Re: magnavox 37MF321D/37 no power
Nailed it! All is working now after replacing IC 7003 and capacitor 2002!
One of the two main boards I "fixed" did not have any standby after replacing the IC, so I need to go back and figure out what I messed up (because that's a change from low volts). I bought one extra IC and cap from digikey so I might just have to start the soldering over again.
The other board fired right up and I have picture and power lights again...it has been running for hours now.
Many thanks BudM and Johnboy1313 ...I...
rsrace
Member
Last Activity: 01-09-2016, 05:42 PM
Joined: 12-20-2015
Location: Baltimore
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Re: magnavox 37MF321D/37 no power
Many thanks Johnboy and BudM. I think I will take a shot at the IC7003 replacement (and the associated capacitor). At the price of the main boards available right now, this seems like the way to go.
I will also check the outputs of the IC to be sure that nothing is shorted...both boards look like they fried right between pin 7 and 8 as shown in many of those other posts I found in BudM's reply and a search I did of the forum.
I like the way you think Johnboy - I need to recoup a bit from this ordeal...Leave a comment:
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Re: magnavox 37MF321D/37 no power
[B]Also, this pretty much confirms a bad main/scaler, doesn't it[/B]?
Helping answer my own question, I plugged in the "replacement" main/scaler board and got the same results.
I then went over both boards using an opti-visor and flashlight and found my original main/scaler had a small "wart" of carbon-like material on IC7003 (see attached picture). The replacement board also had a lot of crud on the same IC and, when I touched it, the corner literally crumbled (see picture with flashlight on). These...Leave a comment:
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Re: magnavox 37MF321D/37 no power
BudM,
Thanks so much for your help on this - especially in light of what turns out to be sloppy troubleshooting on my part. (I could not find an emoticon for kicking myself)
Yes - makes perfect sense - I follow.
With your input, I remeasured. <and am embarrassed>
Inverter on/off: I measured the collector of transistor 7078 at 2.45v when "on" and then it slowly bleeds to 0 when off. I guess I was so used to signals on for 2 secs then off, I did not wait long...Last edited by rsrace; 01-03-2016, 01:32 PM.Leave a comment:
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Re: magnavox 37MF321D/37 no power
Capacitor 2062 of the PSU (I think it shows a different number on the schematic for the 32" board; the big 450V cap, lead to lead): When the inverter light is ON, I have 399VDC. When it goes out, I drop to 164VDC...Last edited by rsrace; 01-02-2016, 11:42 AM.Leave a comment:
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Re: magnavox 37MF321D/37 no power
If I am reading it right, the STANDBY is always "off" (.003v then .000v) - pin 9.
The inverter on/off never drops - it is always rock steady at 2.45v...Leave a comment:
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Re: magnavox 37MF321D/37 no power
BudM - just updated... if the print is right, Standby is Pin 9 of 1089 which is never present (.003v). Inverter on/off is pin 5 of the same connector which is a steady 2.45v
The seller claimed the scaler was working. That and $5 will get you a coffee at Starbucks. (I don't have any reason to believe it is working except that it is EXACTLY the same symptom as my original). All measurements above are on my ORIGINAL boards....Last edited by rsrace; 01-02-2016, 10:24 AM.Leave a comment:
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Re: magnavox 37MF321D/37 no power
So, in recording these voltages on the PSU, a small discovery - they voltages change when the red light on the Master Inverter board goes out (and the screen goes from slight greyish to black). To turn the light back on, one must either unplug the TV and repower it, or toggle the power button TWICE.
So BudM - this means [B]I DO have 24v on coil 5079[/B] [I]but[/I] only when the inverter light is lit. Then it bleeds to 0v.
The first set of voltages is red light ON, the second set, red light off (ON/OFF)....Leave a comment:
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Re: magnavox 37MF321D/37 no power
Using the schematic BudM attached (which does not show the 37" - but I have yet to find one that does so I am following the schematic and the physical board and have yet to find differences), [B]I have the 16V at D-16 [/B]on the print, [B]I have the 24A voltage at C-16[/B], [B]I do not have the 24V off coil 5079[/B] at the same F-16 location.
I [B]do have 16V on 1089 pin 1&2[/B] at F-1. I also [B]have 24V at pin 3[/B] at F-1. Pins 4&5 of 1089 are very low voltages (mv). [B]I do not have standby on pin 9 of...Leave a comment:
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Re: magnavox 37MF321D/37 no power
...and back panel layout. Power supply and main are in the center "box", with backlight/inverter master? on left (viewed from back) and slave? on right. IR power-switch is lower left in picture.
The only markings on the chassis label are LC370WX1 (SL) (04) and 37065K4635051 F12C.
I have been using service manual TPE1.0U LA....Leave a comment:
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Re: magnavox 37MF321D/37 no power
Pictures of both sides of the Power Supply Board, Main Scaler Board, and the IR-Power Switch board plus a schematic of the Power Supply showing where I do not have expected signals.
Many thanks for any insight. Let me know if there is something else I should have photo'd.
Randy...Leave a comment:
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magnavox 37MF321D/37 no power
Magnavox 37MF321D/37 television. I am referencing the Service Manual posted in another similar thread and reading off the troubleshooting flowchart and 7.4 power supply schematic. I have read every other thread on this forum with similar problems...just haven't hit the "magic" solution yet.
No power light on front LED/manual power switch (or the remote for that matter). No picture, sound, or menu. [B]Pushing power switch will show a slight grey screen for 2-3 minutes (backlight?) and then go dark.[/B] I also see a red LED on the backlight/inverter board (Master?) which... -
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I am an electronics (they called it computer hardware back then) engineer by training but that was a long time ago when dinosaurs still roamed the earth and the Intel 8086 was THE chip of choice, bit/slice microprocessor design was seen as the future, and no one needed more than 1k of ram. Now I pretty much stick to fixing stuff around the house and a lot of audio/amplifier/guitar modifications. I found this forum searching for answers and schematics for a flat screen television that I am trying...Leave a comment:
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