Re: troubleshooting TV SMPS sequence
BudM,
Thanks Budm, great job you and everyone. the first time I checked the 5vsb with the scope on the small1W board, there was alot of signal distortion sitting on top of the 5.36V going just below 5V. I did change the cap C616 on the 1W board and that cleared up the distortion.
what you're saying is there are two 5V stndby voltages, one on 1W board and another on the PS itself?
anyway, glad I made it through the storm. your tireless efforts on so many posts is unbelievable. glad you kept an eye out...
ilikesteel
Badcaps Veteran
Last Activity: 04-19-2023, 10:23 AM
Joined: 07-26-2012
Location: washington, nj
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Re: troubleshooting TV SMPS sequence
CApLeaker,
Thanks again. it was a great learning experience for me. I think I developed some extra troubleshooting skills because of it.
thanks again.
ilikesteelLeave a comment:
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Re: troubleshooting TV SMPS sequence
"bump"Leave a comment:
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Re: troubleshooting TV SMPS sequence
CapLeaker-Budm-BudWich-EVERYONE who contributed to this thread,
It Works!!!! The TV came right up, MENU screen came right up, looks beautiful.
could not have even thought to repair this TV without this forum and all the great people who contribute their time and effort to repair a TV they have never laid eyes on. Just amazing brilliance by all on this forum.
Special thanks to CapLeaker, Budm and BudWich who seemed to have offered much of their time and have educated me a little...Leave a comment:
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Re: troubleshooting TV SMPS sequence
CapLeaker-BudM,
Hell, I couldn't wait for tomorrow to check it!!!!
I found a replacement for C44 10uf 50V. changed it. I believe the ld7550b is actually IC#12. I followed trace and made sure we're talking the right component.
are you ready for this???
Main Cap now has 384V STEADY
checked voltage on + side of C44 which goes to Pin 5 Vcc on ld7550b.
measured 12.54V STEADY!!
measured Pin 2, feedback comp, 2.09V STEADY.
...Leave a comment:
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Re: troubleshooting TV SMPS sequence
CapLeaker,
I will check that tomorrow. yes, I replaced the cap C36 right away, before doing any measurements resistance or voltage.
By the way, I could not find [COLOR="Red"]F2[/COLOR] anywhere on the board, bottom or top side, I just don't see it. I checked real close, but did not find it.
Neg of main cap is my GND. also, I do have [U]two [/U]probes for the 314 oscilloscope, just say'n.
Thanks..
ilikesteelRe: troubleshooting TV SMPS sequence
CapLeaker,Leave a comment:
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Re: troubleshooting TV SMPS sequence
BudM and CapLeaker.
you guys are something else!
ok made some resistance measurements and voltage measurements.
first, I found a direct replacement for Cap C36 47uf 50V. replaced it.
R73 marked 220 22ohm resistor, measured 21.6 ohms
R17 and R19 were marked 472, 4700 resistor, measured 4600 ohms.
[B]The voltages measurements were made with the main cap NEG lead as my GND lead to the DVM.[/B]
attached are two photos of schematic with voltage...Leave a comment:
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Re: troubleshooting TV SMPS sequence
BudM,
WOW. Great deducing!! I will try and follow you directions and make measurements you requested.
I think what you're saying is with the Pin 9 Vcc pin oscillating between 6.6-8.3v, the rest of the outputs on TDA 16888 are being affected by the same oscillation causing problems.
Manny Thanks
ilikesteelLeave a comment:
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Re: troubleshooting TV SMPS sequence
BudWich,
noted BudWich. let's see what CapLeaker has to say. the problem must be on the hot side.... I think. I'm not too familiar with PFC circuits and their components. If somebody says "you have to have xxV at this point, I can check it and report bck what I measured. it's unclear to me what voltages are right and wrong. it's interesting but a little over my head.
thanks
ilikesteelLeave a comment:
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Re: troubleshooting TV SMPS sequence
CapLeaker-BudWich,
OK, made some measurements on IC TDA 16888. I [U]did not[/U] make any PS output voltages with the scope this time.
main Cap = 366v-367v.
THR1 = 6.6 ohms measured in circuit, no power.
R67 marked with 221, 220 ohm resistor measured .215 on 2K scale. (215 ohms)? measured in circuit no power.
now for the TDA 16888. many of the voltages are oscillating similar to the secondary readings. how can that be, they're on two different sides of the PS, Hot and Cold....Leave a comment:
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Re: troubleshooting TV SMPS sequence
CpLeaker-BdWich,
I can recheck the IC tda 16888 on the pins you requested. I did it with the DVM before running a pigtail wire from the NEG of MainCap as the gnd.
Can I check that with the scope, using the scope GND connected to the pigtail wire from the main cap NEG?
I'll try and provide more accurate data in reference to the scope setup and where I'm testing.
just for info, all measurements on the secondary side of the PS I used the chassis GND, or the 3 GND pins on the PS connector...Leave a comment:
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Re: troubleshooting TV SMPS sequence
CapLeaker,
with voltage/div set at .5V per division, using a 10X probe, that would make each division 5V, NO? second pic, clearly shows an approximate strong 10V level, with the big clocking/square wave looking pulse jumping up to almost 30V. that's what it looks like to me.
it's hard to hold the scope probe on the cathode of DS3 and fiddle with scope. the clip on the end of the scope probe cannot get enough of a bite on the center leg of the diode. I may have to improvise.
if I'm getting a funky...Leave a comment:
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Re: troubleshooting TV SMPS sequence
Budwich-CapLeaker,
I found a replacement for the 470uf on the 5 VSB board. same 470uf, just a higher voltage rating. afterwards, when I plugged the TV power cable into TV, I had the scope on the 5 vsb. It came right up to about 5.30 volts. now there was a little bit of noise on the signal, but it was very close to the max voltage . line nothing like the previous photo with all the ripple changes in it.
However, The +12 and +24 still have the voltage changing with about a 2V swing as shown on the scope photos previous....Leave a comment:
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Re: troubleshooting TV SMPS sequence
CapLeaker BudWich,
ok I understand what you're saying. can I make scope measurements where the signal comes out of the secondary of the transformer for each rail safely? can the scope measure the voltage at an increased frequency rate before the diodes?
I guess since you haven't suggested it, I cannot make any safe measurements with scope on the primary side, right?
I'll look for a 470uf Cap with a similar voltage to replace on the 5V VSB board. for now I will leave the PS it as it is with NO LOAD...Leave a comment:
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Re: troubleshooting TV SMPS sequence
Budwich,
remember, I spread those two signals out so I could capture on camera the fall and rise of the signal. It does not look like ripple. it's almost like a square wave or a degrading square wave signal that has a definite cycle of low to high. we're talking about a 2V swing from low to high. when I switched the time back the other way (to the left), you see two solid lines jumping up and down.
where could that kind of signal be generated from?
on the 5V vsb, that's a jump of about...Leave a comment:
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Re: troubleshooting TV SMPS sequence
just a BUMP.Leave a comment:
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Re: troubleshooting TV SMPS sequence
CapLeaker,
Guess photos didn't attach. here theya re....Leave a comment:
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Re: troubleshooting TV SMPS sequence
CapLeaker and Co,
here we go again.
powered TV on, NO LOAD on the PS, +12 and +24 are only on the PS.
attached are 3 photos of the results I received.
I used a X10 probe. and the GND line is the very bottom line on the scope screen.
The first photo is the +24V.
.5V per voltage/division
.1 of a volt Time/Division
looked like 18V-22V change, note the photo.
The second photo is the +12V
.2V per Voltage/Division
.1V Time/Division...Leave a comment:
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Re: troubleshooting TV SMPS sequence
CapLeaker,
OK, will do and report back.
thanks
ilikesteelLeave a comment:
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Re: troubleshooting TV SMPS sequence
CapLeaker,
how can I check for ripple at the same time? also, can I gnd the scope to the DC gnd of the PS?
thanks,
ilikesteelLeave a comment:
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