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Magnavox RS2744 A402 wont power on   Goto page 1, 2, 3  Next  
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tom418



Joined: 03 Aug 2014
Posts: 18
Location: New England

PostPosted: Sun Aug 03, 2014 12:00 pm    Post subject: Magnavox RS2744 A402 wont power on Reply with quote

My Magnavox RS2744A402 (chassis 27Y100-00AA) suddenly wont turn ON (with or w/o remote).

Recently I had trouble turning it OFF. I found that if I used the remote fromthe Zenith DTV converter, pressing TV OFF would only result in the screen turning brighter, or seeing close captions. Then, pressing converter off on the remote would turn off both TV and converter!

But getting back to the problem: Now the set will not turn on at all. I've made one repair a few years ago, and that was to resolder a thermistor in the degauss circuit (My picture had a bullseye pattern that someone politely told me how to fix). Aside from that, it's a great 27 in CRT tv. So if anyone can help, please DO!!
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JTS1957



Joined: 21 Jan 2009
Posts: 2324
Location: Far, Far Away

PostPosted: Sun Aug 03, 2014 4:20 pm    Post subject: Reply with quote

Replace C432 100ufd 200volt if it hasn't been changed in the past.
tom418



Joined: 03 Aug 2014
Posts: 18
Location: New England

PostPosted: Sun Aug 03, 2014 5:15 pm    Post subject: Reply with quote

JTS1957:

I took a look at the PC board, and there are what look like burn (or at least brown marks) under this electollytic cap.!!

I think you're on to something. I'll order one , try it and post back.


Thanks!!!!!!!!!
tom418



Joined: 03 Aug 2014
Posts: 18
Location: New England

PostPosted: Tue Aug 19, 2014 11:09 am    Post subject: Magnavox won't power on Reply with quote

I changed the cap (with identical capacitance and voltage rating, and brand-Nichicon). The TV still wont turn on.

Is there a relay that the 115V power sourse goes through? Everytime it did power up, there was some noise inside. Or is that for the degaussing circuit?
JTS1957



Joined: 21 Jan 2009
Posts: 2324
Location: Far, Far Away

PostPosted: Tue Aug 19, 2014 6:55 pm    Post subject: Reply with quote

First, I don't have access to the EXACT schematic for your set. I am using one from the same era, but with a different chassis number. So take with a grain of salt.

No relay that I see.
Check:
LOCATION Number: F401 VALUE: 2.5 Amp
LOCATION Number: R432 VALUE: 1000 Ohm
LOCATION Number: IC410 VALUE: STR30130 Regulator

See if yours uses a Q400. If IC410 shorted, check Horizontal Output transistor Q502.


Last edited by JTS1957 on Tue Aug 19, 2014 10:12 pm; edited 1 time in total
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tom418



Joined: 03 Aug 2014
Posts: 18
Location: New England

PostPosted: Tue Aug 19, 2014 9:33 pm    Post subject: Reply with quote

OK I'll do that. I also saw someones youtube video on fixing non-powering Magnavox sets. He changed the same cap you mentioned, and also said that if a set is operated with that cap defective, other components can be fried in the process.

I did see one fuse that's intact. Don't know if it's the 2A one you mentioned, but I'll check it out tomorrow. I'll take a look at the resistor and regulator you mentioned also.
JTS1957



Joined: 21 Jan 2009
Posts: 2324
Location: Far, Far Away

PostPosted: Tue Aug 19, 2014 10:28 pm    Post subject: Reply with quote

tom418 wrote:
other components can be fried in the process.


NOT in my experience (where complaint seems not related C432 replaced as preventative - most C432 actually bad only charred/opened R432).

22 sets/Various defects (Customer vs actual):

No Vertical Sweep - Then: B-Plus Too High
Bad Picture and Will Not Turn Off
No Sound on Remote But will change Ch's - From TV Will not turn off
NONE. Picture Shakes
None Picture Pulls - Hunt for Station
None Hum Bar and Picture Pulls
None Picture Pulls
Sound - Vertical Lines - No Picture
Dead Also Horizontal (out of sync) lines in pix at 120 volts
NONE. 75 ohm box inside loose
NONE. No Ch. Displays - Interface board loose inside
NONE. Resistor Charred - Dead
NONE. Appears as if Horizontal hold is off frequency
NONE. Was dropped? - Out Of Focus - Power Button? N401 "Flashing" Ticking Noise
Not Good - What Room Resistor Charred - Dead
From 195 No Picture Not good
1405 Wouldn't work on Smart Loader
Not Goot Been Dropped?
NONE Mis-converged at TOP & BOTTOM - Center OK
NONE ?
Makes Sounds
NONE Picture Rolls, etc.

Troubleshoot and repair Power Supply. Replace above. Resolder suspicious joints on Main P.C. Board.
JTS1957



Joined: 21 Jan 2009
Posts: 2324
Location: Far, Far Away

PostPosted: Wed Aug 27, 2014 4:15 pm    Post subject: Reply with quote

It's been a week ... Well?
tom418



Joined: 03 Aug 2014
Posts: 18
Location: New England

PostPosted: Sat Oct 04, 2014 10:54 am    Post subject: Reply with quote

Hi JTS1957!!!

Sorry for the delay in getting back, but I had other things going on like starting a new job (teacher) AND I got the service manual.

So I changed C432 as suggested (board was way darkened underneath).
Still no power up. Using the schematic and power supply description, I attempted to measure voltage at "Test Point 8" , located at end of fuse 401. It's supposed to be 160v, but I got zero. Checked f401 for continuity: It was open. So I measured voltage at other end of fuse (relative to ground), and my meter pegged instead of getting 160 volts. So: Am I correct to assume that the regulator IC 410 is faulty? The service manual says that the 4 diodes that make up the bridge rectifier are protected by the fuse 401. Is there a chance that the fuse blew in time to save the bridge rec? Or should I order the 4 diodes also?
JTS1957



Joined: 21 Jan 2009
Posts: 2324
Location: Far, Far Away

PostPosted: Sat Oct 04, 2014 12:18 pm    Post subject: Reply with quote

Is the service literature a pdf? If so, how can I get a copy so we are referencing the same, values specifically?

The DC voltage on either side of that fuse (if fuse is good) should be 160VDC. Are you referencing to C405 negative (ground).

You have changed the fuse? Does it continue to blow?
DC voltage across C405?
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