Question about Samsung SyncMaster 753S 17" CRT Monitor

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Power transistor having 4 legs no. begining with 7 DP

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It's DP704C STR

Posted on Nov 27, 2008

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Posted on Jan 02, 2017

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Where can I get the scematic for the Veco 21 STC voltage control circuit board?


try mailing the manufacturer

hot transistors are usually shorted out, or driving a short!!

a multimeter across the 3 transistor legs (TO-3 transistors have 2 legs & the case which is the 3rd leg) will reveal if they're dead (remove the transistors first as the circuit may give a false reading) - if you get a zero ohms reading between any of the legs it's dead - don't forget to check the smaller driver transistors too,, as a dead main transistor will kill its smaller driver transistor

speakers are marked,, usually 4 ohms or 8, though sometimes 16 ohms - use a multimeter to ensure you have something very close to these values according to the label on the speaker box & measure from the wires at the point where they connect to the amp

power the unit without any speakers or speaker wires connected,, if the transistors still get hot, you're very likely looking at bad transistors

Feb 21, 2015 | Audio Players & Recorders

1 Answer

The power button on my monitor flashes but will not trun on


There is a chance that you may have a couple bad capacitors on the power-inverter board but more than likely the problem will be a shorted out transistor. There are 4 on the inverter side of the board and one set may have gone bad. Capacitor problems may have caused the transistors to fail. Transistors are probably c5706 or c5707 and are black with 3 legs going though the board.
You would have to open it up to check and would need an ohm meter to verify if the transistors are shorted out.

Aug 18, 2010 | Dell 1703FPt 17" TFT LCD Flat Panel...

1 Answer

Ihave a technics reciever model sa-g90 it plays then it trips and shows overload. what should i replace?


Check out the power supply parts first. Then check out the main amp section (on the heatsink).
Look out for burnt or damaged parts. If it uses transistors and you have a ohm meter, test them for shorts. IE one probe on one leg and the other probe on another leg of the transistor. If you get the meter behaving like the probes were touching one leg it's shorted.

Jan 13, 2010 | Audio Players & Recorders

1 Answer

Hum coming from unit


If there is no picture,and the set will not power on,then the horizontal out put is shorted causing the set to shut down on a protect signal. You can check it yourself if you have a multimeter. Look for a 3 legged transistor on a metal heat sink and put the multimeter in diode scale. The outer two legs will always read 0, but the middle to outer legs should NOT. If it does,then the horizontal output is the culprit but the tv needs to be serviced anyway to make sure that there is not an underlying problem that caused the output to short to begin with.
This is also the answer to 90% of picture tube (CRT) televisions that have either lost power and/or lost picture.

Nov 01, 2009 | RCA F32650 32" TV

1 Answer

T1500-1bd burnt mosfet


First of all is the mosfet your talking about in the output section or in the power supply section? Most car amps use mosfets in the power supply section, some use them in the output section. To test the transistors in your amp, take a digital volt meter and set it to diode check. Then take the leads and put them accross the first and third legs of the transistors. Usally the red test lead on the first leg and black test lead on the third leg of transistor. If you get a reading of 000 then transistor is shorted. If you get a reading below 600 then transistor is on it's way out if not allready or it's next to a shorted transistor that is it's complimentry output transistor. comonly you will have 2 transistors working together, one NPN and one PNP per a channel, or 4 of them in a bridged type output circuit depending on the watts and how man channels your amp has. I was just looking at the specs of this amp and it's got me confused. It says it's a 2 channel but looking at all the info on different pages it says at 4ohm:200wattsx4 and at 2ohms:300wattsx4 and 1 channel mono 600watts into 4ohms. weird for a 2 channel. anyway that is how you test your transistors. Same way for the power supply section but, you will come accross a couple or more switching diodes that look like transistors and you will get a 000 reading when you test those like I specified. They rarely go out and most of the time there is only 2 of them. They will have a diagram like a diode on the front showing you which way the power flows. Let me know what you find out. Your amp should have went to protect mode if you smoked a mosfet.

Feb 08, 2009 | Audiofonics ADF-243 Car Audio Amplifier

1 Answer

Screen goes black,with sound


No picture sound ok
Note 1 a Raster is the name for a screen made of lines of brightness
Note 2, A Blank raster has no snow or picture, its just a lit up screen

Sound ok but no raster.
First increase tube's first anode voltage (knob on the loptx) to see if the screen is just too dark.
if after you have turned up the bottom knob on the loptx, there is still no brightness,check, for crt heaters, and EHT 25kv and focus voltage (2kv) and A1's/Screen/G2 voltage is 300-600v.
and check for field timebase (height), the next thing to check is the sandcastle pulse.
If it's present, colour decoder chip is probably faulty or lacks supply from the LT regulators.

NO LINE DRIVE If it's absent,check the line driver, locate the loptr(big and usually has heat sink).
follow the print from the base back to the driver stage , where you will usually find a tiny transformer with 4/5 pins
resolder it, even if it looks good,then with power on, check for voltage on all its pins, 2 should have LT(12v to 32v) or HT (90v to 150v), if not there follow the print back and look for either a transistor(linedrivetr), or the feed voltage line (maybe regulated),
If the voltage is ok on two of the driver transformer(drvtx) legs, the look from the base of the driver transistor to locate the timebase chip
and check round its pins for a 12v supply line, if there ,replace the timebase generator chip

Method of testing line drive, remove line output transistor, and connect a normal red led, across the B/E (longest leg to base), and when you power up the led should lite up.


Trace the pcb back from the BASE leg to find the line driver stage,
Its usually a very small transformer (4/5 legs) and a transistor connected to it,
The driver transformer legs(pins) will be two with voltage and two without
The two with power will either be about HT level (110v=145v) or about LT level(25v)
If not then trace back and look for a biggish 3w resistor.
linedrv.jpg
If the voltages are correct the look for line pulses from the Timebase oscillator chip to the base (some overvolts protection circuits remove pulses if ht is too high).
If the voltage is low and the feed resistor is getting hot then check the base of the driver transistor if its HI over 0.5V then its being turned on by the timebase oscillator chip (protection ?)
If the voltage is zero check the feed resistor
If all seems normal check that 12v is getting to the timebase oscillator chip (IC) (12v regulator?)
Method of testing line drive, remove line output transistor, and connect a normal red led, across the B/E (longest leg to base), and when you power up the led should lite up.

Hope it may help you;
Regards,
VOTIT

Oct 10, 2008 | Philips 42FD9954 42 in. Plasma HDTV

1 Answer

ZX-8100


I'm not familiar with that particular amp but generally, the only transistors that burn are the ones in the power supply. If the adjacent transistors had numbers like IRFZ44, IRF3205 or similar, the burned transistor is likely the same as the ones next to it.

Confirm that the center and right-most leg of the burned transistor and the transistor next to it are directly connected by large traces on the circuit board. Also confirm that the center leg goes to the large windings of the power transformer. If it passes these tests, the transistor is one of the power supply FETs. The numbers on the adjacent (parallel connected) parts will be the same as the burned one.

Jul 16, 2008 | Volfenhag ZX-8200 Car Audio Amplifier

1 Answer

Car Amplifier


Check the power transistors which usually have their cases screwed to the main heatsink/body of the amp case. They are usually large black cases with 3 legs soldered to the main board.
If any of them are shorted out inside the amp will go in to protection mode. you can test them in the circuit but it's best if you can detatch at least 2 of the legs when testing. If you don't understand the meter readings for transistors you can test them with a continuity tester which will bleep if the transistor is shorted inside.
First put the two probes from the meter on to the first 2 legs, if it bleeps it's probably shorted in side, if it does'nt that junction of the transistor is probably ok.
Then try leg 2 and 3 and the same for leg 1 and 3.
If all 3 legs bleep which ever way round you do it, the transistor will need replacing.
Depending on the power of the amp there are 8 large transistors, 4 for each channel.
Good luck with it.

Mar 16, 2008 | Lanzar 2H 1000W MOSFET AMP Car Audio...

2 Answers

One fuse keeps blowing


what size fuse is it usually you use at least a 40

Feb 09, 2008 | Sony XM-2252HX Car Audio Amplifier

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