[TechAssist] Re: GE TV CTC177AA3 - 25GT503 - Dead - No SMPS startup - FIXED
- From: "David Lessard" <mr_fixit@xxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Mon, 8 Mar 2004 15:27:34 -0500
Problem ended up being an open STK730-010. I compared pins from the good
and bad devices and noticed that the two last pins 10 & 11 were open on
the bad STK and 0 ohms on the good device. Don't know what this means
but that was the difference when I compared good to bad.
The following was provided to me from a fellow tech and proved to be
very helpful, so here it is:
The regulator IC U4101 may be the problem. Areas to check are the 160vdc
at pin 1 of T4101(referenced to hot ground for u4101 measurements) and
pins 11 and 12 of U4101, 1.6vdc on pin 4 of U4101, -40vdc on pin 1 of
U4101, and - 33vdc on pin 2 of U4101. If the 160vdc is missing, suspect
damage to the bridge diodes CR4001, 2, 3, 4 and R4001 (2.7 ohm 15watt
res) of being open. If the 160vdc checks ok and pin 4 of U4101 is low,
then remove and check the resistor R4104 (1.5meg ohm 1/4watt). If pin 4
of U4101 is high (above 4vdc) then U4101 is defective. If all the
voltages seem to be ok, then check your secondary diode (referenced to
cold ground)CR4106 and CR4107 off T4101.
Check the keyscan voltages on pins 6, 7,and 8 of U3101 (4.9vdc and
equal)
along with pin 5 of U3101 (0vdc). Check the DC level on the data and
clock pins of the U3201 (eeprom and should be 4.9vdc on both). There
should activity on the data and clock lines at plug in for about two
seconds. Then press the power button and you should see activity for
approximately 5 seconds then quit. If all these test good, check the
voltage at pin 24 of U1001 (6.5vdc in standby) and press the power
button, the voltage at pin 24 should drop to 2.2vdc. If this voltage
drops, then check Q4301, R4305, and C4306.
David Lessard
Alexandria Electronics
50 Harrison Street
Alexandria, Ontario
K0C-1A0
mr_fixit@xxxxxxxxxxxx
-----Original Message-----
From: techassist-bounce@xxxxxxxxxxxxx
[mailto:techassist-bounce@xxxxxxxxxxxxx] On Behalf Of Al Gutz
Sent: Saturday, March 06, 2004 10:48 PM
To: techassist@xxxxxxxxxxxxx
Subject: [TechAssist] Re: GE TV CTC177AA3 - 25GT503 - Dead - No SMPS
startup
David
On the secondary of transformer there is a large diode which may be
shorted (not sure of the number without schemo) and a 10 or 20u 200V cap
I think C105. The cap goes bad and shorts the diode which in turn kills
the STK. The diode is mur480. The 1.5 meg is located between the stk and
the deguss thermistor
Al G
David Lessard wrote:
>
> When plugged in I don't hear the usual startup sound of the SMPS. SMPS
> appears to be dead. I've checked the following, R4001, CR4106, CR4704,
> R4702 and R4517. I believe the problem is the STK73-010 SMPS
> driver/regulator. Is there anyway of confirming this is the problem or
> do you guys just normally swap these without giving it a second guess.
> Does the standby power work off the SMPS because I can't measure
+5volts
> anywhere?
>
> Thanks in advance,
>
> David Lessard
> Alexandria Electronics
> 50 Harrison Street
> Alexandria, Ontario
> K0C-1A0
>
> mr_fixit@xxxxxxxxxxxx
>
>
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