troubleshooting DAC 19M008 power supply

[mikeh1]

I found this site while searching for troubleshooting tips for a Viewsonic VA1912wb3 monitor with a DAC 19M008 power supply, that doesn't seem to power up; no green power light and no picture. I have replaced some bulging Capxon caps on the power supply board, 3 of the 220uf/25v and 2 of the 1000uf/25v. I found and removed a solder blob shorting two of the leads of one of the 8 pin DIP ICs. I also resoldered the connections to the two transformers, they looked a bit gray.

Are there any other parts that I should replace?

[sabre504]

Re: troubleshooting DAC 19M008 power supply

First check that you have power at the main cap (the 400v 120uf) set to DC and report voltage .
Then check the output pins on the board also report findings if you have not already checked these

[sabre504]

Re: troubleshooting DAC 19M008 power supply

If you are not getting correct voltages at the secondary output
Check fuses on the back of the power board F102 and F200 (pic 1)

If you have correct voltages chsck voltage regulators on the video board (pic 2)

I have posted pics as a guide your boards may be diffrent we need pictures really

[mikeh1]

Re: troubleshooting DAC 19M008 power supply

I was able to check both fuses, both are OK. I'm not very familiar with circuit design, but I know how to work a VOM. How would I go about testing the 400v 120uf cap? (It is a Capxon, but it is not bulged out like the ones I replaced.)

[mikeh1]

Re: troubleshooting DAC 19M008 power supply

I just checked the 400v 120uf cap with a VOM (no power to board), no continuity, and when testing for DC volts shows 2V DC. Does this mean that this cap is OK?

[sabre504]

Re: troubleshooting DAC 19M008 power supply

You will have to apply mains power to the board ,
Set your meter to DC depending on what the increments are it must be set above 400v (ie 600-750-1000).
Place red probe on the positive leg and black on the negative leg (marked with white stripe)
Careful high voltage report reading .

This is not to test the cap itself but to check that it is getting the correct voltage to run the board and the result will help others help you where to test next

[mikeh1]

Re: troubleshooting DAC 19M008 power supply

I'm getting 200v DC at the cap

[sabre504]

Re: troubleshooting DAC 19M008 power supply

What is your mains voltage

[mikeh1]

Re: troubleshooting DAC 19M008 power supply

What is your mains voltage

120 VAC

The multimeter I'm using has a setting on the DC side for 250v/1000v, and a separate socket for the 1000v setting. Using it that way, the cap read 50v on the 250v scale.(there is no 1000v scale on the meter)

I'm going to get a newer multimeter so I can more accurately read the voltage

[sabre504]

Re: troubleshooting DAC 19M008 power supply

You should be getting a reading of approx 168v

120 x 1.4

But try the pins on the output socket and see what readings you get
Voltages should be marked on the board under the pins

[mikeh1]

Re: troubleshooting DAC 19M008 power supply

with new meter got 165.5 vDC

[mikeh1]

Re: troubleshooting DAC 19M008 power supply

You should be getting a reading of approx 168v

120 x 1.4

But try the pins on the output socket and see what readings you get
Voltages should be marked on the board under the pins

do I measure each pair of pins or from each pin to ground?

[sabre504]

Re: troubleshooting DAC 19M008 power supply

For now you just want to test the 13.8v pin and the 5v pins

[mikeh1]

Re: troubleshooting DAC 19M008 power supply

For now you just want to test the 13.8v pin and the 5v pins

the two 13.8v pins measure 14.2v and the 5v pins measure 0v

[sabre504]

Re: troubleshooting DAC 19M008 power supply

Test each side of the fuse F102 to make sure there is no voltage

If no voltage then we are at the point that we are going to need actual pics of your board

[mikeh1]

Re: troubleshooting DAC 19M008 power supply

Test each side of the fuse F102 to make sure there is no voltage

If no voltage then we are at the point that we are going to need actual pics of your board

getting 4.75v across the fuse F102

[sabre504]

Re: troubleshooting DAC 19M008 power supply

Then you should have the same at the pin

[mikeh1]

Re: troubleshooting DAC 19M008 power supply

Then you should have the same at the pin

do I test across the two 5v pins or separately test each one to ground?

[sabre504]

Re: troubleshooting DAC 19M008 power supply

Try each pin to ground

[mikeh1]

Re: troubleshooting DAC 19M008 power supply

looks like the fuse F102 is bad, with the new meter I'm getting a reading of 180 ohms

I was getting 5v on the inboard side of the fuse and nothing on the other side, so I rechecked the fuse. One side of the fuse also has a small solder blob that's not smooth, like it heated up the solder a bit.