B
Brad
Hi,
I have a "Super Dog" Curtis Mathes/Samsung TV model CM27001S
(mfg. 11/01) in my shop. I have SM (.PDF file).
I didn't list every test I did because the post is very long.
UPDATE:
I replaced IC501, TDA6107Q (video amp IC), but the problem remains.
Pin 5 of IC501 is used as a "black current measurement output" (from IC info).
On the TV schematic, IC501 pin 5 circuit is labeled "IK". I tested the few
parts in this circuit (AOK). The "IK" circuit connects to pin 50 "BLK IN" of
the "jungle" IC (64 pins) "Micom & Chroma" TDA9387PS. When the picture
starts to show, the DC voltages rises quickly (3.3V black) then TV turns off.
I put a 50UF cap on IC501 pin 5 to "retard" the rising voltage. The TV stays
on, but the screen remains black. Pin 50 of the "jungle" IC inputs to
"contra/bright/OSD...." components in the "jungle" IC.
Is it possible a defect in the "jungle" IC is causing the TV to turn off?
Thanks in advance, Brad
--------------------------------------------------------------------------------------------------------------------
FROM PREVIOUS POSTINGS & REPLIES:
The TV will turn on. There is around 27KV (measured) for the CRT. There
is vertical deflection and good sound, but just as the picture begins to show,
the TV turns off. Note: This happens every time you turn on the TV.
Note: Regulated B+ is 130V (measured). Caps have low ESR. A 200 ohm
dummy load on +130V doesn't cause voltage to drop at all.
I unplugged the CRT pcb and the TV stays on. I plugged it back onto the
CRT and turn "screen" (FBT) to minimum. I turn on the TV and it says on, but
when I turn up the "screen" slowly, just as the picture begins to show, TV
turns off. Note: I tested the CRT and it is AOK. I scoped FBT with "screen"
turned all the way down. Very good FB pulses which doesn't change at the
point the TV turns off (by advancing the "screen"). The "Xray" circuit is
NOT the cause (tested).
I opened the ABL line and put a 10K resistor from the FBT ABL pin to
ground. The ABL line, now isolated, will be unaffected by FBT/HV trippler
"effects". The ABL circuit has a 79K resistor to regulated B+ and a 6.8K
resistor to ground which will keep the voltage constant on the now isolated
ABL line. With "screen" turned all the way down, the TV stays on. As I
slowly advance the "screen", I see a good quality picture for a split second,
then the TV turns off.
I disconnected the HV lead from CRT and isolated it so no arcs occur.
This in effect, removes a "load" (when picture shows) on the HV trippler/FBT.
The TV still turns off.
I opened up the screen circuit on the CRT PCB and used an external
adjustable power supply to supply the screen voltage to G2 in the CRT on a
chance that if G2 shorts, it wouldn't "effect" shut down, but the blasted TV
still turns off. I am just about ready to give up.
I have thought about this at great length and I wondered about what
actually changes when the picture begins to show. Remember, one test,
the HV lead was disconnected. With minimum G2 voltage, there is no
K (RGB) current in the CRT. When K current begins to flow, the source
is coming from TDA6107Q. It may be possible this IC "breaks down"?
I have a "Super Dog" Curtis Mathes/Samsung TV model CM27001S
(mfg. 11/01) in my shop. I have SM (.PDF file).
I didn't list every test I did because the post is very long.
UPDATE:
I replaced IC501, TDA6107Q (video amp IC), but the problem remains.
Pin 5 of IC501 is used as a "black current measurement output" (from IC info).
On the TV schematic, IC501 pin 5 circuit is labeled "IK". I tested the few
parts in this circuit (AOK). The "IK" circuit connects to pin 50 "BLK IN" of
the "jungle" IC (64 pins) "Micom & Chroma" TDA9387PS. When the picture
starts to show, the DC voltages rises quickly (3.3V black) then TV turns off.
I put a 50UF cap on IC501 pin 5 to "retard" the rising voltage. The TV stays
on, but the screen remains black. Pin 50 of the "jungle" IC inputs to
"contra/bright/OSD...." components in the "jungle" IC.
Is it possible a defect in the "jungle" IC is causing the TV to turn off?
Thanks in advance, Brad
--------------------------------------------------------------------------------------------------------------------
FROM PREVIOUS POSTINGS & REPLIES:
The TV will turn on. There is around 27KV (measured) for the CRT. There
is vertical deflection and good sound, but just as the picture begins to show,
the TV turns off. Note: This happens every time you turn on the TV.
Note: Regulated B+ is 130V (measured). Caps have low ESR. A 200 ohm
dummy load on +130V doesn't cause voltage to drop at all.
I unplugged the CRT pcb and the TV stays on. I plugged it back onto the
CRT and turn "screen" (FBT) to minimum. I turn on the TV and it says on, but
when I turn up the "screen" slowly, just as the picture begins to show, TV
turns off. Note: I tested the CRT and it is AOK. I scoped FBT with "screen"
turned all the way down. Very good FB pulses which doesn't change at the
point the TV turns off (by advancing the "screen"). The "Xray" circuit is
NOT the cause (tested).
I opened the ABL line and put a 10K resistor from the FBT ABL pin to
ground. The ABL line, now isolated, will be unaffected by FBT/HV trippler
"effects". The ABL circuit has a 79K resistor to regulated B+ and a 6.8K
resistor to ground which will keep the voltage constant on the now isolated
ABL line. With "screen" turned all the way down, the TV stays on. As I
slowly advance the "screen", I see a good quality picture for a split second,
then the TV turns off.
I disconnected the HV lead from CRT and isolated it so no arcs occur.
This in effect, removes a "load" (when picture shows) on the HV trippler/FBT.
The TV still turns off.
I opened up the screen circuit on the CRT PCB and used an external
adjustable power supply to supply the screen voltage to G2 in the CRT on a
chance that if G2 shorts, it wouldn't "effect" shut down, but the blasted TV
still turns off. I am just about ready to give up.
I have thought about this at great length and I wondered about what
actually changes when the picture begins to show. Remember, one test,
the HV lead was disconnected. With minimum G2 voltage, there is no
K (RGB) current in the CRT. When K current begins to flow, the source
is coming from TDA6107Q. It may be possible this IC "breaks down"?
