Polaroid FLM-373B Power LED but no picture, already tried replacing caps

[pattheslat]

I have a Polaroid FLM-373B that was displaying fairly normal "bad capacitor" problems- the power LED went from red to blue, but the TV wasn't actually coming on.

I opened it up and no capacitors appeared to be bulging or leaking, but I understand that the CapXon caps used in this TV can sometimes go bad with no external indications, so I replaced the ones that seemed to normally go bad. This didn't fix the problem, so next I replaced all the easily accessible caps on the board (except the two big ones, which my local electronics supply store didn't have- they're Samxon, which I think is a reputable brand, so I figured they're probably alright). This still didn't fix it.

Before I order the big capacitors and/or try to battle the little ones hidden under the heatsinks (worst design ever), is there anything else I should be trying?

I've checked voltage coming out of the power board- all voltages are fine when the power button is first pressed, then there is a faint click and they all drop to zero.

Any help would be greatly appreciated.

[tom66]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Did you use Sanyo caps for other parts?

Can you post a picture of the main board... In my experience this often goes bad with Proview TVs.

[selldoor]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Hi - Im just a learner myself so can only suggest obvious things. Have you checked that you put the caps in the right way round?
Have you checked for poor joints?

Picture of back of board could do with being a bit brighter/clearer so the
writing can be read ( not easy when its black on green)

I attach a pic of part of your board - on the bit circled in red the solder seems to bridge - is it supposed to?

When the experts get on to this they will want to know what the replacement caps were that you used.

[PlainBill]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

You made a number of mistakes which wasted time and money.

1. The symptom - power LED goes from red to blue, no picture - is NOT typical of bad caps. It CAN be due to bad caps, but is more likely due to a bad main board, inverter, tcon.

2. You are correct, caps can fail without obvious signs. However, when troubleshooting a problem where bad caps is not the most likely cause, replacing caps that have not obviously failed is a poor approach.

3. When replacing caps, both brand and series are important considerations. Panasonic FR, FM, FC series caps are excellent replacement caps for use in a power supply. Panasonic M, NHG, and EB are unsuitable. A similar situation exists with Saxmon.

4. The pictures are pretty good, but one important piece of information is barely visible. The output connectors are labeled on the back side of the board. With symptoms like these, one of the first steps should be to check if the proper output voltages are present. If, for example, +5.1V and +12V are present, but +24V is missing it is possible to focus on a small part of the power supply. If all are present, look to the main board as the cause of the problem.

PlainBill

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

You made a number of mistakes which wasted time and money.

1. The symptom - power LED goes from red to blue, no picture - is NOT typical of bad caps. It CAN be due to bad caps, but is more likely due to a bad main board, inverter, tcon.

2. You are correct, caps can fail without obvious signs. However, when troubleshooting a problem where bad caps is not the most likely cause, replacing caps that have not obviously failed is a poor approach.

3. When replacing caps, both brand and series are important considerations. Panasonic FR, FM, FC series caps are excellent replacement caps for use in a power supply. Panasonic M, NHG, and EB are unsuitable. A similar situation exists with Saxmon.

4. The pictures are pretty good, but one important piece of information is barely visible. The output connectors are labeled on the back side of the board. With symptoms like these, one of the first steps should be to check if the proper output voltages are present. If, for example, +5.1V and +12V are present, but +24V is missing it is possible to focus on a small part of the power supply. If all are present, look to the main board as the cause of the problem.

PlainBill

1. It seemed from my various searches on this model of TV that this symptom was typical of capacitors, but it is possible I was mistaken.

2. Having read on here that the black CapXons tended to fail without showing any outward symptoms, and knowing that replacements would be in stock locally, I figured it wouldn't be a bad place to start. If this hadn't been the problem, I'm only out ten bucks in parts, and if I DO get the TV working, it won't be using low quality capacitors anymore.

3. Nichicon PJ

4. The board outputs all proper voltages for a couple seconds, then there is a slight click and they drop to zero.

I attach a pic of part of your board - on the bit circled in red the solder seems to bridge - is it supposed to?

It does look bridged in the picture, but it actually isn't- even if it was, though, I believe the two are supposed to be connected (which you can see by looking at the printing on the PCB)

Can you post a picture of the main board... In my experience this often goes bad with Proview TVs.

Would a mainboard problem cause power board output voltages to drop out after it's turned on? Either way everything looks alright on it to me, but I'll get a picture in just a minute.

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Here are a couple pictures of the (visible side) of the mainboard

[tom66]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Here are a couple pictures of the (visible side) of the mainboard

Argh! Another Proview fail. (Crap TVs.)

See picture. Press firmly down on main board near these pins and see if it starts working (while installed in TV of course.)

They use some kind of stupid parallel port to connect the main board to the rest of the TV. When you unscrew the case to get to the main board and power supply, you loosen this connector and it gives strange symptoms ranging from no power LED, no sound, no backlight etc.

I repaired a Bush TV which used a very similar design. It also had bad caps; the two 1000u/10V(?) ones near the upper transformer and one 1000u/35V. After replacing the caps I could not figure out why it would not work. I found it would work when upside down but not when upright! You can imagine my frustration. I then proceeded to remove the main board assembly and looked at the parallel port and thought nothing about it until 15 minutes later I realised why it wasn't working. Now works fine .

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Argh! Another Proview fail. (Crap TVs.)

See picture. Press firmly down on main board near these pins and see if it starts working (while installed in TV of course.)

They use some kind of stupid parallel port to connect the main board to the rest of the TV. When you unscrew the case to get to the main board and power supply, you loosen this connector and it gives strange symptoms ranging from no power LED, no sound, no backlight etc.

I repaired a Bush TV which used a very similar design. It also had bad caps; the two 1000u/10V(?) ones near the upper transformer and one 1000u/35V. After replacing the caps I could not figure out why it would not work. I found it would work when upside down but not when upright! You can imagine my frustration. I then proceeded to remove the main board assembly and looked at the parallel port and thought nothing about it until 15 minutes later I realised why it wasn't working. Now works fine .

Already tried that, unfortunately (I searched the forum and saw your response to someone else who was having a similar problem).

[tom66]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Do *all* the output voltages drop when the power supply appears to switch off?

In standby, are any voltages present? (There should be at least one.)

If the inverter (red+black only) connector is disconnected, is the behaviour different?

---

This problem can also be caused by a bad LDO. An LDO regulates voltage. I've highlighted several devices. For each device, read off the part # and ref-des (the letter+number on the board next to it, e.g. U5, U7...) Then, using your multimeter, measure the voltages on each pin relative to the metal case of the TV. (Do this while the TV is trying to switch ON (LED is blue.)) No need to measure the metal tab; it's internally connected to the middle pin.

[PlainBill]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Would a mainboard problem cause power board output voltages to drop out after it's turned on? Either way everything looks alright on it to me, but I'll get a picture in just a minute.

Standard lecture #3. The power supply in this TV uses a standard design. There is a standby supply (+5VSB) which is on whenever the power is applied. There is a main supply which is turned on to power the major part of the main board and the inverter. The board also has a PFC front end.

A typical startup operation goes like this: The TV is plugged into AC power. The standby supply comes up and (if present) a standby LED comes on. The power button is pressed. The main supply and PFC front end are enabled, the processor runs a few tests, and if a problem is found, the main supply is turned off. If no problems are found, the proper input is enabled and the inverter is turned on.

If ALL output voltages drop including the +5VSB, it is a power supply problem. If the +5VSB stays up, there is a problem, most likely on the main board.

PlainBill

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Do *all* the output voltages drop when the power supply appears to switch off?

In standby, are any voltages present? (There should be at least one.)

If the inverter (red+black only) connector is disconnected, is the behaviour different?

---

This problem can also be caused by a bad LDO. An LDO regulates voltage. I've highlighted several devices. For each device, read off the part # and ref-des (the letter+number on the board next to it, e.g. U5, U7...) Then, using your multimeter, measure the voltages on each pin relative to the metal case of the TV. (Do this while the TV is trying to switch ON (LED is blue.)) No need to measure the metal tab; it's internally connected to the middle pin.

Sorry, should have mentioned that the +5VSB is behaving as it should. It does the same thing whether or not the inverter is connected. I'll go check on the LDOs right now.

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Readings from the LDOs, taken left to right if pins are facing downward:

U3: 0, 3.30, 5.15
U4: 0, 1.798, 3.30
U5: 0, 3.29, 5.12
U6: 0, 1.798, 3.28
U7: 0, 3.28, 5.14
U13: 0, (no pin), 4.34
U33: 0, (no pin), 3.53

One thing that seems strange to me is that I was reading these voltages even after the power supply cut out and wasn't supplying any power other than the +5VSB.

[tom66]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Readings from the LDOs, taken left to right if pins are facing downward:

U3: 0, 3.30, 5.15
U4: 0, 1.798, 3.30
U5: 0, 3.29, 5.12
U6: 0, 1.798, 3.28
U7: 0, 3.28, 5.14
U13: 0, (no pin), 4.34
U33: 0, (no pin), 3.53

One thing that seems strange to me is that I was reading these voltages even after the power supply cut out and wasn't supplying any power other than the +5VSB.

Those voltages seem okay but could you redo U13/U33 but use the tab for pin #2?

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Sure thing, U13 is 2.506, U33 is 1.950

[tom66]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Sure thing, U13 is 2.506, U33 is 1.950

What's the part # (1084xxxx) on U33? Strange reading there - closest is 1.8V or *maybe* 2V (But I haven't seen that before. Not a common voltage.)

[tom66]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Just found a service manual for this TV:

Unfortunately, no schematics of the main board...!

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

U13 is 1084-25PE 96315, U33 is 1084 PE 35419.

I found that service manual earlier, has to be the most worthless one I've ever seen. Its solution to most problems seems to be "replace control box".

[tom66]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Most of the cheap brands are the same, they don't care about the customer.

Is it possible you are mistaken in reading 35 and it could be 33? Either way, that regulator is most likely bad and could certainly cause your problem.

Vizio TVs have a problem with a certain U33 failing, but I think that it is a coincidence that it happens to have same ref des.

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Is it possible you are mistaken in reading 35 and it could be 33? Either way, that regulator is most likely bad and could certainly cause your problem.

On what, the "35419" of the part number? I just double checked and it is definitely a 35 there.

[pattheslat]

Re: Polaroid FLM-373B Power LED but no picture, already tried replacing caps

Any idea where I could find that component? Searching Google is coming up with absolutely nothing.