Thomson 55UA7706 LCD TV startup problem?

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

1) The pictures of the boards are very poor, I cannot read the pin label (the oin names are printed on the bottom side of the board) of the connector of the power supply board that goes to the LED driver board.

Yes, below is new, do they help?

2) Were you getting 24V to the LED driver board? And now you don't since you start playing with FSFR1700XSL and D404?

This 24V comes to inverter board from psu pin no. 10 (marked red). And yes, I have 22.92V before but after disconnect/reconnect this 14pin cable, I dont have this anymore, also, no standby.

3) The 24VDC is generated by FSFR1700XSL so the circuit was working. I do not understand why you start messing with the FSFR1700XSL.

Because (also question 4) ) one technician suggested to measure C401 22uF/50V voltage and there is 1.6V, they told that I must check this part of circuit, I then measure this SMD components and find this zener conducted both ways, soldered it off and checked with a zener tester - same result, 0.0009V zener voltage.

4) As you can see that D404 is connected in parallel with resistor. So when you check D404 off the board, does it show conduction and low resistance (<10 Ohms) in both directions.

See previous.

5) Right now you need to get the FSFR1700XSL working again before going back to troubleshooting the backlights issue, or just buy a new power supply board assembly that match the number on the barcode sticker, not the blank PCB part number..

I dont know this zener real name value - if I order new FSFR1700XSL and if there is this broken zener...i dont think that this new IC helps, they also fail probably.

6) Where is the pin that is supposed to have 56V?

In inverter board, pin 11 to 14 is marked 56V, in PSU, pins 12 to 14 is marked as 60/120V, 11 is not connected (see 1. (PSU connector) and 4./5. picture (inverter connector).
Pictures 2 and 3 is LED stripe connectors from inverter board.

Last 2 pictures is PSU FSFR1700XSL circuit top and bottom view

[Diah]

Re: Thomson 55UA7706 LCD TV startup problem?

before we got lost.... lets follow yours POST
this is your first POST.

Inverter board can get from the main power supply as follow voltages:

+24V (I have there +22.66V)
+56V (I have 0 (zero)V)

after i asked you to disconnect 24V socket and plug in again.. you wrote at POST No 8

Results are:

P_DIM +0.430V
Fuse F1 from T-CON, +11,988V (both sides)

Measured at inverter board IN DC MODE:
+56V pins: measured +41.45mV it is not very stable also - here seems something wrong ????????????
+24V pin: measured +22.92V (little low but not very?)
PT pin: measured +0.55mV
BL_ON: measured +3.109V (little low?)
P_DIM: measured +0.4316V
3D_EN: measured +0.62mV

so the inverter turned on and the 56V exist but low 41.45V.
it mean you have LED back light issue or Inverter issue. that's all before you went to play at HOT AREA... BTW i think your measurement to the zener Diode wrong... you need with Ohm testing that read resistance at one direction only.

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

before we got lost.... lets follow yours POST
this is your first POST.

Look next answer

after i asked you to disconnect 24V socket and plug in again.. you wrote at POST No 8

Yes, I wrote this but there is +41.45mV , not 41.45V. There is over 1000x lower value this +56V rail.

the inverter turned on and the 56V exist but low 41.45V.
it mean you have LED back light issue or Inverter issue. that's all before you went to play at HOT AREA... BTW i think your measurement to the zener Diode wrong... you need with Ohm testing that read resistance at one direction only.

Then is only possible that inverter itself is bad, this OZ9998, all other semiconductors is good. And If you need I can take picture this zener measurements - virtually https://i.ytimg.com/vi/GwRyAGgpbPg/maxresdefault.jpg but I have 1000ohm resistor and adjustable supply, if I now get new THT zeners from manufacturer packaging I get good results - for example, same setting, 3.6V zener I get very close (to name value) results (if you need how close - how many I measure?), If I get 15V zener then I get also very close results, also 12V and this other zeners which located near FSFR1700XSL give me result 18.028V for example. This broken one gives me 0.0009V reading and 0 ohm (multimeter reading) but if this really helps, I can measure until to 0.001ohm resolution but - do this help?
continuity test/diode test gives me also short "peep" signal, both sides.

What DMM I using now? Fluke 110 and UNI-T UT139E, there is virtually no difference, only second show me 1 count more.

Once again, this very low +56 rail...this is only tens of millivolts - and this sends me from the beginning.

Today morning I re-measured again new LED strips and sure that new ones is good, all LEDs lit.
87.7V is one group voltage (18 LEDs).
If this helps also I can post picture my DIY tester (circuit is here: https://www.drive2.ru/c/513423827611419614/ ) but if this LED lit then there is no errors. Old LED stripes which located at this moment inside a panel, they are definitely broken because they lit very weakly.


E: maybe my writing skill barrier is really high but I mean milli-Volts at there 41.45milli-Volts, not Volts

[Diah]

Re: Thomson 55UA7706 LCD TV startup problem?

aha... mV was easy to write 0.41 any way ..so now you have of sure zener defect and back light strings defect. i would say start first by replacing the BL and when you got the correct zener will be easy to you for further trouble shooting in case there were more issue

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

OK.
I once thought that I marked with a dot, not a comma... My country also have a comma for this kind of separation, but I get previously resented that I used a comma and tried to prevent now

Anyway I need to figure this zener value out now and new inverter or ICs. I drew a diagram but i will only get the component measuring device tomorrow or the day after tomorrow, so if i get it done maybe it will give some overview to find out the value of the suitable zener. OK, lets see

[budm]

Re: Thomson 55UA7706 LCD TV startup problem?

Your post #21:
"This 24V comes to inverter board from psu pin no. 10 (marked red). And yes, I have 22.92V before but after disconnect/reconnect this 14pin cable, I dont have this anymore, also, no standby."
Are you now saying you do not even has standby Voltage?

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

I finally got new PSU chip and now is still only one problem - this damaged zener.

Like as I say some time ago, I was measured all components which located near this FSFR1700XSL chip and clear is that this D404 (some kind of zener) is damaged BUT - how can I be sure what value zener this must be?
I draw this part of PSU zircuit and measured all little SMD parts, this circuit is below and there is also componets values which I measured.

Now - how I can calculate this D404 value? Or rather what does this value depend on, on which should I proceed? There is no this kind of zener circuitry in FSFR1700XSL datasheet.
If I choose an incorrect zener - I am afraid thst this ends badly to new FSFR1700 chip?

Therefore - how I can choose correct value zener?

[dick_barton]

Re: Thomson 55UA7706 LCD TV startup problem?

The data sheet for the IC says VAR (Autostart Reset Pin Input Voltage) = MAX VLcc
VLcc on the data sheet says maximum 25V

So it's possible that the zener may be somewhere around that value.

https://cdn.badcaps-static.com/pdfs/...04400a7892.pdf

[Diah]

Re: Thomson 55UA7706 LCD TV startup problem?

well till now i never faced Glass Ziner defect. buy any value glass ziner and compare the test with diode mode. LOL

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

Yes, this is weird but - I was measured this maybe tens of times and compared to others and this is clear that this zener is defective. I dont know why? Also, first time I have this fault but lets see when new IC is in place and also new zener.

I have now 17V, 18V and 24V SMD zeners too. I think that maybe I`ll try then 18V here?

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

topic locked

Zener has a 18V value. If this zener breaks, then also FSFR1700 fails and need to be replaced, no empti place here! Although it may seem to work even without this zener it not work without a zener.
Now this TV works again.

[budm]

Re: Thomson 55UA7706 LCD TV startup problem?

Thanks for the follow-up.