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No power on Uniden Grant LT

I have checked/replaced the inline fuse, used a multimeter to check the reverse power diode (I get an ''open'' reading between red and black terminals on the radio) , still no power, no lights, nothing. For about a month, the meter light on the radio would dim when you key the mic, then finally it would not turn on at all.

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  • bromotor Mar 11, 2009

    I have since found and repaired a burnt piece of foil on the pcb.... NOW,,,, it reads as a destroyed reverse power diode.  I will replace that and post further.  Thanks.  

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4 Suggested Answers

Benimur
  • 6966 Answers

SOURCE: VHF transmit power

Hi, It is not typical but neither is there a problem with the radio. Transmit Power output is loosely dependent on the: 1. Frequency or channel you are transmitting. Normally, Marine Band VHF are calibrated for max (25 in your radio) at Ch16 or 156.800Mhz; 2. If the SWR of the antenna is not a flat 1.0, power tends to go down; 3. After some time, the TX side of the radio needs to be re-calibrated; 4. Power Supply - some radios will push max output only when powered with 13.8 and tends to go down when used with 12 volts. Hope this be of some help/idea. Post back should you need additional information. Good luck and kind regards.

Posted on Oct 04, 2007

tparsenault
  • 170 Answers

SOURCE: blown fuse and reverse polarity diode

Check around the pcboard where the dc goes to the board, sometimes the foil will burn. Also chec the transformer, Chec that one of the wires did not come off the plug in the back. When you replaced the protection diode did it blow again? If not keep checking for opens on the pc board. When you said it was dead do you mean no lights at all or no tx and rx?

Posted on Jan 26, 2009

tparsenault
  • 170 Answers

SOURCE: Mini Magnum Radio not transmitting after Final Replaced

Not knowing what kind of equipment you have, its hard to say, but .10 watt? Sounds like the buffer or driver also got involved. Usually you get 1/4-1/2 watt to the driver on a stock radio. I would also check the bias resistors like you suggested. Also check for burnt foil around the final you replaced. Good just be a slightly damaged circuit. Let me know if this helps.
Tom

Posted on Feb 04, 2009

steve132003
  • 98 Answers

SOURCE: uniden grant lt transmit and receives normally but

Sounds like a "short" if it affects modulation + power. Try to inspect board with magnifier for solder bridges, and bad resistors. Change a few resistors near back with new ones. take out slugs near back finals like L10 or L20's not sure if its same as Uniden Pc68xl. but try that. I found turning L19 up to top gave great Modulation. clip D9, Sread coils 1/16 inch in back. Try to get lower carrier. Carrier does not mean anything much. Modulation is what you need. With less Carrier it may cool down that chip. It may be too wound out.

Posted on Mar 31, 2011

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1 Answer

Yamaha no power


you need to check the power supply input of your amplifier using a multimeter set your tester into a dc voltage reading.then measure the power input you must have a DC voltage supply reading..open the cover check the fuse an open fuse will turn the unit to no power.there are causes of blown fuse a shorted power transistor at the circuit will blown the fuse you need to replace faulty transistors before putting up a new fuse...check also the diode at the power supply section ,faulty diode could lead to the same problem..

Sep 30, 2011 | Yamaha P-2500 Amplifier

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

Dont turn on


first check the supply of the TV, check if there is 110V or 220V on your voltmeter if there is a supply, check for busted fuse that is open reading on the multimeter on a diode test. replace the fuse with the right specifications to avoid further damage, then if it is not turning on after the fuse is replace check the power supply of the TV is is located on where the main plug of the TV is mounted. maybe there is a shorted transistor of diode.

Jul 22, 2011 | Televison & Video

1 Answer

I have a Natioanl NN-6207 Microwave,I have replaced the magnetron and the fuse, every time I switch the microwave on it makes a loud humming noise and blows the fuse. The magnetron has two terminals F and...


F and Fa could be the problem but.... You must check the power diode and the high voltage capacitor. One of these is most likely the reason the fuse failed in the first place. Ground the HV capacitor by holding an insulated screwdriver well back on the handle. The locate the Power Diode that will have at least ONE terminal that connects to the capacitor. Power doides are either 3'8 inch wide and 2 inches long or round an liik like a bit resistor with no color markings. ' Check the HV capacitor by rading each terminal to the case of the capacitor (no shorts allowed)
Then read across the capacitor terminals with the meter set on R x 10K. Watch for an initital jump in resistance and then it drifts up to infinity. Reverse test lead positions and you must get the same result. Resistance and then drift to infinity. Any other reading.... infinity in both directions, short to the case or short across the 2 terminals = bad Cap.
If after you perform the above tests and you still have the problem ... knowing you might pop another fuse there are 3 door switches. 2 of them will read resistance / continuity across the terminals when the door is close and one of them will read continuity across the terminals when the door is open. One of the 3 switches has 3 wires on it... the 3rd wire shorts the magnetron power when the door is open and the power relay / HV circuit is powered. This is a built in blow the fuse to prevent magnetron operation with the door open.

I think your are going to find that either the power diode or the HV Capacitor has failed.

Thanks for choosing FixYa,
Kelly

Apr 16, 2011 | GE Microwave Ovens

2 Answers

How to identify a defective rectifier diode


You can check a rectifier diode using a multimeter - Set the meter to the lowest ohm range and place the probes at each end of the diode. Take a reading then reverse the probes at the ends of the diode and take a reading again.
A good diode will show a low reading when the diode conducts and a high reading when it does not conduct when the probes are swapped around.
A bad diode will show a low reading (short circuit) when it the measurements are taken both ways.
A bad diode will show a high reading (open circuit) when it the measurements are taken both ways.

This is may not be accurate if the diodes are still soldered to the circuit board, you may need to unsolder one leg of the diode free of the circuit board and then carry out the measurements to get a true reading on the diodes.

Mar 23, 2011 | Computers & Internet

1 Answer

GE JE1160 1100 Watts Microwave Oven seems to have no power. The wall outlet tests ok but the microwave appears dead. It worked fine yesterday.


Hi and welcome to FixYa, I am Kelly

Often it is a simple part replacement. There are 4 parts that can usually cause this.
- The Fuse fails as a result of another component failure
- The most common failure is the power diode. You remove the chassis to gain access and then make sure you hold a screwdriver by the HANDLE and ground the large capacitor at least 3 times across the terminals. Then you can check the diode by using an ohm meter across the terminals. It should read continuity in one direction only. (reverse lead polarity) If it reads in both directions OR there is no continuity then the diode has failed.
- Next you test the high voltage capacitor by reversing the leads and watching each time for a jump in resistance then the meter returns to infinity. (Diode must be disconnected) No jump in resistance after reversing the test leads or constant resistance = bad capacitor.
- Lastly the Magnetron could have failed. You read resistance of the leads of the Magnetron with one lead disconnected. You must read resistance. No resistance = bad magnetron

I used model JE1160WD001 as an example since you did not include a complete model number. However, the parts I am referring to are common to all JE1160 models.

All parts except the fuse can be found here:
http://www.appliancepartspros.com/partsearch/model.aspx?model_id=212857

The fuse should be a 15 Amp 125 VAC Slo-Blow Fuse. Available at any hardware or Appliance parts source.

A failed door interlock switch will cause the fuse to immediately fail if the micro-switch fails in the door open position.

This is a pretty simple microwave and you should be able to bring it back to life. Just keep in mind repair parts costs vs replacement if you have failed magnetron.

Thanks for choosing FixYa,
Kelly

Jan 22, 2011 | GE JE1160 Microwave Oven

1 Answer

I have a Samsung CS1660 microwave. The slow-blow fuse between the HV transformer and the capacitor has blown. What is the easiest way to determine what went wrong.


Sometime the fuse will just blow bcause someone slowly opened the door without pressing STOP or PAUSE first. The door interlock switch at that point will blow the fuse.

Usually the reason the fuse blows is that the HV Diode has failed. You check this with a multi meter on resistance by reading across the 2 terminals AFTER making sure the capacitor no longer has a charge on it by grounding across the 2 capacitor terminals at least 3 times. The diode will read continuity in one direction only. (reversing the leads)

Also the HV capacitor can have failed by shorting out.

The HV Cap should show a jump on an analog meter as you reverse the leads then return to infinity.

Lastly the Magnetron can have failed. (Short)

All of the above are checked using an analog multimeter. Nothing fancy... a $5.00 meter will do the trick.

The replacement fuse will either be 15 A or 20 A. Look at the markings on the old fuse and replace it with a like fuse. HOWEVER... if any of the above problems still exist the fuse will just blow again.


Thanks for using FixYa!

Kelly

May 01, 2010 | Microwave Ovens

1 Answer

Blown fuse and reverse polarity diode


Check around the pcboard where the dc goes to the board, sometimes the foil will burn. Also chec the transformer, Chec that one of the wires did not come off the plug in the back. When you replaced the protection diode did it blow again? If not keep checking for opens on the pc board. When you said it was dead do you mean no lights at all or no tx and rx?

Jan 26, 2009 | Uniden GRANT LT 2-Way Radio

2 Answers

Power was reversed now radio keeps bowing fuse and will not come on


Hello hubcap,

 

When the power was reversed this shorted out one of the components, possibly an Operational Amplifier. This tells me that there is no diode protection and possibly the circuitry is exposed directly to the input power supply. The fix would be to find the shorted component with the use of a schematic and a multimeter. Once you correct the shorted component then if possible you can add diode protection by putting a diode (forward biased direction) in the path of the positive line.

 

Again you will need a schematic, and a multimeter to work on this problem.

 

I hope this helps,

 

Thank you,

 

Shuttle83

Oct 12, 2007 | Uniden PC78ELITE 40-Channels Base CB Radio

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