ViewSonic VT2430 power cycling

[Mr Bill]

I've got a viewsonic vt2430 that basically won't turn on. It will go from stanby to on and show the viewsonic splash screen the back off and repeats forever. You can't turn the tv off either once its doing this cycle, you have to pull the plug from the wall. Doing a breif google search alot of people are having this issue but i haven't came across a solution yet.

When i opened it up to check the power supply it has 2 types of caps. Elite and Her-Mei

I removed every capacitor and checked the esr and capacitance and they were all 0.00 and the capacitance was well within the allowed 20%. I did however find 2 caps (22uf &47uf) that the esr was .4-.5ohm. I swapped them out with a couple panasonic fc's i had in my box-o-stuff that the esr was 0.01-.06

The 22uf cap is the startup cap and the fc that replaced it had an esr of .01.

The PWM controller is a Green-Mode PWM Controller with High-Voltage Start-Up Circuit and Adjustable OLP Delay Time (LD7576PS). When i checked ground to all the other pins, most were in the k-mohm range but i did find pin 4(ground) to pin 3(CS, Current sense pin, connect to sense the MOSFET current) to have a reading of 98ohms. Now would this be an issue causing the PWM controller not to start up completely? I did do a voltage check at the startup cap amd it was 20.86v-21.22v. It slowly rose then fell back when the blue led went off then back on when its doing its repeat cycle.

I haven't checked the caps on the main board yet. I am unsure if this type of issue would be the power supply not turning on due to a fault or the main board telling the power supply to cycle. Here are a few pics of the main board and power supply.

Thanks

[budm]

The CS (current sensing) pin has a low resistor (100 Ohm) one end is connected to pin 3, the other end is connected to the Source resistor (less than 1 Ohm) of the MOSFET that drives the transformer, the more current the MOSFET draws the more voltage will be develop across the sensing resistor, that is how the SMPS IC figures out when to go into shutdown mode, the sensing level is up to the designer of the circuits. You can see how it done on page 1.
So 100 Ohm reading may be correct, you need to look for that resistor on pin 3 to verify.

This is an always on power supply (it runs the minute you apply power to the board), how about the 5Vdc, is it fluctuating also. It may have shorts in the inverter circuits that is drawing too much current so it is in startup/shutdown mode.
Good pictures on the bottom side of the board (PS/INVERTER), P/N as printed on the board?

[Mr Bill]

Originally Posted by budm

This is an always on power supply (it runs the minute you apply power to the board), how about the 5Vdc, is it fluctuating also. It may have shorts in the inverter circuits that is drawing too much current so it is in startup/shutdown mode.
Good pictures on the bottom side of the board (PS/INVERTER), P/N as printed on the board?

In standby 2 pins read 5.15v steady but 2 other pins read 13v. I don't know if it is suppossed to be 13 instead of 12. I haven't located a service manual yet. Here is a picture of the bottom of the power supply. It's not the best but i won't be able to get a good picture until tomorrow when the sun is out. I did notice on the backside of the power supply there are 2 sop-8 mosfets. Its a n-channel and a p-channel in one package. On the one the D1 & D2 are sorta solder bridged together but the other one is not.

The mosfet is a 4503ss

Could this possibly be an issue causing the shutdown?

Thanks

[budm]

That solder bridge looks bad but all those pins supposed to be tied together anyway, it is bride setup to drive both inverter transformers.
One thing is that it only has one transformer to supply all the voltages, so if the 5Vdc or the 12 (13Vdc) is steady, then the main power supply is working properly. If that is the case, you need to look some where else for problem, since you had indicated that you have to pull the plug that means the Main board is not functioning. Start looking at the caps and 3-pin voltage regulator IC on that board.
If you have 6V very small lamp (grain of wheat from Radio Shack), you can attach that to the 5VDC line, it should stay lit without flickering.

You should get 6V, 12V, I put two 12V in series when I check 16/18/24V section. 6V for 5V section.
http://www.radioshack.com/product/in...ductId=2102814

They are great for troubleshooting.

[Mr Bill]

Bud,
I found the service manual.

http://elektrotanya.com/viewsonic_vt.../download.html

The 13v i mentioned in post #3 it is actually suposed to be 12v. I checked the pins in stanby and i am getting 5.15v and 13.1v. When i turn the tv on the 5.15v goes to 4.99v and the 13.1v goes to 13.56v

Would it be safe to assume the power supply is the likely culprit causing the tv to shutdown and restart? I did check the caps on the mainboard and they tested within spec. The voltage regulators are giving the correct voltages too.

[budm]

Your power supply is OK (4.99V is really good, the 12V no load from Inverter would be higher than 12V). Something on the main board, I will have to study the service manual first.

[Mr Bill]

The best solution i could find for this issue is a corupt firmware. According to some, the SRS sound somehow jacks up the firmware causing the mainboard to continuously cycle. I've read people having this issue the second day they owned it. Sent it back and the replacement did the same thing 2 days later.

[ricosavy]

What about EEPROM replacement will that work

[ricosavy]

I heard shopjimmy sells the EEPROM chip that repairs this problem has any one tried it I think it runs like $25 for one.any input would be helpful.

[Coshelectronics]

Bill, Did you ever find the solution to this?

[ricosavy]

As far as me no ,the eeprom they sell works on one main board.the one i have they still do not offer replacement eeprom.like bill said it is eeprom corrupt.

[Coshelectronics]

Ok, I have one on the bench. I was hoping someone might of sourced a replacement eeprom.

[lucky13]

Originally Posted by Coshelectronics

Ok, I have one on the bench. I was hoping someone might of sourced a replacement eeprom.

This TV needs a firmware update. You need to take it to the nearest Viewsonic service center. They should have the jig and firmware to flash it. Getting another eeprom chip that still has the old f/w is not the solution.

[lgcyber]

Originally Posted by lucky13

This TV needs a firmware update. You need to take it to the nearest Viewsonic service center. They should have the jig and firmware to flash it. Getting another eeprom chip that still has the old f/w is not the solution.

Anybody with a firmware for this? We cant find any Viewsonic Service Center in our country. Maybe someone can help me? Thanks.