Riddled TV Repair Forum

chumba · Joined: 01 Jul 2009 Posts: 66

Measured no DC voltages on D802 cathode/C805 "+"/ IC803 pin #3 (nor any voltages on its 4 other pins).
D001 cathode measures +11.5 VDC.
Q002 Emitter measures +5 VDC.

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JTS1957 · Joined: 21 Jan 2009 Posts: 1330 Location: Far, Far Away

You say you DO have 5 volts stand-by at Q002 emitter, but NOT at IC001 pin 61 & pin 22? Being separated by only foil traces and a coil, I'd say - impossible.

The reason you don't have any DC voltages on any pin of IC803 is that the relay (RL801) is not being closed.

chumba · Joined: 01 Jul 2009 Posts: 66

Re-measured IC001 pin 61 & pin 22, and yes they both have +5 VDC.
Why isn't relay RL801 closing? Naturally I'm measuring open between P1 & P2 and it doesnt click at all even when Power button pressed.
Do you suspect anything wrong with Q001? Two pins likely were shorted together by the meter lead. Should Q001 connect to D002 cathode? I dont measure continuity between the two but it looks like they should based on the PCB foil.

JTS1957 · Joined: 21 Jan 2009 Posts: 1330 Location: Far, Far Away

Refresh my memory: "P1 & P2?" (?Relay "contacts" possibly?)

Turn on is as follows:
1) Pressing the "power" button should cause the voltage at pin 5 of IC001 to "change."
2) This should cause pin 31 to change state (If was low [~0V] should go high [~5Volts]/If was high should go low). Since pin 31 is connected to the base of Q001 this too should change state. As the transistor is turned ON/OFF the relay should follow suit.

You mentioned possibly shorting pins of that transistor and also wanted to know what else was connected to it. To test this transistor accurately it would be best to remove it from the circuit. Removing, and testing while it's removed is hard, even for "professionals." Another way is to "isolate" two of its three leads. Removing the relay by either taking it out completely or by "floating" its "coil" pins and also removing D002 (completely or "float" one side) should isolate the collector lead. Lifting one end of R003 or "floating" Pin # 31 of IC001 should isolate the base lead. You can then test Q001 without taking it off the board.

chumba · Joined: 01 Jul 2009 Posts: 66

â€¢ Pressing the "power" button does change the voltage at pin 5 of IC001 (+5 / 0 VDC)
â€¢ However IC001 pin 31 nor the base of Q001 change state when power button pressed (0 / 0 v).
DCVolts measured on Q001 are +8.7, +4.1 & 0.

â€¢ Removed RL801 & floated IC001 pin 31 and measured Q001 in diode mode: 0.25/0.25, 0.57/0.76, 0.81/0.7 --> Q001 seems to be bad, eh? What part # is Q001 (it is a tiny surface mount and cant read it)?

â€¢ Also measured resistance across all 4 pins of RL801 out of circuit and none of the combinations of pins had continuity -- would that make this relay bad?

[Also forget what I said about P1 & P2 - those were pins on another part.]

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JTS1957 · Joined: 21 Jan 2009 Posts: 1330 Location: Far, Far Away

Q001 MSD601-RT1 (NTE2408)
RL801 TSEH8007

You need to specify which pairs of pins of Q001 for voltages and diode mode tests.
The two pins of relay across D002 should read approx. 270 ohms.
Does the "pin" of pin 31 toggle (like pin 5) with it floating?

chumba · Joined: 01 Jul 2009 Posts: 66

You need to specify which pairs of pins of Q001 for voltages and diode mode tests.
-> Q001 pins were not marked on PCB. Now with the part # and datasheet I found the pin assignments and Q001 measures as:
B to E: 0.25/0.25; B to C: 0.57/0.76; C to E: 0.81/0.7.

-> The two pins of relay RL801 across D002 measure 274 ohms (and open on switch contact side).

Does the "pin" of pin 31 toggle (like pin 5) with it floating?
-> The isolated pin 31 on the IC itself does NOT toggle when "Power" button pressed, it just stays at +5 VDC.

JTS1957 · Joined: 21 Jan 2009 Posts: 1330 Location: Far, Far Away

Transistor IS BAD.
Relay is good.
IC still undecided. Neutral

chumba · Joined: 01 Jul 2009 Posts: 66

Measurements on IC001 with RL801 removed:
Pin 61, pin 22, & pin 5 have +5 VDC.
Pin 59 has 3.6 VDC & pin 60 has 3.9 VDC.
Is there a way to get basic measurements without a scope for pins 59,60, 62 & 63? Using an analog meter, I measure ~8 VAC steady on pins 59 & 60 and no "pulsing" (meter needle movement) when panel switches are pressed.
Pin 62 has 2.0 VDC & steady 1.5 VAC.
Pin 63 has 2.2 VDC & steady 10 VAC.

JTS1957 · Joined: 21 Jan 2009 Posts: 1330 Location: Far, Far Away

Scope is best way to observe signal's changes and overall shape.
Analog meter won't do that. Smile

I'm really concerned by pin 31 not toggling when the power button is pressed.