Nr4ps
Member
Last Activity: 04-05-2024, 06:46 AM
Joined: 12-26-2023
Location: Waldorf, MD
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I never figured this out. I don't think it can be the replacement LD7913 that I installed because, according to the datasheet that chip doesn't even turn on until the brownout protection pin is above a certain voltage - and the capacitor on that pin won't charge. -
I don't know if this addresses that thought correctly, but to a quick test in reverse bias the four zeners in that cluster that I didn't replace seem to break down at about the right voltage:
Zd900 6.1V (labeled 6V2)
Zd902 12.7V (labeled 13B)
Zd904 15.9v (labeled 16B)
Zd907 24V (labeled 24B)
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The kit on ebay includes the same four parts that I already replaced. I've been looking for a bad solder joint but not finding anything. Everything I resoldered has continuity to where it seems like it should. CN202 looks fine, and I think that connector is just for getting power to the backlight anyway. Wish I understood more how this thing was supposed to work. I was hoping to avoid buying a whole new board, but maybe I'm just being stubborn at this point.Leave a comment:
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C910 measures 64 uF in-circuit. I imagine that means there's another capacitance in parallel with it somewhere and that's not all due to that tiny ceramic cap. But it's not shorted. Is that good enough or shall I desolder it?
R915 is also one of the components I originally replaced. It measures 4.7 ohms.
For C904B I found a 15uF 200V capacitor that I put in, and it still doesn't charge. This is with IC901 installed again. (Original measures good at 10.5 uF out of circuit, by the way.)
Thanks for your ongoing suggestions. I'm a little impressed you haven't...Leave a comment:
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ZD909 and D950B were two of the components that were originally blown and I had to replace. Replacements were tested out of circuit. I also measured R907 A and B at about 2 ohms in circuit.
IC901 datasheet attached.
I'll get back to you on C910 and trying to find a closer replacement for C904B....Leave a comment:
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I tried 100 uF 100V and still nothing.Leave a comment:
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Original was 10uF 50V. I replaced with 0.47uF 50V (closest I had). Still doesn't charge. I think I'm going to have to figure out more about how this thing is supposed to work. 120 VAC comes in and gets converted to 170 VDC at BD1, labeled in photo. Right now, pins 2 and 3 of T901 sit at 170VDC relative to that same negative post. I guess an AC component is supposed to ride on top of that to energize the transformer, but I'm not getting any.Leave a comment:
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C904B doesn't charge with IC901 removed either.Leave a comment:
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Yeah, I was thinking about that... IC901 came from eBay because it's hard to find anywhere else, and it's the one part of the four that I don't know of any way to test. Maybe if I remove it from the board again I can at least see if that somehow allows C904B to charge to a couple volts such that IC901 would start if it were present.Leave a comment:
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I can't find anything wrong with any of them. I even pulled most of the diodes out of circuit to make sure it wasn't an illusion that they were working. Capacitors seem fine. Resistors seem fine. Even the tiny resistors on the back of the circuit seem roughly correct.
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The markings on the transformer are below. I couldn't find a data sheet for the transformer, but another badcaps post suggests that the primary is 2~3, The vcc feedback is 1~4 Pins 5~7 are the secondary. Resistances measurements are no more than a few ohms across each pair, so I don't think the transformer is blown but it's not getting any AC voltage on 2 and 3.
MP-130I (01)
AV-DP11153 DELTA
DCUM 1418(06)H60
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Thanks! PC902 seems to be in good working order.
Can anyone tell me what all those pins on T901 are for? Is that a multi-tap output to make a variety of voltages?...Leave a comment:
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I decided to try the 814 with no luck. But I notice that pin 2 on IC901, the brownout pin, is connected by way of R919 (approx 130k) to VCC and R918 (approx 128k) to ground. That pin needs to be above about 1V before the chip will even turn on. And I think that's my problem. If I'm tracing that correctly, something needs to charge C904B to a couple volts before this chip will do anything. I'm trying to figure out where that's supposed to be coming from. Like I said, D902B read good out of circuit. I get 1.2 ohms across R908A, B, and C. From there, it's connected to pin 1 on T901. Is that supposed...Leave a comment:
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C904B is good. I believe the optocoupler in question is PC902. I don't have any LT816 on hand. Could I substitute LT814 or better to wait to get the right part? Thank you for your help.Leave a comment:
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Ah, thanks. Lowest reading between pins of Q800 is 9.6k.
IC901 is LD7913JGM6 and I replaced it with the same.
How to test the photocouplers?Leave a comment:
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Thanks. I can't see what Q800 is under the heat sink, and I'm not sure what the correct way to test it is, but in-circuit (which I'm sure is not the correct way to test it but hoping to minimize further desoldering and resoldering) with my meter in diode test mode I get 0.63V or 1.93V across the outer legs depending on polarity. Plugging it in, the center leg is at 169V while the other two are 0V.
I'm trying to make sense of the data sheet for IC901. I assumed the VCC pin would power the chip but I think the chip is supposed to actually charge the capacitor on that pin. Attached is...Leave a comment:
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Vizio DPS-167DP-1 failure
I'm trying to troubleshoot a DPS-167DP-1 A power supply board from a Vizio M552i-B2 tv. The tv would no longer turn on, and I found the usual melting on IC901, with D950B and ZD909 shorted and R915 open. Sounds like this is a pretty common failure, so I replaced all four components expecting it to be an easy fix but it's still not working.
I checked D801 and it's fine. I get about 170V DC across the main filter capacitor C800A. I'm not getting any voltage on the 5V standby pins in connector CN101, nor any voltage on the VCC pin of IC901, which is presumably why it's not working --...
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