Question about Toshiba 27AF45 27" TV

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Two of the diodes are shorted, change all four out with higher spec. diodes. will not power up, any suggestions ? thanks

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Check the fet Q502 (2SK3326), Ic504 the opto-isolator (PC817), and D517 for leakage. Use a dmm with diode testing - test froward then reverse, if you get any sustained readings both ways replace it with an NTE552. Also check R510 100 ohm....
Bill

Posted on Nov 27, 2007

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Hi. My uhf band cp 200 won't power up because it was placed in a charger .Please tell me what protection diodes I need to replace, and it's proximal location. Thank You.


Chargers have higher voltage ratings than the one it charges. It also lacks the needed filters to supply the exact direct current which damaged your equipment but first check if it blows up your fuses when you connect the power supply. If it does check for Zener Diodes usually connected to the mains of the equipment to simulate the simple crowbar effect of protection. If it does not blow up your main fuse then the fuse might be in the circuit board of your base unit. Zener Diodes are cased in striped crystal that short circuits itself when applied with reverse or higher voltage rating power supplies. You will need a multimeter positioned at continuity to test this. Remove it and replace the fuse then apply power, it will light up but remember to replace the damaged part for protection.

Feb 23, 2016 | Radio Communications

Tip

Shorted Rectifier Diode (fuse keeps blowing)


jdvillanueva_14.jpg
This CRT tv is dead set, no reaction when the power button is pressed(no standby led light). I've open the back panel and check the faulty parts.
jdvillanueva_15.jpg

As you can see the fuse was badly burnt-out indication of excessive current due to short circuit.
jdvillanueva_17.jpg

I've checked the parts feeding the AC line to the power supply board (Power cord, VDR, Ceramic capacitor, Coil, Posistor, Degaussing coil) one by one and I've found out that one of the four rectifier diode has a leak which caused the glass fuse burnt-out.
Here's how to test the rectifier diode.

Good Diode
Note : Forward and reverse bias depend on what type of ohmmeter are you using, here I'm using a Japan Standard(Sanwa Brand).
jdvillanueva_21.jpg

Using an ohmmeter set it to X10 to see much easier the leak from the diode in reverse bias.

Forward Bias : test the diode by connecting the red test prod of the tester to anode and then the black test prod to cathode of diode. You will see the pointer will reads a faily low resistance(above picture).
jdvillanueva_22.jpg

Reverse Bias : test the diode by connecting the red test prod of the tester to cathode and then the black test prod to anode of diode. You will see at the picture(above) that the pointer didn't react (remains in infinity). This is a good diode.


Bad(leaky) Diode
jdvillanueva_23.jpg

Forward Bias will reads fairly low resistance.
jdvillanueva_24.jpg

Reverse bias unlike the good diode the pointer will also reads a fairly low resistance.

After confirming that the diode caused the fuse from blowing I've decided to replaced all four diodes since I have a lots in my stocks.
jdvillanueva_25.jpg

Remember that when you installing the new diode on the board, make sure that you will make it in the right polarity.

jdvillanueva_26.jpg

This steps is also applicable in the DVD Player,Flat panel, Projection, LCD TV, you have to disregard only the posistor and degaussing coil.

Have a nice day!
Thanks for using Fixya.

Jdvillanueva

on Mar 02, 2011 | Televison & Video

1 Answer

Short internal power supply


please check for any blown fuses, if there is replace with the same value, do not replace it with a higher value. also check resistors near the rectifier diodes, check full wave diodes & ic regulators, if you find an error replace with the same value or specs.

May 30, 2013 | QSC Audio Players & Recorders

1 Answer

Jenn air microwave JMV 916 BAS won't power up


The magnetron has probably shorted, and in rare cases the power transformer will fail, "but unlikely"

Mar 27, 2012 | Jenn-Air JMV8000 Microwave Oven

1 Answer

The power supplies / ac adapters for my AW-871 speakers were both lost in a recent move. The speakers show input of 15v center + but no power spec. Do you have a suggestion for replacements? Thanks for...


Higher voltage then required is not so recommended, internal circuit may over voltage driven. some power amp max limit may fall within 18V only. See this link If your speaker power less then 30w you can choose 15V 2A will do or else select higher spec.

Jul 23, 2011 | Acoustic Research 900MHz Wireless Stereo...

1 Answer

JVC RX 505v stereo receiver keeps blowing fuses. Replaced fuse with specified rating (125v 5 Amp) but still keeps blowing fuse. Fuse appears black inside and I see a flash when I apply power. Can...


The likely cause of this is a dead short in the power supply. I don't receal the specifics of this unit, but there should be a set of four(4) diodes or a single bridge rectifier in the main power supply area. Check this/these for a direct short using a diode checker. Other than that, the output transistors being shorted can cause hte same symptom. Without seeing the actual unit, I can not tell for sure. If you know how, check the output transistors as well. Report your results here.

Dan

Nov 30, 2010 | Audio Players & Recorders

1 Answer

Hello, Bob here. Trying to repair my NorthStar 5500. The generator has no output. (distrobution box disconnected) looking on the output directly from the wireless generator. Do these go bad and are there...


on the end of the rotor their is a Diode as well as a varistor these will go bad common in these units and cause a power loss these are attached to the rotor by a strip some like a pc board some a insulated tang to say remove the 2 one on each side Diode part# 778959 varistor part# 778961 manufacture numbers you should be able to go to any electronic store like radio shack and cross ref the numbers as to the diode i don't have the spec's but when you find it it will have the voltage rating get the next size up it is better to go to a higher voltage what the diode does it acts like a 1 way valve power flows one way and if their is a spike it wont allow it to come bach and damage parts before it it will also act like a fuse to sorts to much it will pop. the varistor varies the flow their sensitive and adjustable if purchased from other than manufactures factory it will need to be adjusted hope one is good and use a multi meter and test the Resistance and adjust the new one to that spec as close as you can at the end plate their is a capacitor part # 778958 replace this as well again go a higher volt rating but do not change the MF value with this said and done.your will have a more stable sign wave and beefier circuitry able to hold up better use lock tight on the screws for these.ther is not any control in the box with the plugs just breakers after replacing these parts and there is still no power then the stator is shorted and will need either re-winding or replaced.
hope this helps.

Aug 27, 2010 | Northstar Generator 9 Hp, 5500 Watt,...

1 Answer

My cobra 29 NW/WX won't power up.


Open the case and hook power inside past the power socket. They do go bad from time to time.

Also, if you never checked the SWR, and you noticed the ant ligh come one ever, you could have burned up your final. You now have a paper weight.

Oh and the protection diode is D28 not 23. It should be a big black one. Also, D8 is another protection diode. they are the only big black diodes in the radio.

Apr 16, 2009 | Cobra 29 LTD CB Radio

2 Answers

Check gage ligh on..


It could be worn camshaft bearings that is lowering your oil pressure. I had the same situation with my 2000 Jeep Cherokee 6 cyl. Changing the oil pressure sending unit did not make a difference. I used a higher viscosity oil and that prolonged the life for almost another year. If you put an oil pressure gauge on it and let it run at a prolonged normal temperature, it will give you a definite answer wheter or not the engine has low oil pressure. The real problem is finding the cause. Camshaft bearings are a likely source. According to the spec book, the I-6 engine had low oil pressure numbers to begin with.

Jan 23, 2009 | 2003 Jeep Grand Cherokee

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