need help to test inverter transformer

[retiredcaps]

Re: need help to test inverter transformer

should i be using the same "under 30 Ohm method" ?

Yes, measure the resistance between pins 1-2, 1-3, and 2-3.

[woaimi]

Re: need help to test inverter transformer

should i be using the same "under 30 Ohm method" ?

[retiredcaps]

Re: need help to test inverter transformer

with the 2 suspected mosfets removed this is what I've got from the rectifier
1-2 =33K
1-3 = 34.5K
1-4 = 33K
2-3 = 1.36M
2-4 = 34.5K
3-4 = 34.6K

The readings above suggest your bridge rectifier is NOT shorted.

Retest the mosfets now that you have removed them and post the readings.

[woaimi]

Re: need help to test inverter transformer

with the 2 suspected mosfets removed this is what I've got from the rectifier
1-2 =33K
1-3 = 34.5K
1-4 = 33K
2-3 = 1.36M
2-4 = 34.5K
3-4 = 34.6K

[retiredcaps]

Re: need help to test inverter transformer

the rectifier resistance report, I start from left the right with 1 being the pin labeled with (-).
1-2 = 453
1-3 = 453
1-4 = 453
2-3 = 1.325M
2-4 = 451
3-4 = 453

Those readings seem a bit strange. They indicate the rectifier is not shorted, but 5 of your readings are all 453 ohms. Desolder the mosfets first. With the mosfets out, retest the rectifier "in circuit" and report the readings again.

[woaimi]

Re: need help to test inverter transformer

please excuse my ignorant! I just wanted to make sure I get some real values other than 1 so I changed the mode setting. Anyhow, I got the mosfets desoldered will test them when i get home tonight.

the rectifier resistance report, I start from left the right with 1 being the pin labeled with (-).
1-2 = 453
1-3 = 453
1-4 = 453
2-3 = 1.325M
2-4 = 451
3-4 = 453
does that look right?
many thanks

[retiredcaps]

Re: need help to test inverter transformer

The pair below
The left one
S-G: with red probe on S = 22 Ohm, with red probe on G = 22 Ohm
The right one
S-G: with red probe on S = 22 Ohm, with red probe on G = 22 Ohm

On the rectifier: meter was set at diode mode

Between (+) and the 2nd leg with red probe on (+) = no reading, with black probe on (+) = 548
Between the 2nd and 3rd leg = no reading
Between the 3rd leg and the (-) with red probe on (-) = 547, with black probe on (-) = no reading

1) Multimeter tutorial. I have written about this before several times and just last week.

2) A multimeter always gives a reading. There is no such thing as "no reading". If your multimeter is displaying "1" on the left hand side of the lcd, it is telling you the measurement is "out of range".

3) For finding a short, we are only interested if the reading is below 30 ohms. We don't care if the actual reading is 200 ohms, 2000ohms, or 2M ohms. So on the lowest scale (200 ohms), if the multimeter shows a "1" on the left hand side of the screen, it is telling you the reading is > 200 ohms. That is, not shorted.

4) Most people understand green means go and red means stop. However, if I say green means don't stop and red means don't go, it messes people up. This is why #3 above is so hard for people to understand.

5) The "pair below" are shorted S-G (22 ohms is shorted). Desolder both and retest out of circuit.

6) For the bridge rectifier test, which I have written many times, I prefer to see this test. Number the bridge rectifier pins 1, 2, 3, and 4. Measure the resistance between pins 1-2, 1-3, 1-4, 2-3, 2-4, and 3-4. Report all readings.

[woaimi]

Re: need help to test inverter transformer

I'm using a cheapy Craftsman model 82141. I changed battery, set to 200 ohm the screen read "1" in open position and 00.3 when probes together. When I check the mosfets at 200 ohm setting I get out of range problem so I switch to 2000 ohm setting instead. Here what I've got from testing multiple times.
Referring to the photo that retiredcaps circled the mosfets
The top one (by itself)
S-G: with red probe on S = 528 Ohm, with red probe on G = 1032 Ohm
G-D: with red probe on G = 1695 Ohm, with red probe on D = no reading
S-D: with red probe on S = 400 Ohm, with red probe on D = no reading

The pair below
The left one
S-G: with red probe on S = 22 Ohm, with red probe on G = 22 Ohm
G-D: with red probe on G = 427 Ohm, with red probe on D = no reading
S-D: with red probe on S = 403 Ohm, with red probe on D = no reading
The right one
S-G: with red probe on S = 22 Ohm, with red probe on G = 22 Ohm
G-D: with red probe on G = 425 Ohm, with red probe on D = no reading
S-D: with red probe on S = 400 Ohm, with red probe on D = no reading

On the rectifier: meter was set at diode mode

Between (+) and the 2nd leg with red probe on (+) = no reading, with black probe on (+) = 548
Between the 2nd and 3rd leg = no reading
Between the 3rd leg and the (-) with red probe on (-) = 547, with black probe on (-) = no reading

[retiredcaps]

Re: need help to test inverter transformer

well, i got the fuses, soldered it in and it blown instantly, so I followed your suggestion. the rectifier is good but I couldn't confirm the mosfets (following your ohm method) as each time i try i get different result.

Always post your actual readings from your multimeter. We have had people state something was "good" only to find out they are mis-interpreting their results.

Also post your multimeter make and model so we know what you are using.

[multimeter]

Re: need help to test inverter transformer

well, i got the fuses, soldered it in and it blown instantly, so I followed your suggestion. the rectifier is good but I couldn't confirm the mosfets (following your ohm method) as each time i try i get different result.

change the battery in your multimeter,and confirm it reads "1" or "0L" when shorting the probes together, set to 200ohm setting

[woaimi]

Re: need help to test inverter transformer

well, i got the fuses, soldered it in and it blown instantly, so I followed your suggestion. the rectifier is good but I couldn't confirm the mosfets (following your ohm method) as each time i try i get different result.

[retiredcaps]

Re: need help to test inverter transformer

What might be the next thing to check?

Circled in red is your bridge rectifier. Circled in yellow is your mosfets. Check both for shorts

I have written procedures on how to check both at least 30 times so search around here.

[woaimi]

Re: need help to test inverter transformer

back from a little summer trip and still waiting for the fuse order to arrive!

I failed to realize that at the first place until seeing your post, I looked at the board again and there it was i guess i learned the hard way. I went to digikey and order another 25 just in case. I'm sure it could be something else that causing the fuse to blow but I'll start from here and hopefully it solves the problem. What might be the next thing to check?

[retiredcaps]

Re: need help to test inverter transformer

I worked it backward and found the missing link in continuity at the little component that I have always suspected for being a fuse from begining.

On the pcb board, there are designators to tell you what the components are. Fuses are usually "F". For example, F100.

http://en.wikipedia.org/wiki/Electro...e_designations

It was indeed a micro slow blow fuse. I couldn't find any at local electronic shops so I ordered from amazon 10 PC's for $5.

Most people here recommend digikey.com for electronic parts. For USA customers, First Class shipping is a very reasonable $2.75 USD ish and parts usually arrive in 48 hours.

I'll update when I get the part, let's hope that will fix the whole thing.

Sometimes a fuse blows due to age. Sometimes not. If you replace the fuse without testing some of the other components, you will be using up those 10 fuses quickly.

Have a festive independence day

[woaimi]

Re: need help to test inverter transformer

Thanks retiredcaps for that thought! I did just that and realized I'm getting no output from that connector. I worked it backward and found the missing link in continuity at the little component that I have always suspected for being a fuse from begining. It was indeed a micro slow blow fuse. I couldn't find any at local electronic shops so I ordered from amazon 10 PC's for $5. I'll update when I get the part, let's hope that will fix the whole thing. I'll attach the photo later so people with the same board can identify the component.

Have a festive independence day

Popeye, I'll take note of that and will make sure the area is well cleaned. Thanks

[popeye]

Re: need help to test inverter transformer

do exactly what retired says and also on the picture of the bottom side of the board i see burn mark this is probably due to that pin being dry jointed i hope you cleaned al the crap off that area or your new tranformer will not make contact,that dry was what caused the problem in the first place

[retiredcaps]

Re: need help to test inverter transformer

If I may, let's start at the very beginning.

On the power board, there is a connector.

List the legend and your readings. For example,

pin 1 says 5V SB - I get 4.99V DC
pin 2 says 12V - I get 11.97V DC

etc

[woaimi]

Re: need help to test inverter transformer

I got a bit crazy at work, finally get sometimes to up load. So, the tv has 3 boards all together: a power/ inverter board, main board, and a tiny board called T-con board. Let me know what you find. Thanks

[woaimi]

Re: need help to test inverter transformer

Thanks selldoor, I will have some pictures uploaded later tonight. As for the tv, yep! seems like there no power to the machine but I got power read at the board entrance connector. There were no fuse that I can find which I find very odd for being a power supply & inverter board.
I take a step back to describe the background. This tv is actually belong to family in a community that I volunteered to work with. They were watching tv and it just shut down without any warning signs/ noise. Since I got some basic knowledge in electronic works, I offered to fix their if possible (no promises were made ) and gave them my son's 32" tube keeping the kids happy. Anyhow, that's how I end up with a this task and that's all I know about the original symptom.
thanks again and stay tuned for the photos

[selldoor]

Re: need help to test inverter transformer

What do you mean by no life at all? To us that means there is no mains power to the machine - the first fuse has blown.

Might help if you could say what the original problem was- from plug in to stable faulty state as some us may have no experience of westinghouse.

Perhaps if we had some photos to work with?
We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed
https://www.badcaps.net/forum/attach...1&d=1290283049

https://www.badcaps.net/forum/attach...7&d=1280167246


Please can you update your profile with country and mains voltage.