Re: Sanyo LCD-42E30FA shuts down after 30 minutes
Ok, another update on this unit. Was running another TV on external antenna so did not have it connected to this unit. Powered up and after 20 seconds or so, the "no signal" icon shows up on the screen and does its normal thing of wandering around. The interesting thing now is that the unit has been running like this for 2 hours, looks quite normal, until I plug in the antenna. Now what it looks like is when the TV is receiving free to air signal( only digital here in Aus), about 30 seconds later, it locks up. Lose picture...
beechman35
Member
Last Activity: 04-26-2018, 03:19 AM
Joined: 01-04-2015
Location: Melbourne Victoria
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Re: Samsung LA32B350F no backlight
Hi Guys, an update on the TV. Found a power supply on Ebay for 35 dollars from a cracked screen unit. Installed and away it goes. Great picture no dead pixels so pretty happy about that. Shame I couldn't get the original supply working but I learnt a heap about switch modes and PFC's which is sure to help me on other repairs. Thanks to all that helped, especially Bud.Leave a comment:
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Re: Sanyo LCD-42E30FA shuts down after 30 minutes
Tried a few more things today. Measured all the voltage reg outputs on the main board and all seam good. What was interesting is the TV worked for a while after I had disturbed the board. Pulled the main board, gave it a gentle twist and reinstalled. TV then worked for about 2 minutes. I am wondering if the CPU had unbonded itself. Have seen this on Xbox units, any thoughts people??
Regards
RobLeave a comment:
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Re: Samsung LA32B350F no backlight
I see all your saying and agree with all. I have checked the voltage ref chip and the voltage is 2.48V so reference is good. All I can think of is a spike somewhere is getting into the comparator CCT and tripping it off line before the regulator can start. I am going to pull all the voltage divider resistors and test out of circuit.
Will let you know
Regards
RobLeave a comment:
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Re: Sanyo LCD-42E30FA shuts down after 30 minutes
Recapped the power supply and that sort of fixed the fails after 30 minutes...... Now it wont start at all !!!!! I am having a great day (NOT). All voltages are there (5V, 12V and 24V), Back lights are lit and the only button that does anything is the power button.
Any clues ??
Thanks guys
RobLeave a comment:
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Re: Samsung LA32B350F no backlight
OK, RB804 refitted. RP823 still removed and wire soldered onto CB805 (again I assumed you meant this cap to measure divider volts)
TV in standby 1.02V, TV switched on, very quick pulse to over 1.5V then settles at 1.2 V. I havnt measured with DSO as yet, but I amd suspect of voltage overshoot somehow. To follow on from this, I measured the main cap voltage CP815 and what I saw was interesting. The voltage with AC supplied is 330V, when TV switched on, very quick kick up and then settles on 328V, but I left the meter connected to cap and...Leave a comment:
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Re: Samsung LA32B350F no backlight
Hi Bud,
Confusion reigns supreme right now. I pulled RP823, the zero ohm link that feeds the PFC chip ( I saw you mentioned RM869 but that is the current sense resistor for the switch mode,) soldered a 1K resistor onto the output of the reg and powered up. 0.7 volt output from the reg. I then pulled one of the chain resistor group (RB804) so there was no voltage sense going to the regulator and now have 15 volts at the emitter of QB801. (obviously no lights due to link still removed). If I measure the voltage at the main cap, I still only...Leave a comment:
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Sanyo LCD-42E30FA shuts down after 30 minutes
Hi Guys,
Sanyo LCD-42E30FA chassis No SSA42UT-00 powers up normally when cold. After 30 minutes of running, noticed picture and sound lost and buttons not responding (no remote so cant test) Slight repeated "chirping" noise noticed. Pulled back cover, nothing obviously noticed so powered up and ran again. Now it wont fail (after and hour anyway). 5 volt, 12 volt and 24 volt rails are good. I am suspecting a heat soak problem with the back on.
Any thoughts?
Regards
Rob S... -
Re: Samsung LA32B350F no backlight
Hi Bud,
Sorry for the delay in replying, but had to fix a problem with engine controller. OK, This is interesting after reading your last post. You say that in the overvolt condition, the regulator circuit will clamp the voltage to around 5 volt. This is not happening and the system is clamping to Zero volts (well 0.7 to be precise). Lots of trialling but no real success, except for something interesting. If I remove the PNP transistor (QB802) the regulator appears to work on by bench set up with the 2 variable power supplies. When...Leave a comment:
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Re: Samsung LA32B350F no backlight
Just refitted the power supply into TV and still no go. Looked at previous post and realised that the results of testing image did not post so will repost it here. Will do some more testing shortly with a storage CRO attached to see if the PFC is tripping overvolt. From what I can see from the two transistors (QB802 and 803), this looks like a crowbar circuit that will trip and latch the power supply off if it senses overvolt. CCT is reset with power cycling. (I think).
Will attach results again and do more soon, (have to do some...Leave a comment:
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Re: Samsung LA32B350F no backlight
Hi Bud, OK, here is the latest with some crazy theories so bare with me. We pulled the 15 volt zener and tested it, found regulating properly so refitted it. Now to save putting the board in and out of the TV, I decided to rig up a variable DC supply to the collector of the opto coupler with a 1 amp diode bridging the opto to simulate it turned on and powered up the bench supply. low and behold, 15 volts at the emitter of QB801. Pulled Fuse FM802S and fed a second low voltage DC supply into the junction of resistor RB807 and RB816 to simulate the...Leave a comment:
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Re: Samsung LA32B350F no backlight
Will test with variable power supply and limiting resistor out of cct to see what voltage the zener is at. Not sure if we have 15V SMD if not, we could temp install an axial to test the TV. Be in touch
Thanks
RobLeave a comment:
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Re: Samsung LA32B350F no backlight
Hi Bud,
Voltages checked and as per attached PDF. Checked the resistor values and they look OK. The Zener appears ok as an in circuit test and if nothing else comes to mind, I will pull it and check the voltage drop....Leave a comment:
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Re: Samsung LA32B350F no backlight
Hi Bud, First off, let me thank you for your efforts on this. As we all know sometimes it just might not be worth fixing something on a commercial basis, but now I just want to know what the hell is wrong for my own personal benefit. OK, the results. PS board installed, all wiring intact. turn on TV, get the welcome audio and then measure the voltages. Collector of QB801 has 18.2 volts, base has 0.5 volts and emitter has0.6 volts. PS board removed and Zb801 checked in circuit and no apparent leakage. Removed QB801, tests normal so refitted. Removed...Leave a comment:
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Re: Samsung LA32B350F no backlight
Hi Bud, Diodes checked and look good as diode check in circuit. we did pull DP805 and check out of circuit for leakage and appears good. Also confirming that the diode is the 31GF6, not the MUR360.Leave a comment:
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Re: Samsung LA32B350F no backlight
Hi Budm
Connected resistor as you describe with the wire to the main board disconnected. Volts at the main filter cap are 331 VDC.Leave a comment:
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Re: Samsung LA32B350F no backlight
Ok, disconnected the wire from pin 1 of CN802 and worked out which jumpers on the power supply board are connected to 5v stby and pwr on/off so I could monitor all voltages. Supplied 240VAC and measured open wire from main board and no volts. Stby pwr at 5.3. Measured link wire that feeds pwr on/off to power supply, no volts. Turn TV on with remote and get power on sound and then measured voltage at wire coming from main board for pwr on/off and measure 4.88 volt(on/off wire disconnected). Measure link wire on power supply board without the 1k...Leave a comment:
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Re: Samsung LA32B350F no backlight
Back again,
Voltage on the yellow cap (listed as main cap in first post) 331 VDC standby mode and 326 in power on mode. Confirmed the power on/off switches to 0.766 measured at pin 1 of plug CN802 with all cables connected.
Pic of main board attached.
Regards
Rob...Leave a comment:
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Samsung LA32B350F no backlight
Hi Guys,
First post so be gentle with me. Samsung 32inch LCD with no backlighting. Power supply board is a BN44-00289B.
Plugging in AC supply, the stby light is lit solid. Power on the TV and Stby light flashes 5 times and then extinguishes with audio welcome tone from speakers. Watched the screen in a darkened room and no flashes from CCFL's. Used the flashlight trick and can see menu when selected. LCD panel appears good with no cracks visible.
Measuring the voltages on the power supply connector I see the following:
Description TV... -
Re: New Members - please post your introductions here
G'day from Downunder.
Rob S from Australia. I have a background in aviation electronics and am a licenced aircraft engineer that sees us working on some fairly heavy end electronics in flight displays and navigation systems. I can never pass up a bargain (read sidewalk shopping) and have an issue with how much "modern" electronic equipment is going into land fill. Need some help on various LCD TV problems.Leave a comment:
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