Sony SDM-HP94P

[stepgr]

Hi Guys
I have this 19" sony monitor which seems to be dead. No power led come on
I can't seem to find and standby voltage when connecting to AC, nothing happens
when pressing the power button, and I'm totally lost! in the primary side there
are 320 Volts on the main capacitorand on the primary side of transformer
but no output. Anybody came across this monitor ? The only curious thing is some small
capacitors on the primary who have very low ESR readings (10mf 50V 0.30 Ohm and 47mf 50V 0.12 Ohm)

Anybody can point me to the right direction ?

[budm]

Re: Sony SDM-HP94P

Do you hear nay ticking sound from the main transformer? Try heating up the primary section with hair dryer to see if the power supply will start up also.

[stepgr]

Re: Sony SDM-HP94P

no, no sound at all , I removed the primary transformer and now I can measure aprox 4 Volts across the diode on the 817 optoisolator (on the primary side ) which previoulsy measure 0 volts , I'm guessing something to do with the tranformer ?

[budm]

Re: Sony SDM-HP94P

Not likely to be transformer. Can you get the P/N on that MOSFET or IC that drives the transformer?

[stepgr]

Re: Sony SDM-HP94P

yeap it reads:
H435
TOP246YN
and it has (sorry) 6 pins

[budm]

Re: Sony SDM-HP94P

Here is the spec sheet, if you look at the application notes on how it is used, you will see that it will be pretty close to how your board is designed.
So check the resistors, diodes, solder joints around that IC. Itstill can be those small start-up/running caps.

[stepgr]

Re: Sony SDM-HP94P

thnks, I will continue tomorow and I'll post my findings here
by the way very nice pdf man, very informative thanks again!

[jetadm123]

Re: Sony SDM-HP94P

If you don't find any issues with the surronding components, then post the voltage readings for each pin of the TOP246. Be careful, high voltage.

[stepgr]

Re: Sony SDM-HP94P

These are the voltages of the IC with regard with the hot ground :
C = 0V
L = 3,73V
S = HOT GROUND
X = 0,320V
D = 306 V

pins L and X are driven from the possitive side of main capacitor through a series
of resistors the ones who produce 3,73 V are marked 4753 and there are four in series
and the 0,320V are four again reading 245.

[jetadm123]

Re: Sony SDM-HP94P

From the spec sheet, it looks like the Control (C) pin needs at least 5.8V for startup to begin. You're seeing 0V. There's at least one cap (and possibly other components) connected to to the "C" pin and ground. Check to see if that cap or one of the other caps is shorted.

[budm]

Re: Sony SDM-HP94P

You know, it will cost less than a dollar to replace the two small caps, one by the opto, and another one by the small blue cap in the primary circuits. There is not much in this power supply since just about everything is in the IC.
See similar design on this one which has bad cap.
http://s807.photobucket.com/albums/y...r%20as%20223W/

[stepgr]

Re: Sony SDM-HP94P

You know, it will cost less than a dollar to replace the two small caps, one by the opto, and another one by the small blue cap in the primary circuits. There is not much in this power supply since just about everything is in the IC.
See similar design on this one which has bad cap.
http://s807.photobucket.com/albums/y...r%20as%20223W/

I did that already if you read my first post (that's how I know that the ESR is low , at least
according to the blue esr meter table which says that a cap at 47mf 50 V is between 1 and 0.6 Ohms and mine reads lower than that) !
Sorry if my English are bad

[tom66]

Re: Sony SDM-HP94P

Check resistance from C to HOT GROUND.

[budm]

Re: Sony SDM-HP94P

"The only curious thing is some small
capacitors on the primary who have very low ESR readings (10mf 50V 0.30 Ohm and 47mf 50V 0.12 Ohm)"

I thought you only made the measurement of the cap's ESR but did not replace them.
By the way, how are the snubber diodes? Are they OK?

[stepgr]

Re: Sony SDM-HP94P

this is an attempt to show you how the board is organized. Capacitors C132 and C130 seem to be OK (I've replaced them also ). The capacitor C131 is SMD can't read anything on it and the resistor R131 in series with C132 is also SMD and reads 6R8 and multimeter read it 7K without the capacitor on board . All diodes and Zeners seem to work OK and C115 is a small blue tantalium I gues anyway it reads 102K 1KV 48 ! . I still can't figure out how the circuit starts !

[budm]

Re: Sony SDM-HP94P

See page4, 5, 6 of the spec sheet: Notes: Please check that value of that resistor that is connected between the Line (L) sense and the B+.
Page4
Pin Functional Description
DRAIN (D) Pin:
High voltage power MOSFET drain output. The internal
start-up bias current is drawn from this pin through a switched
high-voltage current source. Internal current limit sense point
for drain current.

Page 5:
The LINE-SENSE (L) pin is usually used for line sensing by
connecting a resistor from this pin to the rectified DC high
voltage bus to implement line overvoltage (OV), under-voltage
(UV) and line feed-forward with DCMAX reduction. In this
mode, the value of the resistor determines the OV/UV thresholds
and the DCMAX is reduced linearly starting from a line voltage
above the under-voltage threshold. See Table 2 and Figure 11.
The pin can also be used as a remote ON/OFF and a
synchronization input.

Page6:
CONTROL (C) Pin Operation
The CONTROL pin is a low impedance node that is capable
of receiving a combined supply and feedback current. During
normal operation, a shunt regulator is used to separate the
feedback signal from the supply current. CONTROL pin voltage
VC is the supply voltage for the control circuitry including the
MOSFET gate driver. An external bypass capacitor closely
connected between the CONTROL and SOURCE pins is required
to supply the instantaneous gate drive current. The total amount
of capacitance connected to this pin also sets the auto-restart
timing as well as control loop compensation.

When rectified DC high voltage is applied to the DRAIN
pin during start-up, the MOSFET is initially off, and the
CONTROL pin capacitor is charged through a switched high
voltage current source connected internally between the DRAIN
and CONTROL pins. When the CONTROL pin voltage VC
reaches approximately 5.8 V, the control circuitry is activated
and the soft-start begins. The soft-start circuit gradually
increases the duty cycle of the MOSFET from zero to the
maximum value over approximately 10 ms. If no external
feedback/supply current is fed into the CONTROL pin by the
end of the soft-start, the high voltage current source is turned
off and the CONTROL pin will start discharging in response
to the supply current drawn by the control circuitry. If the
power supply is designed properly, and no fault condition
such as open loop or shorted output exists, the feedback loop
will close, providing external CONTROL pin current, before
the CONTROL pin voltage has had a chance to discharge to
the lower threshold voltage of approximately 4.8 V (internal
supply under-voltage lockout threshold). When the externally
fed current charges the CONTROL pin to the shunt regulator
voltage of 5.8 V, current in excess of the consumption of the
chip is shunted to SOURCE through resistor RE as shown in
Figure 2. This current flowing through RE controls the duty cycle
of the power MOSFET to provide closed loop regulation. The
shunt regulator has a finite low output impedance ZC that sets
the gain of the error amplifier when used in a primary feedback
configuration. The dynamic impedance ZC of the CONTROL
pin together with the external CONTROL pin capacitance sets
the dominant pole for the control loop."