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TJM2005
Member
Last Activity: Yesterday, 09:03 AM
Joined: 08-17-2013
Location: Lancaster, OH
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IC902 is back in and everything seems to be working now!
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Hello everyone,
Wanted to give an update:- I bench tested both ZD907 and D902B at 16V and a 5KΩ resistor and they both tested OK.
- I tried to solder leads onto C904B and the wire was too stiff causing the solder pad to pull off.
- I got a replacement today and put it back on.
- I tried to test it using T/R = C and my function generator with a 10KΩ resistor. If I did the math right I got 1.8nf.
- VCC is now study at 13.64V
- I get 168V on the drain pins during standby
- 388V when I power it on.
- The backlights and white power lights all came on.
- I have another
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Ok, I played around some tonight.
- First I removed just IC902 and tested, I am now getting 13.6V VCC.
- The corner of the IC chipped off as I was trying to remove it and I slightly damaged one of the small pads, although I should be able to jump it back to the trace.
- Is this something I can source from Mouser?
- C904A
- That would be this one correct? Any Idea what it should be, I can't see any markings on it, I can hardly pick the darn thing up haha.
- ZD907
- Looks like markings: 24B NZ
- D902B
- Looks like markings: LT423 UG1004
- I haven't had a chance to get the power supply out and
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- First I removed just IC902 and tested, I am now getting 13.6V VCC.
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I attached a cap between IC901 VCC and hot ground.
With my meter connected it bounces between 10 and 15 volts.
Is there anything else I should check while I have it hooked up like this?
...Leave a comment:
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- Can you identify IC902? Or post a clear photo of the markings?
- Sorry I thought you was talking about the PC902, I now see IC902 on the bottom side.
- looks like an S101 /408A
- If you can isolate the vcc pin from the rest of the circuit and only connect a 10~47µf cap from H-ground to only that pin and see if the ic can charge the cap.
- I have extras 22uf 50v caps
- Or try removing one end of ZD907 (it may be zenering at 1 volt?) and try to isolate IC902 VCC pin if you can (careful not to break pin)
- Is this the correct pinout? VCC would be under the letter A of 408A on the chip?
- I
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- Can you identify IC902? Or post a clear photo of the markings?
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- ZD907 / .74 no shorts
- The blue line should be the connection from the comp pin to PC902
- It is the only pin on the hot side with continuity to the comp pin, amongst PC901 - PC903.
- I pulled PC902 from the board and powered it on, I am still getting 1.6V at VCC.
- It doesn't seem to be bad, I posted a couple of pictures of the old one vs a new one.
- I gave the flux a good cleaning, I forgot to clean it after I swapped the chip this afternoon.
OLD Octo:
New LTV-816 https://www.mouser.com/ProductDetail/859-LTV-816
...Leave a comment:
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- Are you measuring from the hot side ground?
- Yes, scope ground on the - pin of the main cap
- Did you check or change the optoisolator?
- No, this would be PC902?
- I have one and could try to swap it out.
- I found this near the bottom of the datasheet, everything else calls out stopping the gate driver:
- Open/Short fault Protection
Some crucial protections are integrated in the LD7913J to
prevent the power supply from damage in open/short fault
condition. The LD7913J will shut down to protect the power
circuit under following open or short conditions:
- Open/Short fault Protection
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- Are you measuring from the hot side ground?
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I just double checked them, both are reading about .47 and are not showing shorted.
I also swapped out IC901 with another one I had, and it didn't make a difference....Leave a comment:
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Update:
I got the two source resistors replaced, as well as the two small caps.- R907A
- R907B
- C904B
- C907
Orange is VCC
Blue Is BNO
...Leave a comment:
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I ordered some SMD replacements, should have them in a couple of days.
From what I could tell they are the 1206 package size.
...Leave a comment:
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I had time today to do some more testing.
I went ahead and threw new caps in for C904B and C907, each of the removed caps tested about 2uf lower than rated and was about 0.15Ω greater ESR than the new replacements.- Source resistors R907A and R907B
- R907A = 5.1 Ω = Looks like 5R70?
- R907B = 4.2Ω = 3R92
- Looking at the picture I noticed one of the solder pads came off and I was able to take a reading.
4.7Ω in parallel with 3.9Ω would be 2.13Ω.
Can you confirm these are the correct values?
Being they are in parallel, is there any reason...Leave a comment:
- Source resistors R907A and R907B
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I had time today to do some more testing.
I went ahead and threw new caps in for C904B and C907, each of the removed caps tested about 2uf lower than rated and was about 0.15Ω greater ESR than the new replacements.- Source resistors R907A and R907B
- R097A = 5.1 Ω
- R907B = Open
4.7Ω in parallel with 3.9Ω would be 2.13Ω.
Can you confirm these are the correct values?
Being they are in parallel, is there any reason it would matter which one has what value?Leave a comment:
- Source resistors R907A and R907B
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Thanks for the info and explanations. I am working long hours the next couple of days, but I will try to test the source resistors when I have a minute. The caps should also be here sometime tomorrow.
There is no secondary voltage anywhere on the CN101 connector. I assume this is to be expected if IC901 isn't yet providing the switching needed to drive the transformer? I can also try to throw a scope on the VCC pin and see what it is doing as power is applied.
Appreciate the help so far....Leave a comment:
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Yes, ZD909 tested shorted even when removed from the circuit.
I put an order in for the C904B and C907 and should have them in a day or so.
I missed that the IC generates its own VCC voltage, is this only during startup then the VCC power comes from the secondary side of the transformer ones it starts switching? Will it power up even if the optocoupler on the COMP pin is bad?
I will plan to replace the caps then retest the VCC, I also ordered another LD7913J as the first one came from e-bay, and I am not sure of an easy way to test that is fully operational.
...Leave a comment:
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DSP-167DP LOW VCC at IC901
Hello,
I am trying to repair a power supply for a Vizio M492i-B2.
Before I started:
Fusible Resistor R915 was open.
ZD909 was shorted.
D950B was shorted.
I have replaced the above parts along with a new IC901 / LD7913J
I now have:
165V on the main cap
IC901 Drain pins: 165V
IC901 VCC: 1.1V
IC901 COMP: 1.1V
IC901 BNO: 0.3V
I pulled the Q800 Mosfet and it checked good.
I also tested the two smaller caps C907 and C904B, they both tested close to the rated value.
Does anyone know of anything...
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