[TechAssist] Re: Samsung TXJ2767 K51A chassis dead
- From: Eric Manuel <tvman@xxxxxxxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Fri, 06 Feb 2004 11:39:21 -0330
Hi Jorge replace C816 it.s off pin#14 of the switch mode trans it,s 1000
uf
it,s near the vert ic heat sink Eric
Eric Manuel
Deer Lake Nfld
Canada
Christopher Barnak wrote:
>
> Jorge,
> I've had this problem before with another T.V. The primary (switching
> side) of the power supply is not regulating. In my case, if turned out
> to be a small cap in the primary side. something like a .1uf or .2uf. It
> tested ok, Capacitance read right on with a cap meter, but it would not
> work.
>
> I've had electrolytics caps read good ESR ,good capacitance, and no
> leakage; but, not work when in circuit when operating voltage come in to
> play.
>
> I don't think that transformer is bad, it's very rare.
> Meter out all traces, from componet to componet in the feedback and
> primary of the SMPS.
> As one technician told me when I say " All parts test good ". He said,
> "but there must be, or it would work ".
>
>
>
> Christopher Barnak, CET
> Norfolk Public Schools
> School Plant Facilities
> 966 Bellmore Ave.
> Norfolk, Va. 23504
>
> Phone 757 628 3385
> Fax 757 628 3392
> cbarnak@xxxxxxxxxxxxx
>
> >>> geo@xxxxxxxxxxxxx 2/6/04 6:36:34 AM >>>
>
> I am about to give up with this. It's a Samsung K51A chassis
> and the main power uspply is giving 10 volts to the HOT collector and
> the rest of the voltages are low by the same proportion..
>
> It uses a 3S1265H as the switching regulator and I already tried
> 2 different new replacements with no luck (actually, the schematic
> shows
> a 3S1265R and I tried a R and a RF -it makes no difference, the RD is
> totally isolated, the R has a metallic tab-)
> I measured component by component, the diodes, caps, ICs and resistors
> are all ok, there is nothing overloading the secondary - cold side of
> the power
> supply, I actually disconnected branch by branch and nothing changed.
> Besides the secondary voltages which are dramatically lowered to a mere
> 10%,
> the voltages at the IC are the following: pin 1) has the correct
> voltage,
> sometimes
> reading higher because it is oscillating somehow. pin 3) -VCC- has
> between
> 11 and 13 volts,
> never reaches 17V as the schematics shows; voltage goes up and down
> all
> the time.
> pin 4) has nothing, schematic shows .9V, Pin 5 has nothing or a few
> mv,
> though schematic
> says 8.2V that is the sync/feedback pin, it is connected to T801,
> maybe
> here applies
> the less-than-10% rule, as with the other windings.
> Besides that, if place a 60 watt bulb as a load on the 130v (leaving
> the
> HOT collector floating
> first), the voltage goes still lower, down to maybe 3 volts or so.
> Conversely if you leave
> all the secondaries floating, the 130 volts raise to nearly 70, but
> goes
> immediately down
> with any light load you place on it or on the other low voltage
> rectifiers.
>
> I'm about to give up. The only unchecked/unchanged component is T801,
> but
> it CAN'T be...
> Any help will be greatly appreciated
>
> TIA
> Jorge
>
> Jorge Camboni, GY Electronics, Richardson, TX
>
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