REPAIRING AND NOT THROWING AWAY

REPAIRING AND NOT THROWING AWAY

Richtige Fernseher haben Röhren!

Richtige Fernseher haben Röhren!

In Brief: On this site you will find pictures and technical information about Service Modes, Circuit Diagrams, Firmware Update procedure, Disassemble procedure, Universal remote control set-up codes, Troubleshooting and more....

If you go into the profession, you will obtain or have access to a variety of tech tips databases HERE IT IS Master Electronics Repair !.

These are an excellent investment where the saying: 'time-is-money' rules. However, to learn, you need to develop a general troubleshooting approach - a logical, methodical, method of narrowing down the problem. A tech tip database might suggest: 'Replace C536' for a particular symptom. This is good advice for a specific problem on one model. However, what you really want to understand is why C536 was the cause and how to pinpoint the culprit in general even if you don't have a service manual or schematic and your tech tip database doesn't have an entry for your sick TV or VCR.

While schematics are nice, you won't always have them or be able to justify the purchase for a one-of repair. Therefore, in many cases, some reverse engineering will be necessary. The time will be well spent since even if you don't see another instance of the same model in your entire lifetime, you will have learned something in the process that can be applied to other equipment problems.
As always, when you get stuck, checking out a tech-tips database may quickly identify your problem and solution.In that case, you can greatly simplify your troubleshooting or at least confirm a diagnosis before ordering parts.

Happy repairing!
Today, the West is headed for the abyss. For the ultimate fate of our disposable society is for that society itself to be disposed of. And this will happen sooner, rather than later.

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..............The bitterness of poor quality is remembered long after the sweetness of todays funny gadgets low price has faded from memory........ . . . . . .....
Don't forget the past, the end of the world is upon us! Pretty soon it will all turn to dust!

©2010, 2011, 2012, 2013, 2014 Frank Sharp - You do not have permission to copy photos and words from this blog, and any content may be never used it for auctions or commercial purposes, however feel free to post anything you see here with a courtesy link back, btw a link to the original post here , is mandatory.
All posts are presented here for informative, historical and educative purposes as applicable within fair use. NOTHING HERE IS FOR SALE !

Tuesday, 2 April 2019

DELL 2208WFP 22 INCH WIDE LCD MONITOR - 2208WFP - SMPS WORKING PRINCPLE

DELL 22 inch WIDE LCD MONITOR - 2208WFP - SMPS WORKING PRINCPLE

DELL MONITOR 2208WFP _ SMPS [Power Supply] _ WORKING 
AC input & EMI filter
  CN850 is a connector for connecting AC Power. F850 is a fuse to protect all the circuit AC. Input voltage is from 90Vto 264V. R850/3851are joined between two inputting main circuit to prevent man from shock. L850 is used to filter low frequency noise. C850and C851are used to discharge the noise that L850 produced. High frequency waves are damped by C852.
High Voltage to Low Voltage Control Circuit
  D850 is a rectifier in which there are 4build-in diodes, inverting AC to DC.  C854 is used to smooth the wave from rectifier. U850 is a highly integrated PWM controller. Typical start-up current for U850 is only 20uA, When current flow through R8 1/R842/R843 gets to Pin 3of U850,with VDD hold-up capacitor C855, U850 is enough for starting up.
  WhenU850 begins to operate Pin8of U850 will output square wave to drive Q850, then the main current flow get to GND bypassing through T850, Q850. Because of the change of current flow, wires in the other side of T850 will induct current. In the same time, the current inducted by wires which
connected T850 Pin 1 and Pin 3, with components of D852, R856 and C855 ,will be supplied to U850 for normal operating.
  When the sense voltage across the sense resistor R859, reaches the threshold voltage around 0.85v, the output GATE drive will be turned off. Every time when the output of power supply is shorted or over loaded, the FB voltage will increase, the build-in PWM output will then be turned off.  Both of two will prevent the power supply from being overheated under over loading condition. The PWM duty cycle is determined by this current sense signal and VFB, the feedback voltage, when the voltage on sense pin reaches V- (PWMcopm) = (Vcomp-2Vf) / 3, A switch cycle will be terminated immediately, Vcomp is internally clamped to a variable voltage around 0. 85V for output power limit.
  When Q850 are turned off, the main current flow will be consumed through D851, C875, R853/R854/R855 and D853, This will prevent Q850 from being damaged under large current impulse and voltage spike.
DC_24V ,12Vand 5VOutput Circuit and Feedback circuit.
  D854&D855 are used to rectify the inducted current. C862 are used to store energy when current is reversed. The parts including L852 are used to smooth the current waves that are from D854&D855, and then 24Vvoltage is supplied.  D880&D881 are used to rectify the inducted current. C881 is used to store energy when current is reversed. The parts including U880 are used to change the voltage from about 13Vto steady 12V, and then 12Vvoltage is supplied.  D856 is used to rectify the inducted current. C874, C864&C875are used to store energy when current is reversed. The parts including L851, and C876are used to smooth the current waves that are from D856, and then 5Vvoltage is supplied.  5Vsupply voltage feed back to PWM controller U850 via R861, R860,and I850,I851.R859,C859 and C863 are used to control response time.  LD7575 implements an OVP function on Vcc .Whenever the Vcc voltage is higher than the OVP threshold voltage, the output gate drive circuit will be shutdown simultaneously thus to stop the switching of the power MOSFET until the next on.
Posted By: FRANK at 00:59
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