Viewsonic VX724 with FSP035-1PI01

[waitery]

Hi all,

I am a first time poster. I have a Viewsonic VX724 with FSP035-1PI01. The power LED is blinking green and the transformer is ticking. I measured the output pin and it is above 12 volts....actually it is fluctuating between 12.37 and 12.44. The board was doing this before I recapped it as well with the CapXon caps that I pulled off. The diodes check out, bridge rectifier and filter caps are good to go and it is producing 12 volts.

I put the board under a scope to check to see if I has a bad solder joint, but everything looks good. I am frustrated at what this could be? Any ideas?

[PlainBill]

Re: Viewsonic VX724 with FSP035-1PI01

Hi all,

I am a first time poster. I have a Viewsonic VX724 with FSP035-1PI01. The power LED is blinking green and the transformer is ticking. I measured the output pin and it is above 12 volts....actually it is fluctuating between 12.37 and 12.44. The board was doing this before I recapped it as well with the CapXon caps that I pulled off. The diodes check out, bridge rectifier and filter caps are good to go and it is producing 12 volts.

I put the board under a scope to check to see if I has a bad solder joint, but everything looks good. I am frustrated at what this could be? Any ideas?

Several.

Did you replace ALL the electrolytic caps on the power supply / inverter board?

What brand and series of cap did you use?

What output pin are you talking about.

Attaching pictures would give us something to refer to when making suggestions.

PlainBill

[waitery]

Re: Viewsonic VX724 with FSP035-1PI01

Several.

Did you replace ALL the electrolytic caps on the power supply / inverter board?

What brand and series of cap did you use?

What output pin are you talking about.

Attaching pictures would give us something to refer to when making suggestions.

PlainBill

Forgive me, yes I replaced the caps with a combination of Nichicon and Rubycon ZL, low esr, 105 degree caps. The pin that I am refering to is the output pin going to the main board. I believe that the issue is on the primary side, as I am getting some erratic swings in power at the cathode side of the diode at D320. Anywhere from 67-64 volts and it swings as the ticking pulses.

The other issue is that I took off of of the red inverter capacitors at C24, as it had blown out the side and split. I am still getting 12.40 volts off the board, it just swings eratically to 12.37 then to 12.44 volts. Here is the photo:

[alexanna]

Re: Viewsonic VX724 with FSP035-1PI01

What dose the voltage do with the logic board disconnected?
If it Stabilizes post pitcures of the logic board.

[jetadm123]

Re: Viewsonic VX724 with FSP035-1PI01

The "ticking" sound is an indication the power supply is trying to start. This is a weird problem because if the supply hasn't started, then why are you getting a 12V output? Next to D320 is C320. C320 looks like the original cap (as evident by the glue on it). This startup cap and D320 are connected to a tertiary winding off the main transformer and produce the VDD required by the PWM controller chip (surface mount chip underneath board, U320). Failure of C320 can cause U320 not to start properly. If pin 7 (VDD) voltage of U320 is fluctuating, then try replacing C320. Also check value of R326 and ZD302, C322 for shorts. I'm assuming you checked D320 for shorts?

[PlainBill]

Re: Viewsonic VX724 with FSP035-1PI01

%#@%^#@T!!! One of the reasons pictures and complete information is helpful is they avoid wasting a lot of time. You have shorted transistors in the inverter. That's overloading the power supply.

PlainBill

[Scenic]

Re: Viewsonic VX724 with FSP035-1PI01

%#@%^#@T!!! One of the reasons pictures and complete information is helpful is they avoid wasting a lot of time. You have shorted transistors in the inverter. That's overloading the power supply.

PlainBill

that, and the ugly yellow glue that becomes conductive. left of the PSU transformer.. (and in several other places)

[waitery]

Re: Viewsonic VX724 with FSP035-1PI01

Bill,

Are you talking about the sm transistors under the interter? If so, how can I test or verify this?

Jetadm123, D320 is good to go, no leakage. Also, C320 is brand new as well. I will follow your guidelines on testing further.

One question though...how does hardened glue become conductive?

Thanks!

[jetadm123]

Re: Viewsonic VX724 with FSP035-1PI01

Bill,

Are you talking about the sm transistors under the interter? If so, how can I test or verify this?

Jetadm123, D320 is good to go, no leakage. Also, C320 is brand new as well. I will follow your guidelines on testing further.

One question though...how does hardened glue become conductive?

Thanks!

I think PlainBill may be referring to Q6-Q9?, surface mount NPN transistors, 2SC4672. Each pair located opposite the CCFL controller chip. With your meter set to resistance, measure across E-B, B-C and E-C for shorts.

[waitery]

Re: Viewsonic VX724 with FSP035-1PI01

I checked out those transistors and the one side where I had removed the blown red capacitor, both had had significantly lowered values. All four were tested in circuit, with the power off. Here are my figures:

Good Capacitor Side (please note the Kilohms measurement.
E-B 6.63k ohms
B-C 746 ohms
E-C 5.74k ohms

No Capacitor Side
E-B 3.7 ohms
B-C 2.8 ohms
E-C 6.2 ohms

Let me know what you think and thank you!

[retiredcaps]

Re: Viewsonic VX724 with FSP035-1PI01

No Capacitor Side
E-B 3.7 ohms
B-C 2.8 ohms
E-C 6.2 ohms

The above readings suggest it is shorted. Remove and retest out of circuit to verify.

[Rtech]

Re: Viewsonic VX724 with FSP035-1PI01

You also need to measure and compare the secondary resistance of the two inverter transformers,as the one next to the capacitor you have removed is notorious for failing.I would also take it out of the board and you may well see burning on the underside of it.

[Rtech]

Re: Viewsonic VX724 with FSP035-1PI01

The inverter transistors referred to,ie 2SC4672,were unobtainable when I looked for some in the UK,and the alternative advised was FCX1052ATA.These are
Medium Powered as opposed to the Low Power of the original, rated at 75volts as opposed to 50volts.Manufactured by Zetex,these were obtained from RS Components,in batches of Qty 10,@45pence each.They are also used on VX710 and 910,and have used about 20 to date with no failures.

[waitery]

Re: Viewsonic VX724 with FSP035-1PI01

Rtech, thanks, I will pull that inverter, check for burning and ohm it to see if there is a problem. Those transistors that RetiredCaps referred to can be had here stateside for 80 cents a piece...a new pair of .15uF caps @250volts tagged onto the order drives the cost up to $6.00 delivered first class mail from Diga-Key....pretty good value.