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Old 12-01-2021, 04:04 AM   #1
gilbert009
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Unhappy I need help identifying the issue with my Magnavox MDR513H dvd recorder!

Hello! I am fairly new at repairing electronics. Recently I came across an old Magnavox MDR513H dvd/hdd recorder. It is not powering on. When the unit is plugged in, I get this really annoying beeping sound coming from the power supply.. I have already tried things like unplugging the unit for a few hours, holding the power button for a minute or 2. Nothing seems to make It work.

I found this guy with the same problem on YouTube -https://www.youtube.com/watch?v=iFVm-SJX-S8
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I checked all over this video's comments but no one really helps him with the issue. except for one comment that seemed legit. (screenshot of the comment is attached.)

if the guy in the comment is correct. I have no idea on how to test this zenner diode to see if mine is indeed bad.

I would appreciate if somebody helped me on how to test it. or maybe somebody knows where I can get a replacement for me to see if this is the issue. I have no idea on the zenner diode specs or how to look it up.

zenner diode markings are 1N4755A A20
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Last edited by SMDFlea; 12-01-2021 at 04:44 AM.. Reason: MDR513H
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Old 12-01-2021, 05:39 AM   #2
lotas
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Default Re: I need help identifying the issue with my Magnavox MDR513H dvd recorder!

1n4755a - 43v 1w
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Old 12-01-2021, 10:19 AM   #3
petehall347
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Default Re: I need help identifying the issue with my Magnavox MDR513H dvd recorder!

if it isnt shorted or open its likely ok .. only way of testing is with a power supply and resistor and voltmeter .. could of course simply test in circuit .
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Old 12-01-2021, 11:31 AM   #4
R_J
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Default Re: I need help identifying the issue with my Magnavox MDR513H dvd recorder!

If that is D2229 it is a 1N4755A zener diode (43v 1watt) on the EV+33v supply. If it is not shorted it is likely ok. Check it with your meter.

Must be some tech that it took him 8 months to find a shorted zener diode. 3 other shops couldn't find it? If the smps is squealing it is usually caused by a short in the secondary, the first thing to check would be the zener protection diodes.
And the likey cause is the elec. capacitor on that line going bad causing the voltage to increase due to not filtering the high frequency ripple.

Last edited by R_J; 12-01-2021 at 11:43 AM..
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Old 12-01-2021, 07:36 PM   #5
gilbert009
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Default Re: I need help identifying the issue with my Magnavox MDR513H dvd recorder!

Quote:
Originally Posted by R_J View Post
If that is D2229 it is a 1N4755A zener diode (43v 1watt) on the EV+33v supply. If it is not shorted it is likely ok. Check it with your meter.

Must be some tech that it took him 8 months to find a shorted zener diode. 3 other shops couldn't find it? If the smps is squealing it is usually caused by a short in the secondary, the first thing to check would be the zener protection diodes.
And the likey cause is the elec. capacitor on that line going bad causing the voltage to increase due to not filtering the high frequency ripple.
Thanks for your help everybody ! Sorry for my lack of knowledge. but what should the zener be reading while in circuit? also what mode should I test it in?
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Old 12-02-2021, 05:55 PM   #6
petehall347
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Default Re: I need help identifying the issue with my Magnavox MDR513H dvd recorder!

if one end goes to ground it should have its rated voltage right across it . but only if its good and the supply to it is working like it should .. first see if its shorted .
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Old 12-02-2021, 06:06 PM   #7
R_J
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Default Re: I need help identifying the issue with my Magnavox MDR513H dvd recorder!

The zener diode can be checked out of circuit with your meter in either diode mode or on the lower resistance scale, it could also have been checked in circuit.
Also check D2213 and D2215, these are also zener protection diodes on that board.
Using diode mode the reading across the diode should be .6xx one way and open circuit the other way.

Last edited by R_J; 12-02-2021 at 06:13 PM..
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