MAGNAVOX RM8341 Can someone just answer this question?????


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MAGNAVOX RM8341 Can someone just answer this question?????

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TVRE
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Oct 25, 2007, 3:39 AM

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MAGNAVOX RM8341 Can someone just answer this question?????	Can't Post

HI
ONCE AGAIN
I have a Magnavox projection TV that is not power up. The problem is somewhere in the low power system. The board gets power in that small section and from the rest to the left it is completely dead.

I get power up to the switch mode transformer and the standby transformer but from there on the other side of both transformers there is no power. CAN SOMEONE IN THUS FORUM PLEASE JUST HELP ME!!!!!! What are know causes.

Using a DMM how do I test capacitors.

Thanks
for any help

rrobor
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Oct 25, 2007, 10:49 AM

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Re: [TVRE] MAGNAVOX RM8341 Can someone just answer this question????? [In reply to]	Can't Post

You can only test capacitors for short with a dmm, some meters have capacitance checks but that is almost worthless. Your first check is the standby supply that should be a very simple low voltage thing, that must be working first to supply the processor, if you have no 5V line the set will not function. Forget the capacitors, unlikely to be that with what you have given.

TVRE
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Oct 25, 2007, 6:06 PM

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Re: [rrobor] MAGNAVOX RM8341 Can someone just answer this question????? [In reply to]	Can't Post

Thanks a lot
In what area would I test for the 5v. When I connected the test leads on both sides of the transformer I get 8v. When I connect a lead to only one side of the transformer and one on ground I get continuity. The other side doing the same,one side on the transformer and the other on ground I get 8v.
Any Ideas

rrobor
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Oct 26, 2007, 4:12 AM

Post #4 of 15 (1428 views)
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Re: [TVRE] MAGNAVOX RM8341 Can someone just answer this question????? [In reply to]	Can't Post

You are in danger of doing the tv or yourself a mischief. First DO NOT measure on the primary of the transformer unless you have to. Never measure voltage across the transformer primary to secondary. standby transformers are usually mains driven so the only measurement there is pull the TV plug switch on, pull off the degauss plug and measure the primary for ohms, none its open. If you do have a primary fault then you have to follow strict rules and know a bit more than I think you do. Set your meter to DC, find the secondary of the standby transformer, there will be a diode on that, find that diode or bridge diode block, that will feed an electrolytic, measure across that electrolytic for DC volts and you would expect that to be under 20V. if it is zero your supply is faulty and you have to chase that down.

TVRE
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Oct 27, 2007, 4:26 AM

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Re: [rrobor] MAGNAVOX RM8341 Can someone just answer this question????? [In reply to]	Can't Post

Thank you so much for your help
I do not get power across the secondary windings of the transformer just continuity. The electrolytic around the secondary windings show zero DC volts. None of the capacitor after the secondary show power just continuity. This also occurs at the switch mode transformer. Can this be a simple component failure or something bigger such as the IC.
Thank you again for your helo

rrobor
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Oct 28, 2007, 5:08 AM

Post #6 of 15 (1395 views)
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Re: [TVRE] MAGNAVOX RM8341 Can someone just answer this question????? [In reply to]	Can't Post

As a transformer can only work with AC volts Im not surprised. You state you get continuety on the capacitors, what do you mean by that?. You must fix the standby supply first so I will ask you to stop trying trying to be technical and look at the supply carefully. I dont know the set so I cant tell you if there is a small chip driving the standby transformer or not so your tests are 1/ test the secondary diode/s on ohms (diode check) for shorts. Each meter reads differently on diodes so I cant give you values but a few hundred ohms one way and open the other. if all that is OK and no diode reads short, test the primary for ohms. As stated the degauss leads may be in the mains so unplug that. Often standby transformers have an inbuilt thermal fuse, is that gone. Next what drives the transformer, is it just mains or is there drive components. IE is there diodes and capacitors in the primary, if so check that out. Also get out of the chopper power supply, that can not work till the standby supply works.

TVRE
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Oct 28, 2007, 9:02 PM

Post #7 of 15 (1384 views)
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Re: [rrobor] MAGNAVOX RM8341 Can someone just answer this question????? [In reply to]	Can't Post

HI
Well I tested the primary for ohms and I do get resistance so I do believe that the primary is OK. The electrolytic that is connect from the secondary only gives me continuity. It does not give me any DC voltage. The capacitors in the primary do give me DC voltage. I do believe that the transformer is ran by the ic.
Thanks again for your help.

rrobor
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Oct 28, 2007, 11:50 PM

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Re: [TVRE] MAGNAVOX RM8341 Can someone just answer this question????? [In reply to]	Can't Post

You keep using the word continuety with regards to a capacitor, I keep asking what do you mean by that and get no reply. Continuety on the transformer is OK it means you get a reading of ohms across the windings, continuety on a capacitor by that definition would mean the thing is stuffed. so try not to talk in technical terms if you are unsure as to what to expect as it gets confusing. It looks like the standby supply is driven by an IC. Google the number of tthat corner IC and see what it does. By what I can see here there is no filter or rectifier to that supply so I suspect it uses one that feeds both. So find a way to check the mains filter capacitor wit power on and read DC with your meter set high. Expect 1/3 more than mains voltage, IE mains 240V expect about 340V DC.

TVRE
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Oct 29, 2007, 3:01 AM

Post #9 of 15 (1372 views)
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Re: [rrobor] MAGNAVOX RM8341 Can someone just answer this question????? [In reply to]	Can't Post

Hi
What I understand as continuity is the beep given to me by the multimeter as a complete circuit. I know that I am not supposed to get continuity on the electrolytic. I do not get power on the capacitor feed off the secondary just the beep. I do get power on the large main filter capacitor. The IC is a Motorola MC34065P which says it is a High
Performance Dual Channel Current Mode Controller. I don't know the test procedures for this IC. Do you believe that this IC can be faulty?
Thanks againg for your help
if you need more pics I can post them.

rrobor
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Oct 29, 2007, 11:31 AM

Post #10 of 15 (1364 views)
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Re: [TVRE] MAGNAVOX RM8341 Can someone just answer this question????? [In reply to]	Can't Post

You cant fix a TV with this meter that goes beep, Perhaps Monty Python could, but that is useless. If you have an ohms range you must use that and read for ohms. A meter should have an ohms range with diode test. A capacitor will take a charge and beep whether good or bad as will a coil. Across any diode you would get a beep due to capacitor or coil, you have tested nothing so how can anyone tell.

TVRE
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Oct 29, 2007, 8:59 PM

Post #11 of 15 (1351 views)
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Re: [rrobor] MAGNAVOX RM8341 Can someone just answer this question????? [In reply to]	Can't Post

OK
Like I said before I have tested the primary for ohms and I get a good reading. What do I do next? I have a meter that measures DC,AC,OHMS,AMPS,DIODE CHECK, AND A WHOLE BUNCH OF OTHER STUFF.Like I said the capacitor off the secondary does not have any DC voltage. Once again how do I test the secondary. The primary is good. I believe that the standby controller IC is functioning.
Thanks

Franky
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Oct 30, 2007, 12:20 AM

Post #12 of 15 (1343 views)
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Re: [TVRE] MAGNAVOX RM8341 Can someone just answer this question????? [In reply to]	Can't Post

I think you chasing a goose,i suggest you follow the tips already given here by some people, don't think that your gonna learn here with us the hole consept of tv repair,besides this, i suggest you get a service manual and aquire an oscilescope to be able to read wave forms, i also suggest you to go to this site and read and read.
http://www.highlandelectrix.fsnet.co.uk/repair/repair.html

rrobor
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Oct 30, 2007, 8:54 AM

Post #13 of 15 (1338 views)
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Re: [Franky] MAGNAVOX RM8341 Can someone just answer this question????? [In reply to]	Can't Post

Well for a start an oscilloscope is a rather expensive toy and unless you have a very sound knowledge of electronics you can blow it up in seconds especially in a power supply. So no, an oscilloscope is a tool used on occasion by a professional, it is not required for most faults, and is not for the amateur. That you have no idea as to what you are doing is obvious. for exmple on the picture posted there seems to be a start up resistor, that will be over 100K but you check by the beep method and have never checked that, Do you know the colour code, do you understand capacitance and inductance. This site is an aid to repairing, not an education system. If you have no idea then this site is not for you.

TVRE
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Oct 30, 2007, 11:25 PM

Post #14 of 15 (1313 views)
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Re: [rrobor] MAGNAVOX RM8341 Can someone just answer this question????? [In reply to]	Can't Post

Hi
I tested the startup resistor and it check out ok. I have found a bad resistor the feeds a voltage regulator IC. I will replace it and see what happens.

Paulpablo
Enthusiast

Oct 31, 2007, 1:55 AM

Post #15 of 15 (1311 views)
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Re: [TVRE] MAGNAVOX RM8341 Can someone just answer this question????? [In reply to]	Can't Post

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