top are quite high as well; pins 4 read +18V with 25w
load, +30v without load.

--
BFriedl
A+ Certified Technician
AIM: UACybercat
** Bear Down Arizona! **
******* Go Cats! *******

 

[BWL]

Looks to me like power supply is working fine. Low voltage supply does not
regulate all voltages. As long as they're that close, it should work. If TV
still won't power up, you've got either a bad vertical IC, and possibly some
bad caps in it's circuit, or possibly a bad dynamic focus IC on convergence
board. To check for bad focus IC, unplug the PA connector and see if it will
start. To check the vertical IC (LA7838), either replace it or check pin1
(should be 9 to 12v), pin 8 (28v), pin 13 (28v), and pin 12 (13.5-14.5v). Pin
12 is the output, and may not show much for a second or two. If the set isn't
making ANY High Voltage, the Horiz Output may have been blown by runaway 130v.

 

[BFriedl]

Looks to me like power supply is working fine. Low voltage supply does not

regulate all voltages. As long as they're that close, it should work. If TV
still won't power up, you've got either a bad vertical IC, and possibly some
bad caps in it's circuit, or possibly a bad dynamic focus IC on convergence
board. To check for bad focus IC, unplug the PA connector and see if it will
start. To check the vertical IC (LA7838), either replace it or check pin1
(should be 9 to 12v), pin 8 (28v), pin 13 (28v), and pin 12 (13.5-14.5v). Pin
12 is the output, and may not show much for a second or two. If the set isn't
making ANY High Voltage, the Horiz Output may have been blown by runaway 130v.

PLEASE MAKE ALL REPLIES TO NEW THREAD:
"Mits VS6015R (again) almost fixed; what next?"

When turned on before I started troubleshooting, I got no HV and no
sound. All I heard was a click sound of main relay turning on. First
thing to go were some inductors on the convergance board. So perhaps it
is the bad dynamic focus IC? Should I try powering this set on without
convergance board in set? Or are there some caps on the vert board that
need checking first?
TIA,
Brian

Here is a repost of March, 2002:

"I was having wiring problems in my house for"
"about 2 months and it recently tripped the"
"circuit breaker. When the power was fixed, I"
"powered up my TV (was on this same circuit)"
"some smoke started to billow out of the front"
"grille below the screen. I took off the black"
"cover and found the convergance board with some"
"fried inductors on it."
""
"Could this have been caused by my power problems,"
"slowly eating away at it with the constant sags"
"and surges?? Or did the ps go bad?"
"Brian"

--
BFriedl
A+ Certified Technician
AIM: UACybercat
** Bear Down Arizona! **
******* Go Cats! *******

 

[BFriedl]

From thread "Need guidance on SMPS repair"

Looks to me like power supply is working fine. Low voltage supply does not
regulate all voltages. As long as they're that close, it should work. If TV
still won't power up, you've got either a bad vertical IC, and possibly some
bad caps in it's circuit, or possibly a bad dynamic focus IC on convergence
board. To check for bad focus IC, unplug the PA connector and see if it will
start. To check the vertical IC (LA7838), either replace it or check pin1
(should be 9 to 12v), pin 8 (28v), pin 13 (28v), and pin 12 (13.5-14.5v). Pin
12 is the output, and may not show much for a second or two. If the set isn't
making ANY High Voltage, the Horiz Output may have been blown by runaway 130v.

When turned on before I started troubleshooting, I got no HV and no
sound. All I heard was a click sound of main relay turning on. First
thing to go were some inductors on the convergance board. So perhaps it
is the bad dynamic focus IC? Should I try powering this set on without
convergance board in set? Or are there some caps on the vert board that
need checking first?
TIA,
Brian

Here is a repost of March, 2002:

"I was having wiring problems in my house for"
"about 2 months and it recently tripped the"
"circuit breaker. When the power was fixed, I"
"powered up my TV (was on this same circuit)"
"some smoke started to billow out of the front"
"grille below the screen. I took off the black"
"cover and found the convergance board with some"
"fried inductors on it."
""
"Could this have been caused by my power problems,"
"slowly eating away at it with the constant sags"
"and surges?? Or did the ps go bad?"
"Brian"

--
BFriedl
A+ Certified Technician
AIM: UACybercat
** Bear Down Arizona! **
******* Go Cats! *******